Revision B – February 2012 

PART 23 ICING AVIATION RULEMAKING 

COMMITTEE REPORT I 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-2

REVISION TRACKING 

Revision - n/c (Jan 2011) 

Location of 

change 

Description 

n/a Original Release 

Revision – A (April 2011) 

Location of 

change 

Description 

Table 1 Added red font color under “Part 23” column – omitted by error. 

Added tables notes in the “Legend and Notes” section – omitted by 

error. 

Section 1 Updated summary progress table 

Section 7 Added Section 7 “Certification Cost Input” to provide cost estimates to 

the FAA economist for the proposed rulemaking per Task 5 

Section 8 Added Section 8 “Operating Cost” to address Task 5 and Task 7. 

Section 9 Added Section 9 “Benefit Summary” to discuss applicable safety 

events applicable to the proposed rulemaking per Task 4. 

Section 10 Added Section 10 “Training Recommendations” to Task 7. 

Appendix E Added Appendix E – Operations Cost Survey 

Appendix F Added Appendix F – GAMA Icing Accident Survey 

Misc Updated table of contents, table of tables, table of appendices as 

required 

Updated abbreviations and acronyms as required 

Minor typographical edits 

Revision – B (Feb 2012) 

Location of 

change 

Description 

Section 1 Changed status of Task 9 to completed 

Section 2 

last paragraph 

on Task 9 

status 

Was “This task will be completed after recommendations are 

submitted for SLD and ice crystals, but prior to development of an 

NPRM so that any proposed rules can be bundled with the SLD and 

ice crystal rules.” 

Section 11 Added Section 11 to address Task 9 
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TABLE OF CONTENTS 

1. SUMMARY ............................................................................................................................... 9

2. BACKGROUND ..................................................................................................................... 10

3. Preamble Discussion ............................................................................................................. 13

A) Subpart B Aspects (including Autopilot) ................................................................................ 13

B) Summary Table of Subpart B part 23 Proposals versus part 25 proposals ...................... 22

C) Subpart B - Means of Compliance Appendix O ................................................................... 33

D) Subpart B - Appendix C Ice Accretions ................................................................................ 39

E) Powerplant Aspects ............................................................................................................... 44

F) Systems and Related Aspects .............................................................................................. 47

4. RULEMAKING RECOMMENDATIONS .............................................................................. 52

A) Subpart B Aspects ................................................................................................................. 52

B) Ice Accretions for showing compliance to 14 CFR 23 Subpart B ....................................... 64

C) Powerplant Aspects ............................................................................................................... 70

D) Systems Aspects .................................................................................................................... 72

5. ADVISORY MATERIALS ...................................................................................................... 75

A) Sub-Part B Aspects ................................................................................................................ 75

B) Powerplant Aspects ............................................................................................................... 75

C) Systems Aspects .................................................................................................................... 82

D) AC 23-17C .............................................................................................................................. 82

6. ALTERNATIVES CONSIDERED ......................................................................................... 84

7. CERTIFICATION COST INPUT ........................................................................................... 92

A) Assumptions ........................................................................................................................... 92

B) Increased Cost Categories .................................................................................................... 94

C) Increased Cost Summary ...................................................................................................... 97

D) Costs for Certification to a Portion ....................................................................................... 100

E) Reduced Costs Categories ................................................................................................. 100

F) Summary ARC Position on Costs ....................................................................................... 101

8. OPERATING COST ............................................................................................................ 103

A) Cost of Available Certification Options ................................................................................ 103

B) Training ................................................................................................................................. 104

C) Design Implications .............................................................................................................. 105

D) Airplane Manufacturing Industry .......................................................................................... 105

E) Actual Cost Data ................................................................................................................... 105

9. BENEFIT SUMMARY .......................................................................................................... 106

A) Icing Accident Database Review ........................................................................................ 106

B) Icing Incident Database Review .......................................................................................... 114

10. TRAINING RECOMENDATIONS ...................................................................................... 116

A) Introduction ........................................................................................................................... 116

B) Disconnects between the Certification and Operations world ........................................... 117

C) Focused Ice Training ............................................................................................................ 121

D) Changes to FAA training and testing material .................................................................... 124
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11. TASK 9 RECOMENDATIONS ........................................................................................... 125

A) Background........................................................................................................................... 125

B) Proposed Rule ...................................................................................................................... 125

C) Options .................................................................................................................................. 127

D) Applicability Of The Proposed Rule .................................................................................... 132

E) Benefit Summary .................................................................................................................. 134

F) Cost Summary ...................................................................................................................... 136

G) Guidance ...............................................................................................................................137
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TABLE OF APPENDICES 

APPENDIX A – PART 23 ICING ARC CHARTER 

APPENDIX B – PART 23 ICING ARC MEMBERS 

APPENDIX C – PART 23 AIRPLANE SEVERE ICING AIRWORTHINESS DIRECTIVES 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

APPENDIX E – OPERATIONS COST SURVEY 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 
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TABLE OF TABLES 

Table 1 - Comparison of Part 25 versus Part 23 Recommendations ............................ 22

Table 2 - Suspected SLD Events .................................................................................. 35

Table 3 - Pre-Activation Ice Accretions - Appendix C 

Continuous Maximum Conditions ........................................................................... 43

Table 4 - Sec. 23.67 Applicable Ice Accretions ............................................................. 56

Table 5 - "Sec. 23.1093 -Table 1" - Icing Conditions for Ground Tests ......................... 71

Table 6 - Aircraft Certified to § 23.1419 Amdt. 23-43 .................................................... 85

Table 7 - Size Assumptions Used for Certification Cost Estimates ............................... 93

Table 8 - Certification Approval Options with Respect to Icing Conditions .................... 93

Table 9 - Regulatory Input - Airframe Analysis .............................................................. 94

Table 10 - Regulatory Input – Flight Testing ................................................................. 96

Table 11 - Summary of Increased Certification Costs for Proposed Rulemaking .......... 98

Table 12 – Detailed Medians for the Aspects of Certification ........................................ 99

Table 13 – Events Applicable to SLD .......................................................................... 106

Table 14 – International Events Applicable to SLD ..................................................... 108

Table 15 – Events Applicable to ICTS Rulemaking ..................................................... 109

Table 16 – SLD Descriptor Distribution ....................................................................... 111

Table 17 – Phase of Flight Distribution........................................................................ 113

Table 18 – SLD Incidents ............................................................................................ 115

Table 19 – Events Applicable to Task 9 Proposed Rule.............................................. 135
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ABBREVIATIONS & ACRONYMS 

Item Description 

μm Micron (one millionth of a meter) 

2EI Two engines inoperative 

3D Three Dimensional 

AEO All Engines Operating 

AFM Aircraft Flight Manual 

AIA Aerospace Industries Association 

AIM Aeronautical Information Manual 

AOA Angle of Attack 

APO FAA Office of Aviation Policy and Plans 

Appendix C 14 CFR 25, Appendix C 

Appendix O Proposed 14 CFR 25 new appendix 

ARAC Aviation Rulemaking Advisory Committee 

ARC Aviation Rulemaking Committee 

ASOS / AWOS Automated Surface or Weather Observing System 

ASRS Aviation Safety Reporting System 

ATC Air Traffic Control 

ATP Airline Transport Pilot 

CFD Computational Fluid Dynamics 

CG Center of Gravity 

CS Certification Standard 

EHWG Engine Harmonization Working Group 

ELOS Equivalent Level of Safety 

FAA AIDS FAA Accident/Incident Database 

FAAST FAA Safety Team 

FADEC Full Authority Digital Engine Control 

FCS Flight Control System 

FIKI Industry abbreviation used generically for aircraft certified for flight in icing 

FITS FAA Industry Training Standard 

FTHWG Flight Test Harmonization Working Group 

FZDZ Freezing Drizzle 

FZRA Freezing Rain 

GA Go Around 

GAMA General Aviation Manufacturers Association 

GD / GU Gear Down or Gear Up (landing gear) 

GW Gross Weight 

ICTS Ice Contaminated Tailplane Stall 

IDS Ice Detection System 

IFR Instrument Flight Rules 

IMC Instrument Meteorological Conditions 

IPHWG Ice Protection Harmonization Working Group 

IPS Ice Protection System 

LWC Liquid Water Content 

MD Minor Damage 

MSL Mean sea level 

MVD Median Volume Diameter 

NATA National Air Transportation Association 

NOAA National Oceanic and Atmospheric Administration 

NPRM Notice of Proposed Rulemaking 

NPRM Notice of Proposed Rulemaking 

NTSB National Transportation Safety Board 

OEI One Engine Inoperative 
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ABBREVIATIONS & ACRONYMS 

Item Description 

PIDS Primary Ice Detection System 

PIREP Pilot Report 

POH Pilot Operating Handbook 

PTS Pilot Test Standards 

RACCA Regional Air Cargo Carriers Association 

S&C Stability and Control 

SD Substantial Damage 

SLD Supercooled large drops 

STC Supplemental Type Certificate 

SW Stall Warning 

TKS Industry abbreviation used generically for fluid depressant ice protection systems 

TO Takeoff 

Type II, III or IV Type of Ground Deicing/Anti-Icing Fluids (reference SAE AMS 1428) 

X-Wind Crosswind 

ZL Freezing Drizzle 

ZR Freezing Rain 
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1. SUMMARY 

The Part 23 Icing Aviation Rulemaking Committee was formed in early 2010 by FAA 

charter to consider the following tasking. The specific tasking requested of the ARC 

was and status is as follows: 

No. Task and Status 

1 

Review the ARAC recommendations related to the proposed part 25 regulations 

and guidance for SLD, mixed phase, and ice crystals, and recommend how they 

need to be modified for part 23. 

Completed 

2 

Recommend part 23 regulations that will codify the guidance in Advisory Circular 

23.1419-2D on activation and operation of ice protection systems, stall warning in 

icing conditions, and ice contaminated tailplane stall (ICTS). 

Completed 

3 

Recommend revision to current § 23.1419 on airplane performance requirements 

in icing that require an exemption to the 61 knot stall speed requirement in icing. 

Completed 

4 

Determine applicable accidents and incidents that can be used for benefits in the 

economic analysis. 

Completed by Revision A 

5 

Summarize certification and operating costs associated with the recommended 

regulations that can be used in the economic analysis. 

Completed by Revision A 

6 

Identify compliance guidance that will be required to facilitate showing compliance 

with the recommendations above. 

Completed 

7 

Identify impact on operations in known and forecast icing and make 

recommendations for icing operations and training. 

Completed by Revision A 

8 

Determine if using 1g stall speed criteria in icing is an option to reduce approach 

speeds and landing distances in icing conditions. 

Completed 

9 

Determine if implementation of NTSB Safety Recommendation A-10-12 is feasible 

for part 23 airplanes for operations in icing conditions (tasking added Q3 2010). 

Completed 
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2. BACKGROUND 

On October 31, 1994, an accident involving an Aerospatiale Model ATR72 series 

airplane occurred in which icing conditions, believed to include freezing drizzle drops, 

were reported in the area. The FAA and others have conducted an extensive 

investigation of this accident. This investigation led to the conclusion that freezing 

drizzle conditions created a ridge of ice on the wing’s upper surface aft of the deicing 

boots and forward of the ailerons. The NTSB concluded that the ridge of ice resulted in 

uncommanded roll of the airplane. The atmospheric conditions (freezing drizzle) that 

may have contributed to the accident are outside the icing envelope specified in 

Appendix C of part 25 of the Federal Aviation Regulations (14 CFR part 25) for 

certification of the airplane. Freezing rain is another atmospheric condition that also is 

outside the icing envelope. These conditions constitute an icing environment known as 

supercooled large drops (SLD). Appendix C of part 25 is also used for certification of 

part 23 airplanes for icing. The effects of SLD on part 23 airplanes are more significant 

than they are on part 25 airplanes. The smaller size of part 23 airplanes results in a 

larger collection efficiency, aerodynamic penalties are higher due to their smaller scale, 

they typically have reversible flight controls, and their power thrust margins are smaller. 

Accident reviews have shown the majority of SLD events belonged to small aircraft (14 

CFR part 23). The operating rules do not prohibit operations in supercooled large drop 

conditions. 

The NTSB issued various safety recommendations to the FAA following the Model 

ATR72 accident. One of the recommendations, A-96-56, states in part that: 

If the manufacturer cannot demonstrate safe operations in certain icing conditions, 

operational limitations should be imposed to prohibit flight in such conditions. 

Flightcrews should also be provided with the means to positively determine when they 

are in icing conditions that exceed the limits for aircraft certification. 

Another recommendation, A-96-54, states: 

Revise the icing criteria published in 14 Code of Federal Regulations (CFR), parts 23 

and 25, in light of both recent research into aircraft ice accretion under varying 

conditions of liquid water content, drop size distribution, and temperature, and recent 

developments in both the design and use of aircraft. Also, expand the appendix C 

icing certification envelope to include freezing drizzle/freezing rain and mixed water/ice 

crystal conditions, as necessary. 

The FAA tasked the Aviation Rulemaking Advisory Committee (ARAC) on December 8, 

1997 (62 FR 64621) in response to the NTSB safety recommendations. Their task was 

to define an icing environment that includes supercooled large drops (SLD) and devise 

requirements to assess the ability of aircraft to safely operate either for the time to exit 

or to operate without restriction in SLD conditions. The ARAC was tasked to consider 

the need to define a mixed phase icing environment (supercooled liquid and ice 

crystals). They were also asked to study the effects icing requirement changes could 
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have on pilot compartment view, airspeed indicating system, static pressure systems, 

and angle-of-attack systems. The task was revised in June 2000 to address 

14 CFR part 25 only. 

In December 2005, the Aviation Rulemaking Advisory Committee’s (ARAC) Ice 

Protection Harmonization Working Group (HWG) completed their final report on 

recommended rulemaking and advisory material related to supercooled large drop 

(SLD) conditions and ice crystal/mixed phase conditions. The committee’s work had the 

support of the Flight Test HWG, the Powerplant Installation HWG, and the Engine 

HWG. The report included recommendations for a new appendix to 14 CFR part 25, 

defining an SLD environment, and a new 14 CFR part 33, Appendix D to address ice 

crystal/mixed phase conditions. Included in the report are recommendations addressing 

14 CFR part 25 aircraft performance and handling qualities, engine installation effects, 

ice protection system requirements, and 14 CFR part 33 engine requirements. ARAC 

approved the report and sent it to the FAA in March 2006. The Ice Protection 

Harmonization Working Group has recently completed a review of available tools for 

compliance and revised the recommended guidance material. The ARAC report can be 

found at: 

http://www.faa.gov/regulations_policies/rulemaking/committees/arac/media/tae/TAE_IP_T2.pdf

A Notice of Proposed Rulemaking (Docket No. FAA–2010–0636) was published in the 

Federal Register on June 29, 2010. 

An Aviation Rulemaking Committee (ARC) was chartered to review the proposed part 

25 regulations and guidance for SLD, mixed phase, and ice crystals, that have been 

recommended by ARAC, and to recommend how they need to be modified for part 23. 

The charter is in Appendix A. 

The ARC task was not to produce an SLD rule from scratch, but to review the proposed 

part 25 rule and compliance guidance already recommended by an ARAC Issue Group 

(Transport Airplane and Engine, TAEIG) for applicability to part 23. An ARC was 

requested, rather than an ARAC tasking, to limit membership to airplane manufacturers 

that have certificated part 23 airplanes for flight in icing, Designated Engineering 

Representatives (DER) that have certified ice protection systems more common on part 

23 airplanes, such as pneumatic, fluid, and electro-thermal, operators of those part 23 

airplanes or groups that represent operators, and organizations who participated in the 

TAEIG working group, such as Transport Canada and EASA. The ARC still allowed 

subject matter experts to be brought in to provide background information. ARC 

membership is in Appendix B. 

The FAA has already taken action on part 23 airplanes, equipped with pneumatic boots 

and reversible lateral control, related to SLD. The FAA issued 25 Airworthiness 

Directives from 1996 to 1998 requiring incorporation of AFM Limitations and procedures 

to recognize SLD and immediately exit severe icing. A list of the ADs is in Appendix C. 
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The FAA also issued a generic issue paper “Roll Control in Supercooled Large Droplet 

Conditions” in July 1997 that has been applied for new certifications on aircraft 

equipped with reversible roll axis controls and pneumatic de-icing boots. The issue 

paper provided some protection against loss of control by providing for means to 

evaluate susceptibility to roll control in SLD conditions. However, it was not intended to 

certify an airplane for unrestricted flight in supercooled large drops or any other 

conditions which are outside of the Appendix C icing envelope. The guidance in the 

issue paper was added to Advisory Circular 23.1419-2D and application expanded to 

any part 23 airplane without a fully evaporative wing anti-ice system. The issue paper 

can be found in the ARAC reports at the following link: 

http://www.faa.gov/regulations_policies/rulemaking/committees/arac/media/tae/TAE_IP_T2.pdf

The scope of these actions is limited because they do not address the underlying safety 

concern of the unknown performance and handling safety margins for airplanes 

operating in freezing drizzle or freezing rain or a mixed phase. Any requirements resulting 

from these actions would not be comparable to those established by the current 

§ 23.1419, which defines safe performance and handling qualities for flight in part 25, 

Appendix C icing conditions. The current rules do not address stall warning in SLD 

conditions, and they do not require an AFM limitation on intentionally flying into SLD. 

As documented in the ARAC report, ice crystal conditions can affect engine operation 

and pitot probes. On part 23 airplanes, documented events of ice crystals affecting 

engine total temperature probes have been reported. Current certification addresses 

these effects on engine operation and critical systems through the issue paper process. 

After the part 23 icing ARC charter was signed, an additional task was assigned to 

address NTSB safety recommendation A-10-12 for part 23 airplanes in icing conditions 

which states: 

For all airplanes engaged in commercial operations under 14 Code of Federal 

Regulations Parts 121, 135, and 91K, require the installation of low-airspeed alert 

systems that provide pilots with redundant aural and visual warnings of an 

impending hazardous low-speed condition. 

This task was completed and Revision B of this report incorporates the ARC 

recommendations. 
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3. PREAMBLE DISCUSSION 

A) SUBPART B ASPECTS (INCLUDING AUTOPILOT)

The proposed part 23 regulation for showing safe flight in Appendix O conditions is 

similar to the proposed part 25 regulation. The same three options are provided. The 

only difference is “capable of operating safely” is defined by reference to the 

applicable 23.21(c) paragraph. Section 23.21 is amended by the addition of 

paragraph (c). This paragraph defines the Subpart B regulations for which compliance 

must be shown with Appendix C and Appendix O ice accretions. As a result, the 

definition of “capable of operating safely” currently in § 23.1419(a) is deleted. 

The ARAC proposal for compliance to part 25 Subpart B regulations with Appendix O 

ice accretions was reviewed. The part 23 ARC agreed with the ARAC 

recommendation that the regulations required for Appendix C be also applicable for 

Appendix O, for those airplanes that are approved for Appendix O. This includes the 

addition of takeoff requirements with gear down, where it may not be accurate to 

assume ice accretion may be negligible. The ARC identified a requirement for a 

separate part II of Appendix O, due to differences in the scenarios for ice accretion 

based on operations for part 23 aircraft. Also, the proposed part 25, Appendix O, part 

II directly references part 25 regulations which are not appropriate for part 23. The 

part 23 definitions for ice shapes are recommended to be incorporated into a new part 

23 Appendix TBD, with Part I of the proposed Appendix defining ice shapes that may 

occur in 14 CFR Part 25, Appendix C icing conditions and Part II of the proposed 

Appendix ice shapes that may occur in 14 CFR Part 25, Appendix O icing conditions. 

Reference section 4B of this report for details on the recommended ice shape 

definitions. 

The part 23 ARC agreed with the ARAC recommendation that allow an option to 

certify an airplane to a portion of Appendix O. The Subpart B regulations required to 

show safe operation in the approved portion of Appendix O are the same as those for 

Appendix C. The part 23 icing ARC also agrees that certifying to a portion of 

Appendix O in-flight will be difficult with current technology. Applicable guidance was 

added to the proposed advisory circular to address the concerns. 

The part 25 proposed guidance has detailed information on the limitations to 

accomplish such a certification. The material was included as Appendix 7 of the 

proposed advisory circular. The part 23 ARC recommends that this material 

eventually be moved to AC 20-73 since it is applicable to both part 23 and part 25 

airplanes. 

The part 23 icing ARC agrees with ARAC that certifying an airplane to a certain phase 

of flight in Appendix O conditions is achievable. The ARC believes certifying to takeoff 

in Appendix O conditions would be the most common phases of flight certified 

because one, operators surveyed stated such an airplane is desirable to minimize 

impact on operations, and two, it may be easier to certify compared to the holding 
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phase. The guidance for takeoff in Appendix O conditions assumes the airplane will 

not hold in Appendix O conditions, but for landing, certification must consider a detect 

and exit holding ice shape. Guidance is included in the draft part 23 advisory material. 

The part 23 icing ARC discussed whether certification for takeoff (and/or landing) can 

be done to either freezing drizzle or freezing rain. The majority and minority positions 

on ARAC were reviewed, as well as current weather reporting technology. The ARC 

acknowledged the ARAC minority position on the percentage of freezing rain events 

being misreported as freezing drizzle, and believes this may be common since FAA 

experience is that snow intensities (currently based on visibility) are misreported half the 

time. The ARC also considered that part 23 airplanes operate at many airports with no 

weather observers. Although the airports with no human observers may have AWOS or 

ASOS, the current technologies of these systems prevent them from reporting freezing 

drizzle. The ARC believes the average pilot of a part 23 airplane will not be able to 

consistently distinguish drizzle from rain. The part 25 majority acknowledged that 

misdiagnosis can occur in discriminating between freezing drizzle and rain, and 

supports improvements in practices and technology to improve reporting accuracy. 

However, the IPHWG judged that the conservatism inherent in the certification practices 

would result in safe operations. This conservatism includes assuming a 12,000 foot 

vertical extent, 99% LWC and an engine out during the climb (per § 25.111 

requirements). 

Another issue is after takeoff, one must assume that FZDZ conditions can change to 

FZRA conditions, or vice versa. When this occurs, an in-flight cue for exceedance of 

certified conditions is mandatory. Technology may be available in 5-7 years to 

determine the drop sizes aloft in terminal areas, but that would only apply to larger, 

commercial airports. It may also be possible in the future for aircraft to develop in-flight 

cues for these types of exceedance, due to advances in weather reporting technology 

and experience with certification of various ice accretions. For now, operational issues 

preclude certifying a part 23 airplane to takeoff (and/or land) in FZDZ or FZRA alone, 

and no guidance is provided at this time. However, the ARC believes the regulation 

should allow the option to certify an aircraft for either condition in anticipation of future 

technologies and advancements. 

The part 23 icing ARC recognized that Type II and IV ground deicing fluids have not 

been approved for many part 23 airplanes, not because it is not possible but because 

airplane manufacturers have not sought the approval. The part 23 icing ARC 

recognized that an airplane approved for takeoff in freezing drizzle and light freezing 

rain will accrete ice before lift-off if not treated with these fluids (The short hold-over 

times provided by Type I in these conditions make takeoff prior to hold-over time 

expiration difficult). Therefore, any aircraft that sought approval for takeoff in FZDZ or 

FZRA conditions would require that the aircraft meet published AFM/POH limitations 

and procedures. This may require prior manufacturer approval of Type II, III and IV 

ground deicing/anti-icing fluids. 

The part 23 icing ARC took a slightly different approach than the part 25 ARAC group 

for “detect and exit”. For "operating safely after encountering Appendix O conditions" 
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and "operating safely while exiting all icing conditions", the part 25 ARAC considered 

that these are not failure cases and the temptation to link this text with the phrase 

"continued safe flight and landing", commonly used in association with system failure 

conditions, should be resisted. The part 25 ARAC considered "detect and exit" cases 

as normal flight conditions arising from an inadvertent encounter with Appendix O icing 

conditions. Hence, the ARAC considered it appropriate to make "detect and exit" for 

Appendix O an integral part of any icing certification for Appendix C icing conditions i.e. 

if an Appendix C icing certification is sought, then "detect and exit" for Appendix O must 

also be addressed. The part 23 icing ARC agreed that detect and exit of Appendix O 

must be considered for a known icing approved airplane, but considered it conservative 

for part 23 airplanes. The part 23 ARC recognized that part 23 airplanes have more 

flexibility in divert options, and continued flight after an SLD encounter may occur less 

frequently. The part 25 ARAC considered all Subpart B regulations applicable to 

Appendix C should be applicable to “detect and exit”, with some exceptions. The part 

23 icing ARC compared the inadvertent Appendix O encounter with an inadvertent icing 

encounter of an airplane not approved for icing. In the latter case, no Subpart B tests 

are required. However, the encounter with Appendix O is different in that pilot 

recognition of Appendix O versus Appendix C is not as black and white as ice/no ice. 

The ARC also considered that Appendix O ice accretions may be more critical than 

Appendix C, and an airplane certified for Appendix C should be shown to be safe 

following an encounter with Appendix O. In reviewing the Subpart B requirements for 

detect and exit, the ARC tried to avoid requirements that could dictate design for an 

environmental condition for which the airplane is not certified. The ARC decided that 

the regulations should address the safety issues that have been learned in Appendix O 

accidents. These are addressed in the following paragraphs. 

PERFORMANCE AND HANDLING QUALITIES FOR "DETECT AND EXIT"

Regarding specifically handling qualities and performance, the discussions in the 

FTHWG addressed the following issues: 

 Performance – The part 25 ARAC assumed that the take-off case need not be 

considered for a "detect and exit" airplane. Hence, with the exception of stall 

speeds, landing speeds and distances and landing climb performance, the part 

25 ARAC considered that performance need not be specifically addressed for 

"detect and exit" certification. The part 23 icing ARC agreed, with the exception 

of a quantitative requirement for landing climb performance. The part 23 icing 

ARC decided that the airplane should be able to go-around following an 

encounter with SLD, particularly since most part 23 events occurred near an 

airport during approach or landing. However, the ARC felt a demonstration of the 

ability to go-around was sufficient. The ARC did not want a quantitative 

requirement in an environment the airplane is not approved for to possibly dictate 

design. Another factor was that the number of SLD events in a go-around was 

small. Some ARC members raised the issue that the commuter category 

approach climb rule be required. The majority of the ARC decided that engine 

out need not be considered for detect and exit because of the limited probability 
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of occurrence and prior history. No combinations of engine failures in SLD are 

noted in the event database. 

Various members of the ARC also questioned why enroute climb performance 

was not considered for the SLD “detect and exit” airplane. The subpart B group 

considered this question and agreed that considering enroute ice was not 

necessary for the “detect and exit” scenario. For flight planning purposes, flight 

into any SLD conditions for a ”detect and exit” airplane would not be considered. 

However, enroute performance provided for an appendix C approved airplane 

would normally include the worst case ice shape tested. At a minimum, the 

enroute ice shape would be used to provide performance in icing conditions. The 

conclusion was that the detect and exit shapes would not provide enough of a 

difference in performance from that tested for appendix C approval to require 

investigation with the specific SLD shape. 

 Handling qualities – The part 25 ARAC proposed, with one exception, that the 

same handling qualities as for flight in Appendix C icing conditions are retained. 

That exception was a take-off case, CS/FAR 25.143(c)(1), addressing 

controllability following engine failure at V2. No justification for a relaxed 

standard of other handling qualities requirements could be identified, bearing in 

mind that "detect and exit" is not a failure case and that the airplane, once clear 

of all icing conditions but retaining the ice accretion, may continue in clear air for 

some time. The part 23 ARC did not recommend that all Subpart B controllability 

tests be accomplished for detect and exit, but did recommend tests that address 

service history of airplanes in icing. These include susceptibility to roll control 

anomalies and ice contaminated tailplane stall. 

 Lateral controllability - The part 25 ARAC reviewed the JAA Interim Policy and 

the FAA ADs published to address roll controllability issues. Several 

manufacturers gave presentations of their experiences in addressing the FAA 

ADs during the part 25 rulemaking effort. The part 25 ARAC concluded that the 

existing requirement is adequate to address roll control but there is a need for 

additional advisory material. This has been added to AC 25-25. The part 23 

icing ARC reviewed the similar guidance in AC 23.1419-2D and thought it should 

be made more clear. Part 23 differs from part 25 in that the 23 rule has a 

quantitative roll rate requirement. The ARC decided that lateral control 

evaluation should be conducted on a detect and exit airplane, but the roll rate 

should be qualitatively, not quantitatively, evaluated. Therefore the lateral control 

evaluation was added to Section 23.143. The ARC reviewed additional tests that 

were proposed by Transport Canada during the part 25 ARAC group work. 

These included lateral control during 10° bank to bank rolls at airspeeds down to 

stall warning, and lateral control during sideslips. The bank to bank tests were 

added as advisory material to 23.201. The ARC decided that lateral control can 

be evaluated during the sideslips conducted to evaluate susceptibility to ice 

contaminated tailplane stall. 
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 Stall warning – The ARC believed stall warning, provided by the same means as 

in non-icing, must be provided with critical detect and exit ice shapes. The ARC 

adopted the three second after stall warning margin requirement proposed for 

part 25, in lieu of the five knot margin required in Appendix C for part 23 

airplanes. The rationale was to avoid designs in which a second icing stall 

warning schedule was required for SLD, the issue being workload and training. 

The ARC believed a stall warning system designed for five knot margin in 

Appendix C could also provide a three second margin in Appendix O. The ARC 

believed a three second margin provided sufficient time to prevent stall, 

especially in the approach and landing phases of flight where the majority of part 

23 events occurred. Since detect and exit ice includes pre-detection ice, such a 

design would also provide stall warning with pre-detection ice, which the ARC 

believes is necessary. A separate rule for pre-detection was therefore not 

required. This follows the philosophy of the proposed part 25 rule published in 

the NPRM. Similar to part 25 as explained in the NPRM preamble, if a design 

with two icing stall warning schedules were proposed, special conditions would 

be required. 

 Approach speed – It is likely that stall speeds could increase with detect and exit 

ice compared to Appendix C ice. The approach speed with Appendix C must be 

at least 1.3 times the stall speed with Appendix C icing. Approach speeds in 

icing are usually increased because the increase in stall speed with Appendix C 

ice is usually above the 3 knot/3% threshold proposed. The ARC was concerned 

with additional increases in approach speed and resulting increases in landing 

distances, and the possibility of overruns. The ARC proposed that the approach 

speed determined for Appendix C may be used for detect and exit if adequate 

maneuver margin is demonstrated at that speed with detect and exit ice 

accretions. 

 Pre-activation ice – Stall warning and susceptibility to ice contaminated tailplane 

stall are evaluated with pre-activation ice in Appendix C icing conditions, under 

current part 23 guidance and part 25 regulations. Part 25 requires a one second 

margin after stall warning if the means of stall warning is the same as non-icing. 

If the means are different, part 25 allows three second margin and acceptable 

stall characteristics. Current part 23 guidance for Appendix C ice accretion does 

not have the three second option. The ARC did not adopt the ARAC 

recommendation to apply the Appendix C pre-activation ice stall warning 

requirements to Appendix O conditions. The ARC was concerned that applying 

the same requirements to Appendix O pre-activation ice may have an overall 

adverse affect on safety by increasing non-icing takeoff and landing speeds. 

Current Part 23 advisory material (AC 23.1419-2D) specifies that stall warning 

margin with Appendix C pre-activation ice be “positive...and adequate.” 

Compliance with this requirement is typically shown by decelerating the airplane 

at 1 kt/sec and demonstrating that a stall can be prevented when recovery is 

initiated one second after stall warning, similar to the test defined in 25.207(h). 

Since, by definition, this test must be conducted with the airplane configured as it 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-18

is prior to IPS activation, any adjustment to the stall warning schedule 

implemented for icing conditions is not active. As a result, the airplane must 

meet this requirement with the non-icing stall warning schedule. Recent industry 

experience is that this requirement can drive the stall warning setting to a lower 

angle of attack (more stall warning margin) than would otherwise be selected. A 

low stall warning AOA can result in insufficient maneuver margin for takeoff and 

landing which potentially drives artificially high takeoff and landing speeds for all 

non-icing takeoffs and landings, which constitute the vast majority of operations. 

Higher takeoff and landing speeds are not desirable from safety (runway 

overruns) or airplane utility perspectives. 

The ice shape roughness associated with Appendix O pre-activation conditions 

may be more critical for stall warning than for Appendix C pre-activation 

conditions which could in turn drive an even lower stall warning AOA setting 

which would further impact non-icing takeoff and landing speeds. 

Testing ICTS susceptibility with pre-activation ice in Appendix O conditions may 

result in reduced flap deflections in non-icing conditions, increasing landing 

speeds further. 

Examination of the Part 23 accident history does not show that accidents 

occurred because the pilot was unaware that the airplane was in icing conditions. 

Furthermore, the proposed requirements for IPS activation based on 1) operation 

in conditions conducive to icing (temperature and visible moisture), 2) first 

indication of ice accretion or 3) input from a primary ice detector are effective at 

minimizing unprotected exposure times in icing conditions. To further minimize 

risk of an event with pre-activation ice in Appendix O conditions, the ARC 

decided to require an Advisory or Primary Ice Detector for commuter category 

airplanes that would otherwise rely solely on visual cues (proposed § 

23.1419(e)(2), which is what was proposed for part 25 airplanes. The ARC 

concluded that since airplanes will continue to be required to meet existing 

Appendix C pre-activation ice stall warning requirements and due to the potential 

negative effect on non-icing takeoff and landing speeds, an additional 

requirement to demonstrate stall warning with ice accretions representing the 

very small exposure time associated with pre-activation Appendix O conditions is 

unwarranted. Another potential mitigating feature is installation of a Low 

Airspeed Alert, which will activate at airspeeds higher than stall warning speed, 

but lower than operating speeds to prevent nuisance warnings. Low airspeed 

alert aspects are to be addressed under ARC task 9 which will be addressed as 

a follow-up recommendation to this report. For reliability requirements of ice 

detection systems see the discussion under systems aspects, reference 

§ 23.1419. 

 Pre-detection ice - The ARC adopted the same philosophy that stall warning and 

susceptibility to ICTS be evaluated with pre-detection ice. However, since detect 

and exit ice includes pre-detection ice, in most cases there would not be a 

requirement to test pre-detection ice. Exceptions may be if design of the stall 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-19

warning system includes a unique schedule for SLD conditions (as discussed 

above in the “Stall Warning” paragraph), or there is an autopilot limitation against 

operation after detection of SLD conditions. 

AUTOPILOT ASPECTS

No regulation changes were proposed, for part 25 to address autopilot operation in icing 

conditions. Icing is not referenced in § 25.1329, but there is detailed guidance in 

Advisory Circular 25.1329 on autopilot operation in part 25, Appendix C icing conditions. 

Change 1 to Advisory Circular 25.1329 was proposed and it adds “applicable” Appendix 

O conditions to the current Appendix C conditions listed as “normal conditions” for which 

the flight guidance system should be designed. Similarly, the ARC believes the current 

guidance on testing autopilots in Appendix C conditions is applicable to Appendix O 

conditions. The current guidance in AC 23.1419-2D, combined with the current part 23 

regulations, have proved sufficient for evaluating the autopilot in Appendix C icing 

conditions. However, the ARC proposes a regulation for an autopilot disconnect 

indication as discussed later. 

There is guidance in Advisory Circular 23.1419-2D on flight testing autopilots in icing 

conditions for which the airplane is certified. For severe icing conditions, current part 23 

certification practice is similar to airworthiness action that was taken on most pneumatic 

boot equipped airplanes, with reversible lateral flight controls, in 1996-1997. The 

following was added to the Airplane Flight manual: 

Limitations section: 

“Use of the autopilot is prohibited when any ice is observed forming aft of 

the protected surfaces of the wing, or when unusual lateral trim 

requirements or autopilot trim warnings are encountered.” 

“NOTE: The autopilot may mask tactile cues that indicate adverse changes in 

handling characteristics; therefore, the pilot should consider not using the 

autopilot when any ice is visible on the airplane.” 

Procedures section: 

“WARNING: If the autopilot is engaged, hold the control wheel firmly and 

disengage the autopilot. Do not re-engage the autopilot until the airframe is 

clear of ice.” 

“Do not engage the autopilot. The autopilot may mask unusual control system 

forces.” 

“If the autopilot is engaged, hold the control wheel firmly and disengage the 

autopilot.” 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-20

The ARC decided that the autopilot should not have to be prohibited for flight in 

Appendix O conditions, particularly in the single pilot, IMC environment, if adequate 

testing was accomplished. The current part 25 guidance and proposed guidance in 

Change 1 of AC 25.1329 were used as starting points for proposed part 23 guidance. 

There is existing guidance in AC 23.1419-2D for evaluating the autopilot in icing 

conditions. The ARC proposes to consolidate the autopilot guidance for all icing 

conditions, Appendix C and Appendix O, into one section of the guidance for new type 

certificates. Appendix 3 of AC 23.1419-2D contains guidance on modified or new 

autopilots STC’s on airplanes approved for flight in icing conditions. 

Testing will be required with applicable Appendix O ice shapes (e.g. detect and exit) if 

autopilot use will be approved. An applicant still has the option to prohibit autopilot use 

for detect and exit aircraft in Appendix O icing conditions. However, since the autopilot 

may be engaged prior to pilot recognition of Appendix O conditions, autopilot flight 

testing has to include “pre-detection ice”. If an autopilot is installed and approved for 

flight in non-icing conditions, or required in non-icing flight for compliance to § 23.1523, 

it will be required for flight in icing conditions based on operational requirements. 

Similarly, if an autopilot equipped airplane is approved for any portion or phase of flight 

in Appendix O conditions, the autopilot will be required to operate in those Appendix O 

conditions. 

The guidance contains requirements for flight testing of ice shapes simulating critical 

Appendix C, detect and exit (or pre-detection), and the approved portions of Appendix 

O. The guidance material retains the requirements to test the autopilot in natural 

Appendix C icing conditions. It is expected that the autopilot will be flight tested in 

natural Appendix O conditions for which the airplane is approved. The ARC also 

recommends that the guidance in AC 23-17B on autopilot systems as a minimum 

reference the autopilot guidance in AC 23.1419-2D. 

When choosing critical simulated ice for flight testing, the effect on autopilot 

performance and operation should be considered. 

The proposed guidance includes flight testing symmetrical ice shapes, there is no 

proposal to flight test asymmetric ice shapes. However, the ARC believed that if 

autopilot use in Appendix O conditions was to be approved, unusual operating condition 

for which the autopilot is compensating must be addressed. This could include 

asymmetric lift due asymmetric wing ice shedding, or possibly the autopilot operating 

near its authority limit due to ice accretion effect on control power or hinge moment. 

The ATR Roselawn accident is one example in which automatic autopilot disconnect 

after reaching authority limit resulted in a loss of control. Although there are no such 

documented events in the part 23 fleet, this could be because of current practice of 

prohibiting autopilot use in severe icing, or it could be these events have occurred but 

not documented due to the lack of flight data recorders in the part 23 fleet The proposed 

change to AC 25.1329 adds asymmetric icing as a “Rare Normal” condition that should 

be addressed, and the ARC believes it should be addressed for part 23 airplanes. The 

ARC proposes a requirement for a “bark before bite” to permit the crew to manually 

disengage the autopilot and take control prior to any automatic autopilot disengagement 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-21

that would result in a hazardous flight condition. A paragraph (i) is proposed to be 

added to Section 23.1329. This requirement would apply only if the autopilot is to be 

approved for use in Appendix O conditions, including detect and exit. The rule specifies 

an indication rather than an annunciation. There may be designs in which control 

position or bank angle would be an acceptable indication. Associated guidance is 

added to the draft AC 23.1419-2D revision. 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B B) SUMMARY TABLE OF SUBPART B PART 23 PROPOSALS VERSUS PART 25 PROPOSALS

The table below summarizes each Subpart B paragraph and the requirements proposed for part 23 deairplanes by the ARC versus proposed for part 25 by ARAC. 

Table 1 - Comparison of Part 25 versus Part 23 Recommendations 

Section Title Proposed 

Part 25 

Part 23 Proposed Pa

 Detect & 

Exit 

 Detect & 

25.21 Proof of compliance 23.21 25.23 Load distribution limits 23.23 25.25 Weight limits 23.25 25.29 Empty weight and 

corresponding CG 

23.29 

25.31 Removable ballast 23.31 25.33 Propeller speed and pitch 

limits 

23.33 

25.101 General (performance) 23.45 25.103 Stall speed 23.49 (a) and (b) only. Stall s

defined to determine opstall warning margin. 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Section Title Proposed 

Part 25 

Part 23 Proposed Pa

25.105 Takeoff 23.53 NOTE 1 25.107 Takeoff speeds 23.51 NOTE 1 25.109 Accelerate-stop distance 23.55 NOTE 1 25.111 Takeoff path 23.57 NOTE 1 25.113 Takeoff distance and takeoff 

run 

 23.59 NOTE 1 

25.115 Takeoff flight path 23.61 NOTE 1 25.117 Climb: general 23.63 NOTE 1  Climb: AEO 23.65 NOTE 1  Takeoff climb: OEI 23.66 NOTE 1 25.119 Landing climb AEO 23.77 Except in lieu of quanti

must be measurably po

 Climb OEI GW<6000 Normal 23.67(a) NOTE 2  Climb OEI GW>6000 Normal 23.67(b) NOTE 2 25.121(a) Climb OEI TO GD Commuter 23.67(c)(1) NOTE 2 25.121(b) Climb OEI TO GU Commuter 23.67(c)(2) NOTE 2 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Section Title Proposed 

Part 25 

Part 23 Proposed Pa

25.121(c) Climb OEI Final TO 

Commuter 

 23.67(c)(3) NOTE 2 

25.121(d) Climb OEI Approach 

Commuter 

 23.67(c)(4) NOTE 2 

25.123(a) Enroute flight path OEI 23.69 NOTE 2 25.123(b) Enroute flight path OEI 23.69 NOTE 2 25.123(c) Enroute flight path 3-4 engine NA NOTE 2  Glide: Single engine airplanes 23.71 NOTE 2 25.125 Landing 23.73 Vref Applicable. 1.3Vs or u

long as maneuver margis to not bump SLD appspeed (runway overrunadequate. 

25.125 Landing 23.75 Dist. Applicable if Vref define

detect and exit greater Vref. May be determin

 Flight characteristics: General 23.141 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Section Title Proposed 

Part 25 

Part 23 Proposed Pa

25.143(a) Controllability and 

Maneuverability 

 23.143(a) Applicable for appropri 23.143(b) It must be possible to m

transition from one flighanother (including turns danger of exceeding thunder any probable opAEO only. May be evawith other flight tests. 

25.143(b)(1) Sudden failure of engine 23.143(b) 25.143(b)(2) Sudden failure of second 

engine 

25.143(b)(3) Configuration changes 25.143(c)(1) Control with OEI in icing TO NOTE 2 25.143(c)(2) Control with OEI in icing Appr. 

& land 

NOTE 2 

25.143(c)(3) Control with OEI in icing Appr. 

& GA 

NOTE 2 

25.143(d) Control force limits 23.143(c) Applicable 25.143(e)-(g) 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Section Title Proposed 

Part 25 

Part 23 Proposed Pa

25.143(h) Maneuver margin 25.143(i) ICTS 23.143(d) Not applicable. 25.143(j) Control – pre-activation ice 23.143(e) Applicable. Evaluated w

low and high airspeed, thrust/power. 

25.143(k) Control – pre-detection ice  Control – detect & exit 23.143(f) Applicable. Evaluated w

low and high airspeed, thrust/power. Longitudinal and laterawith sideslips expected 

 Lateral control evaluation 23.143(g) Specific tests added to 25.145(a) Pitch down capability 23.145(a) NOTE 3 25.145(b) Configuration changes 23.145(b) NOTE 3 25.145(c)&(d) GA w/complete flap retract– no 

loss of altitude 

 23.145(b)(3) NOTE 3 

 1.5g capability above 

Vmo/Mmo 

 23.145(c) NOTE 3 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Section Title Proposed 

Part 25 

Part 23 Proposed Pa

 Power off glide gear and flap 

extended 

 23.145(d) NOTE 3 

 Landing with primary FCS 

failure 

 23.145(e) NOTE 4 

25.145 Longitudinal control 23.145 NOTE 3 25.147(a) Directional control – OEI 23.147(a) NOTE 2 25.147(b) Directional control – 2EI 25.147(c) Lateral control – OEI 25.147(d) Lateral control - 2EI 25.147(e) Lateral control margin – AEO  Sudden engine failure – 2 sec 

delay 

 23.147(b) NOTE 2 

 Control with primary lateral 

FCS failure 

 23.147(c) NOTE 4 

25.149 Minimum control speed 23.149 NOTE 2  Acrobatic maneuvers 23.151 NOTE 5  Control during landings 23.153 NOTE 3 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Section Title Proposed 

Part 25 

Part 23 Proposed Pa

 Elevator control force in 

maneuvers 

 23.155 NOTE 3 

 Rate of roll 23.157 Rate of roll evaluated q

compliance to 23.143(g

25.161 Trim 23.161 NOTE 3 25.171 General (stability) 23.171 NOTE 3 25.173 Static longitudinal stability 23.173 NOTE 3 25.175 Demonstration of Static Long. 

Stab. 

 23.175 NOTE 3 

25.177 Static lateral-directional 

stability 

 23.177 Evaluated during sides

ICTS evaluation. 

25.181 Dynamic stability 23.181 NOTE 3 25.201(a) (b)(d)(c)(1) 

23.201 & 23.203 

Applicable. Use pass/f23.1419-2D: Roll may s15 degrees if characterdetermined to be safe. 

25.201(c)(2) Turning stall 3 kt/sec 23.203(a)(2) NOTE 5 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Section Title Proposed 

Part 25 

Part 23 Proposed Pa

25.203 Stall characteristics 23.201 & 

23.203 

Applicable except use from AC 23.1419-2D. level and turning stalls accelerated turning sta

25.207(a) Stall warning 23.207(a) Applicable.  Means of stall warning 23.207(b) Applicable. 25.207(b) Means of stall warning same in 

icing 

23.207(i) Applicable plus means 

same as non-icing and 

25.207(c) 5 knot/5% margin to stall 23.207(c) 25.207(d) 3 knot/3% margin to Vsr 23.207(c) See 25.143(h) Maneuver margin 23.207(d) See 23.73 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Section Title Proposed 

Part 25 

Part 23 Proposed Pa

25.207(e) 3 sec margin to stall in icing 23.207(h) Adopt part 25 3 sec in 

knot in icing. Reasons3 sec is adequate timeapproach and landing pevents occur Relaxing margin in SLD one SW schedule for icseparate SLD SW scheimplemented? A switcavoid that – workload isintentional non-complia

25.207(f) Stall warning 1.5g turns 2 

kt/sec 

23.207(e) Shouldn’t be required t

current part 23 practice 

25.207(g) Abnormal configuration of high 

lift 

25.207(h) Stall warning pre-activation ice 23.207(g) 25.207(i) Stall warning pre-detection ice Not included in part 25 

pre-amble explains shodetect and exit ice shap

 Acrobatic airplane stall 

warning 

23.207(f) 

 Spinning 23.221 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Section Title Proposed 

Part 25 

Part 23 Proposed Pa

25.231 Ground and water Longitudinal 

S&C 

23.231 Applicable – no dedica

25.233 Ground and water Directional 

S&C 

23.233 Applicable – no dedica

guidance similar to App sideslip data for x-wind 

25.235 Taxiing conditions 23.235 Not applicable 25.237 Wind velocities 23.233  Operation on water 23.237 Applicable – no dedica25.239 Spray characteristics 23.239 25.251(a) Vibration & buffeting 23.251 Applicable . Evaluation 

Vne, airspeed shown to accretion, reduced spethe AFM for SLD exit./* 

25.251(b) – (e) Vibration & buffeting 23.251 25.253(a) High speed characteristics & 

recovery 

23.253 

25.253(b) Maximum speed for S&C nonicing 25.253(c) Maximum speed for S&C icing 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Section Title Proposed 

Part 25 

Part 23 Proposed Pa

25.255 Out-of-trim characteristics Legend and Notes:  Not required  Required – specific language added  Required – referenced in § 25.21(g) Red text Not required in 23.1419 Amdt. 23-43 NOTE 1: Airplane is assumed to takeoff clean and not takeoff into SLD conditions. NOTE 2: Service history shows part 23 SLD accidents not due to engine failure. NOTE 3: No dedicated tests required. Controllability, trim and stability evaluated concurrently with oth

NOTE 4: Service history shows part 23 SLD accidents not due to flight control failure. NOTE 5: Not required or typically evaluated currently for Appendix C icing conditions. 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-33

C) SUBPART B - MEANS OF COMPLIANCE APPENDIX O

The proposed part 23 guidance material for Appendix O was derived from the 

proposed part 25 proposed guidance. A description of the simulation tool limitations 

for Appendix O and guidance for airplane components in the different Appendix O 

distributions are provided. Some of the details are omitted and the part 25 guidance is 

provided as reference. As in part 25, as the tools mature, the part 23 guidance will be 

revised. 

APPENDIX O ICING ENVELOPE 

The ARC adopted the proposed freezing drizzle and freezing rain definitions in the 

proposed part I of Appendix O of part 25. The ARC proposes that part 23 regulations 

reference part I of Appendix O of part 25. The ARC charter did not intend to change 

the part I definitions, and there is no reason to, since the ARC cannot rationalize why it 

should be different, since the environment is not changed by the category of airplane 

flying in it. The ARC did, however, question the proposed liquid water content at the 

cold freezing drizzle conditions as discussed below. 

APPENDIX O ICE ACCRETIONS 

The ARC reviewed the proposed ice accretions in proposed part 25, Appendix O, part 

II. The ARC decided that part 23 should adopt a part 23 appendix to define ice 

accretions in part 25, Appendix O, part I conditions, and not reference part 25, 

Appendix O, part II, for the following reasons: 

 Part 25, Appendix O, part II references part 25 sections; and 

 The ARC modified the detect and exit ice accretions. 

The ARC agreed with the part 25 proposal that takeoff and failure ice shapes would 

not be required for a detect and exit airplane. The ARC proposed initial modifications 

for detect and exit ice accretions as follows: 

 Enroute ice accretion was limited to airplanes with an altitude capability below 

30,000 feet, since airplanes with capability above 30,000 would cruise above 

that altitude. This rationale and the 30,000 ft. number is the same rationale for 

the guidance in AC 23.1419-2D on fluid capacity for fluid ice protection 

systems. Enroute ice was also limited to 55 nm. This distance is in guidance 

in AC 23.1419-2D for runback ice and covers 90% of status clouds according to 

data in ADS-4. The ARC was looking for means to limit the requirement to 

calculate enroute ice, since the ice accretion amount is usually addressed by 

the 45 minute hold, and some manufacturers address the 45 minute hold and 

not enroute. 

 Pre-activation ice was deleted. See discussion earlier in this report. 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-34

 Landing ice was re-defined. Since it was expected most part 23 airplanes 

would land if Appendix O was encountered during approach and landing, a goaround was deleted. It was replaced with a 17.4 nm exposure, initially with 

approach flaps and the last 6 nm (outside marker distance) in either Appendix 

C or O, whichever was more critical. 

Two additional revisions were made for “detect and exit” after a review of alternatives: 

 The phases of flight required for analysis was reduced to holding and approach; 

and 

 The ambient temperature that must be analyzed for “detect and exit” ice 

accretions in Appendix O was limited to -13°C and above. 

One of the alternatives considered by the ARC was simplification of detect and exit ice 

accretions. The ARC recognized that four different Appendix O distributions combined 

with four different flight phases would require much tunnel test and analyses. As a 

result, the ARC eliminated enroute phase and landing phase for detect and exit, so 

only holding and approach phases remained. The rationale was that the ice accretion 

determined during these phases could account for the remaining phases. 

The ARC did an initial review of part 23 icing events in suspected SLD conditions and 

determined that most events, 39%, occurred during the approach phase. So the ARC 

determined that ice accreted during the holding phase, which may have preceded the 

events, and the approach phase, should be evaluated. The landing phase had the 

next highest amount of events, 31%. Even though the majority of these events were 

hard landings and non-fatal, the ARC believes the ice accretion determined during the 

approach phase would be sufficient. The proposed landing phase profile differed from 

the approach in that the last 6 nm was at landing flaps versus approach flaps. If the 

design did develop substantial ice accretion behind the protected area during the 

approach, it most likely would serve as an accretion site at the lower angle of attack 

with landing flaps, and shadow the upper wing surface. Flight testing would still 

include landing and go-around demonstrations (3% of events), and the ARC believes 

a stall protection system and AFM procedures developed with approach ice shapes 

would be sufficient for these phases. Also, the ARC proposed approach phase 

included transiting 17.4 nm in Appendix C after an SLD exposure (which could be 

critical since the SLD ice accretions would serve as a new accretion site for Appendix 

C drops), much higher than the ARC proposed landing phase. The remaining part 23 

SLD events occurred in climb, cruise, and descent (26% of events). The ARC 

believes the holding phase adequately addresses these. A descent may be critical 

due to low bleed and low angle of attack, but the only proposed part 25 profile which 

includes a descent is the approach definition, which is included in the ARC 

recommendations. 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-35

Another alternative considered was evaluating the need to consider freezing drizzle 

conditions at very cold conditions. Some members of the ARC reviewed the FAA 

technical report on the data and analysis used for development of the 14 CFR part 25 

Appendix O definitions (DOT/FAA/AR-09/10) and noted that most of the data used in 

the analysis was collected at ambient temperatures above -10°C which suggests a 

reduced probability of occurrence with decreasing ambient temperatures similar to 

Appendix C. An evaluation was presented to the ARC of the effects of the larger drops 

on a fluid based ice protection system is used on many part 23 aircraft. The cold 

temperature prolonged holding conditions become the design driver for these types of 

systems due to the increased water catch of the large drops. The ARC also considered 

that many part 23 aircraft have limits on the available energy for thermal ice protection 

systems and reconsidered the need to use the same hold criterion as used in part 25. 

The consensus of the ARC was that the need to consider this long of a hold in freezing 

drizzle and freezing rain was reduced both by the reduced probability of holding, 

combined with the reduced probability of the SLD conditions at the cold extremes. As 

such, it is recommended that the holding criterion in SLD, be limited to ambient 

temperatures above -13°C. The ARC was also concerned that an assumption of a hold 

in SLD icing conditions at the cold extreme could be a driver for the stall speed 

setpoints, which could increase landing speeds. This increase in landing speeds could 

have an unintended adverse effect on safety. The review of the event history indicates 

that most in-flight events occur at a total temperature near 0°C, with no evidence of 

issues due to prolonged holds at cold extremes. Suspected SLD events for which flight 

data recorder data on temperature is listed in Table 2. 

Table 2 - Suspected SLD Events 

Model Flight Altitude 

(ft) 

OAT

(oF) KCAS Distance (nm) 

Time 

(min) KTAS TTOT

(oF) 

ATR-72 4184 10000 24.7 175 54.1 16 203 34.5 

ATR-72 GE 791 18000 14.0 195 78.3 18 261 30.1 

EMB-120 3272 7000 17.0 180 8.2 2.5 196 26.0 

4000 24.0 166 7.2 2.5 172 31.0 

EMB-120 5054 17000 24.8 150 10.0 3 200 34.3 

EMB-120 7233 10000 15.8 170 NA 196 24.9 

C-560 Pueblo 7000 17.6 155 8.5 3 169 24.4 

C-560 Eagle River 1000 29.0 NA 

SF-340 3008 

8000 24.8 180 3.4 1 201 34.4 

9000 23.0 180 3.4 1 205 33.0 

10000 21.2 165 3.2 1 191 29.8 

In addition, the reported temperature at the destination airport was reviewed for part 23 

suspected SLD events on approach and landing. For 21 such events, the average 

ambient temperature was 29.2°F, the median was 32°F, and the coldest was 12°F 

(-11.1°C). This recommendation provides a balance of safety, yet provides less design 

penalties (weight, energy, etc.) for part 23 designs. Advisory material is recommended 

to clarify this change. 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-36

For Appendix O conditions for which approval is sought, the ARC recommends the 

same ice accretion definitions as proposed for part 25 with three modifications: 

The proposed part 23 regulation definition for hold will not include 45 minutes. The 

draft guidance will define 45 minutes for Appendix C conditions. For Appendix O, 45 

minutes for hold will be defined for OAT at and above minus 13°C. Below minus 

13°C, the hold duration and the enroute phase can be limited the time required to 

transit 17.4 nm. See the discussion above for rationale on not considering the coldest 

temperatures. 

The landing phase definition will include a go-around in accordance with AFM 

procedures versus a climb at the minimum balked landing climb gradient. The ARC 

proposes that the go-around may be accomplished with flaps other than landing flaps if 

the applicant demonstrates the procedure to be safe. Takeoff approval in freezing 

drizzle or light freezing rain must include the climb through a freezing drizzle or freezing 

rain layer which may extend higher than the 1,500 feet AGL takeoff phase. The ARC 

believed the maximum vertical extents defined in proposed Appendix O were too 

conservative (12.000 feet and 7,000 feet, respectively for FZDZ and FZRA). The ARC 

analyzed data from “An Inferred Climatology of Icing Conditions Aloft, Including 

Supercooled Large Drops. Part I: Canada and the Continental United States,” published 

in the November 2007 publication of the Journal of Applied Meteorology and 

Climatology. For FZDZ and FZRA, 90% of vertical extents were less than 6,000 feet 

and 3,500 feet, respectively. A value of 90% has been used previously in horizontal 

extent for runback ice accretion. A definition of climb with these vertical extents was 

added to be used for takeoff approval. 

To summarize, part 23 regulations will reference the following: 

Supercooled Water Icing 

Conditions 

Definition of Icing 

Conditions 

Airframe Ice Accretions 

for Showing Compliance 

to Subpart B 

Stratus and Cumulus 

clouds 

Part 25, Appendix C, 

Part I 

Part 23, Appendix TBD, 

Part I 

Freezing Drizzle and 

Freezing Rain 

Part 25, Appendix O, 

Part I 

Part 23, Appendix TBD, 

Part II 

There are concerns that this structure may lead to confusion. The ARC recommends 

that the FAA consider establishing a new part 23 Appendix (or Appendices) that 

incorporates all the part 23 icing conditions and ice accretion definitions, negating the 

need to reference part 25 appendices or a portion of them. 

The ARC reviewed a comment in the part 25 SLD rulemaking docket pertaining to an 

icing parameter developed by researchers based on their icing flight tests on a 

University of Wyoming King Air 200T (comment 11.1 in docket FAA-2010-0636). This 

parameter is the mathematical product of 80VD (drop size in microns for which 80% of 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-37

the liquid water content is in drop sizes smaller) and LWC (liquid water content in g/m3

). 

Icing conditions were encountered that resulted in rapid increases in drag and stall 

speed beyond stall warning. The ice accretion which led to these severe encounters 

were described as sharp edges ice formations, 0.08 to 0.16 inch in height, that do not 

touch each other. The ARC could not gain access to any documentation such as 

photographs. The severe icing encounters correlated to an 80VD*LWC range of 

approximately 22 to 68 at an ambient temperature of around -8°C. 

The ARC reviewed ice accretion photograph from several icing tunnel projects as 

follows (80VD calculated using calibration data from the NASA IRT): 

1. Two minute inadvertent encounter at an 80VD=65, OAT= -10°C from a runback 

research project (DOT/FAA/AR-07/16) 

2. SLD runs in the NASA IRT to support the ARAC IPHWG in which 80VD ranged 

from 96 to 164, OAT= -9.9 to -6.5°C 

3. Intercycle/residual icing research at an 80VD=20, OAT= -9.8°C (DOT/FAA/AR06/48) 

4. Intercycle/residual icing research at an 80VD=39, OAT= -9.6°C (DOT/FAA/AR06/48) 

5. Certification project (proprietary data reviewed by FAA only) at an 80VD=52, 

OAT= -6.7°C 

The roughness levels reviewed are associated with a range of temperatures, airspeeds, 

freezing fractions as well as the drop size and liquid water content parameters. Many of 

the cases reviewed were well outside the proposed Dow/Marwitz criteria, but significant 

roughness effects are apparent. By inspection, it can be concluded that these cases 

outside the proposed criteria could produce adverse drag effects. Although an 

exhaustive research effort was not performed, the roughness levels for point 4 are 

among the most benign of those reviewed even though it lies in the center of the 

proposed "adverse" icing region. Roughness levels for points 1 and 5 also lie in the 

“adverse” 80VD region and do not appear different than roughness documented outside 

the adverse region. Roughness densities were varied and there were cases where 

roughness elements did not touch each other. The review suggests that the proposed 

"adverse" icing criteria is an over-simplification of the complex icing physics that occur. 

In addition, the proposed criteria suggests that one type of icing conditions would be 

severe for all aircraft, regardless of the type of ice protection system used, or the 

protected area extents. This simplistic approach cannot be justified given the 

differences in the accident rates between differing types of aircraft and systems. 

The rulemaking approach proposed for both part 25 and part 23 considers the 

complex icing physics through a combination of icing tunnel testing of representative 

aircraft models which capture variations in icing physics, and actually does include 

icing conditions in the “adverse” region. The Appendix O freezing drizzle (MVD>40) 

MVD is 110 μm. Using the NASA IRT calibration data, this corresponds to an 80VD of 

249 μm. At -8°C, the Appendix O LWC for this distribution is 0.24 g/m3 (it was 

erroneously high in the NPRM published on June 29 2010). This results in an 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-38

80VD*LWC = 59 which is in the adverse region. Therefore, certification testing to 

Appendix O will include conditions in the adverse region. The ARC does recognize 

that the certification tunnel runs should document the details of roughness elements 

for simulated ice shape flight testing, and an appropriate note is added to the guidance 

material. 

NATURAL SLD FLIGHT TEST

The part 23 ARC adopted the part 25 proposal regarding the requirement to flight test 

in measured, natural icing conditions, which is required for Appendix C icing 

conditions in §§ 23.1419 and 25.1419. For compliance to §§ 23.1420 and 25.1420, 

flight test in measured, natural Appendix O conditions is listed as one of the means of 

compliance. The language “as found necessary” was removed by the ARC. The ARC 

believed the part 25 language was too vague as to who decided whether natural icing 

flight tests were required. The ARC also decided to write guidance that was specific 

on whether flight testing in natural Appendix O would be required. The ARC believed 

that if flight in any portion of Appendix O was to be approved, (e.g. § 23.1420(a)(2) or 

(a)(3)) flight test in those portions should be conducted. The ARC believed that 

Appendix O conditions for which an airplane is approved should not be treated 

differently than Appendix C, particularly if there is less experience with the simulation 

tools in Appendix O compared to Appendix C. The ARC recognized that flight test 

safety was one of the issues raised during IPHWG deliberations, but the ARC believed 

the fleet pilot should not be the first pilot exposed to these conditions if the airplane is 

allowed to operate indefinitely in these conditions. Carrying the instrumentation 

needed to measure Appendix O drop sizes is also an issue with part 23 airplanes. 

The ARC decided that there may be some phases of flight, such as takeoff, where 

freezing drizzle or rain conditions will be reported. For these phases, which may be a 

common phase applicants seek approval for, instrumentation would not be required. 

For a detect and exit airplane, the ARC wanted to make it clear that flight test in 

natural Appendix O conditions would not be required for a part 23 airplane if certain 

conditions were met. The conditions are as follows: 

1. For the Appendix O distributions where the capability exists1, icing tunnel tests 

or icing tanker tests and analytical codes are used to determine critical ice 

shapes on lifting surfaces. 

2. The simulated, critical ice shapes are flight tested to show compliance with 

applicable Subpart B regulations. 

 

1 Current icing tanker or icing tunnel simulation techniques are limited to FZDZ. For FZRA techniques 

see Appendix 7 of the recommended AC materials. 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-39

3. Appendix O detection method(s) are certified as described in the Advisory 

Circular. 

4. Subsequent designs may be able to use similarity to past certifications. 

D) SUBPART B - APPENDIX C ICE ACCRETIONS

Task 2 & 3 - The part 23 icing ARC reviewed the current requirements for Appendix C 

which requires compliance to Subpart B performance, stability, controllability, and 

maneuverability regulations with Appendix C ice accretions. The part 23 icing ARC 

proposes the following changes, which provides relief from the current rule: 

STALL SPEED (TASK 3):

Section 23.1419, amendment 23-43, required “...airplane performance...must not be 

less than that required in part 23, subpart B.” The stall speed requirements of § 23.49 

are included in subpart B performance. For part 23 aircraft that do not meet the 

emergency landing requirements of § 23.562(d), the stall speed at maximum weight 

must not exceed 61 knots. Flight testing of deicing boot-equipped aircraft with 

simulated intercycle/residual ice has shown stall lift coefficient losses of 17 percent to 

23 percent with flaps extended. These lift losses were experienced on an airplane 

equipped with a stick pusher and on an airplane whose stall was defined by 

aerodynamic wing stall. This can represent a significant performance penalty for new 

aircraft if they had to be designed to meet the 61-knot stall speed requirement with ice 

on protected surfaces. Recently certificated single engine part 23 airplanes would most 

likely not meet this requirement since their no-ice stall speed in landing configuration is 

at or near 61 knots. Performance penalties would be large. As an example, 

calculations for one certificated single engine airplane show that useful load in icing 

would have to be reduced by 40 percent in order to meet the 61-knot stall speed 

requirement with no major redesign. 

In the notice of proposed rulemaking published in the “Federal Register” on 

October 3, 1990 (55 FR 40598), for the proposed rule that was to become amendment 

23-43, the FAA stated the background for imposing subpart B requirements on part 23 

airplanes versus part 25 transport airplanes: “The justification given was that normal 

and transport category airplanes must operate in about the same icing environment, but 

the normal category airplane is more likely to remain in icing conditions for longer 

periods of time because it may not have the performance capability to exit the icing 

environment as readily as transport category airplanes.” Normal category airplane 

airfoils, being smaller than those of transport airplanes, are much more efficient 

collectors of ice and their percentage drag increase in icing conditions are larger than 

transport airplanes. The requirement to meet subpart B performance was added to 

guarantee there would be a given level of excess power that could be used to exit icing 

conditions. An increase in stall speed in icing would not prevent an airplane from 

meeting the subpart B performance requirements if it was accounted for in analyses and 

testing. 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-40

For airplanes that did not meet the 61-knot stall speed requirement with critical ice 

accretions, guidance was added to Advisory Circular 23.1419-2C, published July 21, 

2004. This guidance discussed compensating features to be considered for an 

exemption to the stall speed requirement of § 23.1419(a), amendment 23-43. The 

rationale was that an exemption with these compensating features would not adversely 

affect safety since it is safer to make a forced landing at higher speed than it is to 

inadvertently stall the airplane. There have been many fatal accidents in icing 

conditions attributed to the latter.

1. The airplane with no ice accretions meets the 61-knot stall speed requirement of 

§ 23.49(c); 

2. The airplane with critical ice accretions as defined in paragraph 13b of this AC 

complies with the stall warning requirements of § 23.207. Stall warning means 

with ice accretion should be the same as in non-icing. 

3. The AFM performance data in icing conditions reflects the higher stall and 

operating speeds. 

4. The airplane with critical ice accretions has acceptable stall characteristics and is 

safely controllable with normal piloting skill as required by §§ 23.201 and 23.203. 

5. The tire requirements of § 23.733 and brake requirements of § 23.735 are met 

with the higher stall and operating speeds. 

6. The ground handling requirements of §§ 23.231, 23.233 and 23.235 and nose/tail 

wheel steering system of § 23.745, if applicable, are met with the higher landing 

speeds. 

7. All other airplane system or testing requirements that could be affected by higher 

operating speeds, such as autopilot and flight director gains are evaluated. 

8. Each seat/restraint system would have to include a safety belt and shoulder 

harness with a metal to metal latching device (this would address STCs on older 

airplanes that do not include § 23.785 in their certification basis). 

9. The airplane certification basis would have to include § 23.1091 at amendment 

23-51 and § 23.1093 at amendment 23-51 to provide the latest regulations for 

engine operation in icing conditions. 

10. The airplane certification basis would have to include § 23.995 at amendment 23-

29. This regulation was promulgated as a result of a National Transportation 

Safety Board (NTSB) recommendation and a 1983 study, which indicated at least 

half of off field forced landings were a result of fuel mismanagement. 

A total of four exemptions were granted from 2008 to 2010. No exemption requests 

were denied. The initial requests were published in the Federal Register and no 

comments were received. In an effort to reduce FAA and industry workload, the FAA 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-41

tasked the Part 23 Icing Aviation Rulemaking Committee to recommend a rule 

amendment to exempt compliance to paragraphs (c) and (d) of Sec. 23.49 for flight in 

icing conditions. The ARC recommended rule changes to exempt these specific 

paragraphs. Since the certification basis of a new airplane model that would include 

the new Sec. 23.1419 amendment would most likely incorporate the regulations listed 

in the compensating features, the ARC determined it was not necessary to incorporate 

the compensating features in the regulations. The ARC recommended to keep a 

history of the issue in Advisory Circular 23.1419. 

TAKEOFF ICE ACCRETION

The AC 23.1419-2D guidance on the performance thresholds for when takeoff ice 

accretion must be considered, and when takeoff speeds and approach speeds must 

be increased, are codified. Consideration was given to accomplish this by only 

amending 23.1419, or possibly the proposed 23.21(c), but the ARC determined it was 

cleaner to amend each affected rule, similar to part 25. 

The part 23 icing ARC was tasked with recommendations on codifying certain 

guidance in AC 23.1419-2D. Recommendations were made in the following areas: 

STALL WARNING

The ARC proposed amendments to 23.207 that would codify the AC 23.1419-2D 

guidance. These proposals would require the means of stall warning and stall warning 

margin to be the same for ice protection system operation as in non-icing operation. It 

also proposes to codify the guidance on pre-activation ice. 

ICE CONTAMINATED TAILPLANE STALL

The requirement to evaluate susceptibility with zero load factor push-overs and 

sideslips is codified. 

LATERAL CONTROL EVALUATION

The guidance in AC 23.1419-2D regarding lateral control evaluation was codified. The 

pass/fail criteria have been missing in the AC and are added to the proposed 

regulation. The IPHWG recommended lateral control evaluations in sideslips and in 

10 deg bank to bank rolls down to stall warning. The 10 deg bank to bank rolls were 

added to the advisory material for 23.201. These tests would be applicable to 

Appendix C and O conditions. 

ACTIVATION OF ICE PROTECTION SYSTEM

The ARC adopted the proposed part 25 requirements, with the exception that the 

proposed part 23 rule would provide an option for immediate activation based on 

visual observation of first sign of ice accretion, for normal, utility and acrobatic 

airplanes approved for flight in icing. The earlier discussion on stall warning and ICTS 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-42

testing with pre-activation ice explains why the part 25 proposal was adopted for 

commuter category airplanes. The ARC believes the smaller scale of the part 23 noncommuter category airplanes allows easier observation of ice accretion, and the part 

23 icing accident database shows that failure to recognize ice accretion is not a safety 

issue. In addition, delays in recognizing visual cues are addressed in the definition of 

pre-activation ice used in stall warning and ICTS evaluations. The proposed part 25 

rule requires either an ice detection system, whose cost is relatively large compared to 

the airframe for a part 23 airplane, or icing system operation based on visible moisture 

and temperature. The latter may result in unnecessary icing system operation which 

is common on part 23 airplanes, and can lead to a shorter system life. 

DEFINITION OF PRE-ACTIVATION ICE

As in part 25, current part 23 guidance addresses stall warning and susceptibility to 

ICTS with pre-activation ice. Pre-activation ice for part 23 airplanes is currently two 

minutes if activation is based on visual cues, and 30 seconds if it based on visible 

moisture and outside air temperature. Part 23 is poorly harmonized with Part 25. Large 

Part 25 aircraft have moved toward Primary Ice Detection Systems (PIDS or IDS), 

which is not a realistic option for much of Part 23 due to equipment cost. This has 

resulted in certification programs with very large pre-activation ice shapes and system 

operating needlessly in non-icing conditions. However, both part 25 and part 23 

guidance have not given credit for an advisory ice detection system. 

The NTSB recommendation is to activate ice protection as icing starts. This is one of 

the primary tenants on the NTSB “Most Wanted List”. Since the flight crew can only 

detect icing by visual observation of ice accretions and ice detectors can potentially 

detect ice below the human visual threshold, it is a given the ice detector could reduce 

preactivation ice shapes. The following chart provides an option that gives credit for an 

Advisory IDS and increases harmonization with Part 25. This guidance gives an 

airplane manufacturer incentive to install an ice detection system with a reduction in the 

time used for defining the preactivation ice shapes. In order to get credit, the system 

cannot be optional equipment, and this must be recognized in the minimum equipment 

list. 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B 

Table 3 - Pre-Activation Ice Accretions - Appendix C Continuous Maximum Conditio

IPS Activation AC 25 Pre-activation Ice 

Accretion

Part 23 Pre-activation Ice Accretion

The left and right columns provide two abe used. The right column provides typbe used in lieu of system specific data. 

Visual of First Indication of Accretion on Reference Surface 

Time to detect (1)+30 seconds (2) +IPS response time 

Time to detect (1)+30 seconds (2) +IPS response time 

2 minute

Potential Icing Conditions (OAT and Visible Moisture) 

+30 seconds (2)+IPS response time 

+30 seconds (2)+IPS response time 

30 secon

Primary IDS and Manual IPS Activation 

IDS response time +10 seconds (2) +IPS response time 

IDS response time(3)+10 seconds +IPS response time

30 secon

Primary IDS and Automatic IPS Activation 

IDS response time +IPS response time 

IDS response time(3)+IPS response time 

20 secon

Advisory IDS No Credit IDS response time (4)

+10 seconds (2) 

+IPS response time 

60 secon

Notes: (1) Total time not to exceed 2 minutes (2) Easily recognizable by the flight crew in all foreseeable conditions (e.g., at night in clouds) (3) Applicant should show that the response time of the ice detector at freezing fractions of one is less than stated time(4) In low freezing fractions conditions, applicant should show that detector will annunciate prior to ice accretion on crit

be accomplished by comparing icing tunnel tests to response times provided by the detector manufacturer. 

(5) Add delay time due to any IPS activation logic
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-44

Advisory IDS have seen limited use in the past; this has not been a result of concern 

over detector effectiveness but of system reliability. The concern is the possibility of a 

flight crew that has become dependent on the IDS that has failed (without annunciation 

of the failure), entering icing conditions and waiting for the now failed IDS to detect ice. 

The ARC believes this concern can be mitigated by requiring a reasonable level of 

operational performance from the Advisory IDS and proposes the SAE AS5498 

Minimum Operational Performance Specification for Inflight Icing Detection System as 

possible specification to allow credit for the Advisory IDS. One issue with the common 

vibrating probe ice detection system is the response time at temperature near freezing. 

Guidance material was added to the advisory material to address these issues. 

The ARC also investigated the possibility of reducing the two minute time for visual ice 

detection for an airplane with a two man flightcrew. The ARC determined that any time 

reduction would be subjective and difficult to demonstrate. 

Task 8 - The ARC was tasked to determine if using 1-g stall speed criteria in icing is an 

option to reduce approach speeds and landing distances in icing conditions. Part 25 

already uses the 1-g stall speed requirement, introduced at amendment 25-108 in 

2002). An equivalent safety finding for the use of 1-g stall speeds, instead of the 

minimum speeds obtained in the stalling maneuver, as the basis for showing 

compliance with certain 14 CFR part 23 performance, and 14 CFR part 36 noise 

requirements, was established for several past part 23 type certification projects. Pilot 

objectivity on stall identification has become a key factor in decisions on flying 

technique, especially where deterrent buffet or excessively low load factors are 

developed during stalls to VSMIN. This can be especially true with ice accretion on 

protected surfaces (e.g., intercycle), in which the lift curve can flatten considerably as 

CLMAX is approached. For a stick pusher equipped airplane where stall would be 

defined by stick pusher speed, operating speeds using the 1-g stall speed criteria would 

be several knots lower than using VSMIN. The ARC recognized there could be an 

advantage. Stall speed would have to be determined in icing the same means as in 

non-icing, which would require re-writing the 23.207 for non-icing conditions, which is 

outside the ARC tasking. Since the option is already available to part 23 applicants, the 

ARC determined no additional guidance is needed for icing conditions. 

E) POWERPLANT ASPECTS

SEC. 23.901 INSTALLATION

This section was reviewed with respect to the reference of icing in (d)(2) which states 

"Ensure that the capability of the installed engine to withstand the ingestion of rain, hail, 

ice, and birds into the engine inlet is not less than the capability established for the 

engine itself under Sec. 23.903(a)(2)". 

It was determined that the consideration of large drops or mixed phase/ice crystals did 

not have an effect on this section as long as it was not interpreted to mean that all ice 

shapes that may form on an airframe in front of an engine are required to be less than 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-45

that tested during the part 33 certification. The recommendation for § 23.1093 includes 

picking up the specific language that includes consideration of ice on "airframe 

components" similar to the part 25 proposal. As such, per the requirements of § 23.901, 

no design feature of the installation should degrade the basic capability of the engine 

with respect to ice ingestion, but the ingestion of airframe ice should be addressed 

under the more specific requirements of § 23.1093. 

SEC. 23.903 ENGINES

This language recommended for part 25 was reviewed and it was determined that it was 

appropriate as drafted and should be recommended for incorporation into part 23. 

However, the ARC recommended advisory material on how to determine acceptable 

service history. 

SEC. 23.905 PROPELLERS

This section was reviewed with respect to the reference of icing in (e) which states "All 

areas of the airplane forward of the pusher propeller that are likely to accumulate and 

shed ice into the propeller disc during any operating condition must be suitably 

protected to prevent ice formation, or it must be shown that any ice shed into the 

propeller disc will not create a hazardous condition". It was determined that this 

requirement would not be affected by the addition of large drop conditions. However, 

the ARC recommends advisory material to clarify the requirements with respect to large 

drop conditions and aircraft approved for flight into icing conditions. 

SEC. 23.929 ENGINE INSTALLATION ICE PROTECTION

Modifications to the requirement are recommended to incorporate reference to the large 

drop environment as well as clarify that this requirement is related to flight in icing 

approvals. Also, recommend modification of the criterion used for thrust loss from 

"appreciable loss" to capture the effect on aircraft performance as defined in proposed 

23.21(c). Since this requirement encompasses the propeller and the engine installation, 

consideration of any applicable systems requirements from sub part E and sub part F 

are also recommended. 

It addition, it is recommended to delete the reference to "wooden propellers". The 

consensus of the ARC is that the requirements should be based on whether the aircraft 

is seeking approval for flight into known icing, not on the construction method of the 

propeller. 

There was consideration given to changing the scope of § 23.929 to propellers similar 

to part 25 and allowing § 23.1093 to be the focus for engine installation effects due to 

the current overlap for engine installation effects between the two paragraphs. The 

ARC elected not to make this change, as it is not required due to the large drop icing 

and there is adequate guidance material published in AC 23-16A to differentiate 

between the engine installation effects of the two paragraphs. 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-46

The review of the event data does not indicate any safety issues related to engine 

installation effects while exiting severe icing conditions. There are events with 

documented speed losses which could be partially attributed to propeller icing. As such, 

the rule language was modified such that the icing environment to be considered for 

propeller icing includes the SLD conditions while exiting the environment, but for engine 

installations consideration of only the approved icing environments is acceptable. 

SEC. 23.1093 INDUCTION SYSTEM ICING PROTECTION

The icing aspects of § 23.1093(a) Reciprocating engines were reviewed and it was 

determined that the current rule language was acceptable without changes. 

The ARAC recommended changes for § 25.1093(b) were reviewed and determined to 

be appropriate for near direct incorporation. As part of this incorporation, the 

consideration of airframe components that could affect engine operation through 

accumulation of icing becomes a specific requirement of this section, rather than the 

more generic prior requirements of § 23.901(d) as discussed in AC 23-16A. 

The recommended ARAC Part 25 language provides for showing compliance with the 

defined icing conditions (Part 25 Appendices C & O, Appendix D of part 33, and in 

falling and blowing snow) within the limitations established for the airplane for such 

operations. This relationship between the aircraft limitations and compliance 

requirements was further clarified with recommended guidance material (for inclusion in 

AC 23-16A) with respect to aircraft that are not certified for icing conditions, and for 

aircraft that show compliance with the requirements of § 23.1420(a)(1) or 

§ 23.1420(a)(2). 

In response to the part 25 NPRM, the Aerospace Industries Association (AIA) submitted 

public comments that would modify the ARAC proposed § 25.1093(b). The intent of the 

ARC is to keep the requirements of § 23.1093(b) and § 25.1093(b) the same, due to 

similar installation requirements between the two parts. However, since the part 25 final 

rulemaking will not be available during the ARC timeframe, this cannot be assured. As 

such, the AIA recommendations were incorporated into the ARC recommendations for 

part 23 as follows: 

1) Recommend changes to idle speed language in § 23.1093(b)(1) to be consistent 

with the engine requirement of § 33.68(a) & (b). 

2) The insertion of the "if any" clause in § 23.1093(b)(2) was added to allow that a 

temperature limitation may not be necessary. The choice of ambient temperature for 

the ground freezing fog rime icing demonstration should be driven by critical point 

analysis as required by § 33.68 (b)(1). This analysis should also be used to show 

that at colder temperatures below the § 33.68 Table 1, Condition 2 test 

temperatures, a more critical point does not exist. The applicant should be permitted 

to use analysis to demonstrate safe operation of the engine at temperatures below 

the required test demonstration. If appropriate, no limitation would then be required 

for the Airplane Flight Manual. 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-47

3) The AIA recommended deletion of Appendix O from the 23.1093 requirements. 

There are no known part 25 events that support a safety concern due to engine 

induction system icing in SLD conditions aloft. In particular, the Part 25 ARAC 

EHWG evaluated all of the known icing-related events since 1988 and found no 

events in SLD conditions aloft. As such, the compliance efforts required for engine 

inlets with respect to large drop conditions will provide no benefit in the regulatory 

analysis. The ARC considered this recommendation in light of part 23 aircraft. 

Given that many part 23 aircraft already have limitations on flight in SLD through 

FAA issued severe icing airworthiness directives, the service history likely does not 

include sustained flights in FZDZ and FZRA. As such, the successful service history 

can be applied to aircraft certified under 23.1420(a)(1). However, for aircraft 

approved for unrestricted flights in portions or all of Appendix O (§ 23.1420(a)(2) or 

(a)(3)), the exposures to such conditions are expected to increase. As such, 

consideration of Appendix O exposures for approved portions per 23.1420(a)(2) or 

(a)(2) is recommended. 

4) Deletion of the ARAC proposed § 25.1093(b)(1)(iii) to be consistent with AIA 

recommendations for § 33.68. The words “stall, surge, or flameout or loss of engine 

controllability (for example, rollback)” are redundant to the requirement for no 

unacceptable loss of power or thrust. The inclusion of “stall, surge, or flameout or 

loss of engine controllability (for example, rollback)” causes confusion. For example, 

as written, a rotating stall, which can cause no noticeable impact to engine operation 

and would only be detectable by special instrumentation could be found 

unacceptable. Therefore, deletion of the stall, surge or flameout language is 

recommended. 

SEC. 23.1521 POWERPLANT LIMITATIONS

The proposed § 25.1251(f) would require limitations to be established for the minimum 

temperature as well as the duration, as discussed in item 2 above for § 25.1093(b)(2). 

Same rationale applies, and the requirements were deleted from the recommendations 

for part 23. 

F) SYSTEMS AND RELATED ASPECTS

SEC. 23.629 FLUTTER.

This section was reviewed with respect to changes that might be required due to unique 

aspects of SLD ice shapes. It was determined that no changes are required. It is 

recommended that ice shapes for the approved portions of Appendix shall be developed 

using the ice shape scenarios and evaluated by analysis similar to current Appendix C 

methods. 
Part 23 SLD ARC REPORT 

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SEC. 23.775 WINDSHIELD AND WINDOWS..

This section was reviewed with respect to changes that might be required due to unique 

aspects of SLD icing. Rule sections (a), (b), (c), (d), (e), (g) and (h) remain unchanged. 

It is recommended that section (f) to be modified to reference the large drop 

environment. 

SEC. 23.1323 AIRSPEED INDICATING SYSTEM.

Due to the wide operating range of aircraft certified under Part 23, it was determined 

appropriate to modify the recommended §25.1323 language in a way more applicable to 

Part 23 aircraft. It is recommended not to modify the regulation or require flight testing 

in natural icing conditions for aircraft certified for IFR only (not approved for flight into 

icing conditions). AC20-73A already provides guidance on using Appendix C as the 

definition of icing conditions for probes on IFR aircraft, which is equivalent to the current 

standards. For aircraft certified for flight in icing conditions, the regulation should be 

changed to require Appendix C and O conditions be met in accordance with 

§23.1420(a). The mixed phase and ice crystal conditions should be required for probes 

on aircraft that operate at altitudes and airspeeds where ice crystal induced airspeed 

anomaly events have occurred in the past and on aircraft where the airspeed indicating 

system serves a critical function as defined in AC 23.1309-1D. It is intended that this 

section reference the same mixed phase/ice crystal conditions as §25.1323, which is 

expected to be Appendix D of Part 33 but has not been finalized at the time of this draft. 

A review of the incident history revealed that issues involving ice crystals occurred at 

high true airspeeds and at altitudes typically above 29,000 ft. Although some incidents 

were reported at lower altitudes they all involved aircraft capable of high cruise speeds 

above 29,000 ft. The 29,000 ft threshold was selected because of the typical 

performance and system complexity increase associated with aircraft capable of 

meeting the RVSM requirements. Mach 0.75 was selected as a result of the incident 

history. 

Guidance is suggested to clarify the policy on the operation of pitot probes under 

emergency battery conditions. A requirement to provide protection for all mixed phase 

conditions under emergency battery operations commonly used on Part 23 aircraft is 

impractical due to the high power requirements at the low voltages of emergency bus 

operation. In addition, the probability of encountering critical mixed phase or ice crystal 

conditions was considered sufficiently low that it should be considered remote (based 

on engineering judgment). Aircraft will still be protected against Appendix C icing 

conditions under the emergency power scenarios. As such, an appropriate level of 

safety is provided without undue burden on the aircraft design. 

NPRM 10-10 suggest that additional freezing rain conditions beyond those in the 

proposed 14 CFR Part 25 Appendix O and 14 CFR Part 33 Appendix D may be added 

to Part 25 after a review of comments and malfunctions. The ARC review determined 

that there is a lack of historical incidents in part 23 aircraft involving pitot probes and 

these types of conditions. This is most likely due to scale effects, such as boundary 

layer concentration factors, and lower true airspeed effects. In addition the requirements 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-49

of operation in the meteorological conditions described by 14 CFR Part 25 Appendix O 

and 14 CFR Part 33 Appendix D provide for testing in freezing rain beyond conditions 

currently evaluated. It is recommended that these additional freezing rain test conditions 

not be adopted, if later added to the Part 25 proposal. 

SEC. 23.1324 ANGLE OF ATTACK SYSTEMS

The new Part 25 proposed rule requiring ice protection for angle of attack system 

sensors was reviewed for applicability to Part 23 aircraft. It was determined to be 

appropriate to require this new regulation for Part 23, if applied similarly to the proposed 

§23.1323 (with respect to aircraft performance and system criticality). It is 

acknowledged that the standard, trailing-vane-style angle of attack sensor should not be 

susceptible to mixed phase or ice crystal accretions by design. However, the angle of 

attack probe designs that sense dynamic pressure for angle of attack (similar to pitot 

probes) can be expected to be susceptible to these conditions. Therefore, it is intended 

that this section uses the same icing conditions and applicability criteria as those 

proposed for §23.1323. 

NPRM 10-10 suggest that additional freezing rain conditions beyond those in the 

proposed 14 CFR Part 25 Appendix O and 14 CFR Part 33 Appendix D may be added 

to Part 25 after a review of comments and malfunctions. The ARC review indicated that 

with respect to AOA detectors the phenomena of concern has been water entering 

mechanical parts that require free movement to operate correctly, then freezing and 

preventing free movement. This can be a result of direct impingement or runback. This 

has been effectively addressed in the past as a Part §23.1309 issue under subpart 

(b)(1) - It must perform its intended function under any foreseeable operating condition. 

No regulatory changes are recommended. Suggested guidance material referencing 

issues to be considered have been added to AC 23.1419. In addition the requirements 

of operation in the meteorological conditions described by 14 CFR Part 25 Appendix O 

and 14 CFR Part 33 Appendix D provide for testing in freezing rain beyond conditions 

currently evaluated. It is recommended that these additional freezing rain test conditions 

not be adopted, if later added to the Part 25 proposal. 

SEC. 23.1325 STATIC PRESSURE SYSTEM.

Section §23.1325(b)(3) was reviewed with respect to the wording “icing conditions.” It is 

recommended that the rule remain unchanged for aircraft certified for IFR only (not 

approved for flight in icing). AC20-73A already provides guidance on using Appendix C 

as the definition of icing conditions for ports on IFR aircraft. It is recommended that 

wording be added to require the icing conditions of Appendix C and the SLD conditions 

of Appendix O in accordance with §23.1420(a) for aircraft certified for flight in icing 

conditions. 

The ARC has determined that static ports are not high efficiency collectors of ice 

crystals by their installation or design. As such the philosophy and guidance of the 

proposed §25.1325 rule to not include requirements for mixed phase or ice crystal 

conditions was upheld here. 
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SEC. 23.1326 PITOT HEAT INDICATION SYSTEMS

As part of the mixed phase icing requirements of §23.1323, higher heat probes will likely 

be required to compensate for the energy required to melt ice crystals. Current pitot 

probes have such high heat levels that many manufacturers provide systems that 

minimize or turn-off pitot heat on the ground prior to takeoff to protect the equipment or 

composite structures. Since accurate airspeed information is only required for safe 

flight, there is no safety benefit to indicating the pitot heat system is OFF for ground 

operations. These types of systems have typically required an ELOS to be compliant 

with the requirements of the current §23.1326. Also, §23.1326(b)(1) conflicts with the 

dark cockpit philosophy employed by many manufacturers by requiring an amber 

indication (typically indicative of a failure caution) for what could be a pilot commanded 

state. Therefore, it is recommend that the rule language be modified so that the safety 

objective of ensuring the pitot heat system is operating as intended during flight be 

retained but also allow alternate methods of compliance on the ground without requiring 

an ELOS. 

SECTION 23.1329 AUTOMATIC PILOT SYSTEM

See discussion under sub part B. 

SEC. 23.1403 ICING INSPECTION LIGHTS.

The current requirement for illumination of ice accumulations is provided by 

§23.1419(d). To address illumination requirements for both appendix C ice accretions 

and appendix O, a new icing requirement is proposed similar to §25.1403. This 

requirement would address critical ice shapes as well as ice accumulations used for 

operation of the ice protection systems, or initiation of aircraft procedures such as 

exiting severe icing conditions. The proposed rule language was drafted to eliminate 

the need for an Equivalent Level of Safety if other, non-visual means were used to 

determine ice formation (e.g. a primary ice detection system for system activation). The 

rule language was drafted to only require icing inspection lights if they are necessary 

and not to require wing inspection lights for aircraft where the wing cannot be viewed 

from the cockpit. 

SEC. 23.1416 PNEUMATIC DE-ICER BOOT SYSTEM.

The requirements of §23.1416 are largely obsolete with the increased scope of 

§23.1309 and §23.1322. In addition, the requirement of §23.1416 (c) for an indication 

of normal operation is in conflict with the dark cockpit philosophy that is in use in many 

modern aircraft. As such, the recommendation is to delete the specific requirement for 

an indication and use the basis of §23.1309 and §23.1322 to provide cockpit 

indications. This will allow the use of both dark cockpit and non dark cockpit types of 

indications as is consistent with the proposed cockpit philosophy. 
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SEC. 23.1419 ICE PROTECTION

A review of the NPRM has resulted in recommended changes to the 14 CFR Part 23, 

§23.1419, and AC 23.1419. 

Recommended Regulatory Changes: 

Icing Inspection Lights – It is recommended that references to icing inspection lights 

be removed from this section and section §23.1403 be added. It is felt that this will 

reduce confusion regarding the means of determining icing conditions and operating 

the ice protections systems and the means of monitoring ice accumulations. The ice 

light requirements would be common to §23.1419 and §23.1420. 

Ice Protection System Operation - The §23.1419 (d) references to the AFM have been 

moved to section h. New requirements were added as §23.1419(d)(e)(f)(g)(h) to 

include the ice protection system activation and ice detector requirements 

promulgated under amendment §25-129. These requirements are further referenced 

under the proposed §23.1420(c).

Recommended Guidance Changes: 

Substantiated visual cue - two of the following methods are required, analysis, icing 

wind tunnel testing, icing tanker testing, natural icing flight testing to validate a visual 

cue. In the unique case of using two methods to validate visual cues on the windows 

of the cockpit, it is recommended that a combination of appendix C natural icing 

encounters validating 3D ice accretion (or impingement analysis) and 3D appendix O 

ice accretion analysis (or impingement analysis) satisfy the two method approach 

described above. 

Ice Detector Reliability Requirements – With respect to ice detector reliability and 

software criticality requirements, for both primary and advisory systems, it is 

recommended that they be consistent with the hazard classification for ice detectors 

resulting from a §23.1309 hazard analysis. For ice detection primary and advisory 

aspects see discussion on pre-activation ice in the subpart B section of this report. 

SEC. 23.1420 SUPERCOOLED LARGE DROP ICING CONDITION.

The requirements of §23.1420 are proposed to be similar to the §25.1420 requirements. 

The discriminator used in the part 25 rule is no longer applicable, as all aircraft certified 

under part 23 will have maximum takeoff weights of less than 60,000 lbs. The 

“approved portions” of 14 CFR Part 25, Appendix O as used in the proposed regulations 

and guidance material is intended to refer to aircraft that are certified against 

23.1420(a)(2) or (a)(3). For aircraft certified against 23.1420(a)(1) the exposures in 

Appendix O are not approved and require exiting all icing conditions. The phrase “with 

exposures in accordance with 23.1420(a)(1), (a)(2) or (a)(3)” is intended to require 

consideration of the environmental conditions within the Appendix O environment, as 

well as the exposure durations as defined in 23.1420 and the ice accretions 

recommended in section 3B of this report. 
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4. RULEMAKING RECOMMENDATIONS 

Rule language changes are denoted by a combination of bold text indicating added or 

changed language with strikeouts indicating deleted text. 

The use of ellipsis "* * * * *" indicates that the omitted rule language is 

unchanged (same format used by the FAA for publication in the NPRM). 

A) SUBPART B ASPECTS

Added new 23.21(c)(1) to define the requirements of “capable of operating safely” in 

part 25, Appendix C conditions. 

Added new 23.21(c)(2) to define the requirements for “capable of operating safely 

following detection and exit of Appendix O icing conditions. 

Added new 23.21(c)(3) to define the requirements to show an airplane can operate 

safely in Appendix C, detect and exit Appendix O, Appendix O or a portion of Appendix 

O. 

Added new (c)(4) to define requirements in icing on weight and cg limits. 

SEC. 23.21 PROOF OF COMPLIANCE

(c) The requirements of this subpart associated with icing conditions apply only if 

certification for flight in icing conditions is desired. If certification for flight in 

icing conditions is desired, the following requirements also apply. 

(1) Compliance with each requirement of this subpart, except §§ 23.49(c), 

23.67(c)(1), 23.77(d) and (e), the sudden engine failure requirements of § 

23.143(b), 23.143(f), 23.145(c), (d), and (e), 23.147(c), 23.149(b) (d), and (f), 

23.207(e) and (h), 23.221, 23.235, 23.239, and 23.253, must be met in the icing 

conditions specified in part I of appendix C of part 25. Compliance must be 

shown using the ice accretions defined in part I of appendix TBD of this part, 

assuming normal operation of the airplane and its ice protection system in 

accordance with the operating limitations and operating procedures established 

by the applicant and provided in the Airplane Flight Manual. 

(2) If the applicant does not seek certification for flight in all icing conditions 

defined in Appendix O of part 25, compliance with §§ 23.49(a) and (b), 23.73(d)(1), 

23.75, 23.77(d), and (e), 23.143(a) for appropriate flight phases, 23.143(b) except 

for sudden engine failure requirements, 23.143 (c) and (f), 23.201 (a), (b), (c) and 

(e), 23.203 (a)(1), (b)(1), (b)(2), (b)(3), (b)(6), and (c), 23.207(a), (b), (d) for 

appropriate flight phases, (h), and (i), 23.231, 23.233, 23.237,and 23.251, must be 

met in the Appendix O icing conditions for which certification is not sought in 

order to allow a safe exit from those conditions. Compliance is only required at 

ambient temperatures of -13 degrees Celsius and warmer in the icing conditions 
Part 23 SLD ARC REPORT 

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defined in part I of Appendix O of part 25. Compliance must be shown using the 

ice accretions for holding and approach phase as defined in part II(b) of Appendix 

TBD of this part, assuming normal operation of the airplane and its ice protection 

system in accordance with the operating limitations and operating procedures 

provided in the Airplane Flight Manual. 

(3) If the applicant seeks certification for flight in any portion of the icing 

conditions of Appendix O of part 25, each requirement of this subpart, except for 

§§ 23.49(c), 23.77(d) and (e), the sudden engine failure requirements of § 

23.143(b), 23.143(f), 23.145(c), (d), and (e), 23.147(c), 23.149(b), unless the 

applicant seeks approval for takeoff in Appendix O conditions, 23.149(d), 

23.203(a)(2), 23.207(e) and (h), 23.221, 23.235, 23.239, and 23.253, must be met in 

the Appendix O of part 25 icing conditions for which certification is sought. 

Compliance must be shown using the ice accretions defined in part II(c) of 

Appendix TBD of this part, assuming normal operation of the airplane and its ice 

protection system in accordance with the operating limitations and operating 

procedures provided in the Airplane Flight Manual. 

(4) No changes in the load distribution limits of § 23.23 and the weight limits of § 

23.25 (except where limited by performance requirements of this subpart), from 

those for non-icing conditions, are allowed for flight in icing conditions or with 

ice accretion." 

Amend takeoff performance requirements for icing by codifying the guidance in AC 

23.1419-2D, except the airplanes that may be required to comply are based on the light 

jet rule. 

SEC. 23.45 GENERAL (PERFORMANCE).

* * * * 

(i) If the applicant seeks certification for flight in icing conditions, performance 

must be determined with engine power losses associated with operating ice 

protection systems, except for takeoff performance if operation of an ice 

protection system is prohibited for takeoff by the Airplane Flight manual 

Limitations section. 

SEC. 23.51 TAKEOFF SPEEDS.

* * * *

(d) For normal, utility, and acrobatic category turbojet powered airplanes without 

a wing leading edge high lift device and commuter category airplanes, if the 

applicant seeks certification for flight in icing conditions, the takeoff speeds 

specified in § 23.51 (a), (b), and (c), must be based on VS1 determined with the 

most critical of the takeoff ice accretions defined in Parts I and II of Appendix 

TBD of this part, as applicable in accordance with § 23.21(c), if the stall speed 
Part 23 SLD ARC REPORT 

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with takeoff ice accretion at maximum takeoff weight with takeoff flaps, gear 

retracted exceeds that in non-icing conditions by more than the greater of three 

(3) knots CAS or three (3) percent VS1. 

(e) In determining the takeoff speeds for flight in icing conditions, the values of 

VMCG and VMC determined for non-icing conditions may be used. 

SEC. 23.53 TAKEOFF [PERFORMANCE.]

(a) For normal, utility, and acrobatic category airplanes, the takeoff distance must be 

determined in accordance with paragraph (b) of this section, using speeds determined 

in accordance with Sec. 23.51(a), [(b), (d) and (e)]. 

(b) For normal, utility, and acrobatic category airplanes, the distance required to takeoff 

and climb to a height of 50 feet above the takeoff surface must be determined for each 

weight, altitude, and temperature within the operational limits established for takeoff 

with— 

(1) Takeoff power on each engine; 

(2) Wing flaps in the takeoff position(s); and 

(3) Landing gear extended. 

(c) For commuter category airplanes, takeoff performance, as required by Secs. 23.55 

through 23.59, must be determined with the operating engine(s) within approved 

operating limitations.

SEC. 23.57 TAKEOFF PATH.

* * * * 

(c) 

(1) 

(2) 

(3) 

(4) 

(5) If the takeoff speeds must be adjusted in accordance with Sec. 23.51 (d), or if 

the degradation of the gradient of climb determined in accordance with Sec. 

23.67(c)(2) is greater than 0.4 percent, the airborne part of the takeoff must be 

based on the airplane drag; 

(i) With the most critical of the takeoff ice accretions defined in Parts I and II 

of Appendix TBD of this part, as applicable in accordance with § 23.21(c), 

from a height of 35 feet above the takeoff surface up to the point where the 

airplane is 400 feet above the takeoff surface; and 
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(ii) With the most critical of the final takeoff ice accretions defined in Parts I 

and II of Appendix TBD of this part, as applicable in accordance with § 

23.21(c), from the point where the airplane is 400 feet above the takeoff 

surface to the end of the takeoff path.

SEC. 23.65 CLIMB: ALL ENGINES OPERATING.

* * * * 

 (c) For normal, utility, and acrobatic category turbojet powered airplanes without 

a wing leading edge high lift device, if the applicant seeks certification for flight 

in icing conditions, the effect of takeoff ice accretion defined in Parts I and II of 

Appendix TBD of this part, as applicable in accordance with § 23.21(c), with must 

be determined if: 

(1) the stall speed with “takeoff” ice at maximum takeoff weight with takeoff 

flaps, gear retracted exceeds that in non-icing conditions by more than the 

greater of three (3) knots CAS or three (3) percent VS1; and 

(2) the degradation of the gradient of climb determined in accordance with 

Sec. 23.65(b) with “takeoff” ice is greater than 0.8 percent.

SEC. 23.66 [TAKEOFF CLIMB: ONE ENGINE INOPERATIVE.]

* * * * 

(g) For normal, utility, and acrobatic category turbojet powered airplanes, if the 

applicant seeks certification for flight in icing conditions, takeoff ice accretion 

defined in Parts I and II of Appendix TBD of this part, as applicable in accordance 

with § 23.21(c), must be accounted for if compliance to Sec 23.65(c) is required.

SEC. 23.67 CLIMB: ONE ENGINE INOPERATIVE.

* * * * 

(e) If the applicant is seeking certification for flight in icing conditions, the effect 

of ice accretion as defined in the following table, in accordance with applicable 

portions of § 23.21(c), must be determined if: 

(1) VS1 with the appropriate ice accretion at maximum takeoff weight 

(maximum landing weight for approach) with takeoff or approach flaps 

as applicable, gear retracted, exceeds that in non-icing conditions by 

more than the greater of three knots CAS or three percent VS1; and 
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(2) If commuter category, the degradation of the gradient of climb 

determined in accordance with Sec. 23.67(c)(2) is greater than 0.4 

percent. 

(3) If turbojet powered normal, utility or aerobatic category, the degradation 

of the gradient of climb determined in accordance with Sec. 23.67 (a) or 

(b) ice is greater than 0.3 percent.

Table 4 - Sec. 23.67 Applicable Ice Accretions 

 Ice accretion

Applicable airplanes Applicable 

regulation

Part I, 

Appendix 

TBD of part 

23

Part II, 

Appendix 

TBD of part 

23

Normal, utility, and acrobatic 

category reciprocating engine 

powered of less than 6,000 

pounds maximum weight

§ 23.67(a)

Not required Final takeoff

Normal, utility, and acrobatic 

category reciprocating engine 

powered of more than 6,000 

pounds maximum weight 

Normal, utility, and acrobatic § 23.67(b)

category turbo-propeller powered 

Normal, utility, and acrobatic 

category turbojet powered with a 

wing leading edge high lift device

Normal, utility, and acrobatic 

category turbojet powered without 

a wing leading edge high lift 

device

§ 23.67(b)

Final takeoff 

Commuter category

§ 23.67(c)(1) Not required Takeoff

§ 23.67(c)(2) Takeoff

§ 23.67(c)(3) Final takeoff

§ 23.67(c)(4) Approach
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SEC. 23.69 [ENROUTE CLIMB/DESCENT.]

* * * * 

 (c) If the applicant is seeking certification for flight in icing conditions, the effect 

of “enroute” ice, as defined in Parts I and II of Appendix TBD of this part, as 

applicable in accordance with § 23.21(c), on climb performance must be 

determined if: 

(1) the enroute climb speed selected in icing is more than the non-icing 

speed by the greater of three (3) knots CAS or three (3) percent VS1; or 

(2) if the service ceiling with “enroute” ice is less than 22,000 MSL. 

SEC. 23.73 REFERENCE LANDING APPROACH SPEED.

* * * * 

 (d) If the applicant is seeking certification for flight in icing conditions, except as 

provided in paragraph (1), VREF must be based on stall speed with the most 

critical of the landing ice accretions defined in Parts I and II of Appendix TBD of 

this part, as applicable in accordance with § 23.21(c), if the stall speed with 

critical ice at maximum landing weight with landing flaps, gear down exceeds that 

in non-icing conditions by more than the greater of three (3) knots CAS or three 

(3) percent VS0.

(1) VREF in the appendix O icing conditions for which certification is not 

sought may be the VREF determined in Sec. 23.73(d) with critical Appendix C ice 

accretions, if the airplane at that VREF complies with the maneuver margin 

requirements of Sec. 23.207(d) with the critical landing ice accretion defined in 

Part II, paragraph (b), of Appendix TBD of this part.

SEC. 23.77 BALKED LANDING.

(a) Each normal, utility, and acrobatic category reciprocating engine-powered airplane 

of 6,000 pounds or less maximum weight must be able to maintain a steady gradient 

of climb at sea level of at least 3.3 percent with— 

(1) 

(2) 

(3) 

(4) A climb speed equal to VREF, as defined in Sec. 23.73(a) and Sec. 23.73(d). 

(b) Each normal, utility, and acrobatic category reciprocating engine-powered of more 

than 6,000 pounds maximum weight and each normal, utility, and acrobatic category 

turbine engine-powered airplane must be able to maintain a steady gradient of climb 

of at least 2.5 percent with— 

(1) 

(2) 

(3) 
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(4) A climb speed equal to VREF, as defined in Sec. 23.73(b) and Sec. 23.73(d). 

(c) Each commuter category airplane must be able to maintain a steady gradient of 

climb of at least 3.2 percent with— 

(1) 

(2) 

(3) 

(4) A climb speed equal to VREF, as defined in Sec. 23.73(c) and Sec. 23.73(d). 

(d) For normal, utility, and acrobatic category reciprocating engine-powered 

airplanes of 6,000 pounds or less maximum weight, if the applicant seeks 

certification for flight in icing conditions, the steady gradient of climb at the 

landing field pressure altitude must be measurably positive with— 

(1) Takeoff power on each engine; 

(2) The landing gear extended; 

(3) The wing flaps in the landing position approved for flight in icing, 

except that if the flaps may safely be retracted in two seconds or less 

without loss of altitude and without sudden changes of angle of attack, 

they may be retracted; and 

(4) A climb speed equal to VREF as defined in Sec. 23.73(d) 

(5) The critical approach ice accretion defined in Part II, paragraph (b), of 

Appendix TBD of this part. 

(e) For normal, utility, and acrobatic category reciprocating engine-powered 

airplanes of more than 6,000 pounds, turbine powered airplanes and commuter 

category airplanes, if the applicant seeks certification for flight in icing 

conditions, the steady gradient of climb at the landing field pressure altitude 

must be measurably positive with— 

(1) Not more than the power that is available on each engine eight seconds 

after initiation of movement of the power controls from the minimum 

flight idle position; 

(2) The landing gear extended; 

(3) The wing flaps in the landing position approved for flight in icing; and 

(4) A climb speed equal to VREF as defined in Sec. 23.73(d) 

(5) The critical approach ice accretion defined in Part II, paragraph (b), of 

Appendix TBD of this part. 

SECTION 23.143 GENERAL (CONTROLLABILITY AND MANEUVERABILITY)

Amend 23.143 by adding the guidance in AC 23.1419-2D for Appendix C icing 

conditions, and the proposals by the Part 23 Icing ARC for Appendix O icing conditions: 

* * * * 

(d) When demonstrating compliance with §23.143 in icing conditions— 
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(1) Controllability must be demonstrated with the ice accretion defined in Parts I 

and II of Appendix TBD of this part, as applicable in accordance with § 23.21(c)(1) 

and (3) and appropriate to the phase of flight; 

(2) It must be shown that a push force is required throughout a pushover 

maneuver down to a zero g load factor, or the lowest load factor obtainable if 

limited by elevator power or other design characteristic of the flight control 

system. It must be possible to promptly recover from the maneuver without 

exceeding a pull control force of 50 pounds; and 

(3) Any changes in force that the pilot must apply to the pitch control to maintain 

speed with increasing sideslip angle must be steadily increasing with no force 

reversals, unless the change in control force is gradual and easily controllable by 

the pilot without using exceptional piloting skill, alertness, or strength. 

(4) It must be possible to readily arrest and reverse roll rate using only lateral 

control input, and the lateral control force must not reverse with increase of 

control deflection. 

 (e) For flight in icing conditions before the ice protection system has been 

activated and is performing its intended function, it must be demonstrated in 

flight with the ice accretion defined in part I(e), of Appendix TBD of this part that: 

(1) The airplane is controllable in a pull-up maneuver up to 1.5 g load factor; and 

(2) There is no pitch control force reversal during a pushover maneuver down to 

0.5 g load factor. 

(f) For airplanes certified under 23.1420(a)(1) (detect and exit), it must be 

demonstrated with the ice accretion defined in Part II, (b) of Appendix TBD of this 

part as applicable in accordance with § 23.21(c)(2), that: 

(1) The airplane is controllable in a pull-up maneuver up to 1.5 g load factor; and 

(2) There is no pitch control force reversal during a pushover maneuver down to 

0.5 g load factor. 

(3) Any changes in force that the pilot must apply to the pitch control to maintain 

speed with increasing sideslip angle must be steadily increasing with no force 

reversals, unless the change in control force is gradual and easily controllable by 

the pilot without using exceptional piloting skill, alertness, or strength. 

Additionally, lateral control force must not reverse with increasing control 

deflection, as the angle of sideslip is increased up to the maximum appropriate to 

the type of airplane.

 (4) It must be possible to readily arrest and reverse roll rate using only lateral 

control input, and the lateral control force must not reverse with increase of 

control deflection. 
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SECTION 23.207 STALL WARNING.

Amend 23.207 by adding the guidance in AC 23.1419-2D for Appendix C icing 

conditions, and the proposals by the Part 23 Icing ARC for Appendix O icing conditions: 

* * * * 

(g) For flight in icing conditions before the ice protection system has been 

activated and is performing its intended function, with the ice accretions defined 

in part 23, Appendix TBD, part I(e) and part II(h), the stall warning margin in 

straight and turning flight must be sufficient to allow the pilot to prevent stalling 

without encountering any adverse flight characteristics when: 

(1) The speed is reduced at rates not exceeding one knot per second; 

(2) The pilot performs the recovery maneuver in the same way as for flight in nonicing conditions; and 

(3) The recovery maneuver is started no earlier than one second after the onset of 

stall warning 

(h) For airplanes certified under 23.1420(a)(1) (detect and exit), the stall warning 

margin in straight and turning flight must be sufficient to allow the pilot to 

prevent stalling (as defined in Sec. 23.201(b)) when the pilot starts a recovery 

maneuver not less than three seconds after the onset of stall warning. When 

demonstrating compliance with this paragraph, the pilot must perform the 

recovery maneuver in the same way as for the airplane in non-icing conditions. 

Compliance with this requirement must be demonstrated in flight with the speed 

reduced at rates not exceeding one knot per second, with the critical detect and 

exit ice defined in part II(b), Appendix TBD of this part. 

(i) In showing compliance with paragraphs (c), (g), and (h) of this section, stall 

warning must be provided by the same means in icing conditions as for non-icing 

conditions. 

SECTION 23.1329 AUTOMATIC PILOT SYSTEM

... 

(i) If the applicant seeks certification for use of the autopilot for flight in 

applicable portions of 14 CFR 25 Appendix O, there must be an indication to 

permit the crew to manually disengage the autopilot and take control prior to any 

automatic autopilot disengagement that would result in a hazardous flight 

condition. 

SECTION 23.1419 ICE PROTECTION

Amend 23.1419 by clarifying when compliance to 23.1419 is required. Amended rule 

would allow installation of ice protections systems, to facilitate exit from inadvertent icing 

encounters, without a requirement for compliance to 23.1419. Capable of operating 

safely is re-defined. The activation of ice protection system guidance in AC 23.1419-2D 
Part 23 SLD ARC REPORT 

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and operation of ice protection system regulations recommended by ARAC for part 25 

are added. 

If certification with ice protection provisions is desired If the applicant seeks 

certification for flight in icing conditions, compliance with the requirements of this 

section and other applicable sections of this part must be shown:

(a) An analysis must be performed to establish, on the basis of the airplane's 

operational needs, the adequacy of the ice protection system for the various 

components of the airplane. In addition, tests of the ice protection system must be 

conducted to demonstrate that the airplane is capable of operating safely in continuous 

maximum and intermittent maximum icing conditions, as described in appendix C of part 

25 of this chapter. As used in this section, “Capable of operating safely,” means that 

airplane performance, controllability, maneuverability, and stability must not be less than 

that required in part 23, subpart B. the airplane complies with the requirements in § 

23.21(c)(1).

* * * * 

(d) A means must be identified or provided for determining the formation of ice on the 

critical parts of the airplane. Adequate lighting must be provided for the use of this 

means during night operation. Also, when monitoring of the external surfaces of the 

airplane by the flight crew is required for operation of the ice protection equipment, 

external lighting must be provided that is adequate to enable the monitoring to be done 

at night. Any illumination that is used must be of a type that will not cause glare or 

reflection that would handicap crewmembers in the performance of their duties. The 

Airplane Flight Manual or other approved manual material must describe the means of 

determining ice formation and must contain information for the safe operation of the 

airplane in icing conditions.

(d) One of the following methods of icing detection and activation of the airframe 

ice protection system must be provided: 

(1) A primary ice detection system that automatically activates or alerts the 

flightcrew to activate the airframe ice protection system; or 

(2) A definition of visual cues for recognition of the first sign of ice accretion 

on a specified surface combined with an advisory ice detection system that 

alerts the flightcrew to activate the airframe ice protection system; or 

(3) Identification of conditions conducive to airframe icing as defined by an 

appropriate static or total air temperature and visible moisture for use by the 

flightcrew to activate the airframe ice protection system; or 

(4) For normal, utility and acrobatic category airplanes, a definition of visual 

cues for recognition of the first sign of ice accretion on a specified surface to 

alert the flightcrew to activate the airframe ice protection system.
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-62

(e) Unless the applicant shows that the airframe ice protection system need not 

be operated during specific phases of flight, the requirements of paragraph (d) of 

this section are applicable to all phases of flight. 

(f) After the initial activation of the airframe ice protection system-- 

(1) The ice protection system must be designed to operate continuously; or 

(2) The airplane must be equipped with a system that automatically cycles the 

ice protection system; or 

(3) An ice detection system must be provided to alert the flightcrew each time 

the ice protection system must be cycled. 

(g) Procedures for operation of the ice protection system, including activation 

and deactivation, must be established and documented in the Airplane Flight 

Manual. 

23.1420 – SUPERCOOLED LARGE DROP ICING CONDITIONS.

The proposed 23.1420 rule is similar to the proposed 25.1420 rule. There is concern 

among some of the ARC members that the rule is vague on when natural icing in SLD is 

required. 

(a) If certification for flight in icing conditions is sought, in addition to the 

requirements of § 23.1419, an airplane must be capable of operating in 

accordance with paragraphs (a)(1), (a)(2), or (a)(3), of this section. 

(1) Operating safely after encountering the icing conditions defined in Appendix 

O of part 25: 

(i) There must be a means provided to detect that the airplane is operating in 

Appendix O icing conditions; and 

(ii) Following detection of Appendix O icing conditions, the airplane must be 

capable of operating safely while exiting all icing conditions. "Capable of 

operating safely," means that the airplane complies with the requirements in § 

23.21(c)(2). 

(2) Operating safely in a portion of the icing conditions defined in Appendix O of 

this part as selected by the applicant. "Capable of operating safely," means that 

the airplane complies with the requirements in § 23.21(c)(3). 

(i) There must be a means provided to detect that the airplane is operating in 

conditions that exceed the selected portion of Appendix O icing conditions; and 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-63

(ii) Following detection, the airplane must be capable of operating safely while 

exiting all icing conditions. "Capable of operating safely," means that the 

airplane complies with the requirements in § 23.21(c)(2). 

(3) Operating safely in the icing conditions defined in Appendix O of part 25. 

"Capable of operating safely," means that the airplane complies with the 

requirements in § 23.21(c)(3). 

(b) To establish that the airplane can operate safely as required in paragraph (a) 

of this section, an analysis must be performed to establish that the ice protection 

for the various components of the airplane is adequate, taking into account the 

various airplane operational configurations. To verify the analyses, one, or more 

of the following methods must be used: 

(1) Laboratory dry air or simulated icing tests, or a combination of both, of the 

components or models of the components. 

(2) Laboratory dry air or simulated icing tests, or a combination of both, of 

models of the airplane. 

(3) Flight tests of the airplane or its components in simulated icing conditions, 

measured as necessary to support the analysis. 

(4) Flight tests of the airplane with simulated ice shapes. 

(5) Flight tests of the airplane in natural icing conditions, measured as necessary 

to support the analysis. 

(c) For an airplane certified in accordance with paragraph (a)(2) or (a)(3) of this 

section, the requirements of § 23.1419(e), (f) and (g) must be met for the icing 

conditions defined in Appendix O of part 25 in which the airplane is certified to 

operate. 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-64

B) ICE ACCRETIONS FOR SHOWING COMPLIANCE TO 14 CFR 23 SUBPART B

The following definitions of ice accretions are proposed to be added in an Appendix 

TBD to 14 CFR 23. The definitions are analogous to the 14 CFR 25 Appendix C, Part II 

and proposed 14 CFR 25 Appendix O, Part II. The definitions were modified to point to 

the appropriate part 23, subpart B references and other changes recommended by the 

ARC to accommodate part 23 aircraft. The Part I of the proposed Appendix 

corresponds to ice accretions as a result of exposure to 14 CFR 25, Appendix C icing 

conditions and Part II of the Appendix corresponds to the ice accretions that may result 

from exposure to 14 CFR 25, Appendix O icing conditions. 

(1) 14 CFR 23 APPENDIX TBD - AIRFRAME ICE ACCRETIONS

(2) PART I - AIRFRAME ICE ACCRETIONS FOR SHOWING COMPLIANCE WITH 14 CFR

23 SUBPART B IN THE ICING CONDITIONS DEFINED IN 14 CFR 25 APPENDIX C PART I.

(a) Ice accretions--General. 

The most critical ice accretion in terms of airplane performance and handling 

qualities for each flight phase must be used to show compliance with the 

applicable airplane performance and handling requirements in icing conditions of 

subpart B of this part. Applicants must demonstrate that the full range of 

atmospheric icing conditions specified in part I of this appendix have been 

considered, including the mean effective drop diameter, liquid water content, and 

temperature appropriate to the flight conditions (for example, configuration, 

speed, angle-of-attack, and altitude). The ice accretions for each flight phase are 

defined as follows: 

(1) Takeoff ice is the most critical ice accretion on unprotected surfaces and any 

ice accretion on the protected surfaces appropriate to normal ice protection 

system operation, occurring between liftoff and 400 feet above the takeoff 

surface, assuming accretion starts at liftoff in the takeoff maximum icing 

conditions of part I, paragraph (c) of 14 CFR 25, appendix C. 

(2) Final takeoff ice is the most critical ice accretion on unprotected surfaces, and 

any ice accretion on the protected surfaces appropriate to normal ice protection 

system operation, between 400 feet and either 1,500 feet above the takeoff 

surface, or the height at which the transition from the takeoff to the en route 

configuration is completed and enroute climb speed is reached, whichever is 

higher. Ice accretion is assumed to start at liftoff in the takeoff maximum icing 

conditions of part I, paragraph (c) of 14 CFR 25, appendix C. 

(3) En route ice is the critical ice accretion on the unprotected surfaces, and any 

ice accretion on the protected surfaces appropriate to normal ice protection 

system operation, during the en route phase. Applicable only to airplanes that 

are not certified to operate above 30,000 feet. 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-65

() Holding ice is the critical ice accretion on the unprotected surfaces, and any ice 

accretion on the protected surfaces appropriate to normal ice protection system 

operation, during the holding flight phase. 

(5) Approach ice is the critical ice accretion on the unprotected surfaces, and any 

ice accretion on the protected surfaces appropriate to normal ice protection 

system operation following exit from the holding flight phase and transition to the 

most critical approach configuration. 

(6) Landing ice is the critical ice accretion on the unprotected surfaces, and any 

ice accretion on the protected surfaces appropriate to normal ice protection 

system operation following exit from the approach flight phase and transition to 

the final landing configuration. 

(b) In order to reduce the number of ice accretions to be considered when 

demonstrating compliance with the requirements of Sec. 23.21(c), any of the ice 

accretions defined in paragraph (a) of this section may be used for any other 

flight phase if it is shown to be more critical than the specific ice accretion 

defined for that flight phase. Configuration differences and their effects on ice 

accretions must be taken into account. 

(c) The ice accretion that has the most adverse effect on handling qualities may 

be used for airplane performance tests provided any difference in performance is 

conservatively taken into account. 

(d) For both unprotected and protected parts, the ice accretion for the takeoff 

phase may be determined by calculation, assuming the takeoff maximum icing 

conditions defined in appendix C, and assuming that: 

(1) Airfoils, control surfaces and, if applicable, propellers are free from frost, 

snow, or ice at the start of the takeoff; 

(2) The ice accretion starts at liftoff; 

(3) The critical ratio of thrust/power-to-weight; 

(4) Crew activation of the ice protection system is in accordance with a normal 

operating procedure provided in the Airplane Flight Manual, except that after 

beginning the takeoff roll, it must be assumed that the crew takes no action to 

activate the ice protection system until the airplane is at least 400 feet above the 

takeoff surface. 

(e) The ice accretion before the ice protection system has been activated and is 

performing its intended function is the critical ice accretion formed on the 

unprotected and normally protected surfaces before activation and effective 

operation of the ice protection system in continuous maximum atmospheric icing 

conditions. This ice accretion only applies in showing compliance to Sec. 

23.143(e) and 23.207(g), 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-66

(3) PART II - AIRFRAME ICE ACCRETIONS FOR SHOWING COMPLIANCE WITH 14 CFR

23 SUBPART B IN THE ICING CONDITIONS DEFINED IN 14 CFR 25 APPENDIX O PART I

(a) General. 

The most critical ice accretion in terms of airplane performance and handling qualities 

for each flight phase must be used to show compliance with the applicable airplane 

performance and handling qualities requirements for icing conditions as defined in § 

23.21(c)(2) and (c)(3). Applicants must demonstrate that the full range of atmospheric 

icing conditions specified in part I of 14 CFR 25, Appendix O have been considered, 

including drop diameter distributions, liquid water content, and temperature appropriate 

to the flight conditions (for example, configuration, speed, angle-of-attack, and altitude). 

(1) For an airplane certified in accordance with § 23.1420(a)(1), the ice accretions for 

each flight phase are defined in part II, paragraph (b) of this appendix. 

(2) For an airplane certified in accordance with § 23.1420(a)(2), the most critical ice 

accretion for each flight phase defined in part II, paragraphs (b) and (c) of this appendix, 

must be used. For the ice accretions defined in part II, paragraph (c) of this appendix, 

only the portion of part I of 14 CFR 25, Appendix O in which the airplane is capable of 

operating safely must be considered. 

(3) For an airplane certified in accordance with § 23.1420(a)(3), the ice accretions for 

each flight phase are defined in part II, paragraph (c) of this appendix. 

(b) Ice accretions for airplanes certified in accordance with § 23.1420(a)(1) or (a)(2). 

 (1) Holding ice is the holding ice defined by part II, paragraph (c)(4), of this appendix, 

for an airplane certified in accordance with § 23.1420(a)(2), or defined by part I, 

paragraph (a)(4) of this appendix, for an airplane certified in accordance with § 

23.1420(a)(1), plus: 

(i) Pre-detection ice as defined by part II, paragraph (b)(3) of this appendix; and 

(ii) The ice accumulated during the transit of one cloud with a 17.4 nautical miles 

horizontal extent in the most critical of the icing conditions defined in part I of 14 CFR 

25, appendix O and one cloud with a horizontal extent of 17.4 nautical miles in the 

continuous maximum icing conditions defined in part I of 14 CFR 25, appendix C. The 

total exposure to the icing conditions need not exceed 45 minutes. 

(2) Approach ice is the more critical of the holding ice defined by part II, paragraph 

(b)(1) of this appendix, or the ice calculated in the applicable paragraph (b)(2)(i) or (ii) of 

part II of this appendix: 

(i) For an airplane certified in accordance with § 23.1420(a)(2), the ice accumulated 

during descent from the maximum vertical extent of the icing conditions defined in part I 

of 14 CFR 25, appendix O to 2,000 feet above the landing surface in the cruise 

configuration, plus transition to the approach configuration, plus: 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-67

(A) Pre-detection ice, as defined by part II, paragraph (b)(3) of this appendix; and 

(B) The ice accumulated during the transit at 2,000 feet above the landing surface of 

one cloud with a horizontal extent of 17.4 nautical miles in the most critical of the icing 

conditions defined in part I of 14 CFR 25, appendix O and one cloud with a horizontal 

extent of 17.4 nautical miles in the continuous maximum icing conditions defined in part 

I of 14 CFR 25, appendix C. 

(ii) For an airplane certified in accordance with § 23.1420(a)(1), the ice accumulated 

during descent from the maximum vertical extent of the maximum continuous icing 

conditions defined in part I of 14 CFR 25 appendix C to 2,000 feet above the landing 

surface in the cruise configuration, plus transition to the approach configuration, plus: 

(A) Pre-detection ice, as defined by part II, paragraph (b)(3) of this appendix; and 

(B) The ice accumulated during the transit at 2,000 feet above the landing surface of 

one cloud with a horizontal extent of 17.4 nautical miles in the most critical of the icing 

conditions defined in part I of 14 CFR 25, appendix O and one cloud with a horizontal 

extent of 17.4 nautical miles in the continuous maximum icing conditions defined in part 

I of 14 CFR 25 appendix C. 

 (3) Pre-detection ice is the ice accretion before detection of 14 CFR 25, appendix O 

conditions that require exiting per § 23.1420(a)(1) and (a)(2). It is the ice accumulated 

during the time needed to detect the icing conditions, followed by two minutes of further 

ice accumulation to take into account the time for the flight crew to take action to exit the 

icing conditions, including coordination with air traffic control. 

(c) Ice accretions for airplanes certified in accordance with §§ 23.1420(a)(2) or 

23.1420(a)(3). For an airplane certified in accordance with § 23.1420(a)(2), only the 

portion of the icing conditions of part I of 14 CFR 25 appendix O in which the airplane is 

capable of operating safely must be considered. 

(1) Takeoff ice is the most critical ice accretion on unprotected surfaces, and any ice 

accretion on the protected surfaces appropriate to normal ice protection system 

operation, occurring between liftoff and 400 feet above the takeoff surface, assuming 

accretion starts at liftoff in the icing conditions defined in part I of 14 CFR 25 appendix 

O. 

(2) Final takeoff ice is the most critical ice accretion on unprotected surfaces, and any 

ice accretion on the protected surfaces appropriate to normal ice protection system 

operation, between 400 feet and either 1,500 feet above the takeoff surface, or the 

height at which the transition from the takeoff to the en route configuration is completed 

and enroute climb speed is reached, whichever is higher. Ice accretion is assumed to 

start at liftoff in the icing conditions defined in part I of 14 CFR 25, appendix O. 

(3) Climb ice is the critical ice accretion on the unprotected surfaces, and any ice 

accretion on the protected surfaces appropriate to normal ice protection system 

operation, during the climb after takeoff. Ice accretion includes ice accreted 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-68

during takeoff phase plus the most critical of climb through 6,000 feet in freezing 

drizzle, or climb through 3,500 feet in freezing rain.

(4) En route ice is applicable only to airplanes that are not certified to operate 

above 30,000 feet. En route ice is the most critical ice accretion on the unprotected 

surfaces, and any ice accretion on the protected surfaces appropriate to normal ice 

protection system operation, during the en route flight phase in the icing conditions 

defined in part I of 14 CFR 25, appendix O. 

(5) Holding ice is the most critical ice accretion on the unprotected surfaces, and any ice 

accretion on the protected surfaces appropriate to normal ice protection system 

operation, during the holding phase of flight. 

(6) Approach ice is the ice accretion on the unprotected surfaces, and any ice accretion 

on the protected surfaces appropriate to normal ice protection system operation, 

resulting from the more critical of the: 

(i) Ice accumulated in the icing conditions defined in part I of 14 CFR 25, appendix O 

during a descent from the maximum vertical extent of the icing conditions defined in part 

I of this 14 CFR 25, appendix O, to 2,000 feet above the landing surface in the cruise 

configuration, plus transition to the approach configuration and flying for 15 minutes at 

2,000 feet above the landing surface; or 

(ii) Holding ice as defined by part II, paragraph (c)(4) of this appendix. 

(7) Landing ice is the ice accretion on the unprotected surfaces, and any ice accretion 

on the protected surfaces appropriate to normal ice protection system operation, 

resulting from the more critical of the: 

(i) Ice accretion defined by part II, paragraph (c)(5)(i), of this appendix, plus ice 

accumulated in the icing conditions defined in part I of 14 CFR 25 appendix O during a 

descent from 2,000 feet above the landing surface to a height of 200 feet above the 

landing surface with a transition to the landing configuration, followed by a go-around 

conducted in accordance with Airplane Flight Manual procedures, from a height of 200 

feet above the landing surface to 2,000 feet above the landing surface, flying for 15 

minutes at 2,000 feet above the landing surface in the maximum flap configuration 

approved for holding, and a descent to the landing surface (touchdown) in the landing 

configuration; or 

(ii) Holding ice as defined by part II paragraph (c)(4) of this appendix. 

(8) For both unprotected and protected parts, the ice accretion for the takeoff phase 

must be determined for the icing conditions defined in part I of 14 CFR 25 appendix O, 

using the following assumptions: 

(i) The airfoils, control surfaces, and, if applicable, propellers are free from frost, snow, 

or ice at the start of takeoff; 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-69

(ii) The ice accretion begins at liftoff; 

(iii) The critical ratio of thrust/power-to weight; and 

 (iv) Crew activation of the ice protection system is in accordance with a normal 

operating procedure provided in the Airplane Flight Manual, except that after beginning 

the takeoff roll, it must be assumed that the crew takes no action to activate the ice 

protection system until the airplane is at least 400 feet above the takeoff surface. 

(d) The ice accretion before the ice protection system has been activated and is 

performing its intended function is the critical ice accretion formed on the unprotected 

and normally protected surfaces before activation and effective operation of the ice 

protection system in the icing conditions defined in part I of 14 CFR 25 appendix O. This 

ice accretion only applies in showing compliance to §§ 23.143(e) and 23.207(g). 

(e) In order to reduce the number of ice accretions to be considered when 

demonstrating compliance with the requirements of § 23.21(c), any of the ice accretions 

defined in this appendix may be used for any other flight phase if it is shown to be more 

critical than the specific ice accretion defined for that flight phase. Configuration 

differences and their effects on ice accretions must be taken into account. 

(f) The ice accretion that has the most adverse effect on handling qualities may be used 

for airplane performance tests provided any difference in performance is conservatively 

taken into account. 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-70

C) POWERPLANT ASPECTS

SEC. 23.903 ENGINES

Add new 23.903(a)(3) to allow for approving new aircraft type certification programs with 

engines certificated to earlier amendment levels. 

(a) Engine type certificate 

* * * * * 

(3) Each turbine engine must comply with one of the following paragraphs: 

(i) Section 33.68 of this chapter in effect on [insert effective date of final rule], or 

as subsequently amended; or 

(ii) Section 33.68 of this chapter in effect on February 23, 1984, or as 

subsequently amended before [effective date of final rule], unless that engine’s 

ice accumulation service history has resulted in an unsafe condition; or 

(iii) Section 33.68 of this chapter in effect on October 1, 1974, or as subsequently 

amended prior to February 23, 1984, unless that engine’s ice accumulation 

service history has resulted in an unsafe condition; or 

(iv) Be shown to have an ice accumulation service history in similar installation 

locations which has not resulted in any unsafe conditions. 

* * * * * 

SEC. 23.929 ENGINE INSTALLATION ICE PROTECTION

Propellers (except wooden propellers) and other components of complete engine 

installations must be protected against the accumulation of ice as necessary to enable 

satisfactory functioning without appreciable loss of thrust when operated in the icing 

conditions for which certification is requested.

If certification for flight in icing is requested: 

(a) Propellers must be protected against the accumulation of ice as necessary to 

comply with the requirements of § 23.21(c)(1), (c)(2), or (c)(3) when operated in the 

icing conditions for which certification is requested, and after encountering the icing 

conditions defined in Appendix O of part 25

(b) Other components of the complete engine installations must be protected against 

the accumulation of ice as necessary to comply with the applicable requirements of 

sub part E and F within 14 CFR 25 Appendix C and the approved portions of 14 

CFR 25 Appendix O.
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-71

SEC. 23.1093 INDUCTION SYSTEM ICING PROTECTION

* * * * * 

(b) Turbine engines. Each engine, with all icing protection systems operating, 

must: 

(1) Operate throughout its flight power range, including the minimum descent idle 

speeds, in the icing conditions defined in appendix C of part 25 of this chapter, 

approved portions of Appendix O of part 25 of this chapter, appendix D of part 33 

of this chapter, and in falling and blowing snow within the limitations established 

for the airplane for such operation, without the accumulation of ice on the engine, 

inlet system components or airframe components that would do any of the 

following: 

(i) Adversely affect installed engine operation or cause a sustained loss of power 

or thrust; or an unacceptable increase in gas path operating temperature; or an 

airframe/engine incompatibility; or 

(ii) Result in unacceptable temporary power or thrust loss or unacceptable engine 

damage 

(2) Idle for a minimum of 30 minutes on the ground in the following icing 

conditions shown in Table 1, unless replaced by similar test conditions that are 

more critical. These conditions must be demonstrated with the available air bleed 

for icing protection at its critical condition, without adverse effect, followed by an 

acceleration to takeoff power or thrust. During the idle operation the engine may 

be run up periodically to a moderate power or thrust setting in a manner 

acceptable to the Administrator. The applicant must document the engine run-up 

procedure (including the maximum time interval between run-ups from idle, runup power setting, and duration at power) and associated minimum ambient 

temperature, if any, the maximum time interval, if any, and these conditions must 

be used in the analysis which establishes the airplane operating limitations in 

accordance with § 23.1521. 

Table 5 - "Sec. 23.1093 -Table 1" - Icing Conditions for Ground Tests 

Condition Static Air 

Temperature 

Water 

Concentration 

(minimum) 

Mean Effective 

Particle 

Diameter 

Demonstration 

1. Rime ice 

condition 

0 to 15°F 

(-18 to -9°C) 

Liquid – 0.3 

g/m3 

15-25 microns By test, analysis 

or combination 

of the two 

2. Glaze ice 

condition 

20 to 30°F 

(-7 to -1°C) 

Liquid – 0.3 

g/m3 

15-25 microns By test, analysis 

or combination 

of the two 

3. Large droplet 

condition 

15 to 30°F 

(-9 to -1°C) 

Liquid – 0.3 

g/m3 

100 microns 

(minimum) 

By test, analysis 

or combination 

of the two 

(1) Each turbine engine and its air inlet system must operate throughout the flight power 

range of the engine (including idling), without the accumulation of ice on engine or inlet 

system components that would adversely affect engine operation or cause a serious 

loss of power or thrust--
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-72

(i) Under the icing conditions specified in appendix C of part 25 of this chapter; and 

(ii) In snow, both falling and blowing, within the limitations established for the airplane 

for such operation.

(2) Each turbine engine must idle for 30 minutes on the ground, with the air bleed 

available for engine icing protection at its critical condition, without adverse effect, in an 

atmosphere that is at a temperature between 15° F and 30° F (between -9° and -1°C) 

and has a liquid water content not less than 0.3 grams per cubic meter in the form of 

drops having a mean effective diameter not less than 20 microns, followed by 

momentary operation at takeoff power or thrust. During the 30 minutes of idle operation, 

the engine may be run up periodically to a moderate power or thrust setting in a manner 

acceptable to the Administrator.

* * * * * 

SEC. 23.1521 POWERPLANT LIMITATIONS.

* * * * * 

(f) Maximum time interval between engine run-ups from idle, run-up power 

setting, duration at power and the associated minimum ambient temperature, if 

any, for ground operations in icing conditions, as defined in § 23.1093(b)(2). 

D) SYSTEMS ASPECTS

SEC. 23.629 FLUTTER.

Unchanged. 

SEC. 23.775 WINDSHIELD AND WINDOWS.

(f) Unless operation in known or forecast icing conditions is prohibited by operating 

limitations, a means must be provide to prevent or to clear accumulations of ice from the 

windshield so that the pilot has adequate view for taxi, takeoff, approach, landing, and 

to perform any maneuvers within the operating limitations of the airplane. the following 

apply: 

(i) The aircraft must have a means to prevent or clear accumulations of ice 

from the windshield so that the pilot has sufficient view along the flight 

path in normal flight attitudes of the aircraft. This includes taxi, takeoff, 

approach, landing and to perform any maneuvers within the operating 

limitations. This means must be designed to function in --- 

(ii) The icing conditions specified in 14 CFR 25 Appendix C and approved 

portions of 14 CFR 25 Appendix O. 
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FEB 2012 - Revision B Page-73

SEC. 23.1323 AIRSPEED INDICATING SYSTEM.

(d) If certification for instrument flight rules is requested, or flight in icing conditions is 

requested, each airspeed system must have a heated pitot tube or an equivalent means 

of preventing malfunction due to icing. In addition, if certification for flight in icing 

conditions is requested, the icing conditions specified below must be addressed:

(1) Appendix C of Part 25, and Appendix O of Part 25, with exposures in 

accordance with 23.1420(a)(1), (a)(2) or (a)(3), and 

(2) The mixed phase and ice crystal conditions of Part 33, Appendix D, if 

the airspeed indicating system serves a critical function or the maximum 

certified ceiling is greater than 29,000 ft MSL and the MMO is greater than 

Mach 0.75.

SEC. 23.1324 ANGLE OF ATTACK SYSTEMS.

If an angle of attack system is provided for any instrument, device, or system 

required by the operating rules of this chapter, and certification for flight in icing 

conditions is desired, each angle of attack sensor must have a means of 

preventing malfunction due to icing. The icing conditions specified below must 

be addressed: 

(1) Appendix C of Part 25 and Appendix O of Part 25 with exposures in 

accordance with 23.1420(a)(1), (a)(2) or (a)(3), and 

(2) The mixed phase and ice crystal conditions of Appendix D of Part 33, if 

the angle of attack system serves a critical function or the maximum 

certified ceiling is greater than 29,000 ft MSL and the MMO is greater than 

Mach 0.75. 

SEC. 23.1325 STATIC PRESSURE SYSTEM.

(b)(3) If a static pressure system is provided for any instrument, device, or system 

required by the operating rules of this chapter, each static pressure port must be 

designed or located in such manner that the correlation between air pressure in the 

static pressure system and true ambient atmospheric static pressure is not altered when 

the aircraft encounters icing conditions. If certification for flight in icing conditions 

is requested, the icing conditions described in Part 25 Appendix C and Appendix 

O, with exposures in accordance with §23.1420(a)(1), (a)(2) or (a)(3) must be 

addressed. An anti-icing means or an alternate source of static pressure may be used 

in showing compliance with this requirement. If the reading of the altimeter, when on the 

alternate static pressure system differs from the reading of the altimeter when on the 

primary static system by more than 50 feet, a correction card must be provided for the 

alternate static system 
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SEC. 23.1326 PITOT HEAT INDICATION SYSTEMS

If a flight instrument pitot heating system is installed to meet the requirements specified 

in Sec. 23.1323(d), an indication system must be provided to indicate to the flight crew 

when that pitot heating system is not operating. The indication system must comply with 

the following requirements: 

(a) The indication provided must incorporate an amber light that is in clear view of a 

flightcrew member., and

(b) The indication provided must be designed to alert the flight crew if either of the 

following conditions exist: 

(1) The pitot heating system is switched "off." during takeoff or in flight, except when 

the outside air temperature is greater than 5° C.

(2) The pitot heating system is switched "on" and any pitot tube heating element is 

inoperative. 

SEC. 23.1403 ICING INSPECTION LIGHTS.

If certification for flight in icing conditions is desired and aircraft procedures are 

dependent on visual observations of airframe ice accretion, a means must be 

provided for illuminating the formation of ice. Any illumination that is used must 

be of a type that will not cause glare or reflection that would handicap 

crewmembers in the performance of their duties. 

SEC. 23.1416 PNEUMATIC DE-ICER BOOT SYSTEM.

Delete this section. 

SEC. 23.1419 AND 23.1420

Systems aspects integrated with sub part B aspects; see the sub part B section above. 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-75

5. ADVISORY MATERIALS 

A) SUB-PART B ASPECTS

See Appendix D for recommended revisions to AC 23.1419-2D 

B) POWERPLANT ASPECTS

Note: The format of AC 23-16A has questions in a bold font. For clarity in 

denoting revisions from existing text, the bold font on the questions is not 

reproduced. To clearly separate questions from responses, indentation on the 

responses is used. 

SEC. 23.901 INSTALLATION

AC 23-16A, reference Paragraph 23.901(d) - (revised material) 

What are some other examples of issues not addressed by engine certification that 

need to be addressed for installation compliance with § 23.901(d)? 

Amendment 25-53 added requirements for ice, hail, and birds similar to those in 

part 33. Examples of installation issues normally not addressed by engine 

certification, but that should be addressed for installation compliance, include the 

following: 

1. Ice build-up on areas where ice shed may be ingested by the engines (for 

example, ice shed from wings and airframe sources into aft mounted engines) 

should be addressed under the more specific requirements of § 23.1093 

(b); and 

2. Consideration of items such as inlet splitters, acoustic liners, and so forth, that 

may be damaged by impact with ice, hail, and birds. 

SEC. 23.903 ENGINES

AC 23-16A, reference Paragraph 23.903 - (added material) 

What are some examples of how to show that "an ice accumulation service 

history in similar installation locations ... has not resulted in any unsafe 

conditions"? 

The intent of this regulation is to ensure that any unsafe conditions from 

prior designs are not carried forward onto new designs. One method of 

compliance would be to review the accident and incident history, any 

airworthiness directives on similar (or derivative) engines installed in 

similar locations and to coordinate with the engine manufacturer on any 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-76

prior service history issues. Any prior unsafe conditions must be 

addressed as part of the aircraft installation certification. 

SEC. 23.905 ENGINES

AC 23-16A, reference Paragraph 23.905 - (added material) 

What is required to show compliance for § 23.905(e) with respect to 14 CFR Part 

25 Appendix O (SLD) conditions? 

For aircraft without approval for flight in icing conditions, compliance for 

§ 23.905(e) for inadvertent encounters with 14 CFR 25 Appendix O may be 

found by similarity to the 14 CFR 25 Appendix C conditions due to the 

similarity of ice volumes over the short durations during exit from all icing 

conditions. For aircraft that will be approved for flight in icing conditions, 

the icing exposures within Appendix O should be consistent with the 

durations used for developing the ice shapes used for demonstrating sub 

part B compliance (reference AC 23.1419-2E). 

When showing compliance to § 23.905(e), can breakup of the ice shape be 

assumed prior to striking the blade? 

There are no standard analytical methods for predicting break of ice 

shapes in flight. AC 20-147A contains some information on break-up as 

applicable to ice shapes used during part 33 testing of turbofan engines. 

For shapes that have similar aspect ratios, similar breakup characteristics 

may be assumed. 

SEC. 23.929 ENGINE INSTALLATION ICE PROTECTION

AC 23-16A, reference Paragraph 23.929 - (added material) 

Have the requirements of § 23.929 been applied to aircraft that are not certificated 

for flight in icing per § 23.1419? 

For an airplane not certificated for flight in icing, compliance to § 23.929 is 

not required. 

For an aircraft certified for flight in icing (§ 23.1419, § 23.1420), what icing 

environments and exposures should be used in showing compliance to this 

requirement? 

The icing exposures should be consistent with the kinds of operation 

authorized under § 23.1525 and the certification option selected under 

§ 23.1420. For aircraft certified under § 23.1420(a)(1), the propeller aspects 

should consider both operations in part 25, Appendix C as well as an exit 

from part 25, Appendix O. For the engine installation aspects, only 

Appendix C icing conditions must be considered. For aircraft certified to 

§ 23.1420(a)(2) or (a)(3), consideration of extended operations in the 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-77

approved portions of part 25, Appendix O must be considered with respect 

to both the propeller and engine installation aspects. The exposure times 

should be consistent with the methods used to develop airframe shapes 

(reference AC 23.1419-2E). 

If ice is determined to accumulate at the engine or cooling inlets during icing 

encounters, then tests should be performed with critical ice shapes, typically 

representing a 45 minute hold, installed on these inlets, or evaluate the 

performance of such systems with tanker or natural icing tests. Tests should 

consider the critical operating temperatures and altitudes within Appendix C icing 

conditions. Tests of the generator cooling system with actual or simulated ice 

accumulation on the inlet should be performed with the maximum icing load on 

the electrical system at representative ambient temperatures. If data is analyzed 

in accordance with § 23.1043, the temperatures need to be corrected only to 32 

degrees F, not a hot day. 

Engine alternate induction air sources should remain functional in the required 

icing environments. 

SEC. 23.1093 INDUCTION SYSTEM ICING PROTECTION

AC 23-16A, reference Paragraph 23.1093(b) - (revised/added material) 

Is an airplane required to comply with § 23.1093 if it is not being certificated to fly 

in icing conditions? 

Yes, compliance with § 23.1093(b) for induction system icing protection is required 

for all normal, utility, acrobatic, and commuter category airplanes certificated under 

part 23 even if the airplane is not being certificated for flight in icing conditions (§ 

23.1419 compliance). Service experience has shown that airplanes can inadvertently 

encounter icing conditions even if the airplane is not approved for flight into icing 

conditions. This is particularly true for turbine engine powered airplanes, which 

typically have a greater operating flight envelope than reciprocating engine powered 

airplanes. These requirements are also those demonstrated during engine 

certification (reference 14 CFR part 33, subpart E, § 33.68, Induction system icing, 

for turbine aircraft engines). 

The icing exposures considered should be consistent with the kinds of 

operation authorized under § 23.1525. The POH/AFM will have limitations 

prohibiting flight into known icing conditions, as such the icing exposures 

considered for compliance with § 23.1093 may be representative of an 

inadvertent encounter and subsequent exit from all icing conditions. 

Delay of approval for flight into icing conditions should be addressed in a 

similar manner to an aircraft not intended for certification for flight into 

icing conditions. Some manufacturers choose to delay icing certification 

until after basic type certification is achieved due to marketing or 

contractual reasons. The aircraft may be fully equipped with airframe ice 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-78

protection systems that are certified from a equipment qualification and 

installation aspect, but have not been approved for flight into icing 

conditions. As such, limitations are required prohibiting flight into icing 

conditions. 

Approvals for § 23.1093 for delayed or basic type certification should be 

based on the limited inadvertent exposure times that are possible for an 

aircraft prohibited from flight into icing conditions. In the event of an 

inadvertent encounter, the engines must operate without a sustained loss 

of power and there must not be a need to shutdown an engine in flight. 

Airframe ice protection systems may be considered part of the engine ice 

protection system if the possibility exists of airframe ice accretions 

shedding into the engine inlets. An example is ice accretion on the inboard 

wing of airplanes with aft fuselage mounted engines. 

Applicants for basic (§ 23.1093) or delayed flight into icing certification 

(prior to §§ 23.1419, 23.1420) may show compliance to §23.1093 with the 

following methods: 

(a) Flight testing in measured natural icing or flight testing behind 

an airborne icing tanker, supplemented by analysis as described in 

paragraph 16 of AC 23.1419-2E, to show the amount of ice that 

accretes in five minutes at critical part 25, Appendix C continuous 

maximum conditions does not shed into any engine; or 

(b) Analysis which shows the mass of ice that accretes in five 

minutes in critical part 25, Appendix C continuous maximum 

conditions is less than the mass of ice shown to be ingested by the 

engine for compliance to § 33.77. This analysis should assume: 

1. The spanwise length of the ice shape is the maximum 

length that can be ingested without striking the inlet lip or 

engine spinner. 

2. The ice shape on the wing leading edge does not break 

chordwise, i.e., the ice above and below the stagnation line 

should be considered. 

3. In lieu of five minutes of ice accretion, credit can be 

used for operational ice protection systems, with the 

exception in paragraph (4). The most critical of the following 

should be used: 

(aa) Two minutes representing delayed system 

activation; 

(bb) Intercycle/residual ice for deicing systems for 

operating speeds above 160 Knots Calibrated Airspeed 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-79

(KCAS). Below 160 KCAS, empirical data should 

substantiate that deicing systems shed ice at each 

cycle. 

(cc) Runback ice in 5 minutes for thermal systems. 

4. Flight testing in measured natural icing or flight testing 

behind an airborne icing tanker would be required for novel ice 

protection systems, such as the graphite thermal deicing 

system. 

Approval for the icing conditions of part 33, Appendix D should similarly be 

based on standard cloud extents and the altitude capabilities of the aircraft. 

If the kinds of operation at the aircraft level change (for example flight into 

icing per § 23.1419 is sought), compliance with § 23.1093 will need to be 

readdressed considering the changes in icing exposures. 

For an aircraft certified for flight in icing (§ 23.1419, § 23.1420), what icing 

environments and exposures should be used in showing compliance to 

§ 23.1093? 

The icing exposures should be consistent with the kinds of operation 

authorized under § 23.1525 and the certification option selected under 

§ 23.1420. The requirements of § 23.1093(b)(1)(i) establish the 

requirements to show operation of the installed engine throughout the 

defined environments, within the limitations established for the airplane. 

For aircraft that will be approved for all of Part 25, Appendix O, the icing 

exposures within Appendix O should be consistent with the exposures 

used for developing ice shapes used for demonstrating sub part B 

compliance. Similarly, for the requirements of § 23.1420 propeller/engine 

installation exposure times should be consistent with the methods used to 

develop airframe shapes reference AC 23.1419-2E. 

For an aircraft certified for flight in icing (§§ 23.1419, 23.1420), what other 

considerations are necessary for compliance to §23.1093? 

Turbine engine ice protection should be automatic once the engine ice 

protection system is activated. The engine must be protected from ice with 

the throttle against the idle stop, which may require an automatic increase 

in thrust when the engine ice protection system is activated. Natural icing 

flight tests should include evaluation of ice protection systems with bleed 

air from engines when the throttle is at the flight idle stop. 

For engine ice protection systems, which for aft fuselage mounted engines 

can include the inboard wing ice protection system, a delay of two minutes 

in the continuous maximum icing conditions of appendix C to part 25 is 

utilized to validate the ice shedding analyses and § 33.77 ice slab test 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-80

results. To minimize flight testing, an applicant has the option of 

conducting this evaluation after the tests in Table 3 are conducted, 

provided the tested ice accretion is conservative for both tests. 

For amended TC's and STC's due to an engine change, the effects of ice 

shedding and the suitability of the ice protection power supply should be 

addressed. 

(a) Ice Shedding. Engine compliance data to § 33.77 should be 

compared between the currently installed engine and the proposed 

engine. If the ice slab used to show compliance is smaller for the 

proposed engine, ice shedding from the airframe should be readdressed. Data on ice shedding may be available from the airplane 

TC holder. Engine inlet lip ice shedding should be addressed. The 

amount of ice mass that could be shed should be compared to a 

similar, approved engine installation or to part 33 engine compliance 

data. 

(b) Effects of Decreased Engine Power, Thrust or Bleed Air on Ice 

Protection System Operation. Bleed air mass flows, pressures and 

temperatures of the proposed engine and of the existing, certified 

engine should be compared. If there is a reduction, the effectiveness 

of the ice protection systems must be substantiated. 

When an APU is modified or added, operation in icing conditions should be 

addressed similarly to engines since APUs are covered by § 23.1093. 

Compliance methods for the large drop environments are limited by the 

current development state of simulation methods. Reliance on available 

simulation methods combined with engineering judgment will be required 

for findings of compliance in the icing conditions of 14 CFR 25, Appendix O 

and 14 CFR 33, Appendix D. See AC 23.1419-2E and AC 20-147B for 

additional guidance on available interim methods and simulation tools. 

What compliance methods are available for the icing conditions of part 33, 

Appendix D? 

The analysis and compliance methods for ice crystal/mixed phase 

conditions are limited by currently available testing and analytical 

methods. The primary concern to be addressed is the potential for 

accumulation of ice crystals within inlet ducting (that can build and shed 

causing engine damage) and potentially the added heat required to melt 

trapped ice crystals. 

Certification of ice crystals/mixed phase conditions for the air data sensors 

used for engine control may be accomplished under Part 33. Any engine 

installation/airframe use of such data should consider the results of the 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-81

qualification testing and ensure that it is applicable for the installation 

certification. 

The FAA has conducted mixed phase icing tests, which indicated that for 

unheated airfoil surfaces, the potential ice accretion was the same or less 

than the same total water content of supercooled liquid water. The overall 

power required for running-wet ice protection was not significantly 

changed between all liquid and mixed-phase conditions. However, the 

local power density was higher around the stagnation area compared to 

purely liquid conditions due to the heat required to melt the impacting 

particles that either fully or partially stick to the surface. For internal flow 

areas with considerable changes in airflow direction, and potential for 

trapping ice particles, the latent heat effect of the ice crystals may be more 

prominent. 

For inlets that have considerable changes in airflow direction, an 

assessment of the potential for areas of accumulation of mixed phase/ice 

crystal conditions within the inlet should be accomplished. Some icing 

tunnel facilities have limited ice crystal capabilities that may be suitable for 

evaluating potential accumulations and/or shedding trends in such 

designs. 

Compliance for pitot-style inlets (without considerable changes in airflow 

direction) or for inlet designs using inertial separation, may be shown 

through qualitative analysis of the design and supported by similarity to 

previous designs that have shown successful service history. 

For the ground icing requirements of § 23.1093(b)(2), what determines whether 

a limitation on maximum time interval is required? 

The intent of the ground icing is to ensure that the aircraft can be safely 

operated in ground icing conditions for extended times, which may be in 

excess of 30 minutes. For aircraft that complete the 30-minute interval and 

exhibit consistent, repetitive build and shed cycles (with or without 

intermediate engine run ups), no maximum time interval would be required. 

For aircraft that complete a minimum of 30 minutes without any engine runups, a run-up should be performed to ensure that ice has not been 

accumulating, just prior to shed. If the run-up does not produce any 

adverse operating effects or engine damage, no maximum time interval 

would be required. If the run-up does produce adverse operating effects or 

damage to the engine, the test should be repeated to determine a shorter 

time interval in which the engine can operate and then complete an 

acceleration without adverse operating effects or damage to the engine. 

This shorter time interval would then become an operating limitation. 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-82

C) SYSTEMS ASPECTS

See Appendix D for recommended revisions to AC 23.1419-2D 

D) AC 23-17C

Add additional materials for AC 23-17ABC at end of the pertinent sections: 

... 

23.1323 Airspeed indicating system 

... 

Amendment 23-tbd and subsequent

This amendment added additional requirements to address supercooled large drops 

and mixed phase/ice crystal requirements. The regulation as applied to IFR aircraft is 

essentially unchanged from prior amendments. For aircraft certified for flight into icing 

conditions, see AC 23.1419-2E or subsequent revision.

... 

23.1326 Pitot heat indication systems 

... 

Amendment 23-tbd and subsequent

This amendment modified the requirements of 23.1326 to alleviate the need for an 

ELOS for pitot systems that are not operated on the ground to protect equipment or 

composite structures or at high ambient temperatures in flight. For more discussion, 

see AC 23.1419-2E or subsequent revision.

... 
Part 23 SLD ARC REPORT 

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23.1329 Automatic pilot system 

AC 23.1329 Section 3(d) 

Note: Requirements for autopilots with respect to icing certification are addressed in AC 

23.1419-2E. 

... 

To show compliance with part 23, § 23.1329, applicable to autopilot system installations 

in small airplanes, the following is acceptable. 

1. RELATED REGULATIONS AND DOCUMENTS 

... 

b. Advisory Circulars 

 ... 

 AC 23.1419-2E "Certification of Part 23 Airplanes for Flight in 

 Icing Conditions", dated TBD. 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-84

6. ALTERNATIVES CONSIDERED 

Before proposing new rulemaking, the FAA considers alternative ways to rulemaking to 

solve the safety issue under consideration. The first two alternatives were considered in 

detail by the Ice Protection Harmonization Working Group and included in the part 25 

NPRM published on June 29, 2010. The part 23 ARC did not study these in detail but 

consider these alternatives valid for part 23. They are repeated here as published in the 

Federal Register on June 29, 2010. 

ALTERNATIVE 1: TERMINAL AREA RADAR AND SENSORS

“The IPHWG considered the use of terminal area radar and ground-based sensors to 

identify areas of SLDs so they can be avoided, rather than require certification for 

operations in SLD. Equipment for detecting and characterizing icing conditions in 

holding areas is being developed. However, the equipment would have limited coverage 

area. For areas not covered by terminal area radar and ground-based sensors, airborne 

radars and sensors are being developed that would identify SLD conditions in sufficient 

time for avoidance. These ground-based and airborne systems are not mature enough 

to provide sufficient protection for all flight operations affected by SLD. Even if the 

equipment was mature, rulemaking would still be necessary to establish safety margins 

for inadvertent flight into such conditions and to provide an option for applicants to 

substantiate that the airplane is capable of safe operation in SLD conditions.” 

ALTERNATIVE 2: ICING DIAGNOSTIC AND PREDICTIVE WEATHER TOOLS

“The IPHWG considered the use of icing diagnostic and predictive weather tools to 

avoid SLD rather than certify an airplane to operate in SLD conditions. Tools have been 

developed that can provide information on icing and SLD potential, but may not report 

all occurrences of SLD. These experimental tools are available on the Internet and can 

be used to provide flight planning information guidance for avoidance of SLD conditions. 

However, rulemaking would still be necessary to establish safety margins for 

inadvertent flight into such conditions and to provide an option for applicants to 

substantiate that the airplane is capable of safe operation in SLD conditions.” 

ALTERNATIVE 3: MAINTAIN CURRENT CERTIFICATION MEANS OF COMPLIANCE

The ARC considered the option of continuing the current method of addressing SLD 

during certification of part 23 airplanes. One reason for considering this is the fact that 

there are no icing related accident of airplanes with the current part 23 icing regulation 

(introduced at Amendment 23-43) in its certification basis. Table 6 lists these airplanes. 

It was also recognized that the icing accident trend has been down, as illustrated in 

Figure 1. 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-85

Table 6 - Aircraft Certified to § 23.1419 Amdt. 23-43 

Models Certified at 

Amendment 23-43 

Year 

Certified 

No. of U.S. Registered Airplanes as of 

November 1, 2010 

Hawker Beech 390 2001 183 

Extra 400 2002 11 

Emivest SJ30-2 2007 5 

Diamond DA-42 2007 164 (tbd certified to 23.1419)

Cessna 510 2007 190 

Embraer 500 2008 87 

Eclipse 500 2008 267 (88 certified to 23.1419)

Cirrus SR22 2009 281 

Embraer 505 2009 7 

Cessna 525C 2010 9 

Part 23 Icing Accidents

0

2

4

6

8

10

12

14

16

18

20

1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010

Year

Number of Events

Takeoff

No Icing Approval

Certified for Icing

Figure 1 - Icing Accident Trend 1990-2010
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-86

A General Aviation Manufacturers Association (GAMA) review indicates that the 

proposed rule will not have a big impact on part 23 airplane safety because it will only 

be applicable to new airplanes. The estimated number of new aircraft manufactured 

and affected by the rulemaking will be small compared to the existing fleet. In addition, 

the number of accidents attributed to icing for part 23 aircraft that are certified for flight 

in icing is a small percentage compared to other causes. Most of the icing events 

reviewed are on aircraft not certified for flight in icing, which will not be corrected by this 

rulemaking proposal. As a result, the ARC would like to emphasize the importance of 

efforts to educate pilots who operate existing airplanes that are not certified for icing on 

the dangers of using those products in icing environments discussed in alternative #4. 

SLD is currently addressed by evaluating susceptibility to roll control anomalies in SLD 

and providing generic SLD cues and exit procedures in the Airplane Flight Manuals 

(AFMs). 

Adopting this alternative would obviously eliminate an increase in certification costs. 

However, the ARC did not recommend this alternative for the following reasons: 

The scope of these actions are limited because they do not address the underlying 

safety concern of the unknown performance and handling safety margins for airplanes 

operating in freezing drizzle or freezing rain or a mixed phase. Any requirements 

resulting from these actions would not be comparable to those established by the 

current § 23.1419, which defines safe performance, stall warning and characteristics, 

and handling qualities for flight in part 25, Appendix C icing conditions. 

The current accepted means of determining the SLD shape is either using an arbitrary 

shape and size, or determining it analytically. The result may be an ice shape that is 

not conservative enough, or too conservative, which may result in over design (cost) or 

a safety impact (unnecessarily high approach and landing speeds). Choosing this 

option would not result in an AFM requirement to prohibit flight in SLD conditions. 

ALTERNATIVE 4: PILOT TRAINING

The ARC recognized that icing training for pilots can be improved. For example, part 61 

requires logbook endorsements for tailwheel, high performance airplanes, and high 

altitude (pressurized) airplanes, but has no such requirements for an airplane approved 

for icing. The ARC looked at two examples (Mitsubishi MU-2 series and Cessna C-208 

series) in which annual icing training is required by airworthiness directive (AD). The 

service history of these airplanes in icing improved dramatically after the ADs were 

issued, although other actions in addition to training were required. If training alone 

without the certification rulemaking described in this report were proposed, it would 

have to be made mandatory to be effective (with testing and recurring refresher 

training). There was not be a consensus in the ARC to propose a part 61 amendment 

to add icing training, and therefore this alternative was not chosen. However, the ARC 

will be proposing additional non-regulatory training to supplement the proposed rules as 

part of Task 7. These training recommendations will be added by revision of this report. 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-87

In addition to SLD, training for ground deicing/anti-icing and airplanes not approved for 

known icing (since these make up a large percentage of events) are recommended. 

RULEMAKING ALTERNATIVES CONSIDERED OTHER THE ACTION PROPOSED

The following are rulemaking alternatives (additional, reduced, or modified rules) that 

were considered by the ARC. 

ALTERNATIVE 5: SIMPLIFY PROPOSED SECTION 23.1420(A)(1)

The ARC considered simplifying proposed 23.1420(a)(1) for “detect and exit” airplanes 

by only requiring an AFM Limitation that prohibits flight in freezing drizzle and freezing 

rain. Proposed 23.1420(a)(2) and (a)(3) apply to airplane seeking approval in a portion 

of Appendix O or all of Appendix O and would still be proposed as is. Adopting this 

alternative would delete the requirement to analyze and test “detect and exit” ice shapes 

and would be a large decrease in certification costs. It also addresses one of the cons 

described in alternative no. 3 above. However, it would not address roll control 

anomalies in SLD, which is accomplished today in certification. It would also not 

address the underlying safety concern of the unknown performance and handling safety 

margins for airplanes operating in freezing drizzle or freezing rain, particularly stall 

warning, or a mixed phase, and therefore was rejected. 

ALTERNATIVE 6: DELETE PROPOSED SECTIONS 23.1420(A)(2) AND (A)(3)

When alternative 5 was discussed, in addition to simplifying paragraph (a)(1) of the 

proposed rule, deleting (a)(2) and (a)(3) was considered. If an applicant wanted 

approval to operate in a portion or all of Appendix O, 25.1420(a)(2) or (a)(3) could be 

added into the certification basis. Adding specific part 23 sub-part B rules could be 

done since Subpart B requirements differ between part 23 and 25. The ARC 

recognized that the certification basis would be difficult to apply consistently (e.g. 1g 

stall speeds, additional administrative expenses- issue papers, FAA/Applicant 

coordination). It was recognized that in some areas, the proposed part 25 requirements 

would be more stringent (holding for 45 minutes at extreme cold OAT; ice protection 

activation requirements) and less stringent in others (certification for takeoff in freezing 

drizzle and not freezing rain, or vice versa). This alternative was not adopted for these 

reasons. 

ALTERNATIVE 7: TAKEOFF IN EITHER FREEZING DRIZZLE OR LIGHT FREEZING RAIN

Operators of part 23 airplanes, particularly in commercial service, want the capability to 

takeoff and land in freezing drizzle and freezing rain. The ARC concurred with the part 

25 ARAC IPHWG that certifying to a portion should be permitted. In addition to 

proposing 23.1420(a)(2), the ARC provides detailed guidance for certifying a part 23 

airplane to takeoff in SLD conditions. The part 25 proposal allows certification for 

takeoff in freezing drizzle and not freezing rain, and vice versa. There are benefits if 

part 23 policy was the same. One, freezing drizzle and freezing rain could possibly 

result in very different ice accretions on a part 23 airplane, which would allow the one 

more critical to be certified and not the other. This would reduce certification cost as 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-88

well as provide an operational capability that would otherwise not be available. The 

latter is important because one of the ARC surveys (Appendix TBD of this report) of 

operators showed a prohibition on freezing drizzle has a larger impact than freezing 

rain. As described in this report, the ARC believed that in the part 23 operating 

environment, with today’s technology, it would not be uncommon to misidentify freezing 

drizzle and freezing rain. Because these ice accretions may have different effects on 

part 23 airplanes, the ARC decided that for now, takeoff certification in Appendix O 

would have to include all of Appendix O. 

ALTERNATIVE 8: MODIFY THE PROPOSED PART 25, APPENDIX O ICING ENVIRONMENT

The ARC analyzed a common ice protection system on part 23 airplanes, the fluid antiice system, for compliance to the proposed part 25, Appendix O icing conditions. It was 

found that the freezing drizzle condition at -25°C OAT was the critical point, requiring a 

large increase in flow rate to maintain an anti-ice solution. This would result in a large 

increase in fluid capacity, resulting in a weight penalty. An increase in analyses and 

tests would also result depending on how the system was to be designed compared to 

the current certified system. Although not analyzed, it is theorized a thermal bleed air 

system may also find this to be its critical condition, requiring additional bleed air. The 

ARC reviewed the research data points that were used for development of the part 25 

Appendix O and the documented icing conditions of icing events, and questioned why 

the liquid water content at -25°C could not be reduced (due to the lack of data in this 

region). The ARC decided it was not appropriate to propose SLD icing conditions 

different from that proposed for part 25. Alternatively, the ARC proposed rule language 

in 23.21(c)(2) to address the issue, and guidance for 23.21(c)(2)(3) for holding duration 

at cold freezing drizzle conditions. The ARC proposal targets the primary safety 

concern of warm Appendix O conditions without undue penalty to part 23 aircraft. 

ALTERNATIVE 9: REDUCE NUMBER OF FLIGHT TESTS OR ANALYSES REQUIRED

The ARC asked itself, are we proposing requirements for D&E airplanes for which 

service history shows no safety issue? Eliminating tests that provide no safety benefit 

would reduce certification cost. The ARC could not justify any revisions to what was 

proposed for certification for flight in Appendix O or an approved portion of it. Any 

reduction would be a reduction of what is currently required for Appendix C icing 

conditions. 
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For a detect and exit airplane, the ARC decided at the beginning of their work to 

propose rules that address the safety concern and not have icing conditions for which 

the airplane is not approved to dictate design. Compliance to the following regulations 

are proposed with detect and exit encounters: 

Section 23.77 Landing climb 

Section 23.143 ICTS 

Section 23.1323 SLD requirements for airspeed indicating systems 

Section 23.1325 Static pressure system 

There have been no documented fatal events due to SLD icing conditions related to any 

of these areas. The part 23 icing ARC decided to retain them as requirements because 

the lack of flight data recorders in the part 23 fleet could be one reason why, but also 

rationalized the following: 

Section 23.77 - Icing research testing documented in FAA Technical Report 

DOT/FAA/06-60, “Propeller Icing Tunnel Tests on a Full-Scale Turboprop Engine,” 

March 2010 showed a significant difference in propeller ice accretion and performance 

between an Appendix O condition and several Appendix C conditions, and therefore 

propeller performance could affect climb capability in Appendix O. There are part 23 

airplanes with documented events in which a forced landing resulted from flight in 

Appendix O conditions. 

Section 23.143 - A ridge behind the protected area could form on the horizontal tail as 

well as the wing, and since an ICTS event has a high probability of being catastrophic, 

the ARC believes it should be tested. 

Section 23.1323 - Pitot probes have high collection efficiency and therefore their 

performance does not change with drop size. Also consider the liquid water content of 

Appendix O is smaller than Appendix C, there should be no performance problem in 

Appendix O. However, ice accretions forward of the probe could affect the position 

error, and since Appendix O conditions could affect all probes at the same time, the 

possibility of misleading airspeed should be evaluated. 

Section 23.1325 - Certification experience has shown some locations of static ports can 

result in ice accretion near them in Appendix O conditions. 

Section 23.629 – The part 25 NPRM proposed that a flutter analysis is required for 

detect and exit shapes. This was a subject that the ARC debated. Flutter experts from 

some airframe manufacturers were consulted and recommended that anything that 

could form on the aircraft should be analyzed, and since applicants will be defining ice 

shapes to use for flight testing exit criteria, they would likely analyze them for flutter 

characteristics. On the other hand, service history shows no events due to flutter of 

SLD ice accretions. In addition, on unprotected surfaces such as wing tips, the mass of 

ice due to SLD is not expected to be higher than due to Appendix C. The ARC decided 

that a flutter analysis would not be required for detect and exit ice accretions. 
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Ice crystal Requirements - Ice crystal requirements for the airspeed indicating system 

are proposed in § 23.1323. There are no documented ice crystal events of pitot probes 

on part 23 airplanes. The documented events on part 25 airplanes show that high 

altitude and high true airspeed are factors. The ARC decided that part 23 airplanes 

which are capable of certain altitude and Mach number should show compliance. 

ALTERNATIVE 10: REDUCE NUMBER OF REQUIRED ICE SHAPES 

Similarly to alternative 9, the ARC asked itself if it could simplify the guidance on ice 

shapes to reduce the amount of analyses, icing tunnel tests, and possibly flight tests 

that would have to be accomplished. Could one ice shape, such as exposure at end of 

the hold, perhaps approach (eliminating landing, enroute, etc.) be used as a simplified 

approach that would provide most of the safety benefit? The ARC reviewed the service 

history and rationalized that analyses of ice accretions for “detect and exit” can be 

limited to the holding phase and approach phase. The ARC could not rationalize doing 

the same for the portions of Appendix O for which the airplane is approved, for the 

same reason as alternative 9. 

ALTERNATIVE 11: ALLOW VISUAL CUE FOR ALL PART 23 AIRPLANES

Section 25.1419 was revised at Amendment 25-129 in 2009 to add requirements for 

activation of ice protection. A visual cue alone is not compliant to 25.1419, an advisory 

ice detection system is required to be installed. Adding an ice detection system 

increases certification cost as well as the cost of the airplane (by at least $TBD). In 

reviewing the service history of part 23 airplanes, pilots typically know when they’re in 

icing. The scale factor and pilot visibility of more accretion surfaces (such as wing 

leading edge) is one difference between part 23 airplanes and part 25 airplanes. The 

ARC, therefore, decided not to require an advisory ice detection system to supplement 

visual cues for normal, utility, and acrobatic category airplanes. However, the ARC 

chose to adopt the part 25 requirements for commuter category airplanes. The larger 

scale factor, and the fact that pre-activation ice in SLD would not be required were 

factors in the decision. 

ALTERNATIVE 12: NECESSITY TO FLIGHT TEST IN NATURAL APPENDIX O CONDITIONS

The necessity to flight test in natural Appendix O conditions was debated during the 

IPHWG and the pros and cons are detailed in the IPHWG report which can be found in 

rulemaking docket F AA–2010–0636. A large con was the cost involved. The ARC 

adopted similar rule language as part 25, making natural icing one of the acceptable 

means of compliance, rather than an absolute requirement. The ARC added specific 

guidance for a path for detect and exit airplane in which natural icing flight tests in 

Appendix O would not be required as one of the means of compliance. The ARC did 

not adopt this for an airplane approved to fly in a portion or all of Appendix O. For 

example, to approve takeoff in Appendix O conditions, the guidance material states 

takeoff demonstrations in natural Appendix O should be accomplished. The majority of 

the ARC believed the airplane should be flight tested in the actual conditions for which it 

is approved, and not put the flying public in that position. The alternative, not adopted, 
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would be to certify approved portions of Appendix O the same manner as detect and 

exit. 

ALTERNATIVE 13: AERODYNAMIC PERFORMANCE MONITOR AS AN ALTERNATIVE TO § 23.1420

Similar to the first two alternatives, this alternative was not discussed in detail by the 

ARC but it is valid for part 23. The discussion in the IPHWG working group report is 

repeated here: 

“The working group considered the use of aerodynamic performance monitors (APM’s) 

to detect sources of boundary layer instabilities similar to those caused by ice 

accretions. The logic is that flightcrews would be alerted to take precautionary actions 

once the wing or a control surface’s boundary layer conditions had reached a safety 

threshold, regardless of what caused the boundary layer disturbance. Several attempts 

have been made to investigate the feasibility of APMs on civil aircraft. Currently no 

APMs are used on commercial aircraft and there is little operational experience to 

establish confidence in the system’s capabilities. The working group concluded that 

APM’s are not sufficiently mature to support a rule based on its technology. However, 

the rule is written broadly enough to allow the use of an APM as a means of compliance 

should the APM’s reach the maturity required to obtain approval for installation on a 

Part 25 (23) airplane.” 
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7. CERTIFICATION COST INPUT 

A) ASSUMPTIONS

As part of the Task 2, ARC members provided input on the estimates on the cost of the 

proposed regulatory changes to assist the FAA in performing the regulatory analysis. 

Both the increase in costs and any potential for reduced costs were considered. 

With the diverse range of aircraft within part 23 and the range of certification levels 

typically sought, some method of sub-dividing the fleet was required. The ARC elected 

to consider both aircraft size and the certification options available to applicants. 

The assumptions used for the certification cost estimates are provided in Table 7 and 

Table 8. 

Cost estimates were limited to the added costs related to the proposed rulemaking. The 

basic costs associated with certification within Appendix C icing are existing 

requirements and are not part of the cost basis. 

Other assumptions used in the estimates were as follows: 

 The costs for amended type certificates considered significant under § 21.101 

will have a similar cost as a new type certification basis. 

 ARC members were to use their anticipated compliance methods (icing tunnels, 

icing tankers, test methods) as the cost basis. 

 For aircraft certified to detect and exit per § 23.1420(a)(1), no testing in natural 

large drop conditions would be required (applicant’s discretion). 

 For aircraft certified for takeoff and landing (approved portion) per 

§ 23.1420(a)(2), flight testing in natural large drop conditions would be required. 

 For aircraft certified without restrictions per § 23.1420(a)(3), flight testing in 

natural SLD would be required. 

 Costs estimates were to include total costs, including both labor hours for direct 

engineering and supporting personnel. Direct non-recurring costs were 

considered all costs that are not direct labor (wind and/or icing tunnel rental, 

additional icing tunnel models, travel, chase aircraft rental, contract services such 

as meteorologist, tool making, etc.) 

 Estimates were provided in labor hours assuming that the FAA economist would 

use the appropriate $/hour rate for such technical engineering activity. 

Some of the rulemaking recommendations would alter compliance methods for basic 

compliance with § 23.1419. These changes were to be included in the estimates as 

differences due to the proposed rulemaking. As a part of this, there was some changes 

made that could reduce some of the existing certification costs within Appendix C 

certifications. ARC members were requested to provide an estimate of these costs to 

be considered in the overall economic balance. 
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Table 7 - Size Assumptions Used for Certification Cost Estimates 

Aircraft Type Assumptions 

Small part 23 aircraft Single reciprocating engine (under 6,000 lbs) 

Large part 23 aircraft Twin turbofan, commuter category (under 19,000 lbs) 

Note: This is intended to capture the upper and lower bounds within part 23. If further subcategories are required, the ARC can provide guidance based on aircraft and certification 

complexity . 

Table 8 - Certification Approval Options with Respect to Icing Conditions 

Option Assumptions 

Basic Certification 

(not approved for 

flight into icing) 

Required for all part 23 certifications 

 This option includes all icing considerations for certification of an aircraft 

that is prohibited from flight into icing conditions. 

 Includes any basic engine requirements such as § 23.1093 (does not 

include § 23.929). 

 Optionally, includes systems and equipment requirements such as pitot 

heat and static source heat requirements for aircraft certified for IFR/IMC 

operations. 

 Includes any ice protection equipment installed on a “non-hazard” basis 

as there are no additional icing rule requirements beyond those for a 

“basic” certification. 

Approval for flight into 

icing per § 23.1419 

Optional Requirement (applicants discretion) 

 Approval for flight into icing is optional within part 23. 

 Many small part 23 single engine aircraft are not approved for flight in 

icing. However, the industry trend is that icing approvals are becoming 

more common on smaller aircraft due to market demand. As such, the 

estimates were provided for both the “Small” as well as the “Large” part 

23 aircraft as defined in Table 7.

 Approval for flight into icing under § 23.1419 is limited to the 

environmental definitions in 14 CFR 25, Appendix C.

Approval to proposed 

§ 23.1420 

Required if aircraft if approved for flight into icing per § 23.1419. 
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B) INCREASED COST CATEGORIES

The increased costs were further divided to account for the different aspects of a typical 

certification. These divisions were as follows: 

Airframe Analysis

The airframe analysis aspect was intended to address aspects of the certification 

related to the airframe ice protection systems and the effect of the airframe ice shapes 

on the performance and handling qualities of the aircraft (not including actual flight 

testing). This type of activity typically includes: 

Table 9 - Regulatory Input - Airframe Analysis

Aspects Activities 

Ice 

Shapes/Impingement 

 Includes any additional analysis required to show 

compliance to the proposed rules for development of 

unprotected ice shapes on areas such as wing tips/roots, 

stabilizers tips/roots, vertical stabilizer (if applicable), 

radomes, etc. 

 Development of the protected area limits on wing, 

propeller, etc. 

 Any potential ice shapes that may form behind the 

protected areas. 

Aerodynamic Effects  This category includes any CFD or other aerodynamic 

analysis required to look at the criticality of ice shapes, 

evaluate the potential performance effects at the airfoil 

and/or aircraft level, as well as SLD cue development 

(wind tunnel testing addressed separately). 

Aeroelastic Stability  Required for approved portions of Appendix O 

Water Catch & 

Thermal Aspects 

 This category includes any required analysis of the 

altered water catch effects due to the proposed 

rulemaking, examples include effect on evaporative or 

running wet anti-ice systems, effect on freezing point 

depressant systems, etc. 

Wind Tunnels

The wind tunnel category includes items such as wind tunnel model rework, wind tunnel 

contract expenses, fabrication of the ice shapes, labor to develop the test plans, data 

analysis, test reports and conduct testing as well as any added costs for travel 

expenses. Model rework aspects limited to necessary modification necessary to 

perform the SLD testing. Does not include the basic cost of the model if it would have 

been build for Appendix C certification efforts. 
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Icing Wind Tunnels

This category was divided into airframe and engine installation aspects. Detail 

tasks/items are similar to the wind tunnel category above, again considering only the 

differences due to the large drop certification efforts. 

Engine Installation

This category considers engine installation effects that would be required for 

certification to proposed §§ 23.903, 23.929 and 23.1093. Considers requirements for 

any analysis, review of service history, shedding aspects and compliance methods. 

Miscellaneous Systems

This category considers the systems and equipment aspects such as §§ 23.775, 

23.1323, 23.1324, 23.1325, 23.1326, 23.1403, 23.1419 and 23.1420. This would 

include any changes to system architecture and integration, system safety 

assessments, SLD ice detector qualification and installation certification, any 

modifications to windshield heat levels, angle of attack and pitot probe requirements, as 

well as any supporting analysis for the above. 
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Flight Testing

This category was subdivided into three areas, dry air shape testing, icing tanker testing 

and natural SLD testing. 

Table 10 - Regulatory Input – Flight Testing

Dry air ice shape testing  Includes test plans, conducting the testing including any 

necessary build-up of the ice shapes for safety mitigation, 

data analysis and test reports. 

 Ice shape definition (drawings, installation instructions), 

fabrication and installation. Analysis of the ice shapes was 

considered under the Airframe Analysis category. 

Icing tanker Testing  Includes icing tanker rental & fabrication if the applicant 

deems necessary for showing compliance. Not all 

manufacturers/applicants will have access to icing tankers, 

requiring alternate means of compliance. 

 Test plans, conducting the testing, data analysis and 

required documentation. 

 Includes cost and time to fly the aircraft to and from the test 

area, and chase aircraft rental as required to document tests

 Flight crews and support personnel such as support 

engineering staff and maintenance personnel 

Natural SLD Testing  Test plans, conducting the testing, data analysis and 

required documentation. 

 Airplane preparation (install instrumentation, painting for 

visibility of ice shedding, cameras, etc.) 

 Includes cost and time to fly the aircraft to and from the SLD 

conditions, and chase aircraft rental as required to 

document tests. 

 Flight crews and support personnel such as support 

engineering staff and maintenance personnel to conduct 

natural ice tests in SLD 

 Icing meteorological support. 

 Specific icing instrumentation for SLD (rental if required) 
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C) INCREASED COST SUMMARY

The estimates reflect the increased costs for applicants for the different types of 

certification. The differences in bids reflect different approaches towards certification 

As an example, some applicants may use more analysis, and less icing and wind 

tunnel tests, not all applicants have access to icing tankers and consequently may 

have more effort expended in icing and/or flight tests. As such, the bid pairs (labor 

and non-recurring costs) should not be split between different estimates. 

The bids reflect the best estimates available at this point in time, but did have 

considerable variance between the different estimates. This is likely a reflection of 

the uncertainties in the certification process (applicants won’t know the full extent of 

work required until a full certification plan is completed and approved), as well as 

what facilities/simulation methods are available to the various applicants. As such, it 

is recommended to use a median approach to the regulatory analysis to more 

accurately reflect the true costs associated with the rule. 

Table 11 provides a summary of the total labor hours and the non-recurring costs that 

would occur for each certification program. It is assumed that the APO will determine 

the appropriate engineering labor rate for use in the analysis. 

For reference on detect and exit certification, most manufacturers assumed one 

Appendix O ice shape configuration for flight test evaluation, although one 

manufacturer assumed three ice shapes. 
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Table 11 - Summary of Increased Certification Costs for Proposed Rulemaking 

Summary

Small Large Small Large Small Large Small Large Small Lar

Estimate A none none 2700 hrs 4890 hrs 6020 hrs 10465 hrs none none 343,000 $ 42

$ 

Estimate B none none no bid 15300 hrs no bid 32300 hrs none none no bid 2,34

$ 

Estimate C none none 1900 hrs no bid 4440 hrs no bid none none 188,000 $ no 

Estimate D none 100 hrs 4096 hrs 4106 hrs 10124 hrs 10074 hrs none 2,000 $ 233,500 $ 48

$ 

Estimate E none none 3324 hrs 5283 hrs 11214.5 hrs 15728 hrs none none 108,231 $ 63

$ 

Summary Median none 100 hrs 3012 hrs 5087 hrs 8072 hrs 13097 hrs none 2,000 $ 210,750 $ 55

$ 

Hours Non-recurr

Basic FIKI Basic 

(non-FIKI) Detect and Exit Unrestricted (non-FIKI) Detect and Ex

Table 12 provides a summary of the total labor hours and the non-recurring costs that would occur for certification considered. As discussed above, separation of the bid pairs (labor and non-recurring) is n
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-99

Table 12 – Detailed Medians for the Aspects of Certification 

Small Large Small Large Small Large Small Large Small 

Median of all bids received, by category:Airframe Analysis none 0 hrs 810 hrs 1158 hrs 1847 hrs 2342 hrs none - $ - $ 

$ 

Wind Tunnels none 0 hrs 80 hrs 614 hrs 160 hrs 1217 hrs none - $ 27,500 $ 

$ 

Icing Wind Tunnels - Airframe Aspects none 0 hrs 208 hrs 296 hrs 434 hrs 768 hrs none - $ 50,000 $ 

$ 

Icing Wind Tunnels - Engine Aspects none 0 hrs 89 hrs 258 hrs 147 hrs 574 hrs none - $ 8,003 $ 

$ 

Engine Installation none 100 hrs 225 hrs 325 hrs 390 hrs 750 hrs none 2,000 $ 1,000 $ 

$ 

Misc - Systems none 0 hrs 364 hrs 740 hrs 804 hrs 1336 hrs none - $ 7,500 $ 

$ 

Flight Test - Dry Air Testing none 0 hrs 463 hrs 1190 hrs 1416 hrs 4274 hrs none - $ 23,500 $ 

$ 

Flight Test - Tanker Testing none 0 hrs 380 hrs 255 hrs 740 hrs 415 hrs none - $ 48,000 $ 

$ 

Flight Test - Natural SLD Testing none 0 hrs 0 hrs 0 hrs 924 hrs 1752 hrs none - $ - $ 

$ 

Hours Non-re

Basic FIKI Basic 

(non-FIKI) Detect and Exit Unrestricted (non-FIKI) Detect an
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D) COSTS FOR CERTIFICATION TO A PORTION

The guidance material recommendations provide guidance for certification to a portion 

of the large drop environment in the context of approving takeoff and landings in such 

conditions. The feedback from the operators within the ARC, indicated that this could 

become a significant operating restriction, and as such market demand may be 

sufficient for a manufacturer to seek such an approval. 

The advisory material recommends additional ice shape scenarios that require 

consideration, and also advises that flight testing in natural large drop icing would be 

required. Additionally, since the certification would still be restricted during certain 

phases of flight, development of exit icing cues and ice shapes would be required. 

The consensus opinion of the ARC was that the certification for approval for takeoff and 

landing is that the costs would be 70% of the difference between a detect and exit 

certification and a full unrestricted certification as noted below. 

Portion Costs Takeoff & Landing ൌ 

∑Detect & Exit Costs ൅70%*ሾ ∑Unrestricted Costs ‐ ∑Detect & Exit Costsሿ

E) REDUCED COSTS CATEGORIES

An effort was made to identify the reduced costs in the same manner as for the 

increased costs as noted in Table 7 and Table 8. The sub-categories were similar to 

the cost evaluation (Analysis, Wind Tunnels, Icing Wind Tunnels and Flight Testing). 

The effort was limited to the reduced costs related to the proposed rulemaking as 

compared to the requirements at 14 CFR 23, Amendment 43. The icing requirements 

of § 23.1419 at amendment 43 were altered to define “Capable of operating safety” as 

the airplane performance, controllability, maneuverability, and stability must not be less 

then that required in part 23, subpart B for Appendix C icing conditions. In addition to 

SLD rulemaking, the ARC proposed changes to § 23.1419 that eliminate certain 

Subpart B requirements. The estimate was intended to assist in determining how much 

of the costs of basic certification to § 23.1419 is reduced. 
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Examples of potential reduced costs were as follows: 

23.49(c) Stalling period - Tests would still be required to define stall speeds with critical ice 

accretions. However, the cost associated with writing and working on an exemption 

request is eliminated. 

Takeoff Determination of takeoff speeds or takeoff performance due to takeoff ice accretions is 

proposed not to be required for reciprocating or turboprop powered normal category 

airplanes. Therefore the cost to determine takeoff ice accretion (additional tunnel tests 

or analysis) and flight testing with takeoff ice accretion (stall and climb performance) 

would not be entered for the small airplane. 

Roll Control 

in SLD 

AC 23.1419-2D requested consideration of the potential for roll control anomalies in 

SLD conditions for aircraft with non-powered roll control surfaces. 

The ARC members reviewed the request and could not identify a significant reduced 

cost. It was the opinion of the ARC members, that the magnitude of any reduced costs 

are well within the uncertainty of the increased cost estimates shown above. As such, it 

is recommended that the potential for reduced costs be acknowledged as a 

conservative factor in the regulatory analysis rather than an explicit calculation. 

F) SUMMARY ARC POSITION ON COSTS

The ARC completed the assigned tasking which was to review the part 25 rulemaking 

and determine an appropriate response for part 23. However, the larger issue of how to 

improve icing safety for the part 23 fleet was not directly addressed by the new 

certification rules. The ARC has concerns over the relatively high certification costs 

associated with the rules proposed with respect to the overall safety benefit on icing 

safety for the part 23 fleet. The GAMA presentation included in Appendix F illustrates 

the limited effect on the current part 23 aircraft. 

As discussed in Section 9 Benefit Summary, the majority of part 23 icing accidents 

occur on aircraft that are not certified for flight in icing. As flight in icing systems are 

optional equipment on many part 23 aircraft, this trend will not be altered by the 

introduction of new certification rules. Additionally, the large quantity of aircraft already 

in the field combined with the relatively low projected production rates will limit the 

overall effect of new certification rules on the part 23 fleet. 

Additionally, all of the icing events have occurred on aircraft built prior to increased icing 

certification standards associated with § 23.1419, Amendment 43 which was introduced 

in 1993. This rule change only considers Appendix C icing conditions, but required the 

aircraft to meet the subpart B standards in icing conditions. This has typically been 

assessed in recent certifications with extensive ice shape testing, simulating 

preactivation, normal operation as well as system failure shapes. The guidance 

material also required severe icing language to be added to the AFMs with generic 

identification cues. The lack of safety events associated the amended icing rules, begs 

the question of whether increased standards of § 23.1419, Amendment 43 provides 

sufficient protection for exiting severe icing conditions, including exposures to part 25, 

Appendix O. Another unintended consequence of the rulemaking is a potential 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-102

decrease in the safety level as more manufacturers/customers may opt for a no-hazard 

system due to the certification requirements and increased flight in known icing option 

costs. 

Most part 23 aircraft will likely elect to comply with the detect and exit option of 

§23.1420(a)(1). The combination of small scale, limited power, and reversible flight 

controls makes it technically challenging to certified to a portion or unrestricted flight per 

§ 23.1420(a)(2) or (a)(3). As a detect and exit aircraft, operations in freezing drizzle and 

freezing rain will be prohibited by AFM limitations which will limit the aircraft exposure to 

conditions when forecast or reported. Significant certification cost reduction could be 

realized by reducing the scope for detect and exit aircraft to determining and validating 

exit cues. The exit procedures for an inoperative ice protection system could be used 

to provide the safety margins desired for a safe return and landing. The system failure 

shapes typically require increased approach and landing speeds as well as potential 

flap limits. While the exact effect of the SLD shapes would not be assessed, a level of 

safety commensurate with the exposure risk could be achieved. 

Alternately, it may be possible to reduce the certification requirements, while 

maintaining the level of safety, based on the accident history review with focus on the 

certification areas that are affected. Using this type of bottoms up approach would 

provide the maximum value for the certification costs. 

While there is a desire to maintain an equivalent level of safety to part 25, the ARC 

recognizes that most part 23 aircraft are operated differently than the part 25 transport 

aircraft. Part 23 aircraft have more operational flexibility, and can operate out of much 

smaller airports. This ability to divert and land at a large number of airports provides 

more options than part 25 operations constrained to specific airports. 
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8. OPERATING COST 

A) COST OF AVAILABLE CERTIFICATION OPTIONS

On the operators’ side for non-recurring costs, a breakdown divided into three 

categories can be envisaged. 

(1) AIRPLANES CERTIFIED TO § 23.1420(A)(1) “DETECT AND EXIT”

It is envisioned that most part 23 airplanes, particularly the airplanes marketed more for 

part 91 operations versus part 135 cargo2 operations, will be certified to “detect and 

exit.” These airplanes will be prohibited from operating in Appendix O conditions, for 

example taking off at an airport reporting freezing drizzle or freezing rain. Based on an 

AOPA survey, it can be assumed that 50% of part 91 operations would not be affected 

since they do not currently operate in these conditions. Based on NATA and RACCA 

surveys, it can be assumed that 50% of part 135 operations would not be affected since 

they do not currently operate in these conditions. This value was obtained by 

combining the 1/3 NATA number with 3/5 RACCA number for light freezing rain 

resulting in 4/8. The RACCA respondents who did not operate in freezing drizzle were 

higher, which is not quite understood. The lower number is used to be conservative. 

These airplanes will have costs associated with the following: 

 Cancelled flight (due to Appendix O conditions at the departure airport) 

 Cancelled flight (due to Appendix O conditions at the destination airport) 

 Diversion by exiting (increased flown distance) 

 Diversion to alternate 

The impact due to diversion by exiting while enroute is small. Part 23 airplanes today 

are required to exit severe icing by an AFM Limitation. Appendix O conditions would 

cause severe icing on many part 23 airplanes. 

(2) AIRPLANES CERTIFIED TO § 23.1420(A)(2) “APPROVED TO OPERATE IN A PORTION 

OF APPENDIX O”

Many of the part 23 airplanes expected to be operated in part 135 cargo operations 

most likely will be certified to takeoff in Appendix O conditions, and almost as much will 

be certified to takeoff and land in these conditions. There are additional certification 

costs for landing. The surveys showed the operators want these capabilities for new 

 

2 The operating rules for cargo versus passenger operations are mostly the same for part 135 operations, 

however part 135 cargo operations typically have more pressures to dispatch into significant weather 

conditions than part 135 passenger operations. 
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airplanes. The only effect on takeoff and landing would possibly be a weight limit 

(resulting in payload decrease) to comply with takeoff, approach, or landing climb 

gradient requirements. These airplanes will have costs associated with the following: 

 Impact on dispatch (performance limited take-offs or landings and payload 

decrease) 

 Diversion by exiting (increased flown distance) 

 Cancelled flight (due to Appendix O conditions enroute) 

The impact due to diversion by exiting while enroute is small as discussed in 

§ 23.1420(a)(1). 

(3) AIRPLANES CERTIFIED TO § 23.1420(A)(3) “APPROVED TO OPERATE IN ALL OF 

APPENDIX O”

It is not anticipated that a part 23 airplane will be certified to this rule due to the small 

scale effects and capabilities of ice protection systems common on these airplanes. 

However, it should not be ruled out completely due to technology advances and/or 

market pressure. Therefore a small percentage of future part 23 airplanes certified to 

this rule should be assumed. The operating costs associated with this option are: 

 Impact on dispatch (performance limited take-offs or landings and payload 

decrease) 

B) TRAINING

Costs due to any increase in training should be considered for the part 135 operators. 

In part 91 operations, airplanes requiring a type rating should be considered. The 

Airline Transport Pilot Practical Test Standards (FAA-S-8081-5F) introduced the 

following special emphasis area at Change 2, July 2008 and therefore training for ATP 

ratings will be affected: 

“Added recognition of wing contamination to icing; adverse effects of wing 

contamination in icing conditions during takeoff, cruise, and landing phases of 

flight; and icing procedures of information published by the manufacturer, within 

the AFM, that is specific to the type of aircraft;..” 

The increased cost would involve training the limitations, any procedure in Appendix O 

different than in Appendix C, and Appendix O recognition cues. Part 135 operators that 

employ dispatchers would also have an increase in cost. 

Costs associated with the training of Air Traffic Control and weather system personnel 

also need to be considered, but it is assumed this was included in the part 25 

rulemaking effort. 
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C) DESIGN IMPLICATIONS

Compliance to the new rules may result in design changes which will affect operators. 

Modifications in the ice protection systems such as an increased bleed and/or engine 

size or increased fluid capacity) will increase cost and/or weight. If engine size or bleed 

extraction remains unchanged, there may be payload reductions to meet climb 

requirements. 

D) AIRPLANE MANUFACTURING INDUSTRY

The new rule will not affect the current fleet. New airplanes with a prohibition on taking 

off and landing in Appendix O will compete with the existing fleet. Except for some very 

recent certifications which adopted recommended language in AC 23.1419-2D, the 

current fleet has no such prohibition. This will lead to either more new certifications 

complying with proposed § 23.1420(a)(2) in lieu of § 23.1420(a)(1), or if the RACCA and 

AOPA surveys are an indication, will lead many to buy a used airplane rather than a 

new one. This would lead to lower sales of new airplanes, which would affect not only 

the airplane manufacturers but their suppliers. Regarding the RACCA survey, the 

question was “presuming you’re considering a new aircraft”. The NATA representative, 

a part 135 cargo operator, commented that they usually buy used airplanes anyway, so 

the impact due to these operators may not be large. 

E) ACTUAL COST DATA

This discussion is meant to guide the FAA economist to the types of recurring costs that 

should be considered. The surveys in Appendix E of this report contain limited 

quantitative data which may be useful to the economist. 
Part 23 SLD ARC REPORT 

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9. BENEFIT SUMMARY 

A) ICING ACCIDENT DATABASE REVIEW

The ARC examined incidents and accidents to identify those which may be considered 

in the benefit analysis of the regulatory evaluation. The ARC would like to acknowledge 

the work of Steve Green, a consultant hired by the FAA to help assemble the part 23 

icing database and identify applicable accidents. Much of the narrative in this section of 

the report was extracted from a draft of Mr. Green’s report to the FAA. 

Three data sources were used - NTSB data, the FAA Accident/Incident Data System, 

and the NASA Aviation Safety Reporting System. The original project that studied part 

23 icing accidents was accomplished in 2007. A total of 187 part 23 icing events were 

considered in the original study. Of these 187 events, 38 of them took place prior to 

1982 and were thus not originally considered, however several of these were reexamined to determine if SLD was present. Four events were rejected from the current 

work following additional examination of their relevance. An additional 7 events were 

determined to present inadequate data for evaluation. Although these 7 events had 

been evaluated for the previous study, it was determined after careful reconsideration 

that they did not have enough data available. Three events that had been deemed to 

present inadequate data in the earlier study were now included in the current 

evaluation. This resulted in 141 original events. An additional 84 events were added to 

this data - 54 events from the ASRS database, 1 from the FAA AIDS data, and 29 

events from the NTSB data. These included events that occurred after the 2007 study, 

and events that were found after a more robust “scrubbing” of the databases. These 

events were then analyzed to determine their applicability to the proposed rules. An 

additional 12 events were removed as a further review indicated the aircraft were not 

approved for known icing. 

The following table lists the accidents applicable to SLD. All aircraft were certified to 

§ 23.1419 at Amendment 23-14 or earlier, including Civil Air Regulations (CAR) 3. No 

aircraft in the events database were certificated under. § 23.1419 Amendment 23-43 

(latest amendment for part 23 icing certification). Since 1979 through 2010, there were 

48 events with a total of 57 fatalities. 

Table 13 – Events Applicable to SLD

DATE AC TYPE LOCATION FATAL INJURY HULL 

LOSS 

01/03/2009 BE-58 Brainerd, MN 0 0 SD 

02/16/2007 CE-340A Council Bluffs, IA 4 0 Yes 

03/20/2006 PA-23-250 Emporia, KS 0 1 SD 

01/25/2006 CE-421C Carson, WA 1 0 Yes 
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Table 13 – Events Applicable to SLD

DATE AC TYPE LOCATION FATAL INJURY HULL 

LOSS 

01/11/2005 BE-65-E90 Rawlins, WY 3 1 Yes 

12/10/2003 CE-441 Vestavia Hills, AL 2 0 Yes 

11/04/2003 CE-208B Bangor, ME 0 0 MD 

12/26/2006 CE-414 Johnstown, PA 2 0 Yes 

12/24/2002 BE-58 Egypt, AR 1 0 Yes 

02/07/2001 BE-65-B80 Sioux Falls, SD 0 1 Yes 

02/07/2001 BE-58 Ainsworth, NE 1 1 Yes 

12/18/2000 BE-58 Huntingburg, IN 0 0 SD 

05/31/2000 CE-414 Monarch, MT 3 0 Yes 

01/24/1999 PA-46-350P Rockford, IL 0 1 Yes 

01/21/1999 BE-95-C55 Pellston , MI 3 0 Yes 

01/08/1999 CE-310R Allentown, PA 0 0 SD 

04/07/1998 CE-208B Bismarck, ND 1 0 Yes 

03/05/1998 CE-208B Clarksville, TN 1 0 Yes 

01/20/1998 CE-208B Grand Island, NE 0 0 SD 

11/13/1997 BE-65-A90 Wheeling , WV 0 0 SD 

11/02/1997 PA-34-200T Lynn, IN 2 0 Yes 

01/08/1997 BE-200 Dallas, TX 0 0 SD 

12/28/1996 BE-65-C90 Rhinelander, WI 0 2 Yes 

02/07/1996 BE-1900D Bradford, PA 0 2 SD 

01/15/1996 MU-2B-36 Malad City, ID 8 0 Yes 

12/22/1995 B-58 Minneapolis, MN 0 0 SD 

10/21/1995 CE-421C Battle Creek, MI 1 0 Yes 

03/05/1995 CE-421C El Prado, NM 4 0 Yes 

03/02/1995 CE-208B Ardmore, OK 0 1 SD 

02/15/1995 PA-23-250 Minneapolis, MN 0 0 SD 

02/14/1995 CE-T310R Grand Island, NE 0 0 SD 

12/08/1994 BE-18 Kansas City, MO 1 0 Yes 

11/25/1993 CE-303-T303 Rogers, AR 2 0 Yes 

01/27/1992 CE-441 Green Bay, WI 0 0 MD 
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Table 13 – Events Applicable to SLD

DATE AC TYPE LOCATION FATAL INJURY HULL 

LOSS 

02/27/1990 CE-208B Denver, CO 1 0 Yes 

03/03/1989 CE-310R Des Moines, IA 0 0 SD 

03/05/1986 MU-2B-60 Eola, IL 5 0 Yes 

02/26/1986 BE-18 Janesville, WI 0 1 Yes 

02/18/1986 CE-402B Rochester, MN 0 0 SD 

11/25/1985 500 (Twin 

Commander ) 

Des Moines, IA 7 0 Yes 

12/04/1984 CE-T310R Lubbock, TX 0 0 SD 

12/05/1983 BE-18-TC45J Kansas City, KS 1 0 Yes 

12/18/1982 CE-310R Gaylord, MI 0 0 SD 

01/06/1982 CE-340A Rolla, MO 0 0 SD 

12/18/1980 BE-60 Denver, CO 0 2 SD 

02/15/1980 BE-18 Olathe, KS 1 0 Yes 

12/04/1979 DHC-6-300 Steamboat Springs, CO 2 20 Yes 

3/21/1984 CE-421C Joliet, IL 0 0 SD 

SD – substantial damage 

MD- minor damage 

The above events only include U.S. events. The following foreign events should be 

mentioned since SLD is suspected and they involve an aircraft type which has 6 events 

in the U.S. table. The first event is an incident in which airplane could not climb. The 

events in Russia and Canada were stall on approach. The Russian event is significant 

because the airplane was equipped with a flight data and voice recorder. 

Table 14 – International Events Applicable to SLD

DATE AC TYPE LOCATION FATAL INJURY HULL 

LOSS 

01/19/2006 CE-208B Florø, Norway 0 0 No 

11/19/2005 CE-208B Moscow, Russia 8 0 Yes 

03/14/1997 CE-208B Simcoe, ON, Canada 1 0 Yes 
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There exist 16 events known to the FAA of thrust rollback in certain turbojet engines of 

part 23 airplanes in suspected ice crystal conditions that do not appear in public 

records. All occurred in cruise at an altitude of 28,000 to 41,000 feet. Blockage of the 

heated total temperature probe causing erroneous data to the FADEC is suspected. 

These events are not available publicly and are not listed. There are 6 documented 

events on part 23 airplanes of possible ice crystals causing erroneous airspeed 

information to systems or the flightcrew. All occurred in cruise at altitudes above 35,000 

ft and at speeds of Mach 0.75 or higher. All events cleared once the aircraft descended 

into warmer altitudes. 

The proposed regulations promulgate guidance on ice contaminated tailplane stall 

(ICTS). The following events are suspected ICTS events that are not included in the 

SLD tables above: 

Table 15 – Events Applicable to ICTS Rulemaking

DATE AC TYPE LOCATION FATAL INJURY HULL 

LOSS

10/13/1978 DHC-6-200 Barrow, AK 1 1 SD 

3/12/1985 DHC-6-300 Barter Is., AK 0 4 SD 

12/14/1987 BAE-3101 Joplin, MO 0 7 SD 

12/26/1989 BAE-3101 Pasco, WA 6 0 Yes 

1/19/1996 PA-34-200T Des Moines, IA 0 1 SD 

Note: An ICTS accident involving a model BAE 3101 in Beckley, WV on January 30, 1991 is not included 

since the airframe ice protection system was inoperative. 
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THE USE OF NTSB PUBLIC DOCKETS

The NTSB maintains a docket for each accident or incident that it investigates. Events 

which took place earlier than about 1992 are stored on microfiche. Those which took 

place after this point are stored digitally. Recently, the Board has started putting their 

full dockets on line. 

In some dockets, only the NTSB Form 6120 is present, and in some of those cases, it is 

not complete. Some dockets are thorough, containing original written statements and 

police reports. They almost always contain a statement from the pilot-in command, 

should he/she have survived, as well as witness statements and ATC transcripts where 

appropriate. The docket also contains photographic evidence, although there is no 

standard for the photographic evidence. 

FAA AIDS reports are not supported by retained documentation. Therefore, additional 

material such as inspector's notes and so forth are apparently only available in rare 

cases, and is not obtainable through a standardized records management system. 

Unfortunately, the lack of a narrative in many FAA reports renders them nearly 

unusable. 

WAS AIRPLANE EQUIPPED WITH ICE PROTECTION SYSTEMS?

A common issue with the NTSB dockets for part 23 airplane events is the lack of 

documentation of the ice protection systems and certification, even when the accident 

clearly involves airframe icing. At one point, during the mid eighties, the Board used a 

field documentation form that contained check boxes for icing equipage and icing 

certification. In many cases, these checkboxes, even though present, were not used. 

Later Board field documentation forms have no provision for the indication of ice 

protection equipment or certification. In 80 analyzed part 23 events, the Board 

documentation, including docket materials, makes no reference to icing certification. 

Indeed, there are 7 cases in which the Board does specify that the airplane is icing 

certificated, but the TCDS certification data indicates that, for that airplane serial 

number, icing certification was not an option. 

There were also a number of cases in which the Board documentation did not formally 

mention icing equipage. In some cases, the icing equipage could be determined 

through the wreckage documentation. In some events it was determined by obtaining a 

marketing photograph available of that particular registration number on the web. This 

was a last resort, as there is really no way to be sure that the ice protection equipment 

visible in the photo was the configuration in use at the time of the event. 

AIRPLANE CERTIFICATION BASIS

There are 85 reports generated by the NTSB which make no reference to icing 

certification at all in either the factual reports or docket materials. Because of the wide 

irregularity in the NTSB data, certification has been assumed when the TCDS allows it 

and the aircraft is evidently equipped. If the serial number was available, either through 
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the report or through a lookup of the registration, the Type Certificate Data Sheet 

information could be accessed to determine whether the serial number fell within the 

range of aircraft that were icing certificated if properly equipped. 

All the aircraft in event database that were certificated for flight in icing were certificated 

under FAR 23.1419, Amendment 23-14, or earlier amendment. No aircraft in the events 

database were certificated under FAR 23.1419, Amendment 23-43. A subset of aircraft, 

such as the Beech King Air 200 and the Bae Jetstream 31, were certificated as Part 23 

airplanes but used a FAR 25 icing certification basis. 

Aircraft that are not certificated for icing account for 54% of the events. This is 

significant and suggests training on these airplanes is needed to impact the icing safety 

record. 

There were two aircraft in the event database that were not certificated for icing, but 

were equipped on a “no-hazard” basis. Both of these events yielded no survivors. Both 

resulted from a stall followed by loss of control; icing was inferred due to ATC 

transmissions, in which both pilots discussed ice accretion. In one case, the TKS 

system was believed to be active; in the other, the operation of the TKS could not be 

determined. In one case, thunderstorms were in close proximity. No other recent “nonhazard” certifications were noted. 

SUPERCOOLED LARGE DROPLET AND GLACIATED CONDITIONS ANALYSIS

Descriptors such as severe ice, freezing rain, freezing drizzle, side window icing, ice 

observed aft of the protected surfaces, heavy icing, large droplets, the presence of SLD 

in the official meteorological report, ice pellets on the ground. There were limited 

references to “SLD” since most of these accidents occurred prior to the 10/31/94 

Roselawn accident and SLD is a term that was coined after that accident. For many of 

the part 23 events with no survivors, prior to 1994, the only indication of SLD were 

ground observations of freezing precipitation. If rain and drizzle were reported and the 

ambient temperature was below freezing, freezing rain and freezing drizzle, 

respectively, was inferred. 

Table 16 – SLD Descriptor Distribution 

Source of SLD % of Total 

Freezing Rain 33 

Freezing Drizzle 29 

Ice Aft of Protected Surfaces 23 

Meteorological Analysis 6 

Freezing Rain Inferred 3 

Freezing Drizzle Inferred 3 

Ice Pellets 3 
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Snow events appearing in approximately in 20% of the events, and suggests another 

training subject. In some circles, it was believed the presence of snow indicated all 

water was glaciated (therefore no airframe ice accretion), however the service history 

indicates snow can coexist with supercooled water. 

The approach and landing events also show that the outside air temperature typically is 

near freezing. For 21 suspected SLD approach and landing events in which 

temperature was reported at the destination airport, the average ambient temperature 

was 29.2°F, the median was 32.0°F, and the lowest was 12.0°F. 

WAS THE EVENT APPLICABLE TO THE PROPOSED SLD RULE?

The presence of SLD alone does not make the event applicable to the proposed SLD 

rule. There must also be evidence that the SLD was a factor in the accident. Examples 

include lift/drag degradation, stall and controllability. A lift/drag degradation appears in 

some form in nearly all of the reports for which detailed information is available, with the 

exception of ICTS events. It is likely that an early and aggressive response to these 

degradations may prevent more severe outcomes. During the analysis of the body of 

events, it was noted that certain types of aerodynamic events were often reported to 

precede the most severe events such as a stall. Generally, these were an airspeed 

decay, reduction in climb performance, inability to climb, inability to maintain altitude, 

inability to maintain a glide path, or a high sink rate. It has been hypothesized that all of 

these events are typical of a change in the lift/drag ratio for the configuration being 

employed at the time. This may be useful to understanding the nature of severe events. 

The most common result of lift/drag degradation in SLD is a hard landing as a result of 

the airplane sinking rapidly in the flare. 

The following are examples in which SLD was present but the event not deemed 

applicable to the proposed rules (one occurrence in each case): 

 Controllability problems on landing roll-out 

 Failed or inoperative ice protection system 

 Airplane took off with contamination 

 Induction air iced over (reciprocating engine) 

 Airplane significantly over gross weight limit 

WINDSHIELD ICING

The presence of windshield icing was a disqualifying condition if no other aerodynamic 

event was found, since the detect and exit requirement will not address windshield icing. 

Windshield icing was exhibited in 29 of 214 part 23 airplane events; however windshield 

icing alone is typically a non-fatal event. 

PILOT AWARENESS OF ICING

In most cases, the flight crew was aware of ice accretion. Only 3% of part 23 icing 

events had evidence in which the pilot was not aware of the icing conditions. There is a 

scale factor, since this number is 12% of part 25 airplane icing events. 
Part 23 SLD ARC REPORT 

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ACTIVATION AND OPERATION OF ICE PROTECTION SYSTEM

A great deal of information about the operation of the IPS is not available from the 

reports, dockets or statements. Qualitatively, a substantial number of events are 

associated with a failure to operate the IPS. Since part 23 airplanes typically are not 

equipped with a flight data recorder or voice recorder, these events involve at least one 

survivor. 

PHASE OF FLIGHT

Most part 23 SLD events occurred during approach and landing. Many of these events 

were non-fatal hard landings. Approximately two thirds of the SLD events on approach 

and missed approach were fatal. An SLD event on climb, cruise, or descent was 

typically fatal. For all flight phases, nearly all of the total hull losses and fatalities 

resulted from events that exhibited a stall. 

Table 17 – Phase of Flight Distribution

Flight Phase % of Part 23 Airplane SLD Events 

Approach 38 

Landing 34 

Descent 9 

Cruise 11 

Climb 4 

Missed Approach 4 

Holding 0 

OPERATING REGULATION

There does not appear to be a relationship between operating rule and number of 

events. Part 135 aircraft were just as likely to be involved in an icing event as Part 91 

aircraft. Considering that Part 135 has a regulatory weather training requirement, and 

Part 91 does not, this point may speak to the effectiveness of that training. 

RECOMMENDATIONS FOR ACCIDENT INVESTIGATION

The investigation of an accident that may involve icing could be greatly enhanced if the 

following steps were taken: 

 Document the ice protection equipment 

 Document the ice protection switch positions, if not destroyed 

 Include the aircraft serial number (NTSB does; FAA does not) 

 Document the status of the ice protection systems (switch positions, pilot 

statements, etc.) 
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 Determine if the airplane was certificated or approved for flight in known icing 

conditions, including any applicable placards 

 If ice was found accreted on the aircraft, document the surfaces on which it was 

found, i.e., leading edge, aft of protected leading edge, antenna, landing gear, 

etc. 

 In general, greater care with dates and registration numbers would be useful. 

B) ICING INCIDENT DATABASE REVIEW

The three sources of data for this project represent three different thresholds of data 

reporting. The first, reported accidents, is a set of data that must meet a defined 

criteria. Because of the severity of these events, it is unlikely that any have been 

unreported. The second source of data, reported incidents, must likewise meet a 

defined criteria; however, since the severity is considerably lower, it is possible for a 

number of these events to have occurred without being reported. The final source, 

NASA ASRS data, has no defined threshold of reporting. Further, the collection of data 

from this source is dependent on pilot awareness of the program, which is not large in 

general aviation pilot community. An ASRS report is included if either an aerodynamic 

event or a procedural failure is reported. However, there is no way to know how many 

similar events have occurred and not been reported; the number is probably 

considerable. 

Because of these factors, statistical evaluation is limited if not impossible. What is 

valuable is the identification of precursor characteristics. In many, if not most, Part 23 

accidents there is almost no data available regarding pilot actions or decisions, simply 

due the absence of survivors or flight data recorders. The value in including the ASRS 

data lies with the study of those perceptions and actions. There are a number of 

patterns in the incidents which can also be seen in those accidents for which a pilot 

statement is available. This suggests a good likelihood that those accidents from which 

no survivor information can be obtained probably looked similar, at least initially. 

The icing incidents support the proposed rulemaking to show adequate climb 

performance and an evaluation of ice contaminated tailplane stall in detect and exit SLD 

conditions. The incidents also show windshield icing over is a common occurrence in 

SLD encounters, but is non-fatal. Most of the indications of FZRA were of in-flight 

observations on the airplane, so it is possible FZDZ was misreported as FZRA. Limiting 

detect and exit encounters to outside air temperatures of -10°C and warmer is also 

supported. The following table contains a list of the incidents: 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-115

Table 18 – SLD Incidents

SOURCE AC TYPE LOCATION REMARKS 

ASRS 101079 Small transport Utica, NY Aircraft could not climb on attempted 

missed approach, windshield 

overwhelmed

ASRS 226123 Light transport Beckley, WV Performance problem in severe icing

ASRS 249506 Small transport Yakutat, AK Had to descend below 10,000 ft.MEA to 

avoid stalling in severe icing

ASRS 323820 PA-31 Covington, OH FZRA encounter on approach, increased 

descent rate on landing, scraped 

obstruction during landing,

ASRS 325031 Commercial 

fixed wing

Springdale, AR Encountered light FZDZ on approach, 

could not maintain glideslope with full 

power

ASRS 326243 Jetstream 31 Chicago/Rockford, IL Encountered FZRA on approach, controls 

sloppy. Pilot speculated that extended 

time would have caused control problems

ASRS 416160 PA-46 Burlington, IL Encountered severe icing at FL190, could 

not maintain altitude or airspeed

ASRS 456868 EMB-110 St. Louis, MO Ice behind protected leading edge cause 

longitudinal control problem

ASRS 457893 BE-55 Port Huron, MI Windshield iced over in FZRA

ASRS 597221 PA-34-200 Cleveland, OH

FZRA encounter overwhelmed all IPS, 

including pitot heat, could not arrest 

descent at 6,000 feet

ASRS 647858 CE-208A Pocatello, ID Could not climb at 10,200 ft., tail vibration

ASRS 82159 Small transport Chicago/Rockford, IL FZRA during descent starting at 8,000 

feet, performance problem

ASRS 845030 MU-2 US Airspeed loss and loss of control with no 

ice on wing leading edge

AIDS 

19911107055879C BE-18 Springfield, MO Encountered severe icing on approach, landed short

AIDS 

20011126038439C CE-208B North Platte, NE Performance problem in heavy icing

NTSB Access 

Database 

20001212X16303(A)

Jetstream 31 Dayton, OH 

Noted ice aft of protected areas, 

uncommanded pitch down with full flap 

extension on approach 
Part 23 SLD ARC REPORT 

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10. TRAINING RECOMENDATIONS 

A) INTRODUCTION

The Part 23 icing ARC undertook a detailed evaluation of all Part 23 aircraft accidents in 

which icing was a causal factor. The accident review determined that icing accidents 

most often resulted from operational errors not related to aircraft certification. 53% of 

icing accidents 1990-2001 (257 total accidents) occurred in aircraft that are not even 

certified for flight into known icing or that have any ice protection equipment. In order to 

have the greatest impact on icing accident rate, the ARC recommends an integrated 

approach be taken that encompasses not only enhancements in the certification of Part 

23 aircraft but also an educational initiative for all operators. This educational initiative 

needs to include all pilots, not only pilots of aircraft certificated for flight into known icing 

conditions. 

The ARC is not recommending training mandated through regulation, but instead a 

focused training initiative / marketing campaign similar to the effective training initiative 

recently administered to improve runway safety. The FAA recently led an effort to 

improve runway safety in the United States (U.S.) by decreasing the number and 

severity of surface incidents and runway incursions. To achieve this end, the FAA’s 

Office of Runway Safety launched a multi-pronged educational initiative with 

collaboration between the FAA and its stakeholders in the aviation community. 

Together with industry, the FAA developed and delivered updated advisory material, 

brochures and interactive programs to a broad audience of pilots and flight instructors. 

The results of this educational initiative are irrefutable. The runway incursion rate 

dropped 50% two years in a row. This achievement is the result of a focused message 

being effectively communicated to the pilot population. For future initiatives such as 

training for intentional or unintentional flight into icing conditions, the ARC recommends 

a similar multi-media outreach reinforced by the safety learning objectives established 

by the FAA. 

This type of training initiative is necessary for flight into icing conditions for several 

reasons. First, the majority of the icing accidents occurred in aircraft that are not 

certified for flight into known ice. These aircraft are not required to contain procedures 

for inadvertent flight into icing conditions only the simple statement that “flight into 

known ice is prohibited”. Therefore, pilots faced with an inadvertent encounter with ice 

have no guidance from the manufacturer on exit procedures, approach configuration or 

speed considerations. Adding to this lack of knowledge is the misconception among 

pilots that all aircraft are aerodynamically tested to some level of ice regardless of the 

certification of the aircraft. For aircraft that are certified for flight into known ice, there is 

great misunderstanding as to how much ice that aircraft is “certified” to carry and when 

the pilot must begin the exit from icing conditions. It doesn’t help matters that the 

certification standard for flight into known ice has changed dramatically over the years 

and that there is little operationally significant material offered to pilots. Secondly, there 

are many, deeply ingrained misconceptions among the pilot population with respect to 
Part 23 SLD ARC REPORT 

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best procedures and practices to follow in icing conditions. Despite greater scientific 

understanding of flight characteristics and aircraft performance in icing conditions and 

with ice adhering to the aircraft, pilots still maintain and perpetuate many false beliefs. 

The only way to alter these misconceptions is through a targeted training effort. 

There are several good examples of icing training available to pilots today, however the 

training can be improved and the message better focused to encompass all the areas in 

which the ARC found deficiencies. It would also be most helpful if training topics were 

developed and final training material promoted by the FAA as in the model of runway 

safety. This would ensure that a focused message is delivered that encompasses all of 

the areas of training recommended by the ARC and that the message is delivered to all 

operators of part 23 aircraft. 

In the evaluation of icing accidents, several topics emerged that requires focused 

training in order to reduce the icing accident rate. Those training topics are listed below. 

In order to have the greatest impact on learning, all the training should be given in 

practical terms. For example, give real world, practical guidance for determining if an 

aircraft is certified for flight into known ice and knowing the limitations of that 

certification; real world, practical guidance of how a wing stall feels and technique for 

recovery versus a tail stall feel and recovery. 

B) DISCONNECTS BETWEEN THE CERTIFICATION AND OPERATIONS WORLD

As was discovered in the recent Part 23 Certification Process Study undertaken by the 

FAA, the Part 23 Icing Certification ARC discovered several disconnects between the 

certification and operations world. Better communication of flight testing parameters 

would ensure pilots understand the information and limitations of flying their aircraft in 

icing conditions. 

(1) THE DIFFERENCE BETWEEN STALL WARNING AND AERODYNAMIC STALL

Pilots need to be made aware of the fact that the stall warning system (stall 

warning horn, etc) may not work properly on an iced-up airplane (particularly one 

certificated before current rules went into effect). The first warning of an 

impending stall may be an aerodynamic buffet or increasing sloppiness of the 

flight controls rather that the stall warning horn, light, stick shaker, etc. 

(2) THE DIFFERENCE BETWEEN WING STALL AND TAIL STALL

Recent emphasis upon empennage stalls on iced-up airplanes may cause pilots 

to NOT use normal stall recovery procedures – reduce angle of attack, add 

power – when a stall is encountered. Pilots should be aware that approach and 

landing with partial flaps will most likely preclude an ice contaminated tailplane 

stall (ICTS), and pilots of newer airplanes in which ICTS is tested should follow 

AFM limitations and procedures. Normal stall recovery procedures should be 

followed unless specific evidence of a tail stall exists, or normal stall recovery 

procedures are ineffective. 
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(3) THE MEANING OF “APPROVED FOR FLIGHT INTO KNOWN ICE”

The ARC recommends that the FAA emphasize the conditions and visual cues 

that define aircraft certification level and emphasize that operationally, no matter 

what the certification, no aircraft has the capability for unlimited safe flight in all 

icing conditions. Training should emphasize a consistent set of icing definitions 

between the operations, certification and weather forecasting with respect to 

known icing and potential icing conditions. Those definitions should be the 

current, FAA approved terms defined in the AIM for “known or observed or 

detected ice accretion”, “forecast icing conditions”, “known icing conditions” and 

“potential icing conditions” as well as information from the FAA legal 

interpretation dated January 16, 2009. That legal interpretation states: “"Known 

icing conditions" involve circumstances where a reasonable pilot would expect a 

substantial likelihood of ice formation on the aircraft based upon all information 

available to that pilot. Known icing conditions exist when a pilot knows or 

reasonably should know about weather reports in which icing conditions are 

reported or forecast.” “A pilot must consider the reasonable likelihood of 

encountering ice when operating an aircraft.” “Area forecasts alone are generally 

too broad to adequately inform a pilot of known icing conditions. Such forecasts 

may cover a large geographic area or represent too long a span of time to be 

particularly useful to a pilot.” A pilot, and his or her proper analysis of that 

information in evaluating the risk of encountering known icing conditions during a 

particular operation. The pilot should consider factors such as the route of flight, 

flight altitude, and time of flight when making such an evaluation. Pilots should 

also carefully evaluate all of the available meteorological information relevant to a 

proposed flight, including applicable surface observations, temperatures aloft, 

terminal and area forecasts, AIRMETs, SIGMETs, and pilot reports (PlREPs). As 

new technology becomes available, pilots should incorporate the use of that 

technology into their decision making process. If the composite information 

indicates to a reasonable and prudent pilot that he or she will be operating the 

aircraft under conditions that will cause ice to adhere to the aircraft along the 

proposed route and altitude of flight, then known icing conditions likely exist. 

(4) THE DIFFERENT CATEGORIES OF CERTIFICATION FOR “FLIGHT INTO KNOWN ICE”

Pilot training should include the level of protection the certification of the aircraft 

provides from a pilot perspective. Since most pilots are not familiar with part 23 

certification standards or the changes that have occurred in icing certification 

over the years, it is important to convey that depending on certification level and 

when the aircraft certification was obtained there is a wide range of conditions 

that were tested or not tested as the case may be. 

In general, aircraft can be classified into three areas: 

1. Airplanes not equipped nor approved for flight in icing conditions. Education 

and training should emphasize the following: 
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a. In-flight icing accidents and incidents involving these airplanes have 

outnumbered those on icing certificated airplanes in recent years. 

b. No flight testing is conducted to show the airplane can safely exit an 

inadvertent encounter - pilots of these airplanes should be aware that 

these airplanes are not tested for “inadvertent” icing encounters. 

c. There are only requirements for engine induction icing, and for IFR 

approved airplanes, ice protection for the pitot and static sources. 

d. Pilots should not believe the myth that “thicker” general aviation 

airplane airfoils are more tolerant of ice accretion. FAA research has 

dispelled that myth, as described in Advisory Circular 20-73A. 

2. Airplanes with ice protection but prohibited from flight in known icing. AOPA 

Safety Advisor No.22 at http://www.aopa.org/asf/publications/sa22.pdf

addresses the subject. 

a. “Non-hazard” systems are meant simply to buy time for a pilot to 

escape from unexpected icing conditions. 

b. Non-hazard systems have no requirement to demonstrate that they 

can protect your airplane during icing conditions. 

3. Airplanes certified for flight in icing conditions. These airplanes can be 

subdivided further by when they were certified: 

a. The earliest certifications were “approved” for flight in icing conditions if 

they were properly equipped. There was no real requirement for 

testing of these systems. 

b. Testing of ice protection systems initially tested for stall buffet only and 

had no icing climb gradient requirements. 

c. New aircraft certified today must meet climb gradient requirements, 

have published climb performance in icing conditions, are tested with 

critical ice shapes, and must meet stall warning requirements with 

critical ice shapes covering the entire span of the wing. 

d. The FAA is in the process of requiring testing of Super-cooled Large 

Droplets for part 23 aircraft. 

For all aircraft, regardless of the certification level: 

 Do not assume that your aircraft was tested for the conditions that you might 

be facing on any given day. 

 Icing conditions can vary greatly from one exposure to another as can it’s 

affect on aircraft performance. 

 No aircraft, regardless of certification level, will be able to indefinitely maintain 

flight in all icing conditions. 
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 Ice protection is primarily used to protect aircraft during transient encounters 

in icing conditions. Always plan to exit icing conditions. 

(5) HOW TECHNOLOGY HAS CHANGED THE PERFORMANCE OF DEICE / ANTI-ICE 

EQUIPMENT

Two areas in which certification information is valuable to pilots are the 

certification assumptions in how ice protection systems are to be operated, and 

their actual performance. For example, fluid systems are designed and tested 

as anti-ice systems. Certification testing assumes there will be no ice on the 

protected parts of the airplane. If ice is allowed to build before activating the 

system, it may take several minutes before shedding occurs. Therefore these 

systems must be activated at the first sign of ice accretion. If ice is observed 

forming on protected parts, the flow rate must be increased. If maximum flow 

rate cannot keep ice off the airplane, the airplane is in severe icing and must exit 

immediately. 

For pneumatic deicing boots, pilots should understand that there may be 

conditions in which ice may not shed completely or at all after a cycle. This is 

particularly true as airspeed or ambient temperature decreases. Pilots of 

airplanes with modern boots should not mistake this as the phenomenon known 

as “ice bridging.” What they are seeing is residual ice which will eventual shed. 

Most airplanes today have “modern” boots – operating pressure of 15 psig or 

higher, “inflation tube diameter of one inch or smaller (some designs have 1 .75 

inch at the stagnation), and fast inflation and deflation times (typically 6 seconds, 

but to the eye, tubes will appear fully inflated in less than a second). Much of this 

information on pneumatic boot performance is in AC 91-74A. Pilots should follow 

their AFM procedures, and also know that early and often cycling of the boots will 

not hurt shedding performance. Since most part 23 icing events occur on 

approach and landing, pilots should cycle boots before configuring for approach. 

Research has shown that ice adhesion inhibitors, for example the product “ICEX” 

for Goodrich boots, greatly improve shedding performance (AIAA-2007-1090, 

“Residual and Intercycle Ice for Lower-Speed Aircraft with Pneumatic Boots”). 

Products not approved by the boot manufacturer or airplane manufacturer should 

not be applied to boots. 

(6) GROUND DE-ICE PROCEDURES``

Training should focus on the importance of the clean aircraft concept and 

approved methods for removing snow / ice from the airframe. Special emphasis 

should be placed on the issues related to using fluids / methods to remove ice or 

snow and reasons why it’s important to only use methods and fluids approved by 

the manufacturer (materials compatibility, pooling of fluids in flight control 

surfaces, etc). 
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C) FOCUSED ICE TRAINING

Previous attempts to educate the pilot population on the dangers associated with icing 

conditions went into great detail on areas that were not necessary or simply added to 

confusion regarding airframe ice. Many training resources for pilots still cover the 

different types of ice (rime, mixed, clear, etc.) however there is little practical training on 

how airframe ice affects aircraft control, for example. The training recommendations 

below should focus on the practical, real world application of the following subjects. 

(1) INTERPRETING WEATHER REPORTS IN ORDER TO PREDICT AREAS OF POTENTIAL 

ICING CONDITIONS

Freezing Rain, Freezing Drizzle, Severe icing, etc and what that means real 

world - Pilots should be familiar with weather conditions likely to cause in-flight 

icing: Freezing rain or freezing drizzle at the surface, temperatures aloft less 

than about +3 degrees Celsius plus high water and content in the air, certain 

types of frontal and orographic activity. It is important for a pilot to know how to 

use weather products to identify the presence and location of such conditions. 

Recently developed NOAA “Java tools” available online can provide forecasts of 

temperatures aloft, air mass water content, and icing probability in map form, 

easily adjustable for various MSL altitudes. 

(2) IDENTIFY AND ADHERE TO PERSONAL MINIMUMS

FAA and Industry emphasize the use and adherence to personal minimums for 

any flight. Weather related personal minimums used in FAA-Industry Training 

Standards (FITS) usually focuses on winds, ceiling and visibility. The ARC 

recommends FITS increase emphasis on icing related personal minimums which 

include “find and avoid” as well as exit strategies based on pilot/aircraft 

capabilities, icing reports and forecasts. This emphasis on icing related personal 

minimums should be included in FITS or traditional training in the industry. 

(3) HOW TO “DETECT” ICE – PREFLIGHT AND AIRBORNE

On newly certificated aircraft, manufacturers may provide specific visual cues to 

warn pilots of icing conditions that exceed the ice protection systems’ capability, 

or require an immediate exit from the icing region. The rate of ice accretion is an 

important factor in effectiveness of ice protection systems. The ice-carrying 

characteristics of individual airplanes may be significantly different. 

(4) DEICE STRATEGIES FOR PREFLIGHT

Training should focus on the importance of the clean aircraft concept and 

approved methods for removing snow / ice from the airframe. Special emphasis 

should be placed on the issues related to using fluids / methods to remove ice or 

snow why it’s important to only use methods and fluids approved by the 

manufacturer (materials compatibility, pooling of fluids in flight control surfaces, 
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etc). Training should include weather related factors in maintaining the clean 

aircraft for takeoff (example: freezing precipitation falling prior to takeoff but not 

adhering to wing). 

(5) DEMONSTRATE HOW EVEN MINUTE ACCRETIONS AFFECT PERFORMANCE

One myth that is prevalent in general aviation is that small amounts of ice result 

in little aerodynamic penalty. With even a minute amount of ice, there is a 

resultant loss of lift and large increase in drag. Research flight tests have shown 

maximum lift losses up to 25% and drag increases of 84% with just the thickness 

of 40 grit sandpaper on the airfoil leading edges. This corresponds to a stall 

speed increase on average of 12 knots. It should be pointed out that this 

roughness level is difficult to remove with pneumatic deicing boots under most 

conditions. 

Another myth floating around is that high speed laminar flow airfoils are more 

susceptible to ice than “thicker,” conventional airfoils. FAA sponsored research 

available in AC 20-73A dispels that myth. 

The roll of angle of attack must also be pointed out. The lift and drag penalties 

are not linear with angle of attack. Going back to report DOT/FAA/AR-06/48, one 

can see that at the angle of attack for normal operational airspeeds (2-6 deg), 

there is no or very little lift loss. As soon as angle of attack increases above 6 

deg, a lift penalty occurs, and the penalty increases with angle of attack. Drag 

increment due to ice also increases with angle of attack. The result is a rapid 

loss of lift as airspeed is reduced below a certain threshold. This explains the 

high number of hard landings in the accident database. 

(6) DEMONSTRATE HOW RAPID ACCUMULATION AFFECTS TIME AVAILABLE FOR EXIT / EXIT 

STRATEGIES

Tests conducted at NASA Glenn Research Center on several modern airfoils 

demonstrated that in some instances, exposure to clear icing for just two minutes 

could double the drag, reduce the maximum lift by 25%-30% and reduce the 

critical angle of attack by 8 degrees (which would correspond to a substantially 

higher stall speed). Training should emphasize that in icing conditions with rapid 

accumulation, there is very little time available for exit. Exit strategies should be 

considered before entering icing conditions and personal minimums set in 

determining when to exit the conditions. 

(7) ATC ASSISTANCE AVAILABLE AND ATC OBLIGATIONS / PIC AUTHORITY

Remove the stigma of requesting immediate assistance from ATC and declaring 

an emergency and teach pilots that rejecting a controller’s instructions is their 

right and obligation if those instructions can lead to an unsafe condition. Final 

authority and responsibility for the safety of a flight rests with the pilot in 

command. ATC may be able to provide PIREP or other information regarding 
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enroute icing conditions. Do not hesitate to request assistance from ATC. 

However, as pilot in command, it is important to be firm with ATC when a pilot 

encounters conditions beyond their airplane’s capability that require an altitude or 

course change. Pilots must have an exit strategy, and communicate needs 

clearly to ATC. If ATC is not responsive, the pilot must advise ATC that if the 

course or altitude requested is unavailable, an emergency will be declared and 

required changes will be made. 

(8) LAST RESORT CHOICE

An off airport landing may be embarrassing but is a better option than 

uncontrolled flight into terrain. 

(9) AUTOPILOT USE IN OR AFTER FLIGHT IN ICING CONDITIONS

The autopilot may mask dangerous airspeed losses - monitor airspeed closely when 

the autopilot is engaged in icing conditions. When ice is accumulating on the 

airplane the autopilot should be disconnected at least once every five minutes to 

ensure normal airplane trim and handling qualities are maintained. Unless 

authorized in the airplane flight manual, the vertical modes of the autopilot that 

maintain a constant rate of climb, decent, or pitch should not be used. Pilots should 

be prepared for the possibility of unusual control forces and flight control 

displacements when disconnecting the autopilot, especially in severe icing 

conditions.

(10) SINK RATE WITH ACCUMULATION

The role of lift/drag degradation in icing events is poorly understood and has not 

been part of icing training or in the literature. Although there is almost always 

some type of lift/drag degradation which precedes a catastrophic event, the most 

common event in which it manifests itself is hard landing. Out of 137 part 23 

airplane icing accidents in the period studied, 37% were hard landings or landing 

short of the runway. Approximately one third of the part 23 accidents identified 

as applicable to the SLD rule are hard landings with no fatalities. This is also 

related to the role of angle of attack as discussed above, since a high angle of 

attack is achieved in the flare. Training should emphasize a slow reduction in 

power during the flare, and the fact the higher drag due to ice will require more 

power to maintain the same sink rate as in non-icing. 

(11) CONFIGURATION AND SPEED CONSIDERATIONS AFTER FLIGHT IN KNOWN ICE FOR 

APPROACH AND LANDING

Approximately 51% of icing encounters result in mishaps during approach and 

landing, and 73% of accidents attributed to SLD occur in these two flight phases.. 

Although the landing events were typically non-fatal hard landings and landing 

short of the runway, two thirds of the events on approach were fatal and were 

typically a stall. The ARC recommends increased training emphasis on 
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approach and landing strategies after icing encounters. Specifically, train 

operational tactics with ice adhering to the aircraft such as delayed descent, 

avoiding prolonged approach vectors, keeping speed up, and delaying/limiting 

flap configuration changes. 

D) CHANGES TO FAA TRAINING AND TESTING MATERIAL

(1) REVIEW TRAINING MATERIALS

o Update training products on FAAST web site. There are numerous 

icing training products and where to start is confusing. One product 

deals entirely with type of ice (rime, mixed, clear). 

o Review NASA training products to determine if they need to be 

revised. 

o Update the Aeronautical Information Manual (AIM). In particular, 

update definition of severe icing, add information on ASOS limitations, 

add information on snow and warm temperatures. 

o Update Advisory Circular 91-74A. 

o Update Airplane Flying Handbook icing information (Chapter 12) and 

add inadvertent icing encounter information to (Chapter 16) 

Emergency Procedures. 

(2) REVIEW KNOWLEDGE EXAM MATERIAL, PREPARE QUESTIONS (IN ORDER OF 

PRIORITY IF NOT ALL ARE SELECTED)

o IFR Non-FIKI or non-equipped airplanes 

o Commercial FIKI 

o ATP FIKI 

(3) DEVELOP LIST OF EMPHASIS ITEMS FOR TYPE RATED AIRPLANES THAT ARE 

CERTIFICATED FOR FLIGHT IN ICING AT CURRENT AMENDMENT AND UNDER SLD

AMENDMENT (ADD THESE TO ATP PTS). EXAMPLES:

o Severe icing recognition- photos 

o Minimum airspeed for flaps up operation and approach and landing 

o Flap limitations 

o Autopilot limitations 

o Stall warning and stall recovery procedures that emphasize reduction 

of angle of attack 

o Add simulated decelerations (1 kt/sec) to first indication of stall with 

autopilot engaged 

o Train first indication of stall in icing conditions (stall warning for new 

airplanes, buffet for certain older airplanes) 
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11. TASK 9 RECOMENDATIONS 

A) BACKGROUND

The following task was added in the third quarter of 2010: “Determine if implementation 

of NTSB Safety Recommendation A-10-12 is feasible for part 23 airplanes for 

operations in icing conditions”. 

The referenced NTSB safety recommendation states: “For all airplanes engaged in 

commercial operations under 14 Code of Federal Regulations Parts 121, 135, and 91K, 

require the installation of low-airspeed alert systems that provide pilots with redundant 

aural and visual warnings of an impending hazardous low-speed condition.” The 

recommendation applies to non-icing as well as icing flight. The ARC was tasked to 

address only part 23 airplanes operating in icing conditions, and therefore decided to 

address part 23 regulations for new type certificates, amended type certificates, and 

supplemental type certificates. 

The ARC reviewed the NTSB safety recommendation letter and noted that the NTSB is 

recommending a system in addition to the stall warning system and an aural indication 

to complement existing visual low airspeed awareness cues: “In this accident, the pilots 

did not likely see the rising low-speed cue on the IAS display, the downward-pointing 

trend vector, or the airspeed indications change to red. As a result, the NTSB concludes 

that an aural warning in advance of the stick shaker would have provided a redundant 

cue of the visual indication of the rising low-speed cue and might have elicited a timely 

response from the pilots before the onset of the stick shaker.” 

The ARC reviewed icing accidents for which there is flight data recorder data. The 

common scenario is a reduction of airspeed, typically 1 – 2 kt/sec leading to a stall. The 

autopilot is engaged in altitude hold or vertical speed mode in a climb, and the flightcrew 

is unaware of the airspeed decay. The flightcrew is aware of the icing conditions and 

the ice protection systems are operating. The FAA has written SAFO06016 and SAIB 

CE-11-18 to make pilots aware of these concerns. 

B) PROPOSED RULE

The ARC decided that a low airspeed alert system is not needed for icing conditions if 

the stall warning system is robust. Current part 23 guidance, which the ARC 

recommends to be promulgated into a rule, requires that the stall warning margin and 

the means of indications be the same as non-icing flight. The stall warning system on 

new part 23 airplanes is designed to function with the most critical ice accretion possible 

in Appendix C conditions. The fact that no airplane certified for icing to latest part 23 

icing regulation (Amendment 23-43) has experienced an icing event supports this 

decision. It is acknowledged that most of these airplanes require a type rating and that 

icing limitations and procedures are training emphasis items. One single engine, 

reciprocating engine airplane certified to the latest amendment requires biennial icing 
Part 23 SLD ARC REPORT 

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training via the AFM limitations section. Many of these airplanes incorporate a glass 

cockpit in which the low airspeed cues are scheduled for icing. The ARC has 

recommended regulations to require stall warning in applicable SLD conditions for new 

airplanes. Therefore, for new airplanes that will require stall warning in Appendix C and 

applicable SLD conditions, the ARC believes a low airspeed alert system should not be 

required. The majority of the ARC discussions, which follows, focused on the existing 

fleet and the feasibility of a rule that would affect amended and supplemental type 

certificates. 

(1) FLIGHT IN ICING VERSUS NON-ICING CONDITIONS

The ARC discussed rule language that would not distinguish icing flight from nonicing flight in consideration of the NTSB recommendation that a low airspeed 

alert would increase safety in non-icing conditions. The ARC decided to 

recommend rule language that only applied to flight in icing conditions for the 

following reasons: 

o The ARC was tasked to only determine recommendations for flight in 

icing conditions 

o The ARC did not have a database of event history for non-icing flights 

and therefore did not have sufficient information to assess the potential 

benefits of a broad action to address operations in non-icing 

conditions. 

o A system to address non-icing flight may be more complicated and 

costly than icing flight. For example, an alert may have to be based on 

angle of attack, rather than airspeed. 

An airspeed alert system for flight in icing, due to higher stall and operating 

speeds, must be active only in icing conditions to avoid nuisance warnings in 

non-icing flight. Therefore, there will be cost associated with tying the system to 

a system such as airframe, propeller, or engine ice protections system. 

(2) AIRPLANES CERTIFIED FOR FLIGHT IN ICING VERSUS NOT CERTIFIED FOR FLIGHT 

IN ICING

The ARC also discussed applicability to an airplane not certified for flight in icing. 

The ARC evaluated part 23 icing accidents in which SLD was not evident. Out of 

these events, 71% of the airplanes involved were not certified for flight in icing 

(that means airplanes not certified under CAR 3 or Part 23). This indicates such 

airplanes inadvertently encountering icing is a larger safety issue than icing 

certified airplanes. However, the ARC decided to apply the rule only to airplanes 

certified for flight in icing for the following reasons: 

o A system designed for inadvertent encounters must be active in nonicing conditions, and nuisance warnings could be a large issue. 

o Envelope protection systems are starting to be certified on part 23 

airplanes. These systems activate at a factor of 1.2 of the non-icing 
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stall speeds, which should provide protection with inadvertent ice 

accretions. 

o Limiting applicability of the rule reduces its cost, 

o Older part 23 airplanes not certified for icing typically do not have glass 

cockpits and therefore applicability of the rule (if 23.1311) would be 

limited anyway. 

(3) AUTOPILOT

The ARC discussed whether a new rule should apply only when the autopilot is 

engaged. Analysis of events indicated 4 out of 69 in which there is evidence of 

no autopilot, or no autopilot upon airplane delivery. All four of these airplanes 

were not certified for flight in icing. Most part 25 icing events with flight recorder 

data and cockpit voice recorder data indicate airspeed decay with autopilot 

engaged. However, documented incidents on part 23 airplanes, combined with 

at least one part 23 event with FDR and CVR data, and the excellent icing 

service history of certain part 23 airplanes with no autopilot at delivery, point to 

the conclusion that the autopilot is engaged for most icing events. Also, since 

the autopilot is disengaged for landing on part 23 airplanes, there should be no 

nuisance during landing flare, which had been discussed as a potential issue. As 

a result, the ARC limited the proposed rule to only when the autopilot is engaged. 

This reduced applicability reduces the cost and targets the specific safety issue. 

A minority of the ARC believed a low airspeed alert should not be tied to the 

autopilot and should function even with the autopilot off. 

Since the targeted safety issue is airspeed awareness when the autopilot is 

engaged, the ARC first looked at adding a paragraph to § 23.1329, similar to 

§ 25.1329(h). The ARC subsequently decided that either § 23.1311 or 

§ 23.1419 was more appropriate. There was no consensus reached on which 

rule would be more appropriate. 

C) OPTIONS

(1) OPTION #1 - RECOMMENDED RULE LANGUAGE FOR § 23.1419

(h) If an automatic pilot system is installed: 

(1) The automatic pilot system must be capable of operation in part 25, 

Appendix C icing conditions. 

(2) For airplanes where ice accretions are present on protected surfaces 

during normal airframe ice protection system operation: 

 (i) When the automatic pilot system is operating, a means must be 

provided to prevent the aircraft from reaching an unsafe low airspeed 

when operating in Appendix C icing conditions 

 (ii) If a cockpit annunciation is the means of compliance, the means must 

be visual and either aural or tactile. 
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Proposed paragraph (h)(1) prevents an applicant complying with proposed (h)(2) 

by a prohibition of autopilot use in icing. NTSB safety recommendations A-06-

51, which is closed with unacceptable action, asked the FAA to require all 

operators of turbopropeller-driven airplanes to instruct pilots, except during 

intermittent periods of high workload, to disengage the autopilot and fly the 

airplane manually when operating in icing conditions. The ARC consensus is 

that the use of an autopilot, even in icing, generally increases safety when 

operating in IMC conditions and especially in single pilot operations which is 

common for Part 23 aircraft. Currently, the use of autopilot is allowed in icing but 

the pilot is advised to periodically disconnect the autopilot to evaluate if any 

controllability issues are being masked. Prohibiting the use of autopilot in icing 

altogether as an alternative means of compliance to this proposed new wording 

would mean pilots would have less use of their autopilots exactly when they are 

likely to need them the most. This could possibly introduce more safety issues 

than it remedies by resulting in loss of situational awareness in IMC conditions. 

The issues raised by the NTSB in their safety recommendation letter are 

mitigated by a means to indicate an unsafe low airspeed as required by this 

proposed rule. The evidence of this is the safety record of airplanes certified for 

icing at Amendment 23-43, in which the stall warning system is designed and 

tested to provide margin with critical Appendix C ice accretions on protected and 

unprotected surfaces. Additional evidence is AD 2007-10-15 on the Cessna 

Caravan which required a Low Airspeed Awareness System. This AD removed 

an interim prohibition on autopilot use in icing and there have been no in-flight 

icing related accidents of the model. A similar example is AD 2001-20-17 on the 

model EMB-120. 

Regarding (h)(1), the ARC recommends a similar rule be added to proposed 

23.1420: “(xx) If an automatic pilot system is installed: 

(xx) The automatic pilot system must be capable of operation in the 

Appendix O icing conditions for which the airplane is approved. 

In paragraph (h)(2), “For airplanes where ice accretions are present on protected 

surfaces during normal airframe ice protection system operation” the ARC noted 

that applicable icing events were only with airplanes in which ice is present on 

protected surfaces in normal system operation (e.g. intercycle or residual ice on 

pneumatic boots). The ARC noted that airplanes equipped with fluid freezing 

point depressant systems and thermal anti-ice systems are not in the accident 

list. The intent of this language is to exclude these airplanes. 

The means required in (h)(2)(i) can be an annunciation or a system that prevents 

the airplane from reaching an unsafe airspeed. A stall warning system that 

complies with § 23.207 with critical part 25, Appendix C ice accretions is an 

acceptable means. Airplanes with a certification basis that includes § 23.1419 at 

Amendment 23-43 or later will have a stall warning system that is compliant. 
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An annunciation need only be based on airspeed, as determined by an analysis 

of icing accidents in which data is available. The annunciation may be based on 

a certain threshold above icing stall speed, or a certain threshold below icing 

operating “bug” speed. If the latter, the AFM Supplement must specify an icing 

operating speed for all phases of flight, and the AFM Supplement must require 

the “bug” speed to be set in icing for all flight phases. 

The ARC recognized that icing stall speed may not be available to modifiers of 

older airplanes, and the icing operating speeds may not be specified. There 

would be a large cost to determine critical ice accretions, manufacture simulated 

ice shapes, and flight test those ice shapes. The ARC analyzed icing stall speed 

data for several pneumatic boot equipped airplanes and determined that a 

generic value of icing stall speed may be used, negating the need for ice shape 

flight testing. The ARC determined a value of a 20% increase in stall speed due 

to critical Appendix C ice accretions may be used by applicants to schedule a low 

airspeed annunciation. Another value may be used if substantiated by the 

applicant. The ARC recognized the 20% value is conservative for most part 23 

airplanes, since the average increase of eight airplanes evaluated is closer to 

14%. However, outlier data of an airplane with a common wing airfoil section 

(NACA 23XXX), drives the 20%. The annunciation should be provided at some 

margin above the icing speed to account for pilot recognition and action initiation. 

The ARC adopted 3 KCAS from § 25.207(e), although an ARC minority voted for 

the part 23 margin of 5 KCAS. The ARC recognized that a non-icing operating 

speed if at 1.3 times non-icing stall speed should not cause a nuisance if the 

annunciation is airspeed based and not angle of attack based. However, the 

absence of nuisance warning is expected to be demonstrated, and if a nuisance 

occurs, the annunciation threshold can be reduced closer to 1.2Vs, but not below 

1.2Vs. 

Since a non-icing operating speed that is at least 1.3 times non-icing stall speed 

is not expected to cause nuisance, the ARC expects in many applications an 

increase in icing operating speed will not be required. Applicants can always 

propose an increase for icing to be conservative. Increases in landing distance 

in this case should be published in the AFM Supplement, if required in the 

certification basis. Increases in landing distance can be determined analytically, 

in the absence of flight test data. 

The ARC members evaluated airplane models for which their company is the TC 

holder. The ARC concluded that most applications the low airspeed 

annunciation will require a flap position indication to avoid nuisance indications. 

The accident record shows a low airspeed annunciation is required for the 

approach phase of flight. An annunciation would not be required for the landing 

flare for two reasons – one, the accident history shows landing flare events are 

typically not fatal, and two, in most designs, it would be difficult to avoid a 

nuisance warning during flare. The ARC studied accidents to determine if an 

annunciation could be required for the approach flap setting and not the full 

(landing), but the result was inconclusive. However, if full flaps were prohibited in 
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icing as a result if ice contaminated tailplane stall susceptibility testing or 

analyses, then an annunciation would not be required for full flaps. 

An envelope protection that prevents the airplane from stalling in icing would be 

an acceptable means of compliance. The modifier in these projects would not 

have icing stall speed data. However, using the generic guidance for 

annunciations, a system that prevents the airplane from slowing below 1.2Vs 

non-icing would be compliant. 

Paragraph (h)(2)(ii) requires a tactile or aural annunciation in addition to a visual 

annunciation. Study of documented icing events show that the flightcrew are not 

adequately monitoring the airspeed indicator. The NTSB noted in their safety 

recommendation letter for A-10-12, that distraction and workload considerations 

may have made it difficult for the pilots to visually detect features on the airspeed 

display depicting the development of a low speed condition (including a trend 

vector and a low-speed cue), so a redundant aural alert might have provided 

them with an effective warning about the decreasing airspeed. 

The means required in (h)(2) does not have to disengage the autopilot. This is 

consistent with the guidance in AC 25.1329-1B for § 25.1329(h), which the ARC 

reviewed. It may be preferable on some designs to leave the autopilot engaged 

and have the pilot make a specific action to take control of the airplane and 

manually disengage the autopilot. If the autopilot disengages without warning, 

an upset may be experienced. In either case, the means and AFM procedures 

should be demonstrated in flight test. 

ADVANTAGES OF 23.1419 VERSUS 23.1311:

 If in 1419, it is clear the proposed rule only applies to airplanes certified for 

flight in icing. 

 Moving proposed rule into § 23.1419 and out of § 23.1311 (or § 23.1329) 

would potentially make this rule applicable to more modification projects. 

Any project that affects safe flight in icing is an "affected" area" and is 

considered in the changed product rule analysis (per § 21.101). 

Alternatively, if the proposed rule stays in § 23.1311, adding an autopilot 

to a known icing certified airplane may not be considered as the affected 

area under § 21.101. As a result, the revised § 23.1311 requirements 

would not be applied. 

 A § 23.1311 rule may inhibit the incorporation of new avionics, which may 

reduce pilot workload and safety. Glass cockpits by themselves may be a 

safety enhancement and are not a factor in icing accidents.. 

 A § 23.1311 is targeting new glass cockpits because implementation of a 

low airspeed alert is much less costly compared to only an autopilot 

installation, but the safety improvement targets autopilot use in icing and 
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not the glass cockpit. A § 23.1311 rule targets new glass cockpit 

modifications because implementation of a low airspeed alert is less costly 

compared to only an autopilot installation. 

(2) OPTION #2 - RECOMMENDED RULE LANGUAGE FOR 23.1311

Add new language to § 23.1311 Electronic Display Instrument Systems: 

(8) If the applicant is seeking certification for flight in icing conditions, 

incorporate visual cues, and either an aural or tactile warning, to provide 

awareness to the pilot that the airspeed is below the reference operating 

speed for the airplane configuration, 

This rule already incorporates language regarding visual display of instrument 

markings in paragraphs (a)(6) and (a)(7). 

ADVANTAGES OF § 23.1311 VERSUS § 23.1419:

 Rule Consistency – There is concern about consistency with previous 

ARC recommendations, which were to specific Subpart B rules and not 

23.1419. 

 Visibility – STC applicants may not be aware of requirements embedded 

within § 23.1419 

 Scope of § 23.1419 – Section 23.1419 outlines certification requirements 

for aircraft ice protection systems (IPS). Although § 23.1419 can apply 

when changes are made to the aircraft that do not directly affect the IPS, 

these are usually changes to the exterior of the aircraft which can affect 

how ice accretes. An applicant would typically not have to show 

compliance to § 23.1419 for changes such as re-wiring the IPS or 

changing the layout of the control panel for example. Systems that are 

independent of the IPS, but which may be affected by icing (i.e. 

windshields, pitots, fuel vents), should be addressed in their own rules. 

 Cost/benefit - Linking this change with § 23.1311 would allow an operator 

to install and/or upgrade autopilots without forcing them to also upgrade 

avionics. At the same time, new avionics systems would be required to 

possess improved low airspeed awareness by a low cost means. It was 

recognized by the ARC that incorporating a low speed alert is much easier 

accomplished with less cost through avionics upgrades, since most part 

23 autopilot systems are not tied to airspeed. However, some ARC 

members felt avionics should not be forced to upgrade if the avionics are 

not the source of the low airspeed event. 

 Practicality on older models - The practicality of requiring operators to 

meet a new § 23.1329 or § 23.1419 new rule seems problematic. The 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-132

operator of an older part 23 airplane with analog gages and either an older 

autopilot or no autopilot at all could benefit from upgrading to a newly 

certified autopilot. Autopilots can be used for holding a heading or altitude 

and for course tracking. Many are capable of making turns, climbs and 

descents in order to do this. Some are capable of holding a desired 

vertical speed in a climb or descent, but this simply means they are 

holding to a desired rate such as 500 ft/min. Even more advanced 

systems have flight envelope protection capabilities. This means that as 

the aircraft approaches stall or overspeed, the autopilot gradually reduces 

maximum bank and vertical speed to keep the wing flying. Unlike an 

autothrottle system, none of these systems will actually affect engine 

settings to maintain a desired airspeed. To do anything more than hold a 

desired rate of climb or descent requires that the autopilot be coupled to a 

primary flight display, requiring an upgrade to a new “glass” avionics 

system. Currently this can be a very expensive upgrade for an individual 

operator and may compel them to keep their existing avionics rather than 

upgrade to a new more capable (safer) autopilot. 

Some members believed aural and tactile warnings are out scope for § 23.1311. 

However, another member stated as (a)(6) shows precedence for requiring the 

speed warning device functionality of § 23.1303(e) (specifically aural warnings) if 

an electronic display is replacing that instrument. 

D) APPLICABILITY OF THE PROPOSED RULE

(1) TYPES OF MODIFICATIONS

 First Time an Autopilot is Certified on an Airplane 

The majority of the ARC believed that the proposed rule should be applied 

to modification projects in which an autopilot is being certified for the first 

time on that particular icing certified model. One member agreed only if 

the modification also included a glass cockpit, which would make 

compliance less costly. One other member disagreed entirely and felt the 

rule should not be applied to autopilots but to new avionics. The issue 

was not only cost to comply, particularly for small airplanes, but this 

member believed if a low airspeed alert was required, it should be 

required regardless if autopilot is engaged or not. This member added 

that an autopilot is a safety enhancement by itself. 

 Replacement Autopilot with No New Modes, Features or Performance 

If the modification involved replacing an existing autopilot on an icing 

certified airplane with a new one that incorporated no new modes, 

features, or change in performance, the new rule should not apply, 

according to the ARC. There was near consensus. Two members stated 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-133

that service history should be used to determine applicability of the 

proposed rule. 

 Replacement Autopilot with New Modes, Features or Performance 

If the replacement autopilot incorporated new modes, features, or 

performance differences, the ARC was almost evenly split as to whether 

the proposed new rule should apply. Three members stated that service 

history should be used as criteria. One member believed that if the new 

autopilot was simple and did not incorporate modes such as altitude hold 

or vertical speed, no, otherwise yes. 

 Glass Cockpit 

If an amendment to 23.1311 is adopted, a glass cockpit upgrade would be 

applicable. If an amendment to 23.1419 were adopted, a glass cockpit 

upgrade by itself would not be an affected area under the Changed 

Product Rule and compliance to the rule would not be required. However, 

if the glass cockpit tied in to the autopilot, then the modification would 

require assessment per AC 21.101 to determine applicability of the 

proposed 23.1419 rule change. 

 Gross Weight Increase 

A gross weight increase reduces airplane performance and increases the 

potential for the airplane to reach the low airspeed regime, and reduces 

the acceleration during stall recovery. A gross weight increase greater 

than 5% is deemed significant under the Changed Product Rule and 

would require assessment per AC 21.101 to determine applicability of the 

proposed 23.1419 rule change. Consideration should be given to an 

engine change, resulting in power/thrust increase, in conjunction with the 

weight increase which may mitigate the above issues. 

 Changed Product Rule 

The ARC discussed the changed product rule, § 21.101, and the 

associated Advisory Circular 21.101-1A, during the applicability 

discussions. Many in the ARC believed that the AC would have to be 

revised if the new rule was to apply to any new autopilot on an airplane 

certified for icing because Appendix 1 of the AC classifies an autopilot 

installation as a “Not Significant” change. The ARC also discussed the 

phrase “and of any other regulation the [FAA] finds is directly related” in

§ 21.101(b) and its guidance in Step 8 in Figure 1 of AC 21.101-1A. This 

criteria may deem the proposed type certification basis to be inadequate – 

that is, the change includes characteristics that were not foreseen during 

the initial (or previously approved) type certification. The ARC believed 

that this may not be universally interpreted and the AC should be revised. 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-134

E) BENEFIT SUMMARY

The ARC reviewed the database described in Section 9 of this report. Accidents 

included in the SLD applicable list in Table 13 of this report were excluded, as well as 

part 23 airplanes that were not equipped nor certified for icing. This included three 

events on airplane models subject to Cessna Service Bulletin MEB97-4. The list was 

then reduced to events in which there was evidence of a loss of control at low airspeed. 

Examples include witnesses observing the airplane descending out of clouds in an 

uncontrolled state, or radar that indicated a loss of airspeed. An example is “"aircraft 

slowed from 270 to 150 ground speed in 4 minutes, then slowed to 100 knots in the next 

12 seconds." An attempt was made to limit the list to airplanes in which an autopilot 

was installed, in accordance with the proposed rule. However, in most events this data 

was unavailable and an installed autopilot was assumed. The resulting applicable list is 

in Table 19. 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-135

Table 19 – Events Applicable to Task 9 Proposed Rule 

DATE AC TYPE LOCATION FATAL INJURY HULL 

LOSS 

1/15/2009 Commander 690C Wray, CO 2 0 Yes

2/9/2007 BE-H18 Great Bend, KS 1 0 Yes

11/29/2005 CE-425 Belgrade, MT 1 0 Yes

12/6/2004 CE-208B1 Bellevue, ID 2 0 Yes

10/29/2003 CE-208B1 Cody, WY 1 0 Yes

11/8/2002 CE-208B1 Parks, AZ 4 0 Yes

5/5/2001 CE-208B1 Steamboat Springs, CO 1 0 Yes

4/4/1999 PA-46-3502 Waldron, AR 1 0 Yes

1/31/1996 BE-65-E90 Flagstaff, AZ 3 0 SD

4/12/1995 BE-65-B80 Great Bend, ND 1 0 SD

2/14/1995 PA-46-310P2 Chippewa, WI 2 2 SD

2/12/1995 690 (Twin 

Commander)

Guthrie, OK 2 0 Yes

1/26/1994 CE-421C McCook, NE 2 3 Yes

11/21/1992 BE-60-A60 Snoqualmie Pass, WA 6 0 Yes

2/14/1990 MU-2B-601 Putnam, TX 5 0 Yes

9/2/1981 MU-2B-251 McLeod, TX 5 0 Yes

12/6/1980 MU-2B-401 Ramsey, MN 5 0 Yes

1/30/1980 690A (Twin 

Commander)

Newcastle, OK 2 0 Yes

4/7/1979 BE-58TC St. Anne, IL 6 0 Yes

1/19/1979 PA-60-601P Grand Rapids, MI 4 2 Yes

SD – substantial damage 

Note 1 - Airworthiness Directives required installation of Low Airspeed Alert systems for flight in icing on 

these airplanes. No icing events since AD. 

Note 2 - Airworthiness Directive required modification of stall warning heating circuit. No icing events 

since AD. 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-136

All aircraft were certified to § 23.1419 at Amendment 23-14 or earlier, including Civil Air 

Regulations (CAR) 3. No aircraft in the events database were certificated under. 

§ 23.1419 Amendment 23-43 (latest amendment for part 23 icing certification). 

The ARC noted that all but three of the airplanes in the list had takeoff gross weight 

above 6,000 lb., and 12 out of the 20 were turboprops. The majority of the ARC 

believes that restricting the rule to airplanes above 6,000 lb. may be an option to be 

evaluated during the economic analysis of the rule. One member believed the rule 

could be targeted to only turboprop equipped airplanes, and one member believed it 

should be targeted to only turboprop airplanes above 6,000 lb. gross weight. One 

technical rationale that supports using the powerplant type criteria is that reciprocating 

powered airplanes have shorter spool up times for airspeed recovery, however one 

observation was that stall recovery with ice accretion is effected by angle of attack 

reduction. If either were pursued, the ARC noted that all the part 23 models in part 121 

service would potentially be subject to the rule, and 74% of the airplanes in part 135 

service are models that would be applicable (80% if all turbine engines were included). 

Therefore limiting the rule applicability as discussed may potentially reduce the rule cost 

and burden on small airplane owners while protecting the majority of the flying public. 

The above analysis was based on SPAS data from May, 2011. 

The ARC made an interesting observation on airplane not certified for icing. Before the 

airplanes not certified for icing were excluded from the applicable Task 9 list, they made 

up 71% of the events. The ARC believes education and training, and the introduction of 

envelope protection systems in the fleet will reduce these accidents. (The latter is 

based on the assumption that envelope protection systems activate at a nominal 1.2 

times non-icing stall speed.) 

F) COST SUMMARY

(1) DESIGN AND CERTIFICATION

The cost to comply with the proposed rule would be a function as to whether the 

modification incorporates a glass cockpit. An autopilot on a part 23 airplane would not 

have airspeed data. The ARC estimates that 86% of autopilot modifications on part 23 

airplanes incorporate a glass cockpit. The costs associated with a glass cockpit 

installation are lower because airspeed information is already available, however the 

glass cockpit software would have to be developed and tested to display a low airspeed 

alert. The ARC does not have the expertise to provide this cost data and recommends 

the FAA obtain this data from avionics manufacturers. These modifications, in addition 

to software and display modifications, would require a signal to indicate an ice 

protection system is activated (to indicate the airplane is in icing conditions) and a flap 

position signal. The average estimate provided by airframe manufacturers on the ARC 

is 140 man-hours. The required modification would require a flight test to determine 

proper function and verify absence of nuisance alerts. The average cost provided by 

airframe,manufacturers is 65 man-hours and $6,000. These estimates assume flight 
Part 23 SLD ARC REPORT 

FEB 2012 - Revision B Page-137

testing will not require ice shapes and the flight test evaluations piggy-back evaluations 

of the autopilot or glass cockpit. 

(2) RECURRING COSTS

The unit cost increase of an autopilot installation should be estimated by the avionics 

manufacturers. Increase in airplane weight is expected to be negligible, and operations 

should be small since operating speeds should not be required on most modifications. 

G) GUIDANCE

Since there was no consensus on whether a proposed new rule should be in § 23.1311 

versus § 23.1419, the ARC did not draft recommended guidance as it did for SLD and 

ice crystals. The ARC believes the following should be addressed in the guidance: 

Acceptable means of compliance (the discussions in section B Proposed Rule) should 

be included) 

Applicability (the discussions in section C Applicability of the Proposed Rule) should be 

included) 

Regardless of which rule is eventually proposed, the ARC recommends edits to AC 

23.1311 in Section 17.7 “Low Speed and High Speed Awareness Cues.” 

 This section should reference the proposed rule and state that for airplanes subject 

to the Task 9 rule, the low airspeed awareness cue should be based on icing V

SO 

when in icing conditions (the ice protection system may be used to indicate this). 

 For airplanes in which the stall warning system is scheduled for icing, the low 

airspeed awareness cue should be based on the icing stall speed. This reflects 

industry practice and the revised AC 23.1419-2E can be referenced. 

 For other part 23 airplanes certified for icing, it is good practice to schedule the low 

airspeed awareness cue on icing stall speed when in icing conditions. 

Part 23 SLD ARC REPORT 

APPENDIX A – PART 23 ICING ARC CHARTER 

FEB 2012 - Revision B Page A-1

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Part 23 SLD ARC REPORT 

APPENDIX A – PART 23 ICING ARC CHARTER 

FEB 2012 - Revision B Page A-2

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APPENDIX A – PART 23 ICING ARC CHARTER 

FEB 2012 - Revision B Page A-3

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APPENDIX A – PART 23 ICING ARC CHARTER 

FEB 2012 - Revision B Page A-4

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Part 23 SLD ARC REPORT 

APPENDIX B – PART 23 ICING ARC MEMBERS 

FEB 2012 - Revision B 

Point of Contact Company 

Karl Berg Honda Aircraft 33Tom Bond FAA Icing Chief Scientist & Technical Advisor 21Greg Bowles GAMA 20Pedro Fernando Almeida Di Donato* ANAC 55Marcelo Leao Domingos Embraer 55Jim Duncan Piper Aircraft 77Chuck Enders FAA Flight Standards, Air Transportation 20John Fisher FAA Engine & Propeller Directorate 78Michael H Grossmann NATA 33Kristine Hartzell AOPA 30John Hazlet RACCA 81Garrett Homan Cirrus Design 21Jim Hoppins Cessna Aircraft 31David Johns* Transport Canada 61Jerry Jordan CAV Aerospace 91Kurt Laurie Cessna Aircraft 31Mário Celso dos Anjos Oliveira Leite ANAC 55Jim Martin* Transport Canada 61Jason Nickel Hawker Beech 31Jerry Ostronic FAA Flight Standards, Air Transportation 41David Parkins Designated Engineering Representative 60Paul Pellicano FAA Small Airplane Directorate 40Andy Pierce FAA Flight Standards, Air Transportation (Part 135) 20Everett Rochon FAA Flight Standards, General Aviation & Commercial 20David Schwartz Piper Aircraft 77Dennis van de Laar National Air Transportation Association 70Gary Welsh Hawker Beech 31* Non voting - foreign airworthiness authority 

Part 23 SLD ARC REPORT 

APPENDIX C – PART 23 AIRPLANE SEVERE ICING AIRWORTHINESS DIRE

FEB 2012 - Revision B 

Airplane Model Docke

Aerostar Aircraft Corporation Models PA-60-600, PA-60-601, PA-60-601P, PA-60-602P, and PA-60-700P Airplanes 97-CE-56Pilatus Britten-Norman Ltd., Models BN-2A, BN-2B, and BN-2T Airplanes 97-CE-54Pilatus Aircraft Ltd., Models PC-12 and PC-12/45 Airplanes 97-CE-53Partenavia Costruzioni Aeronauticas, S.p.A. Model P68, AP68TP 300, AP68TP 600 Airplanes 97-CE-51Mitsubishi Heavy Industries, Ltd., MU-2B Series Airplanes 96-CE-61Harbin Aircraft Manufacturing Corp., Model Y12 IV Airplanes 97-CE-50Empresa Brasileira de Aeronautica S.A. Airplanes. (Embraer) Models EMB-110P1 and EMB-110P2 Airplanes 96-CE-02Dornier Luftfahrt GmbH, 228 Series Airplanes 96-CE-04De Havilland, Inc., DHC-6 Series Airplanes 96-CE-01The Cessna Aircraft Company, 208 Series 96-CE-05The Cessna Aircraft Company, Model T210R Airplane 98-CE-19The Cessna Aircraft Company, Models T210, P210, P210R Airplanes 97-CE-62The Cessna Aircraft Company Models T303, 310R, T310R, 335, 340A, 402B, 402C, 404, F406, 414, 414A, 421B, 421C, 425, and 441 Airplanes 97-CE-63Jetstream Aircraft Limited Models 3101 and 3201 Airplanes 96-CE-07The New Piper Aircraft PA-23, PA-30, PA-31, PA-34, PA-39, PA-40, and PA-42 Series Airplanes 98-CE-77The New Piper Aircraft Corporation Models PA-46-310P and PA-46-350P Airplanes 97-CE-60Beech Aircraft Corporation Models 99, 99A, A99A, B99, C99, B200, B200C, 1900, 1900C, and 1900D Airplanes 96-CE-03Raytheon Aircraft Company 200 Series Airplanes 98-CE-17Raytheon Aircraft Company Models E55, E55A, 58, 58A, 58P, 58PA, 58TC, 58TCA Airplanes, and 60, 65-B80, 65-B90, 90, F90, 100, 300, and B300 Series Airplanes 97-CE-58Raytheon Aircraft Company Model 2000 Airplanes 97-CE-59AeroSpace Technologies Of Australia Pty Ltd., Models N22B and N24A. 97-CE-49SIAI Marchetti, S.r.1 Models SF600 and SF600A Airplanes 97-CE-64SOCATA--Groupe AEROSPATIALE, Model TBM 700 Airplanes. 97-CE-55Twin Commander Aircraft Corporation Models 500, 500-A, 500-B, 500-S, 500-U, 520, 560, 560-A, 560-E, 560-F, 680, 680-E, 680FL(P), 680T, 680V, 680W, 681, 685, 690, 690A, 690B, 690C, 690D, 695, 695A, 695B, and 720 Airplanes 97-CE-57Fairchild Aircraft Corporation, SA226 and SA227 Series Airplanes 96-CE-06

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

U.S. Department 

of Transportation 

Federal Aviation 

Administration

Advisory 

Circular

 

Subject: CERTIFICATION OF PART 

23 AIRPLANES FOR FLIGHT IN 

ICING CONDITIONS

Date: 

Initiated by: ACE-100

AC No: 23.1419-2E

FOREWORD 

This Advisory Circular (AC) sets forth an acceptable means of showing compliance with Title 14 

Code of Federal Regulations (14 CFR), part 23, for the approval of airplane ice protection 

systems for operating in the icing environment defined by part 25, Appendix C, and part 25, 

Appendix O. 

Earl Lawrence 

Manager, Small Airplane Directorate 

Aircraft Certification Service. 

 

AC 23.1419-2E 

iii)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

CONTENTS

Paragraph Page

 1. What is the purpose of this AC? ............................................................. 1 

 2. Who does this AC apply to? ................................................................... 1 

 3. Cancellation ............................................................................................ 1 

 4. Applicability ........................................................................................... 1 

 5. Related Regulations and Documents ...................................................... 1 

 6. Related Reading Material ....................................................................... 3 

 7. Background ............................................................................................ 6 

 8. Planning .................................................................................................. 6 

 9. Design Objectives ................................................................................... 7 

 10. Analyses and Ground Testing ................................................................ 7 

 11. Flight Test Planning ............................................................................... 20 

 12. Flight Tests ............................................................................................. 21 

 13. Performance and Flying Qualities .......................................................... 30 

 14. Supercooled Large Drop (SLD) Conditions ........................................... 44 

 15. Ice and Icing Conditions Detection ........................................................ 57 

 16. Ice Shedding ........................................................................................... 63 

 17. Autopilot ................................................................................................. 64 

 18. Placarding and AFM .............................................................................. 67 

 19. Instructions for Continued Airworthiness .............................................. 75 

 20. Ground Deicing Fluids ........................................................................... 79 

Appendix 1 Definitions .............................................................................................. A1-1 

Appendix 2 Guidelines for Determining Certification Basis on Flight in Icing 

 Approval STCs and Amended TCs.................................................... A2-1 

Appendix 3 Guidelines for Supplemental Type Certificates (STC) and 

 Amended Type Certificates on Airplanes .......................................... A3-1 

Appendix 4 Guidelines for Certifying Ice Protection Systems on Airplanes 

 Not for Flight in Icing Approval (“Non-Hazard” Basis) ................... A4-1 

Appendix 5 Guidelines for Approval of Replacement Parts for Airframe 

 Deicing Systems................................................................................. A5-1 

Appendix 6 Part 23 Subpart B Tests for Section 23.1419 at Amendment 23-XX ..... A6-1 

Appendix 7 Summary of Engineering Tools for Compliance to § 23.1420 .............. A7-1 

Appendix 8 Example Flight Test Program for Compliance to § 23.21(c)(1) A8-1

Appendix 9 Example Flight Test Program for Compliance to § 23.21(c)(2) - 

 Takeoff in part 25, Appendix O Icing Conditions A9-1
AC 23.1419-2E

iv 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

TABLES 

Number Title Page

1 Fluid Capacity .................................................................................. 16 

2 Ice Accretion Definitions .................................................................... 33 

3 Natural Icing Performance and Handling Qualities Tests ................... 39 

4 Flight Test Tolerances ......................................................................... 40 

5 Failure Ice Accretion Flight Tests ....................................................... 45 

6 Appendix O Detect and Exit Ice Accretion ........................................ XX 

7 Appendix O Ice Accretion .................................................................. XX 

8 Appendix O Ice Accretion Roughness ............................................... XX 

9 Autopilot Test Conditions ................................................................... XX 

10 Autopilot Low Airspeed Tests ............................................................ XX 

11 Autopilot Alert Test Conditions ......................................................... XX 

5-1 Summary of Test Requirements for Replacement of 

 Airframe Deicing Components ....................................................... A5-1

6-1 Part 23 Subpart B Tests for Section 23.1419 at Amendment 23-XX .. A6-1
AC 23.1419-2E 

5)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

1. What is the purpose of this AC? This Advisory Circular (AC) sets forth an acceptable 

means, but not the only means, of demonstrating compliance with the ice protection 

requirements in Title 14 of the Code of Federal Regulations (14 CFR) part 23. The Federal 

Aviation Administration (FAA) will consider other methods of demonstrating compliance that an 

applicant may elect to present. This material is neither mandatory nor regulatory in nature and 

does not constitute a regulation. 

2. Who does this Advisory Circular (AC) apply to? The guidance provided in this document 

is directed to airplane manufacturers, modifiers, foreign regulatory authorities, and FAA small 

airplane type certification engineers, and their designees. This AC applies to airplane ice 

protection systems in any normal, utility, acrobatic or commuter category part 23 airplane. 

3. Cancellation. AC 23.1419-2D, Certification of Part 23 Airplanes for Flight in Icing 

Conditions, dated April 19, 2007, is canceled. In addition, all policy related to the certification 

of ice protection systems on part 23 airplanes, issued prior to this AC, and is superseded by this 

AC. 

4. Applicability. The guidance provided here applies to the approval of airplane ice protection 

systems for operating in the icing environment defined by part 25, Appendix C and Appendix O. 

The guidance should be applied to new Type Certificates (TCs), Supplemental Type Certificates 

(STCs), and amendments to existing TCs for airplanes under part 3 of the Civil Aviation 

Regulations (CAR) or its predecessor regulations, and part 23, for which approval under the 

provisions of § 23.1419 and § 23.1420 is desired. 

5. Related Regulations and Documents. 

a. Regulations. By their adoption in amendment 23-14, which shows their requirements 

are directly related, §§ 23.929, 23.1309, and 23.1419 are applicable to a part 23 airplane icing 

certification program regardless of the certification basis for the basic airplane; however, for 

those airplanes certificated in accordance with part 3 of the CAR or earlier, and through part 23 

at amendment 23-13, the application of these sections may be limited to the equipment being 

used for ice protection. Some systems that were previously approved on the airplane may need 

to be modified to improve their reliability when those systems are utilized as part of that 

airplane's icing approval. 

(1) With the adoption of amendment 23-43, § 23.1419 was revised to do the following: 

to specify that the performance, controllability, maneuverability, and stability must not be less 

than that required by subpart B of part 23; add the requirement for flight testing in measured, 

natural icing conditions; provide specific test requirements; clarify the requirements for 

information that must be provided to the pilot, and allow approval of equivalent components that 

have been previously tested and approved, and that have demonstrated satisfactory service if the 

installations are similar. 
AC 23.1419-2E 

6 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(2) Prior to the adoption of amendment 23-43, some part 23 airplanes were certificated 

for flight in icing using § 25.1419. 

(3) In addition to the previously mentioned requirements (§§ 23.929, 23.1309, and 

23.1419), other sections must be applied depending upon the ice protection system design and 

the original certification basis of the airplane. Refer to AC 20-73A, Appendix C, Table C-2. 

Many of the requirements in Table C-2 of AC 20-73A are also applicable, even without approval 

for flight in icing conditions. Further guidance on establishing a certification basis for flight in 

icing approval can be found in Appendix 2 of this AC. 

(4) Amendment 23-XX added a requirement to comply with § 23.1420 for airplanes 

seeking certification for flight in icing, which adds requirements for flight in supercooled large 

drop (SLD) conditions. Amendment 23-XX also: 

(a) Added SLD requirements for propellers in § 23.929, windshields in § 23.775, 

and static ports in § 23.1325. 

(b) Added SLD and ice crystal requirements for engines in § 23.1093(b) 

(c) Added SLD and ice crystal requirements for pitot probe in § 23.1323, and 

added § 23.1324 for angle of attack/stall warning sensor instruments, 

(d) Revised the Subpart B requirements in § 23.1419 

(e) Codified ice protection system activation and operation guidance in § 23.1419 

(f) Deleted § 23.1416 because the requirements are addressed in §§ 23.1309 and 

23.1322. 

(g) Replaced the requirement for illumination of ice accumulations provided by 

§23.1419(d) with a new §23.1403. 

b. ACs. Copies of current editions of the following publications may be downloaded from 

the FAA's Regulatory and Guidance Library (RGL) www.rgl.faa.gov or obtained from the U.S. 

Department of Transportation, Subsequent Distribution Office, Ardmore East Business Center, 

3341 Q 75th Avenue, Landover, MD 20785: 

AC 20-73A “Aircraft Ice Protection,” August 16, 2006. 

AC 20-115B “Radio Technical Commission for Aeronautic, Inc. Document 

RTCA/DO-178B,” January 11, 1993. 

AC 20-117 “Hazards Following Ground Deicing and Ground Operations in 

 Conditions Conducive to Aircraft Icing,” December 3, 1982. 
AC 23.1419-2E 

7)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

AC 20-147 “Turbojet, Turboprop, and Turbofan Engine Induction System Icing 

and Ice Ingestion,” February 2, 2004. 

AC 21-16F “RTCA Document DO-160 versions D, E, and F, "Environmental 

Conditions and Test Procedures for Airborne Equipment,” November 

19, 2009. 

AC 21-40A “Guide for Obtaining a Supplemental Type Certification,” 

 September 27, 2007. 

AC 21.101-1 “Change 1, Establishing the Certification Basis of Changed

 Aeronautical Products,” April 28, 2003. 

 

AC 23-16A “Powerplant Guide for Certification of Part 23 Airplanes and 

 Airships,” February 23, 2004. 

AC 23-17B “Systems and Equipment Guide for Certification of Part 23 

 Airplanes,” April 12, 2005. 

AC 23.629-1B “Means of Compliance with Title 14 CFR, Part 23, § 23.629, Flutter,” 

 September 28, 2004. 

AC 23.1309-1D “System Safety Analysis and Assessment for Part 23 Airplanes,” 

January 16 2009. 

AC 91-74A “Pilot Guide Flight in Icing Conditions,” December 31 2007. 

AC 120-58 “Pilot Guide Large Aircraft Ground Deicing,” September 30, 1992. 

AC 120-60B “Ground Deicing and Anti-icing Program,” December 20, 2004. 

AC 135-16 Ground Deicing & Anti-icing Training & Checking,” December 12, 

 1994. 

AC 135-17 Pilot Guide-Small Aircraft Ground Deicing (pocket),” December 14, 

 1994. 

Copies of the current AC may be purchased from the Superintendent of Documents, P.O. 

Box 371954, Pittsburgh, PA 15250-7954. Make check or money order payable to the 

Superintendent of Documents: 

AC 23-8B “Flight Test Guide for Certification of Part 23 Airplanes,” August 14, 

 2003. 
AC 23.1419-2E 

8 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

6. Related Reading Material.

a. FAA Orders. 

FAA Order 8110.4C, “Type Certification,” October 26, 2005. 

b. FAA Technical Reports. The following FAA technical reports can be obtained from 

the National Technical Information Service in Springfield, Virginia 22161: 

(1) FAA Technical Report DOT/FAA/CT-88/8, "Aircraft Icing Handbook" (March 

1991), includes reference material on ground and airborne icing facilities, simulation procedures, 

and analytical techniques. This document represents all types and classes of aircraft and is 

intended as a working tool for the designer and analyst of ice protection systems. 

(2) FAA Technical Report ADS-4, "Engineering Summary of Airframe Icing Technical 

Data," and Report No., FAA-RD-77-76, "Engineering Summary of Powerplant Icing Technical 

Data," provide technical information on airframe and engine icing conditions, and methods of 

detecting, preventing, and removing ice accretion on airframes and engines in flight. Although 

most of the information contained in ADS-4 and FAA-RD-77-76 reports is still valid, some is 

outdated, and more usable information is now available through recent research and experience, 

and is included in the Aircraft Icing Handbook. 

(3) FAA Technical Report DOT/FAA/AR-01/91, "A History and Interpretation of 

Aircraft Icing Intensity Definitions and FAA Rules for Operating in Icing Conditions" 

(November 2001), provides a good reference for understanding icing operational rules. 

(4) FAA Technical Report DOT/FAA/AR-02/68, "Effect of Residual and Intercycle Ice 

Accretions on Airfoil Performance" (May 2002), details icing tunnel testing to determine 

intercycle and residual ice on a 23012 airfoil, and wind tunnel testing of uniform sandpaper and 

intercycle ice shapes. 

(5) FAA Technical Report DOT/FAA/CT-TN86/11, “Fluid Ice Protection Systems,” 

July 1986. 

(6) National Aeronautics and Space Administration (NASA)/TP—2000-209908, 

“NASA/FAA Tailplane Icing Program: Flight Test Report” (March 2000), provides reference 

information on Ice Contaminated Tailplane Stall (ICTS). Assumptions, ice shapes, and certain 

other data are not necessarily representative or appropriate for use with other projects. The 

above report and other reference material on ICTS are also available at the NASA Glenn 

Research Center Icing Branch website: icebox.grc.nasa.gov. 

(7) FAA Technical Report DOT/FAA/06-60, “Propeller Icing Tunnel Tests on a FullScale Turboprop Engine,” March 2010 
AC 23.1419-2E 

9)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(8) FAA Technical Report DOT/FAA/AR-09/10, “Data and Analysis for the Development of 

an Engineering Standard for Supercooled Large Drop Conditions,” March 2009 

(9) FAA Technical Report DOT/FAA/AR-09/13, "Technical Compendium From Meetings of 

the Engine Harmonization Working Group", April 2009. 

c. Technical Standard Order (TSO): A copy of the current edition of the following 

publication may be obtained from the Federal Aviation Administration, Aircraft Certification 

Service, Aircraft Engineering Division, Technical Programs and Continued Airworthiness 

Branch—AIR-120, 800 Independence Avenue, SW, Washington, DC 20591 or from the FAA 

website at www.faa.gov: 

TSO-C16 “Air-Speed Tubes (Electrically Heated),” September 1, 1948. 

TSO-C16a “Electrically Heated Pitot and Pitot-Static Tubes,” October 6, 2006. 

TSO-C54 “Stall Warning Instruments,” October 15, 1961. 

d. SAE Documents. The Society of Automotive Engineers (SAE), Inc. Aerospace 

Recommended Practice (ARP) and Aerospace Information Report (AIR) documents are 

available from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001 or from their 

website at www.sae.org: 

ARP4761 “Guidelines and Methods for Conducting the Safety Assessment Process on 

 Civil Airborne Systems and Equipment,” December 1, 1996. 

AIR4367 “Aircraft Ice Detectors and Icing Rate Measuring Instruments, “Revision 

A, July 2007. 

ARP5624 “Aircraft Inflight Icing Terminology,” March 3, 2008. 

AIR1168/4 “Ice, Rain, Fog, and Frost Protection,” July 1990. 

 . 

ARP4087 “Wing Inspection Lights – Design Criteria,” September 12, 2006. 

AS393 “Airspeed Tubes Electrically Heated,” August 14, 2002. 

AS8006 “Minimum Performance Standard for Pitot and Pitot Static Tubes, “April 

28, 1988. 

AS403 “Stall Warning Instrument,” July 15, 1958. 
AC 23.1419-2E 

10 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

The SAE and a working group for Task 11A of the FAA Inflight Aircraft Icing Plan have 

developed the following documents: 

ARP5903 “Droplet Impingement and Ice Accretion Computer Codes, October 16, 

 2003. 

ARP5904 “Airborne Icing Tankers,” October 21, 2002. 

ARP5905 “Calibration and Acceptance of Icing Wind Tunnels,” September 18, 2003. 

AS5498 “Minimum Operational Specification for Inflight Icing Detection Systems," 

October 2001. 

e. Miscellaneous Documents. 

(1) British Specification (BS) 2G-135, “Specification for Electrically-Heated Pitot and 

Pitotstatic Pressure Heads,” 1967. 

(2) American Society for Testing and Materials (ASTM) G76-95, “Standard Test 

Method for Conducting Erosion Tests by Solid Particle Impingement Using Gas Jets”

7. Background. 

AC 20-73A contains a detailed history of ice protection regulations for part 23 airplanes. 

8. Planning.

a. Flight in Icing Approval. The applicant should submit a certification plan in accordance 

with FAA Order 8110.4C and AC 20-73A. The certification plan should describe all of the 

applicant's efforts intended to lead to certification. This plan should identify, by item to be 

certificated, the certification methods that the applicant intends to use. It should provide for a 

certification checklist. Regarding § 23.1419, it should clearly identify analyses and tests, or 

references to similarity of designs that the applicant intends for certification of the ice protection 

system. These methods of showing compliance should be agreed upon between the applicant 

and the FAA early in the type certification program. Detailed guidance for STCs or amended 

TCs on part 23 airplanes approved for flight in icing can be found in Appendix 3 of this AC. It is 

imperative that the applicant obtains FAA concurrence prior to conducting certification tests. 

b. Installations without Flight in Icing Approval. There may be times when applicants 

may want to certificate an ice protection system installation but do not want to obtain flight in 

icing approval. In the past these systems have been called “non-hazard” installations. This 

means that the aircraft is prohibited from flight in icing conditions but there is some ice 

protection to facilitate an exit from an inadvertent icing encounter. Guidance for the approval of 

these types of ice protection systems can be found in Appendix 4 of this AC. 
AC 23.1419-2E 

11)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

c. Replacement Parts for Airframe Ice Protection Systems. The requirements leading to 

approval of replacement airframe deicing systems or airframe thermal deicing or anti-icing 

systems are detailed in Appendix 5 of this AC. 

9. Design Objectives. The applicant must demonstrate by analyses and tests that the 

airplane is capable of safely operating throughout the icing envelope of part 25, Appendix 

C. The envelope can be reduced for airplanes certificated for operation where systems or 

performance limitations (e.g., altitude), not related to ice protection, exist. Airplanes must 

also be able to safely operate in or exit the icing conditions defined by part 25 Appendix 

O. 

The applicant, however, has several certification options available for Appendix O icing 

conditions. The airplane can be certified for— 

 The ability to detect Appendix O conditions and safely exit all icing conditions, 

 The ability to operate safely throughout a portion of Appendix O icing conditions and 

safely exit all icing conditions when that portion of Appendix O is exceeded, or 

 The ability to operate safely throughout all the Appendix O icing conditions. 

Sections 23.1419 and 23.1420 provide specific airframe requirements for certification for 

flight in the icing conditions defined in Appendices C and O. 

The “approved portions” of 14 CFR Part 25, Appendix O as used in the proposed regulations and 

guidance material are intended to refer to aircraft that are certified against 23.1420(a)(2) or 

(a)(3). For aircraft certified against 23.1420(a)(1) the exposures in Appendix O are not approved 

and require exiting all icing conditions. The phrase “with exposures in accordance with 

23.1420(a)(1), (a)(2) or (a)(3)” is intended to require consideration of the environmental 

conditions within the Appendix O environment, as well as the exposure durations as defined in 

23.1420 and 14 CFR 23 Appendix TBD which contains ice shape definitions for exposure to 14 

CFR 25, Appendix C and Appendix O for part 23 aircraft. 

10. Analyses and Ground Testing. The applicant normally prepares analyses to 

substantiate decisions involving application of selected ice protection equipment and to 

substantiate decisions to leave normally protected areas and components unprotected. Such 

analyses should clearly state the basic protection required, the assumptions made, and 

delineate the methods of analysis used. All analyses should be validated either by tests or 

by methods agreed to by the FAA. This substantiation should include a discussion of the 

assumptions made in the analyses and the design provisions included to compensate for 

these assumptions. Analyses are normally used for the following: 

a. Areas and Components to be Protected. The applicant should examine the areas listed 

in AC 20-73A to determine the degree of protection required. 
AC 23.1419-2E 

12 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

An applicant may find that protection is not required for one or more of these areas and 

components. If so, the applicant should include supporting data and rationale in the analysis for 

allowing them to go unprotected. The applicant should demonstrate that allowing them to go 

unprotected does not adversely affect the handling or performance of the airplane. 

b. Ice Accretion Analyses. 

(1) Impingement Limit Analyses. The applicant should prepare a drop impingement 

and water catch analysis of the wing, horizontal and vertical stabilizers, propellers, and any other 

leading edges or protuberances such as antennas that may require protection. This analysis 

should consider the various airplane operational configurations and associated angles of attack. 

This analysis is needed to establish the upper and lower aft droplet impingement limits that can 

then be used to establish the aft ice formation limit and the extent of the protection surface 

coverage needed. The applicant should consult AC 20-73A, “Aircraft Ice Protection” for more 

detailed information. 

(2) Critical Ice Accretions. The critical ice accretions for which operational 

characteristics are to be evaluated should be determined for each flight phase as discussed in 

paragraph 13.b. of this AC. The parameters to be considered are the flight conditions (e.g., 

airplane configuration, airspeed, angle of attack, altitude) and the icing conditions of part 25, 

Appendix C (temperature, liquid water content, mean effective drop diameter). The applicant 

should substantiate the critical mean effective drop diameter, Liquid Water Content (LWC), and 

temperature that result in the formation of an ice accretion that is critical to the airplane's 

operational characteristics. For deicing systems, intercycle, residual, and runback ice accretions 

should be considered. 

(3) The 45-Minute Hold Condition. The 45-minute hold criterion should be evaluated 

when determining critical ice shapes for which the operational characteristics of the overall 

airplane are to be analyzed. See AC 20-73A for more information. 

(a) A mean effective droplet diameter of 22 microns and a liquid water content of 

0.5 gm/m3

 with no horizontal extent correction are normally used for this analysis; however, the 

applicant should substantiate the specific values used, including temperature, which represent the 

critical conditions for the airplane's performance and handling qualities. Critical flight conditions 

should be considered such as weight and speed for critical angle of attack, and airspeed and 

altitude for maximum water catch. For example, minimum holding speed should be evaluated, 

but a higher airspeed that the airplane may operate at may be more critical because of the lower 

angle of attack and higher water catch. 

(b) The critical ice shapes derived from this analysis should be compared to 

critical shapes derived from other analyses (climb, cruise, and descent, approach) to establish the 

most critical simulated ice shapes to be used during dry air flight tests. 
AC 23.1419-2E 

13)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

c. Airframe. 

(1) Structural Analyses. 

(a) The structural analyses should include analyses which establish that critical 

ice build-ups on antennas, masts, and other components attached externally to the airplane do not 

result in hazards. Flight tests in simulated or natural icing conditions or with simulated ice 

shapes may be used to substantiate the structural analyses; however similarity to previous 

approved designs is a common method of compliance. 

(b) Determine that the temperature gradient produced on heated windshields does 

not adversely affect windshield structural integrity. 

(2) Flutter Analyses. AC 23.629-1B, “Means of Compliance with Title 14 CFR, Part 

23, §23.629, Flutter,” provides guidance for showing compliance with §23.629. Aeroelastic 

stability analyses should use the mass distributions derived from ice accumulation up to and 

including those that can accrete in the applicable icing conditions in part 25, Appendices C and 

approved portions of Appendix O. This includes any accretions that could develop on control 

surfaces. The analyses need not consider the aerodynamic effects of ice shapes. 

(3) Means for Inspecting upper Wing Surface in Ground Icing Conditions. On some 

high wing airplanes, the wing upper surface cannot be reached for a tactile inspection, or visually 

observed from the ground. Part 23 airplanes may operate into airports without any ground 

equipment. For these airplanes, the design should incorporate provisions to allow the flightcrew 

close access to the wing upper surface to facilitate a pre-takeoff contamination inspection. 

Recessed steps and handles in the fuselage, in proximity to the wing leading edge, would be one 

example. 

d. Power Sources. 

(1) Power Source Analysis. The applicants should evaluate the power sources in their 

ice protection system design. Electrical, bleed air, and pneumatic sources are normally used. A 

load analysis or test should be conducted on each power source to determine that the power 

source is adequate to supply the ice protection system, plus all other essential loads throughout 

the airplane flight envelope under conditions requiring operation of the ice protection system. 

(2) Effect on Essential Systems. The effect of an ice protection system component 

failure on power availability to other essential loads should be evaluated, and any resultant 

hazard should be prevented on multi-engine designs and minimized on single-engine designs. 

The applicant should show that there is no hazard to the airplane in the event of any power 

source failure during flight in icing conditions. Two separate power sources (installed so that the 

failure of one source does not affect the ability of the remaining source to provide system power) 

are adequate if the single source can carry all the essential loads. 
AC 23.1419-2E 

14 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(a) Two-Engine Airplanes require two sources in accordance with § 23.1309(c). 

All power sources that affect engine or engine ice protection systems for multi-engine airplanes 

must comply with the engine isolation requirements of § 23.903(c). 

(b) Single-Engine Airplanes. Section 23.1309(a) requires that the ice protection 

system be designed to minimize hazards to the airplane in the event of a probable malfunction or 

failure. Failure condition classifications of “major”, “hazardous” or “catastrophic” are 

considered hazards. Complete loss of the airframe ice protection system has been considered at 

least “major” on past single engine certification programs. Since experience has shown that the 

failure of generators currently in service is probable, for example, systems that utilize a 

generator, such as an alternator, would require two sources of electrical power. This is also 

consistent with past project specific guidance on interpretation of § 23.1309, which stated that 

the level of safety in a single engine airplane is established by engine reliability and the ice 

protection system should not compromise it. For other types of power sources, additional 

reliability evaluation of the power source under system loads and environmental conditions may 

be required if a single source system is planned. 

(c) Load Shedding. Determine if load shedding can be accomplished after a 

partial failure condition. If applicable, a load shedding sequence should be provided so the pilot 

may assure that adequate power is available to the ice protection equipment and other necessary 

equipment for flight in icing conditions. 

(3) Electromagnetic Compatibility. The effect, if any, of ice protection system 

operation on other airplane systems must be determined to show compliance to § 23.1309(a). 

(a) Designs should minimize Magnetic Direction Indicator (MDI) deviations. If 

the ice protection system causes greater than an l0-degree deviation, then the placard requirement 

of § 23.1327 (amendment 23-20) should be applied in lieu of previous requirements. Refer to 

AC 23-17B for guidance on using a magnetic compass as a mitigating factor in a system safety 

assessment for cockpit heading display. 

e. Failure Analysis. AC 23.1309-1D provides guidance and information for an acceptable 

means, but not the only means, for showing compliance with the requirements of § 23.1309(a) 

and (b) (amendment 23-49) for equipment, systems, and installations in 14 CFR, part 23 

airplanes. The regulatory requirements are in § 23.1309. Substantiation of the hazard 

classification of ice protection system failure conditions is typically accomplished through 

analyses and/or testing. It has been standard industry practice to assign a probability of 

encountering part 25, Appendix C icing conditions of “one” for an airplane certificated for flight 

in icing. 

(1) During the analyses, each identifiable failure within the system should be examined 

for its effect on the airplane and its occupants. Examples of failures that need to be examined 

include: 
AC 23.1419-2E 

15)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(a) Those that allow an ice shape to accrete in size greater than design levels , to 

accrete asymmetrically, or accrete in areas that were normally protected; or 

(b) System failures such as loss of pneumatic boot vacuum, overheat of a thermal 

system, or leak in a hot air bleed air line. 

(2) A probable malfunction or failure is any single malfunction or failure that is 

expected to occur during the life of any single airplane of a specific type. This may be 

determined on the basis of past service experience with similar components in comparable 

airplane applications. This definition should be extended to multiple malfunctions or failure 

when: 

(a) The first malfunction or failure would not be detected during normal operation 

of the system, including periodic checks established at intervals that are consistent with the 

degree of hazard involved; or 

(b) The first malfunction would inevitably lead to other malfunctions or failures. 

A procedure requiring a pilot to exit icing conditions would not be acceptable after any failure 

condition that would become catastrophic within the average exposure time it takes to exit icing 

conditions. 

(3) Power Source Failure. Assure that no probable failure or malfunction of any 

power source (electrical, fluid, bleed air, pneumatic, and so forth) will impair the ability of the 

remaining source(s) to supply adequate power to systems essential to safe operation during icing 

flight. 

(4) Failure Annunciations. Warning information must be provided to alert the crew to 

unsafe system operating conditions and to enable them to take appropriate corrective action in 

accordance with § 23.1309(b)(3). 

(a) The requirement for warning information in § 23.1309(b)(3) is dependent on 

the severity of the failure, not dependent on the probability of the failure. 

(b) A means to indicate to the crew when the ice protection system is not 

receiving adequate electrical power, bleed air pressure, vacuum, or fluid pump output, and so 

forth, as appropriate, and it is functioning normally. Annunciation would not be required for 

obvious, inherent failures, such as failure of a fluid windshield system. 

1. Pneumatic deicing boots should be shown to operate at the pressure 

threshold of the annunciation. 

2. Annunciation when the boots are receiving adequate pressure has been 

used in previous certifications. For boots that cycle automatically, annunciation lights may be 

provided when the boots are not receiving adequate pressure when commanded, in lieu of lights 

that illuminate during each inflation cycle. This promotes the dark cockpit concept, and it’s 

easier to detect the presence of a light rather than the absence of a light. 
AC 23.1419-2E 

16 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

3. Annunciations of failures should be consistent with § 23.1309(b)(3) and 

§ 23.1322. 

(5) Circuit and Protective Devices. 

(a) Determine that the design incorporates electrical overload protection that 

opens regardless of operating control position. 

(b) Verify that the design is such that no protective device is protecting more than 

one circuit essential to continued safe flight (for example, pitot heat and stall warning transducer 

heat are considered separate essential circuits and should be provided separate protection). 

(c) Ice protection monitor and warning circuits should be considered separate 

from control circuits and each should provide individual circuit protection. 

(d) On airplanes equipped with dual power sources, a power distribution system 

having a single bus and a single circuit breaker protecting the ice protection system is not 

acceptable.

(6) Windshield Heat Systems. . For detect and exit aircraft, failures of the 

windshield system need not be considered in combination with Appendix O exposures due to the 

low probability of occurrence. A probable single failure of a transparency heating system should 

not adversely affect the integrity of the airplane cabin or create a potential danger of fire. 

(7) Appendix O Icing Conditions. 

(a) Airplanes Certificated to Operate in Appendix O or a Portion of 

Appendix O Conditions (§ 23.1420 (a)(2) and § 23.1420(a)(3)). 

1. The system safety analyses accomplished for flight in part 25, Appendix C 

icing conditions should be accomplished for flight in the part 25, Appendix O icing conditions 

for which the airplane is certified to operate. 

2. The applicant may assume that the average probability for encountering 

Appendix O icing conditions is 1 x 10-2 per flight hour. This probability should not be reduced 

based on phase of flight. 

3. Flight testing of failure ice shapes should be accomplished to validate 

hazard classifications and AFM exit procedures. 

(b) Airplanes Certificated to Detect and Exit Appendix O Icing Conditions (§ 

23.1420(a)(1) and § 23.1420(a)(2)). 
AC 23.1419-2E 

17)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

1. It is not necessary to conduct system safety assessments for flight in the 

icing conditions defined in appendix O of part 25 of this chapter for which the airplane is 

certified to safely exit following the condition's detection. 

2. A system safety assessment is required for any system utilized to detect 

icing conditions for which the airplane is not certified. 

(c) Detection of Appendix O Conditions for which the Airplane is not 

Certified 

1. An applicant may assume that the hazard classification for an 

unannunciated encounter with Appendix O conditions while the ice protection system is 

activated is hazardous, in accordance with AC 23.1309-1D, provided that the following are true.

(aa) The airplane is similar to previous designs with respect to Appendix 

O icing effects, and 

(bb) The applicant can show that the icing event history of all 

conventionally designed airplanes is relevant to the airplane being considered for certification. 

2. If an aircraft is not similar to a previous design, an assessment of the hazard 

classification may require more analysis or testing. One method of hazard assessment would be 

to consider effects of ice accumulations similar to those expected for aircraft being certified 

under § 23.1420. Such ice shapes may be defined from a combination of analysis and icing 

tanker or icing wind tunnel testing. Aerodynamic effects of such shapes could be evaluated with 

wind tunnel testing or, potentially, computational fluid dynamics. Hazard classification typically 

takes place early in a certification program. Therefore, a conservative assessment may be 

required until sufficient supporting data is available to reduce the hazard classification. 

3. Visual Cues. Typical system safety analyses do not address the probability 

of crew actions, such as observing a visual cue before performing a specified action. As advised 

in AC 23.1309-1D, quantitative assessments of crew errors are not considered feasible. When 

visual cues are to be the method for detecting Appendix O conditions and determining when to 

exit them, the applicant should assess the appropriateness and reasonableness of the specific cues 

(see section 15 of this AC for additional guidance). 

f. Similarity Analyses. 

(1) In the case of certification based on similarities to other type certificated airplanes 

previously approved for flight in icing conditions, the applicant should specify the reference 

airplane model and the component to which the reference applies. Specific similarities should be 

shown for physical, functional, thermodynamic, pneumatic, aerodynamic, and environmental 

areas. Analyses should be conducted to show that the component installation and operation is 

equivalent to the previously approved installation. 
AC 23.1419-2E 

18 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(2) Similarity requires an evaluation of both the system and installation differences that 

may adversely affect the system performance. An assessment of a new installation should 

consider differences affecting the aircraft and the system. Similarity may be used as the basis for 

certification without the need for additional tests provided: 

(a) Only minimal differences exist between the previously certificated system and 

installation, and the system and installation to be certificated; and 

(b) The previously certificated system and installation have no unresolved icing 

related service history problems. 

(3) FAA Order 8110.4C should be consulted regarding the use of previously approved 

FAA data. 

(4) If there is uncertainty about the effects of the differences, additional tests or 

analyses, or both, should be conducted as necessary and appropriate to resolve the open issues.

g. Induction Air System Protection. The induction air system for airplanes is 

certificated for ice protection in accordance with § 23.1093. See AC 23-16C for more 

information. 

h. Propeller Ice Protection. 

(1) An analysis should be provided for part 25, Appendix C icing conditions that: 

(a) Substantiates the chordwise and spanwise ice protection coverage 

(b) Substantiates the ice protection system power density or fluid rate 

(c) Calculates intercycle ice accretions and resulting efficiency losses. 

(2) See AC 20-73A for additional guidance on propeller analysis. 

i. Pitot Probe Ice Protection.  Section 23.1323(d)(1) requires the airspeed indicating 

system on aircraft certificated for flight in icing conditions to be designed to protect against SLD 

icing conditions. At a minimum, the pitot probe ice protection must be capable of handling the 

portion of the SLD environment the aircraft is certificated to operate in per section 23.1420(a) – 

detect and exit SLD, partial SLD operations, or unlimited SLD operations. The compliance 

should include any effects of ice accretions upstream of the probes that may disrupt the airflow.

(1) Applicable Icing Conditions. For aircraft approved for flight into icing, the pitot 

probe ice protection must be designed to 14 CFR 25 Appendix C and Appendix O icing 

conditions with exposures in accordance with 23.1420(a)(1), (a)(2) or (a)(3).
AC 23.1419-2E 

19)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(2) TSO Authorizations. Compliance with the technical standard order (TSO) 

qualification standard for electrically heated pitot probes (TSO-C16a) is not sufficient by itself to 

demonstrate compliance with § 23.1323(d)(1). TSO C16a, “Electrically heated pitot and pitotstatic tubes,” references Society of Automotive Engineers (SAE) Aeronautical Standard AS8006 

and supplements the icing requirements with specific part 25, Appendix C icing conditions and 

specific liquid water content tests from British Specification (BS) 2G.135 “Specification for 

Electrically-Heated pitot and Pitot-Static Pressure Heads.” However it does not contain tests for 

Appendix O icing conditions. The applicant is responsible for showing that the pitot heat is 

adequate for the applicable Part 25 Appendices C and O icing conditions, and Part 33 Appendix 

D mixed phase and ice crystal conditions. If this proof of compliance is not obtained in flight 

tests, analysis and/or icing tunnel test data should be submitted. Compliance to the probe water 

catch aspects of Appendix O may be found by similarity to the Appendix C environment due to 

the reduced water contents.

(3) Mixed Phase Icing and Ice Crystals. Section 23.1323(d)(2) specifies mixed phase 

and ice crystal conditions that are required for certain aircraft. Recent cloud characterization 

research has indicated that approximately 40 percent of icing condition events consist of liquid 

water drops and ice crystals (mixed phase icing conditions). Also, glaciated atmospheric 

conditions, which consist solely of ice crystals, are encountered during aircraft operations. The 

operating rules do not prohibit operations in mixed phase and ice crystal icing conditions. Recent 

incident history indicates that flightcrews have experienced temporary loss of or misleading 

airspeed indications that can be attributed to mixed phase icing or ice crystal conditions. The vast 

majority of incidents for which there is data have occurred during operation at high altitude and 

high airspeed. Pitot tubes are mounted such that they typically are high efficiency collectors of 

ice crystals. Encountering high concentrations of ice crystals can lead to blocked pitot probes as 

the energy required to melt the ice crystals can exceed Appendix C and O design requirements. 

Therefore, aircraft certificated for operation at altitudes higher than 29,000 feet MSL and speeds 

above Mach .75 have the additional requirement of protecting against mixed phase icing and 

glaciated ice crystals. These requirements also apply to lesser-performing aircraft where loss of 

or misleading airspeed information causes substantial risk for the flight. The terminology used 

in section 23.1323(d)(2) of “critical function” is defined in AC23.1309-1D as “a function whose 

loss would prevent the continued safe flight and landing of the airplane.” Potential examples of 

this include fly-by-wire aircraft or aircraft with airspeed-dependant control schedules. It is the 

responsibility of the applicant to determine whether the hazard is critical by using the appropriate 

system safety analyses. 

(a) Applicable Icing Conditions. For aircraft that meet the performance or 

system criticality criteria described in 23.1323(d)(2), the pitot probe ice protection should be 

designed to meet the mixed phase and ice crystal conditions defined by Part 33, Appendix D.

(b) British Specification 2G.135, “Specification for Electrically-Heated Pitot 

and Pitot-Static Pressure Heads.” Some pitot tube manufacturers now elect to use the icing 

environment of British Specification (BS) 2G.135 “Specification for Electrically-Heated Pitot 

and Pitot-Static Pressure Heads,” as modified by the maximum rate that the icing tunnel facility 

can produce ice crystal conditions to test probe performance in mixed-phase and ice crystal 

conditions. Icing tunnel testing such as this, with simulated mixed-phase and glaciated icing, is 
AC 23.1419-2E 

20 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

an acceptable way to demonstrate compliance with § 23.1323(d)(2) when combined with 

analysis to reach the extents of the Part 33, Appendix D environment. 

(c) Probability of Mixed Phase or Ice Crystal Conditions. As noted above, 

recent cloud characterization data indicates a high probability of occurrence for mixed phase 

icing conditions. There are no accepted standard data for the probability of mixed phase icing 

conditions, or for the probability of total water content levels within such conditions. However, 

the total water content of such conditions is a distributed probability similar to Appendix C. The 

most probable mixed phase icing conditions are at relatively low total water contents, with the 

highest total water contents being least probable. In addition, the critical high water content ice 

crystal conditions typically are associated with high altitude cumulus activity, which has limited 

standard extents within part 33, Appendix D. For aircraft that rely on batteries for emergency 

power supplies on pitot heater systems, compliance with Appendix C icing conditions should be 

shown over the duration of the emergency. For systems that comply with the Appendix C 

conditions under these conditions, the probability of critical mixed phase and ice crystal icing 

conditions may be considered as remote.

(d) Water Contamination. Evaluation of proper drainage should be evaluated as 

installed on the aircraft. Meteorological conditions that may need to be considered include 

flight through drizzle or rain prior to cold soaking the aircraft. Pitot, AOA and stall warning 

systems should operate after such an encounter. 

(4) Pitot Heat Indication Systems. A system for indicating to the pilot and flight crew 

when the pitot heat is off or not working is required by Section 23.1326. The indication must be 

presented to the flight crew if the pitot heat system is commanded ON and any heating element is 

not operating. Also, the indication is required if pitot heat is switched OFF during takeoff or in 

flight if the potential for icing conditions exist. The indication may be presented using the 

electronic flight instrument system, crew alerting system, or a system with similar functionality 

if the airplane is equipped with such a system.

(a) Ground Operation. Some pitot probe heating systems may generate heat 

levels high enough to require additional system logic or procedures to minimize or turn off the 

pitot heat while on the ground (with little or no airflow) in order to protect equipment or 

structure from thermal damage. Since accurate airspeed information is only required for safe 

flight, there is no safety benefit to indicating the pitot heat system is OFF for ground operations. 

(b) Dark Cockpit Concept. Applicants may employ the “dark cockpit” 

philosophy when displaying system status and indications to the flight crew. When the pitot heat 

system is commanded to the OFF state by the flight crew and the potential for icing conditions 

does not exist, it is not required to indicate that the pitot heat is OFF. Icing conditions cannot 

exist when OAT is above freezing. A +5°C threshold has been accepted to provide a safe margin 

in case a sudden drop in temperature is encountered when flying in IMC. 

j. Angle of Attack and Stall Warning Sensor Protection. Similar to the airspeed indicating 

system, Section 23.1324 requires that each sensor installed for the angle of attack system must 
AC 23.1419-2E 

21)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

have a means to prevent malfunction from icing conditions. This includes any sensor (such as 

lift detector or lift transducer) that is used in the stall warning systems. Section 23.1324 requires 

a heated angle-of-attack system sensor or equivalent means to prevent malfunction due to icing 

conditions. 

(1) Icing Approval. For aircraft approved for flight into icing, the angle of attack and 

stall warning ice protection must be designed to 14 CFR 25 Appendix C and Appendix O icing 

conditions with exposures in accordance with 23.1420(a)(1), (a)(2) or (a)(3) and ice crystals per 

14 CFR 33, Appendix D.

(2) Types of Systems. 

(a) Vane. Conventional, vane-style angle of attack sensors are not likely to be 

susceptible to ice crystals. A qualitative analysis based on the service history on vane angle-ofattack sensors is an acceptable means of compliance. 

(b) Multi-purpose probes. Some angle of attack probes sense dynamic pressure 

differentials (similar to pitot probes) to calculate angle of attack. This type of probe can be a 

high efficiency collector of ice crystals in the same manner as pitot probes. For such probes, 

applicants should address the ice accretion characteristics for ice crystals and protection against 

mixed phase and ice crystal conditions. 

(3) Position Error. Consideration should be given to ice formations on the airframe 

in the vicinity of the sensor mounting location that may affect the sensor's operation. 

(4) TSO Authorizations. Compliance to the TSO qualification standard for stall 

warning instruments (TSO-C54) is not sufficient by itself in demonstrating compliance to the 

installation requirements of § 23.1324. TSO-C54, “Stall Warning Instruments”, requires 

compliance to the performance specifications of SAE Aeronautical Standard AS403A with some 

exceptions and additions. This standard is non-current. The requirements include a test to 

demonstrate deicing and anti-icing capability, but only temperature and airspeed are specified. 

The precipitation test conditions of AS403A include moderate icing conditions for Type II 

instruments. However, "moderate" is not defined. The applicant is responsible for showing that 

stall warning heat is adequate throughout the appropriate icing conditions. If this proof of 

compliance is not obtained in flight tests, analysis and/or icing tunnel test data should be 

submitted. 

(5) Water Contamination. Consideration should be given for the impingement or 

runback of water that may freeze within sensing devices that require the free movement of components as 

part of their sensing functionality. Meteorological conditions that may need to be considered include. 

flight through rain prior to cold soaking the aircraft. Pitot, AOA and stall warning systems should operate 

after such an encounter. 

k. Static Pressure Systems. Each static port design or location should be such that correlation 

between air pressure in the static system and true ambient pressure is not altered when flying in icing 
AC 23.1419-2E 

22 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

conditions. For aircraft certified for flight into known icing, the applicable icing conditions are defined 

by Part 25, Appendix C and the applicable portions of Part 25, Appendix O (in accordance with 

23.1420(a)). Mixed phase icing and ice crystals have not been shown to cause issues with static pressure 

systems and therefore do not need to be addressed. Means of showing compliance include anti-icing 

devices, alternate source for static pressure, or demonstration by test that the static port does not accrete 

ice under any condition. When the port is heated, a thermal evaluation should be conducted to 

demonstrate that the ice protection is adequate. Consideration should be given to ice formations on the 

airframe in the vicinity of the port mounting location that may affect the static pressure measurement.. 

l. Fluid (Freezing Point Depressant) Systems. Freezing point depressant fluid systems 

have been successfully certificated on part 23 airplanes. However, this type of system is not as 

common as other ice protection systems and that prompted the FAA in 1986 to publish 

information on certification of these systems in DOT/FAA/CT-TN86/11. Certification 

highlights from this publication are repeated below. 

(1) Analyses. The two critical analyses required are the fluid flow rate required and an 

evaluation of the operational angles of attack, which will dictate chordwise coverage. 

(2) Fluid Capacity. The fluid capacity does not have to exceed the maximum 

endurance of the airplane but the minimum should be as follows in Table 1. 

TABLE 1. FLUID CAPACITY 

Airplane Type Minimum Fluid Capacity is the greater of: 

Airplanes with maximum operating altitude 

above 30,000 feet 

90 minutes or 15 percent of the maximum 

airplane endurance based on the flow rate 

required in continuous maximum icing 

conditions 

Airplanes with maximum operating altitude 

30,000 feet and below 

150 minutes or 20 percent of the maximum 

airplane endurance based on the flow rate 

required in continuous maximum icing 

conditions 

(3) Fluid Quantity. 

(a) There should be a fluid quantity indicator to allow the crew to determine how 

much longer the fluid will last. The fluid quantity indicator should be evaluated to determine 

that it is plainly visible to the pilot and that the indicator provided can be effectively read. 

(b) If it is desired that the airplane be dispatched with less than full fluid in the 

reservoir, the AFM should contain a chart or table to allow the crew to determine the minimum 

fluid level. The AFM limitations should state a minimum dispatch fluid level that is the higher 

of the following two values: 

1. 90 minutes based on the flow rate required in critical continuous 

maximum icing conditions, correcting for cloud horizontal content. 
AC 23.1419-2E 

23)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

2. 45 minutes based on the flow rate required in critical continuous 

maximum icing conditions, with no correction for cloud horizontal extent.

(4) Fluid Characteristics. 

(a) The freezing point depressant fluids used become a gel at very cold 

temperatures and the temperature extremes to which the airplane will be operated should be 

considered when evaluating the reservoir, pump and plumbing installations. 

(b) Certain fluids used in ice protection systems, such as the alcohol used in older 

propeller systems, are flammable. Components of these systems must meet the flammable fluid 

protection requirements of § 23.863. No components of these systems may be installed in 

passenger or crew compartments without the protection required by § 23.853(d) (prior to 

amendment 23-34) or § 23.853(e) (after amendment 23-34). An accessible shutoff should be 

provided in systems using flammable fluids. 

(c) The effect of fluid ingestion into engines, Auxiliary Power Units (APUs), and 

accessories should be evaluated. The compatibility of the fluid with engine components should 

be examined to verify that adverse reactions such as corrosion or contamination do not occur, or 

are prevented through inspection or other measures 

(d) The effect of fluid compatibility with electrical contacts and with airframe 

components, particularly composite materials, should be evaluated. The applicant should verify 

that adverse reactions such as corrosion or contamination do not occur, or are prevented through 

inspection or other measures (for example, if ethylene glycol is a component fluid, then silver 

and silver-plated electrical switch contacts and terminals should be protected from contamination 

by the ethylene glycol to avoid a fire hazard). 

(e) There should be sufficient AFM and maintenance manual warnings on 

handling fluids. AL5 is 85 percent mono-ethylene glycol, which is considered extremely toxic. 

(f) Another freezing point depressant fluid, TKS80, is available. Icing tunnel 

tests of TKS80 and AL5 fluids have shown that they perform differently. The fluid reservoir 

should be placarded to permit only the fluid(s) that have been tested during certification. 

(g) To avoid confusion, the fluid filler tank cap should be distinguishable from 

other caps such as fuel and a placard stating approved fluid should be located near the filler cap. 

(h) There should be adequate drainage in the areas that hold or can receive 

spillage from leaks. 

(5) Windshield Visibility. The effect of the fluid on windshield visibility should be 

evaluated to show compliance to § 23.775(f) if either the windshield or propellers are protected 

with a freezing point depressant system. On many of the approved installations the windshield 

system is turned off just prior to landing. 
AC 23.1419-2E 

24 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

m. Cockpit Displays 

(1) Stall Warning Schedule. Indication should be provided to the pilot that the icing 

stall warning schedule is active if AFM limitations or procedures (e.g. higher approach airspeed) 

are changed from non-icing. 

(2) Low Airspeed Awareness. If a low airspeed cue is provided, it should be based 

on icing stall speed when the stall warning is on the icing schedule.

n. Windshield Heat Systems 

For certification in the icing conditions specified in Appendix O, the time increment for the 

windshield should be consistent with the approved portions per 23.1420(a)(2) or (a)(3). 

Acceptable methods of compliance include analysis validated by natural icing, tanker or dry air 

testing

11. Flight Test Planning. When operating any airplane in an icing environment, degradation 

in performance and flying qualities may be expected. The primary purposes for flight testing an 

airplane equipped for flight in icing conditions is to evaluate such degradation, determining that 

the flying qualities remain adequate, and that performance levels are acceptable for this flight 

environment. For airplanes with a certification basis of 23-43 or higher, § 23.1419(a) requires 

that an airplane comply with the performance, stability, controllability and maneuverability 

regulations of part 23, Subpart B. Flight testing in measured, natural icing conditions is required 

by § 23.1419(b) unless similarity is used as the method of compliance. In addition, unless 

similarity can be used, § 23.1419(b) requires at least tunnel testing, dry air testing, or airborne 

tanker testing. 

a. Flight tests for a typical part 23 airplane icing certification are generally conducted in 

three stages: 

(1) Initial Dry Air Tests With Ice Protection Equipment Installed And Operating. 

Initial dry air tests are usually the first steps conducted to extend the basic airplane certification 

to evaluate the airplane with the ice protection system installed and operating. The initial dry air 

tests are conducted to verify that the ice protection system does not affect the flying qualities of 

the basic airplane in clear air. Dry air tests are also used to verify proper ice protection system 

operation, collect protected surface temperature data to validate thermal analysis, and evaluate 

the effect of increased electrical and/or bleed demands on the engines and other installed 

systems. 

(2) Dry Air Tests With Predicted Simulated Ice Shapes Installed. Dry air tests with 

predicted, simulated critical ice shapes installed are usually the second step for certification for 

flight in icing. Airplane performance and handling characteristics are evaluated with these 

simulated ice shapes. 
AC 23.1419-2E 

25)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(3) Flight Tests in Icing Conditions. Flight tests in icing conditions, which may 

include artificial icing tests such as flight behind an airborne icing tanker aircraft, are normally 

employed to demonstrate that the ice protection system performs under flight conditions as the 

analysis or ground test indicated. These demonstrations should be made at various points 

(targeting critical points) in the icing envelope of part 25, Appendix C and Appendix O as 

recommended in paragraph 14(f) of this AC to verify the airplane's ability to safely operate 

throughout that icing envelope. 

b. Flight Test Safety. FAA Order 4040.26A “Aircraft Certification Service Flight Safety 

Program” should be consulted for flight test risk assessments and risk mitigations. Many ice 

shape test flights, and stall testing with ice accretions, are considered high risk. Many applicants 

have equipped their ice shape flight test airplane with a stall/spin chute.

12. Flight Tests. The following sections cover the major flight tests and/or analyses normally 

performed to substantiate the flight aspects of an ice protection system: 

a. Initial Dry Air Tests with Ice Protection Equipment Installed. Depending upon the 

detailed design of the ice protection system, some preliminary ground tests of the equipment may 

be warranted to verify the basic function of each item. Quantitative data on such items as 

temperatures of thermal devices, fluid flow rates and flow patterns on liquid devices, or operating 

pressures of pneumatic components may be obtained as necessary to verify the system designs. 

The airplane should be shown to comply with the certification requirements when all ice protection 

system components are installed and functioning. This can normally be accomplished by 

performing tests at those conditions found to be most critical to basic airplane aerodynamics, ice 

protection system design, and powerplant functions. Several commonly used ice protection system 

components are discussed below to illustrate typical flight test practices. Other types of equipment 

should be evaluated as their specific design dictates. 

(1) Pneumatic Leading Edge Boots.

(a) Operation. Boot inflation rate and inflated boot shape are important parameters 

in ice accretion removal. Tests should demonstrate a rapid rise and decrease in operating pressures 

for effective ice removal. This pressure rise time, as well as the maximum operating pressure for 

each boot, should be evaluated throughout the altitude band of part 25, Appendix C—Mean Sea 

Level (MSL) to 22,000 feet above MSL—unless performance constraints or aircraft limitations 

unrelated to the ice protection system in the AFM restrict the airplane to a lesser altitude range.

(b) Minimum Operating Temperature. Boots should be operated in flight at the 

minimum envelope temperature (-22 degrees Fahrenheit (F) of part 25, Appendix C, to 

demonstrate adequate inflation/deflation and throughout the entire flight envelope. Boots should 

be operated near the proposed AFM operating temperature limit, if below -22 degrees F, to 

demonstrate that no damage occurs. The appropriate speed and temperature (if any) limitation on 

activation of boots should be included in the AFM. 
AC 23.1419-2E 

26 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(c) Effect of Inflated Boots. The operation of the boots (inflation) should have no 

hazardous effect on airplane performance and handling qualities. An example of an unacceptable 

hazardous effect is that some boot inflation sequencing schemes result in abnormal pitch attitude 

changes. If there are anomalous pitch changes in any configuration, appropriate information or 

limitation should be in the AFM. This can be shown by inflating the boots at several speeds in the 

flight envelope from stall speed to (VNE + VD)/2 or (VMO + VD)/2 and observing the reaction of the 

airplane. This test can be hazardous and should be approached in a build-up manner by inflating 

the boots at incremental airspeeds starting from the middle of the flight envelope. 

(d) Water Contamination. Consideration should be given to the potential for 

accumulation of liquid water inside the pneumatic deicing boots, which could freeze within the 

system and prevent proper operation. The pneumatic and boot arrangement should be examined 

for low points, which may collect water, and consideration should be given to the installation of 

water drainage points. Periodic inspection and drainage procedure instructions should be 

provided in the appropriate manual. Similarly, placement of the pressure sensor(s) should be 

evaluated to prevent misleading boot inflation indications. An evaluation of the effectiveness of 

water/air separators and/or drainage holes should be accomplished by flying through 

precipitation followed by a verification of proper boot inflation at freezing altitudes.

(2) Electric Propeller Boots.

(a) Dry Air Function Flight Test. 

1. System Function. When flying in dry air, the systems should be 

monitored to confirm proper function. It is suggested that system current, brush block voltage 

(between each input brush and the ground brush), and system duty-cycles be monitored to assure 

that proper power is applied to the deicers. 

2. Temperature Measurements. If not furnished by the manufacturer, 

surface temperature measurements may be made during dry air tests. These surface temperature 

measurements are useful for correlating analytically predicted dry air temperatures with 

measured temperatures or as a general indicator that the system is functioning and that each 

deicer is heating. 

3. Vibration. The system operation should be checked throughout the full 

certificated Revolutions Per Minute (RPM) and propeller cyclic pitch range expected during 

icing flights. Any significant vibrations should be investigated. 

(b) Maximum Temperature. Consideration should be given to the maximum 

temperatures that a composite propeller blade may be subjected to when the deicers are 

energized. It may be useful to monitor deicer bond-side temperatures. When performing this 

evaluation, the most critical conditions should be investigated. For example, this may occur on 

the ground (propellers non-rotating) on a hot day with the system inadvertently energized. 
AC 23.1419-2E 

27)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

Service difficulty reports have indicated propeller damage during de-ice/anti-ice system 

activation during maintenance without the engines running. 

(c) Precipitation. The system should be monitored to confirm proper function in 

precipitation. There have been designs that allowed water to reach the electrical brush blocks 

and prevent their operation. 

(3) Electric Windshield Anti-Ice. 

(a) Thermal Analysis Validation. Dry air flight tests should be conducted in 

support of the systems design, as required. Inner and outer windshield surface temperature 

evaluations of the protected area may be needed to support thermal analyses. Thermal analysis 

should substantiate that the surface temperature is sufficient to maintain anti-icing capability 

without causing structural damage to the windshield. In the case of add-on plates, temperatures 

of the basic airplane windshield, inside and out, may also be needed, particularly with 

pressurized airplanes. 

(b) Cockpit Visibility. An evaluation of the visibility, including distortion 

effects through the protected area at maximum heat, should be made in both day and night 

operations to show compliance to § 23.775(f).

(c) Size of Protected Area. The size and location of the protected area should be 

reviewed for adequate visibility, especially for a circling approach and landing conditions. 

Crosswinds and runway light visibility during instrument landings need to be considered. 

(4) Air Data. See paragraph 10.i., 10.j.and 10.k of this AC. 

(5) Fluid (Freezing Point Depressant) Systems. 

(a) Fluid Coverage. Dry air testing should include evaluation of fluid flow paths 

to determine that adequate and uniform fluid distribution over the protected surfaces is achieved. 

Colored fluid or colored water with camera documentation may be used. A range of angles of 

attack should be evaluated with both high and low volume rates. Inlets or openings where fluid 

ingestion will have a detrimental effect should be evaluated. 

(b) Aircraft Performance. Dry air testing should also include performance 

testing with the system operating since drag increases have been documented on previous 

certification programs. 

(c) Temperature. The system should be functionally tested at the minimum part 

25, Appendix C ambient temperatures. 

(d) Windshield. The fluid anti-ice/deice systems may be used to protect 

propellers and windshields, as well as leading edges of airfoils. The fluid for windshield fluid 
AC 23.1419-2E 

28 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

systems, and for propeller fluid systems forward of the windshield, should be tested to 

demonstrate that it does not become opaque at low temperature.

(e) Cockpit Annunciations. Means of indicating fluid flow rates, quantity 

remaining, and so forth, should be evaluated to determine that the indicators are plainly visible to 

the pilot and that the indications provided can be effectively read. 

(8) Compressor Bleed Air Systems. The effect of any bleed air extraction on engine 

and airplane performance should be examined and shown in the AFM performance data. The 

surface heat distribution analysis should be verified for varying flight conditions including climb, 

cruise, hold, and descent. A temperature evaluation may be necessary to verify the thermal 

analyses. If a minimum engine speed is required for ice protection system operation, the ability 

to perform normal and emergency descents should be evaluated. If compressor bleed air is used 

for anti-icing an engine cowl that is made of composite material, a thermal analysis/survey 

should be conducted to assure there is no engine cowl delamination or other structural failure. 

(5) Ice Inspection Light(s). The installation should be evaluated for both in and out of 

clouds during night flights to determine that adequate illumination exists in the required areas 

(activation of ice protection systems and/or identification of severe icing cues), and that 

excessive glare, reflections or other distractions to the flight crew do not exist. The evaluation 

should consider flight both in and out of cloud, but may be accomplished without flight into 

actual icing conditions. The Airplane Flight Manual or other approved manual material must 

describe the means and location for determining ice formations. 

b. Dry Air Tests with Simulated Ice Shapes.

(1) Why Do Simulated Ice Shape Flight Testing? The installation of simulated ice 

shapes allows airplane performance and handling characteristics to be evaluated in stable dry air 

conditions with the critical ice shape being held constant (no change of ice accretion due to 

erosion, shedding, and so forth, that can occur with natural ice shapes). Dry air flight tests with 

simulated ice shapes installed also result in a considerable reduction in the amount of flight 

testing that would otherwise be required to accumulate the test ice shapes, and then evaluate their 

effects on airplane performance and handling characteristics in stable air. 

(2) Flight Test Safety. Dry air tests with simulated ice shapes can be hazardous if not 

approached safely; therefore, the dry air flight test evaluation should be performed using a buildup technique, considering increases in spanwise coverage of simulated ice shapes prior to full 

span ice shape tests. 

(3) Simulated Ice Shapes. 

(a) Critical Ice Accretions. Consideration should be given to the type of ice 

protection systems (for example: mechanical, fluid, thermal, or hybrid), and the most adverse ice 

conditions (shape or shapes, texture, location, and thickness) for the relevant aerodynamic 

characteristics for the following, as appropriate: pre-activation ice, intercycle ice, failure 
AC 23.1419-2E 

29)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

conditions, runback ice, and residual ice. Consideration should also be given to unprotected 

areas. See paragraph 13b for more information. These predictive methods should be 

conservative and should address the conditions associated with the icing envelope of part 25, 

Appendix C, that are critical to the airplane's performance and handling qualities in critical 

phases of the airplane's operational envelope, including climb, cruise, descent, holding pattern, 

approach, and landing. Ice shapes critical for performance may not necessarily be critical for 

handling qualities. See AC 20-73A for more information on determining critical ice shapes and 

corroboration of these ice shapes with natural icing flight test ice accretions. See AIAA-2007-

1090, “Residual and Intercycle Ice on Lower Speed Aircraft with Pneumatic Boots” for more 

information on critical ice shapes for pneumatic deicing boots. 

(b) Ice Detection Systems. For aircraft that have an ice detection system, 

consideration must be given to delays in ice detection and annunciation. These delays may 

include slow ice detector response at temperatures near freezing (low freezing fraction as 

discussed in AC 20-73A) and the number of probe heat cycles utilized for annunciation or 

automatic ice protection activation. An applicant should provide a temperature versus response 

time plot for their installed ice detector and show that, at temperatures for which runback ice 

occurs on critical surfaces that either the response time is less than 60 seconds or runback ice has 

not yet formed during the response time. Runback ice should be evaluated empirically and 

should be evaluated using the same means of compliance as the detector response time data. An 

applicant may then take credit for an advisory ice detection system and use a shorter time to 

determine pre-activation ice. 

(c) Engine and Cooling Inlets. See AC 23-16B. 

(4) Flight Test Objectives. 

(a) Performance. The effect of the ice shapes on stall speeds and airplane climb 

performance should be determined. Stall warning margins and maneuvering capability should 

also be evaluated. Operating speeds, stall warning speeds, and AFM performance information 

should be adjusted, if necessary, to provide acceptable performance capability and stall warning 

margins. The computation of the effects of ice on AFM performance should include reductions 

in engine power or thrust resulting from the applicable operating mode of the ice protection 

system. 

(b) Handling Qualities. Handling characteristics are expected to degrade in 

icing conditions and should be investigated to determine that the “airplane is capable of 

operating safely.” For certification basis at amendment 23-XX and higher, the subpart B 

requirements defined in § 23.21(c)(1) also apply in icing conditions. This is addressed in 

paragraph 13a. The results of these tests may be used in preparing specific AFM operating 

procedures and limitations for flight in icing conditions. 

(c) Air Data Calibrations. If ice accretion is predicted to alter the position error 

of the production air data system (e.g. radome ice accretion), the position error would need to be 
AC 23.1419-2E 

30 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

determined using air data calibration flight tests (i.e. tower fly-by, trailing cone, speed course) 

with the critical, simulated ice shapes determined by analysis. 

c. Flight Tests in Icing Conditions. Flight tests in measured natural icing and the use of 

simulated icing tools such as airborne icing tankers and icing wind tunnels are normally 

employed to demonstrate that the ice protection system performs under flight conditions as the 

analysis or other tests indicate. They are also used to confirm the analyses used in developing 

the various components (for example, ice detectors) and ice shapes and, in the case of natural 

icing tests, to confirm the conclusions reached in flight tests conducted with simulated ice 

shapes. Testing should be accomplished at various points in the icing envelope of part 25, 

Appendix C, to verify the airplane's ability to safely operate throughout that icing envelope. 

(1) Instrumentation. Sufficient instrumentation should be planned to allow 

documentation of important airplane, system and component parameters, and icing conditions 

encountered. Analysis should be accomplished to show that the location of the instrumentation 

will allow measurement of freestream conditions (or appropriate correction factors). See AC 20-

73A for guidance on measuring the icing conditions. The location of all external instrumentation 

installed for icing flight tests, including cameras and visual devices, should be analyzed to verify 

that ice-shedding hazards are not introduced.

(2) Documentation of Ice Accretion. Ice accumulation on unprotected and protected 

areas, and behind protected areas, should be observed and documented. Remotely located 

cameras either on the test airplane or on a chase airplane have been used to document ice 

accumulations on areas that cannot be seen from the test airplane's flight deck or cabin. Visual 

devices such as rods and/or paint stripes may be used to aid in visual dimensional analysis of ice 

accretions. Care should be taken since some measuring devices may accrete ice and alter 

analysis of accretions on a surface of importance. Surfaces may be painted a dark color since 

rime and mixed ice accretions may be difficult to see on white surfaces. The edges of paint 

stripes can be efficient ice collectors if not smoothed and must be accounted for. 

(3) Is Instrumentation Always Needed? The need for icing instrumentation on 

specific tests may be considered with respect to the type of testing and similarity to prior 

measured natural icing exposures. In some cases, external icing instrumentation packages may 

have an effect on the aircraft handling characteristics, or the ice thickness maybe the significant 

variable. Comparison of ice thickness and general correlations to prior measured icing 

conditions may be sufficient for some types of testing. 

(2) Artificial Icing. 

(a) Why Do Artificial Icing Tests? Testing in artificial icing environments such 

as icing tunnels or behind airborne icing tankers represents one way to predict the ice protection 

capabilities of individual elements of the ice protection equipment. The high liquid water 

content and large drop size conditions of Appendix C are easily simulated and not frequently 

encountered in natural icing flight tests. Due to the usually small dimensions of the artificial 
AC 23.1419-2E 

31)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

icing environment, testing is usually limited to sections of lifting surfaces, to components having 

small exposed surfaces such as heated pitot tubes, antennas, air inlets including engine induction 

air inlets, empennage, and other surfaces having small leading edge radii and windshields. 

(b) Airborne Icing Tankers. An artificial icing exposure may be obtained by the 

use of onboard spray nozzles forward of the component under examination or by flying the test 

airplane in the cloud generated by an airborne icing tanker. Recommended procedures for 

airborne icing tanker testing, including instrumentation requirements, are in SAE ARP 5904, 

“Airborne Icing Tankers.” 

(c) Icing Tunnels. Icing tunnel tests have been accepted for definition of preactivation, intercycle, residual, and runback ice on protected surfaces with the following 

considerations: 

1. Scaling. A full-scale test article is preferable due to uncertainties in ice 

accretion scaling. Refer to AC 20-73A for more information on scaling test parameters. 

2. Conformity. The test article must be conformed. Although parts of the 

ice protection system may be simulated, critical system parameters must be conformed. An 

example would be deicing boot steady state pressure, and pressure rise time and decay time. 

3. Tolerances. Ice protection system tolerances on the production airplane, 

such as boot operating pressure, must be accounted for. 

4. Operational Consideration. Proposed ice protection system operation 

(activation procedures, ice detection system delay, and deicing boot cycle times) must be 

accounted for in the test matrix. 

5. Spray Times. If the facility cannot produce the required LWC, spray 

times can be adjusted to provide the equivalent water catch for part 25, Appendix C cloud lengths. 

If large ice shapes or runback ice is expected, test ambient temperature may have to be adjusted to 

provide an equivalent freezing fraction. Temperatures can change the ice adhesion/shed 

characteristics and this should be taken into account when adjusting test parameters. The test 

matrix should include sufficient time in continuous maximum conditions to evaluate the stability 

and cyclic nature of intercycle and residual ice. Certain unique design features, such as stall strips 

mounted on deicing boots, may not readily shed ice and spray times up to 45 minutes need to be 

evaluated. 

6. Test Section. An outboard wing section is usually tested since it is 

typically more critical for aerodynamic degradations due to the reduced scale relative to the wing 

root (on wings incorporating significant taper ratios). It will also have higher water collection 

efficiency and may operate at a lower angle of attack, thereby promoting greater aft impingement 

of droplets on the suction surface. For thermal systems, the outboard sections also represent the 

extremities of the bleed air system where temperature and pressure losses are the greatest, which 
AC 23.1419-2E 

32 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

can be critical for runback accretions. The distribution of icing cloud parameters along the test 

span should be taken into account. 

(3) Natural Icing. 

(a) Why Do Flight Tests In Natural Icing Conditions? Section 23.1419(b) 

requires flight test in measured natural icing conditions. Flight tests in natural icing conditions 

are necessary to demonstrate the acceptability of the airplane and ice protection system for flight 

in icing conditions. AC 20-73A provides additional information that would be useful when 

establishing a natural icing flight test program. 

(b) What Icing Conditions Should Be Tested? 

1. Continuous Maximum Icing Conditions. At least one exposure to 

icing conditions within the part 25, Appendix C, continuous maximum envelope should be 

obtained. The exposure should be sufficiently stabilized to obtain valid data. It is often difficult 

to obtain temperature stabilization in brief exposures. Additional exposures may be required to 

allow extrapolation to the envelope critical conditions by analysis. Test data obtained during 

these exposures may be used to validate the analytical methods used and the results of any 

preceding simulated icing tests.

2. Intermittent Maximum Icing Conditions. Past experience has shown 

that flight testing in natural intermittent maximum icing conditions may be hazardous due to 

accompanying severe turbulence and possible hail encounters that may extensively damage the 

test airplane. When design analyses show that the critical ice protection design points (that is, 

heat loads, critical shapes, accumulation, and accumulation rates, and so forth) are adequate 

under these conditions, and sufficient ground or flight test data exists to verify the analysis, then 

hazardous flight testing should be avoided. 

3. Part 25, Appendix O Icing Conditions – See paragraph 14.f. of this 

AC regarding the necessity to flight test in Appendix O conditions. 

4. Number of Icing Encounters. There should be sufficient icing 

encounters to achieve all test plan objectives. The natural icing performance and handling 

qualities matrix in Table 3 of this AC consists of at least three encounters which may occur on 

one or multiple flights. 

(c) How Much Ice Should Be Allowed to Accrete? 

1. Normal Ice Protection System Operation. Sufficient data should be 

taken to allow correlation with dry air tests using simulated ice shapes. Handling qualities and 

performance should be subjectively reviewed and determined to be in general correlation with 

those found in dry air testing. Refer to Table 3. for performance, stability, control and 

maneuverability requirements. 
AC 23.1419-2E 

33)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(aa) Holding. A target accretion thickness equivalent to the 45-

minute duration encounter in Appendix C Continuous Maximum on an unprotected part of the 

wing. 

(bb) Landing. A target accretion thickness equivalent to a 5-minute 

duration encounter in Appendix C Continuous Maximum on an unprotected part of the wing. 

2. Pre-activation Ice. Dependent on activation of ice protection as defined 

in Table 2. 

3. Two Minute Delayed Ice Protection System Activation. For engine 

ice protection systems, which for aft fuselage mounted engines can include the inboard wing ice 

protection system, a delay of two minutes in the continuous maximum icing conditions of 

appendix C to part 25 is utilized to validate the ice shedding analyses and § 33.77 ice slab test 

results. To minimize flight testing, an applicant has the option of conducting this evaluation 

after the tests in Table 3 are conducted, provided the tested ice accretion is conservative for both 

tests. 

(c) What Should Be Evaluated During Natural Icing Tests? All systems and 

components of the basic airplane should continue to function as intended when operating in an 

icing environment. AC 20-73A, Appendix P provides a checklist that may be used in drafting a 

natural icing test plan. Some additional considerations are: 

1. Engine operation and equipment operation Natural icing flight tests 

should include evaluation of ice protection systems with bleed air from engines when the throttle 

is at the flight idle stop. Refer to AC 20-147 for additional guidance for turbojet engines.

2. Fuel system venting should not be affected by ice accumulation. 

3. Ice shedding. See paragraph 16 of this AC. 

4. Stall Warning and Maneuver Margin. The stall warning margin 

should be evaluated with various ice accretions as summarized in Table 3. See paragraph 13.c. of 

this AC and the guidance for § 23.207 in Appendix 6. 

NOTE 1: For safety, this test and any stall or handling qualities tests should be 

accomplished in daytime visual meteorological conditions, after accreting ice. 

5. Performance, Stability, Controllability. See paragraph 13.c.

6. Ice detection cues or ice detection system operation. See paragraph 

15 of this AC. 
AC 23.1419-2E 

34 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

7. Ice inspection lights should be evaluated in natural icing and night 

conditions to verify that they illuminate ice build-up areas, are adequate under the conditions 

encountered, and do not introduce objectionable glare. Evaluate the cabin defogging system's 

capability to clear side windows for observation of boot ice protection system operation and ice 

accumulation. If a defogging system is not provided, the windows should be easily cleared by 

the pilot without adversely increasing pilot workload. 

8. Flight Control Systems. Primary and secondary flight control surfaces 

should remain operational after exposure to icing conditions. Evaluations should confirm that 

aerodynamic balance surfaces are not subject to icing throughout the airplane's operating envelope 

(weight, Center Of Gravity (CG), and speed), or that any ice accumulation on these surfaces does 

not interfere with or limit actuation of the control for these surfaces including retraction of flaps, 

slats and/or landing gear for a safe go around from the landing configuration. 

9. Autopilot. See paragraph 17 of this AC. 

10. Vibration and Buffet. Should be evaluated, including propeller 

vibration. 

11. Pilot Workload. The workload in icing conditions should be evaluated 

when showing compliance to § 23.1523. Ice detection, ice protection system operation and 

monitoring, and autopilot operation and monitoring (including periodic disconnects), as a 

minimum should be evaluated. 

12. AFM. AFM limitations and procedures should be evaluated. 

13. Performance and Handling Qualities in Appendix C Icing Conditions. Airplane 

performance and handling qualities are degraded by ice accumulations in various ways depending 

upon type, shape, size, and location of these accumulations.

a. Flight Tests 

(1) Section 23.1419 at Amendment 23-XX or Later. Airplane performance, 

controllability, maneuverability, and stability may be degraded from the non-iced airplane but 

must not be less than certain requirements in part 23, subpart B, as defined in § 23.21(c)(1). 

Guidance for each applicable subpart B regulation, as related to icing, is in Appendix 6 of this 

AC. Unless noted otherwise, the guidance is applicable to all airplane categories for which 

compliance to § 23.1419 is being shown. 

(a) Configurations and Flight Conditions. The handling qualities test matrix for 

ice shapes can be reduced from the basic (no ice) matrix, with concurrence from the administrator, 

to configurations and flight conditions that were deemed critical based on the no ice testing (basic 

aircraft certification). However, as a minimum, stability and controllability should be evaluated at 

minimum holding speed in holding configuration and VREF in all approved approach and landing 
AC 23.1419-2E 

35)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

configurations. It is not required to test at high airspeeds. Instead, the maximum airspeed defined 

in the guidance for 23.251 may be used. It is not required to test flight conditions at altitudes 

above the part 25, Appendix C icing envelopes. 

(2) Section 23.1419 prior to Amendment 23-XX. See prior revisions of AC 

23.1419-2E. 

b. Ice Accretions. 

(1) Airframe Ice Accretions. 

(a) Definition of Ice Accretions. The most critical ice accretions in terms of 

handling characteristics and/or performance for each flight phase should be determined. The 

parameters to be considered are the flight conditions (e.g., airplane configuration, airspeed, angle 

of attack. altitude) and the icing conditions of part 25, Appendix C (temperature, liquid water 

content, mean effective drop diameter). Table 2 summarize the ice accretions defined in part 23, 

Appendix TBD, part I. . 
AC 23.1419-2E 

36 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

TABLE 2. ICE ACCRETION DEFINITIONS, part I of APPENDIX TBD OF PART 23 

Ice 

Accretion 

Normal, Utility and Acrobatic 

Categories or Turbojet Airplane with a 

takeoff configuration that includes 

leading edge high lift devices 

Commuter Category or Turbojet 

Airplanes with a takeoff configuration 

that does not include leading edge high 

lift devices 

Takeoff Not required. Ice accretion occurring between liftoff 

and 400 feet above the takeoff surface, 

assuming accretion starts at liftoff in the 

“takeoff maximum icing’ conditions, on: 

 unprotected surfaces; and 

 the protected surfaces 

 appropriate to normal IPS 

 operation; or 

 the protected surfaces if IPS 

 operation is prohibited for takeoff. 

 (It should be assumed no flight 

 crew action to activate the ice 

 protection will occur until at least 

 400 feet above the ground level, 

 or higher if specified in the 

 AFM.) 

“Takeoff maximum icing” conditions 

defined as: 

 cloud liquid water content of 

 0.35 g/m3

; 

 cloud droplets Mean Effective 

 Diameter (MED) of 20 microns; 

 and ambient air temperature at 

 ground level of minus 

 nine degrees Centigrade (C) 

This ice accretion may be simulated by 

100 grit sandpaper on the leading edge, 

unless another roughness is 

substantiated. 
AC 23.1419-2E 

37)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

TABLE 2. ICE ACCRETION DEFINITIONS, part I of APPENDIX TBD OF PART 23 

Ice 

Accretion 

Normal, Utility and Acrobatic 

Categories or Turbojet Airplane with a 

takeoff configuration that includes 

leading edge high lift devices 

Commuter Category or Turbojet 

Airplanes with a takeoff configuration 

that does not include leading edge high 

lift devices 

Final 

Takeoff 

Not applicable. Same as “takeoff” ice except ice 

accretion occurs between liftoff and 

1,500 feet above the takeoff surface. 

Enroute Ice accretion on the unprotected surfaces, and any ice accretion on the protected 

surfaces appropriate to normal ice protection system operation, during the en route 

phase, in part 25, Appendix C, continuous or intermittent maximum icing 

conditions. 

Holding Ice accretion on the unprotected surfaces, and any ice accretion on the protected 

surfaces appropriate to normal ice protection system operation, during a 45-minute 

hold in part 25, Appendix C, continuous maximum icing conditions. 

Approach 

And 

Landing 

Ice accretion on unprotected surfaces same as “Holding” ice, and ice accreted on 

protected surfaces appropriate to normal system operation during an approach and 

landing. Upper surface impingement due to reduced angle of attack with flap 

extension, ice on flap leading edge, and ice on leading devices when extended 

need to be addressed. Runback ice has been observed to develop on leading edge 

slats on some designs when extended, but not when retracted. Duration of 

approach and landing phase is 5 minutes at the critical Appendix C Continuous 

Maximum Icing Conditions. 

PreActivation The ice accretion prior to normal system operation is the ice accretion formed on 

the unprotected and normally protected surfaces prior to activation and effective 

operation of any ice protection system in continuous maximum atmospheric icing 

conditions. Pre-activation ice is a function of ice detection procedures, ice 

detector system design and performance, and operating procedures, as shown in 

below: 

IPS Activation Part 23 Pre-activation Ice Accretion 

(The left and right columns provide two 

approaches that may be used. The right column 

provides typical values that may be used in lieu of 

system specific data)

Visual of First Indication of 

Accretion on Reference Surface 

Time to detect (1)

+30 seconds (2) 

+IPS response time 

2 minutes (2)

Potential Icing Conditions 

(OAT and Visible Moisture) 

+30 seconds (2)

+IPS response time 

30 seconds(5)
AC 23.1419-2E 

38 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

TABLE 2. ICE ACCRETION DEFINITIONS, part I of APPENDIX TBD OF PART 23 

Primary IDS and Manual IPS 

Activation 

IDS response time(3)

+10 seconds 

+IPS response time 

30 seconds(3)(5)

Primary IDS and Automatic IPS 

Activation 

IDS response time(3)

+IPS response time 

20 seconds(3)(5)

Advisory IDS(3) IDS response time (4)

+10 seconds (2) 

+IPS response time 

60 seconds(4)(5)

Notes: 

(1) Total time not to exceed 2 minutes 

(2) Easily recognizable by the flight crew in all foreseeable conditions (e.g., at night in clouds) 

(3) Applicant should show that the response time of the ice detector at freezing fractions of one is 

less than stated time. 

(4) In low freezing fractions conditions, applicant should show that detector will annunciate prior 

to ice accretion on critical surfaces. This may be accomplished by comparing icing tunnel 

tests to response times provided by the detector manufacturer. 

(5) Add delay time due to any IPS activation logic

Intercycle See Appendix 1 of this AC for definition. For airspeeds below 160 KCAS, 

empirical data should substantiate that deicing systems shed ice at each cycle. 

Residual See Appendix 1 of this AC for definition. 

Runback See Appendix 1 of this AC for definition. This ice type is frequently a byproduct 

of partially evaporative (running wet) ice protection systems and thermal deicing 

systems, but can also occur on mechanical ice protection systems at a small 

temperature band near freezing. Empirical data should be obtained on thermal 

systems due to current lack of capability of analysis codes to calculate shape and 

location of runback ice. Empirical data should be obtained on mechanical IPS 

airfoils at the following conditions, as a minimum, at the LWC values within part 

25, Appendix C: 

Ice 

Accretion 

Normal, Utility and Acrobatic 

Categories or Turbojet Airplane with a 

takeoff configuration that includes 

leading edge high lift devices 

Commuter Category or Turbojet 

Airplanes with a takeoff configuration 

that does not include leading edge high 

lift devices 

Runback 

(Cont.) 

 a. total air temperatures of 24 degrees to 35.5 degrees F; 

 b. time required to transit a continuous maximum cloud of up to 55 nm, 

correcting liquid water content for horizontal extent. 

Thin, rough A thin layer of ice that may occur on or aft of protected surfaces of operating 

mechanical deicing systems, such as pneumatic deicing boots. Should be 

simulated with 16-20 grit sandpaper and chordwise extent should consider any 

impingement aft of protected areas with substantiated roughness. The extents 

should consider the largest MVDs and drop distributions effects. 
AC 23.1419-2E 

39)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

TABLE 2. ICE ACCRETION DEFINITIONS, part I of APPENDIX TBD OF PART 23 

Critical The ice accretion, applicable to the phase of flight that has the most adverse effect 

on performance and flying qualities. For protected surfaces, pre-activation and 

normal IPS operation (intercycle ice, residual ice, thin, rough ice, and runback ice, 

if applicable), should be accounted for. In order to reduce the number of ice 

accretions to be considered when demonstrating compliance: 

 (1) The more critical of takeoff ice and final takeoff ice may be used throughout 

the takeoff phase. 

Holding ice may be used for the en route, holding, approach, landing, and goaround flight phases if it can be substantiated to be more critical than the ice 

accretions in those phases. 

Holding ice may also be used for the takeoff phase provided it can be 

substantiated to be more critical than takeoff ice and final takeoff ice.

 (4) The ice accretion that has the most adverse effect on handling characteristics 

may be used for climb performance tests provided any difference in climb 

performance is conservatively taken into account.

 (5) In some instances the shapes determined in the various flight phases and flight 

conditions may be “enveloped” into one critical shape. 
AC 23.1419-2E 

40 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(b) Shape and Texture of Simulated Ice. The shape and texture of the 

simulated ice should be developed, and substantiated by agreed methods. The ice shapes should 

be agreed to by the FAA prior to ice shape flight testing. 

1. Common practices for developing ice shapes include: 

(aa) Use of validated computer codes; 

(bb) Flight in measured natural icing conditions; 

(cc) Icing wind tunnel tests; and 

(dd) Flight in a controlled artificial icing cloud (e.g. airborne icing 

tanker). 

2. Natural icing or airborne tanker testing may show ice shapes or accretion 

locations more critical than those simulated. Ice shape testing of critical test points would then 

need to be re-flown with these more critical shapes. 

(c) Ice Adhesion Inhibitors. For the determination or validation of pre-activation 

and normal IPS ice accretions on deicing boots, the application of any ice adhesion inhibitor such 

as ICEX is not permitted for natural icing flight tests, artificial icing flight tests or icing tunnel 

tests. This is because the use of ICEX cannot be controlled in operations and the effectiveness in 

operations degrades over time. Other products that enhance appearance or life should also not be 

applied. Deicing boots can be cleaned at the start of a natural icing or artificial icing test program 

per recommended maintenance procedures. 

(2) Propeller Icing. Deicing boot manufacturer’s analyses show that intercycle ice 

does exist with propeller deicing systems and their analyses do not account for ice runback. 

Propeller icing research (Paragraph 6.b., Reference 7) shows that propeller icing efficiency in 

icing conditions varies greatly with icing conditions and deicing system design. The research 

results support the assumption of a nominal thrust penalty shown in Figure 1.

 

(a) Airplane performance in icing conditions should include the propeller 

efficiency losses caused by propeller intercycle ice. This may be accomplished 

by analysis. 

(b) Propeller efficiency loss should be the value in Figure 1 to account for 

propeller runback ice and intercycle ice, unless data substantiates another 

amount. The applicant can assume there is zero efficiency loss at an airplane 

total temperature of 0 °C, and interpolate between this temperature and the -

5°C static temperatures in Figure 1.
AC 23.1419-2E 

41)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(c) Airplane performance during natural icing flight testing should be 

quantitatively compared with performance during ice shape flight tests. On 

reciprocating and turboprop powered airplanes, if there is degradation in 

performance compared to the ice shape results, propeller efficiency losses due 

to propeller ice accretions should be investigated. 

Appendix C Propeller Efficiency Loss

0.0%

5.0%

10.0%

15.0%

0.6 0.7 0.8 0.9 1

Helical Tip Mach Number

Propeller Thrust Loss, %

-5 C OAT

-10 C OAT

-15 C OAT and colder

Figure 1 – Appendix C Propeller Thrust Loss

(3) Failure Ice Accretions. Flight tests with failure ice shapes representing failures 

not shown to be extremely improbable should be conducted to validate hazard classifications and 

to develop procedures for safe operation following a failure. For example, this testing may show 

that landing flap settings may have to be reduced following failure of the empennage ice 

protection system. 

(a) Failure ice accretion is defined as: 

1. “Holding” ice as defined in Table 2 for unprotected surfaces; and 

2. For protected surfaces, one-half the accretion specified for unprotected 

surfaces (22.5 minutes) if the associated AFM operating procedure requires the airplane to leave 

the icing conditions as soon as possible, unless another value is agreed to by the responsible 

aircraft certification office. 
AC 23.1419-2E 

42 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

3. For failure conditions that are: (a) not annunciated to the flight crew, or 

(b) annunciated to the flight crew, but the associated AFM procedure does not require exiting the 

icing conditions, the guidance in this AC for a normal (i.e., non-failure) condition is applicable 

with the failure ice accretion 

(b) If the failure is annunciated, and the AFM procedure requires exiting icing 

conditions, the applicant may propose an ice accretion based on a realistic exit scenario in lieu of 

the 22.5 minutes ice accretion. This failure scenario should account for the time it takes: 

1. For the system to annunciate the failure (e.g., one deicing boot cycle); 

2. For the pilot to decide on a course of action and notify Air Traffic 

Control (ATC) (e.g., two minutes); and 

3. To exit the icing conditions. 

(c) The time to exit should include a 180-degree standard rate turn and transiting 

a 17.4-nautical mile, part 25, Appendix C continuous maximum cloud. Besides the design 

standard 17.4 nautical mile horizontal cloud extent, a cloud extent of 46-nautical miles (adjusted 

for liquid water content per part 25, Appendix C), which is expected for 10 percent of icing 

encounters, should also be considered in the safety analysis. The exit scenario shall include the 

possibility that the airplane may have to climb 4,000 feet out of icing if it results in a longer time 

than traversing the part 25, Appendix C cloud. 

c. Natural Icing Flight Tests. Whether the performance and handling qualities flight 

testing has been performed with simulated ice shapes or in natural icing conditions, additional 

limited flight testing described in this section should be conducted in natural icing conditions. 

Where flight testing with simulated ice shapes is the primary means for showing compliance, the 

objective of the tests described in this section is to corroborate the handling characteristics and 

performance results obtained in flight testing with simulated ice shapes. It is acceptable for some 

ice to be shed during the testing due to air loads or wing flexure, etc., or during transit to a higher 

altitude or test area for safety reasons. However, an attempt should be made to accomplish the 

test maneuvers as soon as possible after exiting the icing cloud to minimize the atmospheric 

influences on ice shedding. During any of the maneuvers specified in Table 3, the performance 

and behavior of the airplane should be consistent with that obtained with simulated ice shapes. 

There should be no unusual control responses or uncommanded airplane motions. Additionally, 

during the level turns and bank-to-bank rolls, there should be no buffeting or stall warning. 
AC 23.1419-2E 

43)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

TABLE 3. NATURAL ICING PERFORMANCE 

AND HANDLING QUALITIES TESTS 

Configuration 

Ice 

Accretion 

Trim 

Speed Maneuver 

Flaps up, 

gear up 

Equivalent to 

45-minute 

hold at 

critical 

conditions, 

normal IPS 

operation. 

Minimum 

Holding 

• Level, 40-degree banked turns; 

• Bank-to-bank rapid rolls, 30 degrees – 

30 degrees; 

• Climb or level performance evaluation; 

• Autopilot tests 

• Straight stall (1 knot/sec. deceleration 

rate, wings level, power off) 

Landing flaps, 

gear down 

Equivalent to 

a 5-minute 

approach at 

critical 

conditions, 

normal IPS 

operation 

VREF

• Level, 40-degree banked turns; 

• Bank-to-bank rapid rolls, 30 degrees – 

30 degrees; 

• Climb or level performance evaluation; 

• Straight stall (1 knot/sec. deceleration 

rate, wings level, power off). 

Flaps up, 

gear up 

Defined preactivation ice, 

IPS off 

Note: Optional. In 

lieu of natural ice 

accretion condition 

testing may be 

accomplished with 

simulated ice shapes

Optional 

• Bank-to-bank rapid rolls, 30 degrees – 

30 degrees at 1.2 VS1; 

• Pull-up to 1.5g / pushover to 0.5g 

• Decelerate to stall warning plus one 

second (1 knot/sec. deceleration rate, 

wings level, power off) Recover using 

the AFM recommended stall recovery 

technique. 

The following test only applies to airplanes in which IPS activation is based on visual cues 

and which pre-activation ice (and subsequent stall warning bias) is considered the critical 

ice accretion for normal IPS system operation, as defined in Table 2. 

Flaps up, 

gear up 

Defined preactivation ice, 

normal IPS 

operation 

Optional 

• Bank-to-bank rapid rolls, 30 degrees – 

30 degrees at 1.2 VS1; 

• Straight stall (1 knot/sec. deceleration 

rate, wings level, power off). 

d. Control System and Stall Protection System Tolerances. The same airplane and 

system production tolerances used in the non-icing tests should be used when evaluating 

performance and handling qualities with ice accretions. Ice protection system production 

tolerances should be addressed during flight testing in natural icing conditions. Examples are 
AC 23.1419-2E 

44 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

provided in Table 4. Stall speed and warning system tolerance are critical when establishing 

tolerances for production acceptance flights. 

TABLE 4. FLIGHT TEST TOLERANCES 

Test Tolerances 

Stall speed 

• Elevator to minimum trailing edge up if stall defined by aft 

control stop 

• Stick pusher, if equipped, set for minimum angle of attack 

• Flap travels should be set to minimum allowable settings 

Stall warning • Set for maximum angle of attack (minimum margin). 

Stall characteristics • Elevator to maximum trailing edge up. 

• Stick pusher, if equipped, set for maximum angle of attack 

Maneuver margin • Stall warning set for minimum angle of attack. 

Natural icing flight tests • Pneumatic boots set for minimum pressure 

• Electrothermal systems set at minimum current 

e. ICTS. To remove the risk of contaminated tailplane stall from the operating envelope of 

the airplane, the applicant should demonstrate by tests or a combination of analyses and tests, 

that the airplane is safely controllable and maneuverable during all phases of flight. 

(1) Background. See AC 20-73A and prior revisions of AC 23.1419-2E. 

(2) Evaluation of Susceptibility to ICTS by Flight Test 

(a) Longitudinal control and susceptibility to ICTS should be evaluated during the 

following flight tests with critical ice shapes installed: 

1. Flap extensions 

2. Recovery from stalls 

3. Level flight accelerations 

4. Longitudinal control tests required by 14 CFR 23.145. 

(b) Susceptibility to ICTS should also be evaluated by conducting the zero-g 

pushover maneuver and steady heading sideslip. 

1. Configuration. 

(aa) All combinations of wing flaps and landing gear should be tested 

beginning with zero flaps up to the maximum flap setting to be approved for landing following 
AC 23.1419-2E 

45)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

an icing encounter. Since increased flap extension will increase the potential for ICTS, flight 

testing should proceed cautiously as the flaps are further extended. 

(bb) Critical weight and CG position (normally full forward at light 

weight). 

(cc) Speeds from 1.2 VS1 or Reference Landing Approach Airspeed 

(VREF)-5 knots, as appropriate to the wing flap position, up to the maximum speed to be 

encountered operationally in a given flap or gear configuration that will not result in exceeding 

Flaps Extended Speed (VFE) or Landing Gear Extended Speed (VLE), as applicable, during the 

maneuver. The speeds VS1 and VREF may have to be redefined with critical ice shapes. 

(dd) Power or thrust: flight idle to maximum go-around. 

2. Ice Shapes: The applicant specifies the critical ice case(s) for 

investigation in terms of location, shape, thickness, and texture, and obtains FAA concurrence 

for the ice shape(s) to be investigated. 

(aa) The critical shape(s) should contribute to the largest adverse 

hinge moment, lowest stall angle, greatest tail lift loss, and lowest control surface effectiveness. 

(bb) More than one shape may require testing. If a clean wing (no ice 

accretion) can result in increased negative Angle-of-Attack (AOA) on the horizontal tail, ice 

shapes on the wing should be removed. The critical ice accretion case(s) should include an 

allowance for the ice shape accreted during any time delays in activation of the ice protection 

system associated with ice detection or observation systems, intercycle and residual ice, runback 

ice, or the accretion that may be reasonably expected in service. 

(cc) It should be noted that ice accreted with the flaps retracted might 

result in a more critical condition than ice accreted with the flaps extended. Ice accretion shape 

and thickness need not be greater than that resulting from exposure to the icing conditions 

defined in Appendix C to Part 25 or the 45-minute hold condition of this AC, whichever is more 

critical. 

(dd) Ice on the vertical stabilizer should also be considered for the 

sideslip case. 

(ee) ICTS susceptibility should be evaluated with pre-activation ice. 

In many cases the pre-activation ice may be simulated by sandpaper ice. A thin ice layer 

simulated by sandpaper has been found to be critical on some aircraft and should be evaluated 

along with critical ice accretions on airplanes with a reversible longitudinal control system. 

(ff) Failure conditions of the ice protection system should also be 

addressed. Maximum landing flap extension with a failed ice protection system may be defined 

at an intermediate position. This should become an airplane limitation for a failure. 
AC 23.1419-2E 

46 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

3. Zero-g pushover maneuver. This is a maneuver to generate a nose 

down pitch rate so as to increase the angle-of-attack of the air flow over the horizontal stabilizer. 

Before the maneuver, the test pilot determines initial entry speeds and pitch attitudes to achieve 

the target load factor and target airspeed as the airplane pitches through approximately level 

flight. 

(aa) The objective of the pushover maneuver is to push the pitch 

control in the nose-down direction to obtain the test load factor (g level) and be at the test 

airspeed as the nose passes through the horizon. Note any lightening of the pitch control push 

force during the build-up to the test end. Begin the maneuver with the airplane trimmed or 

trimmed as nearly as possible at the test power, configuration, and test (target) speed. The 

airplane is dived to gain sufficient airspeed above the test airspeed to allow a pull-up (nose above 

the horizon), followed up by a rapid pitch over as the test airspeed is approached to achieve the 

test load factor and airspeed as the nose passes through the horizon. 

(bb) The pushover series begins by moving the control column 

forward while evaluating for any reduction of required control force or force reversal. Continue 

the test points incrementally by increasing the amplitude of forward control inputs to obtain 

lower target load factors until a zero-g flight condition is obtained or, if limited by elevator 

power, to the lowest load factor attainable. The target load factors need to be maintained long 

enough to allow an evaluation of the longitudinal force required. During the pitch down 

maneuver, the test pilot should not change the rate of longitudinal control or reverse control 

movement as this may alter pitch rate and tail surface geometry to disqualify that test point. 

(cc) For pre-activation ice, the pushover maneuver can be 

accomplished to 0.5g rather than 0g, preceded with a pull-up to 1.5g. The criteria below in (ee) 

through (gg) apply to the pushover, and for the pull-up, the airplane must demonstrate suitable 

controllability and maneuverability throughout the maneuver, including recovery, with no 

tendency to diverge in pitch or other indications of a stalled tailplane. 

(dd) For failure ice accretions, when the failure is annunciated to the 

flight crew and the procedures are to exit icing conditions, the pushover maneuver can be 

accomplished to 0.5g rather than 0g.

(ee) A push longitudinal control force must be required throughout 

the test maneuver. Stop the test if a control force lightening to less than zero, or a pull pitch 

control force is required to achieve the test load factor (g level). 

(ff) The airplane must demonstrate suitable controllability and 

maneuverability throughout the maneuver, including recovery, with no tendency to diverge in 

pitch or other indications of a stalled tailplane. It must be possible to recover from the pushover 

without exceeding a 50 lb. pull force. 

(gg) During the pitch-down maneuver, any pilot produced change in 

elevator deflection toward the nose-up direction disqualifies that test point. 
AC 23.1419-2E 

47)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

4. Steady state sideslip maneuver. Establish the airplane incrementally in 

a straight, steady heading sideslip, up to the sideslip angle appropriate to normal operation of the 

airplane used to demonstrate compliance with § 23.177, Static directional and lateral stability. 

The airplane should demonstrate suitable controllability and maneuverability throughout the 

maneuver with no tendency to diverge in pitch

(c) Other Parameters that May Indicate a Stalled Tailplane. If the test 

aircraft is instrumented, the following parameters may indicate a stalled tailplane:



 The relationship of pitch rate (q) versus elevator deflection (δE) after the 

elevator is returned Trailing Edge-Up (TEU). If stalled, the elevator could deflect substantially 

before the airplane pitch rate starts to return to zero. This also appears as reduced elevator 

effectiveness, CmδE. 



 If the elevator stalls, the aircraft will continue toward zero-g regardless 

of the force applied by the pilot to return to one-g flight. This may be determined by examining 

the slope of the plot of vertical load factor (Nz) vs. pitch control force (FELEVATOR) after the 

elevator is returned TEU.



 Flow visualization methods (tufts) will usually indicate the onset of 

destabilization by flow reversal over a substantial portion of the suction (lower) surface of the 

horizontal tail. This indication often appears slightly before pilot tactile force cues. Critical tests 

would have to be repeated without the tufts to demonstrate the tufts have no effect on tail stall. 

(4) Compliance by Analysis. For turbojet powered airplanes with irreversible, 

powered pitch control systems, the flight tests described in paragraph 13 (e) (2) (b) may not be 

necessary. However, a detailed analysis, as a minimum, should show that: 

(a) The airplane has adequate (consult Small Airplane Directorate) margin to tail 

stall angle of attack; and 

(b) Airplanes of similar size, configuration and operating envelope have 

demonstrated an acceptable service history with respect to ICTS. 

(5) AFM Limitations and Procedures. 

(a) Maximum landing flaps may be limited to the “takeoff/approach” configuration 

due to ICTS characteristics, either with normal operation of the ice protection systems or with a 

failed horizontal tail system. This is true regardless of the certification basis. 

(b) If sandpaper ice results in ICTS susceptibility and limited flap deflection for 

landing, the AFM procedure for limiting flap should be based on visible moisture and temperature 

rather than airframe ice accretions if the flight crew cannot see the tail. 
AC 23.1419-2E 

48 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

f. Pneumatic Deicer Boots. Section 23.1419(d) contains requirements for 

boot activation. See paragraph 15 of this AC for guidance. Deicing systems must 

have a mode that will automatically cycle the system, or alert the pilot to cycle the 

system, after activation, in accordance with § 23.1419(f). 

g. Emergency and Abnormal Operating Conditions. Flight investigations should be 

conducted to verify that, after pilot recognition of emergency and abnormal operating conditions, 

the AFM procedures are effective, recommended airspeeds are safe and that the airplane can be 

landed safely. These demonstrations should be conducted with anticipated residual ice 

accumulation on normally protected surfaces. The tests in Table 5 represent a sample matrix for 

a part 23 airplane with failure ice shapes defined in paragraph 13b(3). 

TABLE 5. FAILURE ICE ACCRETION FLIGHT TESTS 

Ice Shape 

Configuration 

Configuration 

and Trim Speed Maneuver 

One wing zone 

failure 

Flaps up and minimum

holding 

• Level, 40-degree banked turns; 

• Bank-to-bank rapid rolls, 30° – 30°; 

• Determine minimum safe airspeed. 

• Approach and landing demonstration 

Empennage zone 

failure 

Full landing flaps and 

VREF

• ICTS evaluation; 

• Sideslips 

Total wing and 

empennage zone 

failure 

• ICTS evaluation 

• Level, 40-degree banked turns; 

• Bank-to-bank rapid rolls, 30° – 30°; 

• Deceleration to stall warning (natural 

acceptable), recover after one second. 

• Approach and go-around demonstration 

Pilot's windshield 

ice protection 

failure 

Full landing flaps and 

VREF

• Approach and landing demonstration 

If the autopilot is intended to be used with the ice shape configurations defined in table 5, the 

manufacturer should also show the airplane can be safely flown and landed with AFM 

procedures. 
AC 23.1419-2E 

49)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

14. Super Cooled Large Drop (SLD) Conditions. Section 23.1420 requires that the airplane 

operate safely in the supercooled large droplet (SLD) icing conditions defined in part 25, 

Appendix O of this chapter. 

a. Icing Envelopes. The conditions included in the part 25 Appendix C icing envelopes 

are unchanged by the addition of Appendix O. See AC20-73A and DOT/FAA/CT-88/8-1 

"Aircraft Icing Handbook" for details on the Appendix C icing envelopes. Appendix O was 

developed to provide a representative icing environment for supercooled large drops (SLD), 

which are not included in Appendix C and which include freezing drizzle and freezing rain 

conditions. An FAA detailed report on the development of Appendix O is available from the 

FAA Technical Center (reference report DOT/FAA/AR-09/10, dated March 2009) 

(1) Appendix O defines freezing drizzle and freezing rain environments by using four 

spectra of drop sizes with associated liquid water content (LWC) limits. Following are the four 

drop size spectra. 

(a) Freezing drizzle with a median volume diameter (MVD) less than 40 

microns. In addition to drizzle drops, which are defined as measuring 100 μm to 500 μm in 

diameter, this environment also contains smaller drops with diameters less than 100 μm. 

(b) Freezing drizzle with a MVD greater than 40 microns. In addition to freezing 

drizzle drops, this environment also contains smaller drops, with diameters less than 100 μm. 

(c) Freezing rain with a MVD less than 40 microns. In addition to freezing rain 

drops, which are defined as measuring more than 500 μm in diameter, this environment also 

contains smaller drops with diameters of less than 100 μm. 

(d) Freezing rain with MVD greater than 40 microns. In addition to freezing rain 

drops, this environment also contains smaller drops with diameters of less than 100 μm.

(2) Use of Appendix C is not changed by the addition of Appendix O. Appendix O is 

designed to be similar to Appendix C and to be used in much the same manner. The principal 

differences between using Appendix O and using Appendix C are that for Appendix O, the 

applicant must now—— 

(a) Consider four icing conditions rather than two when determining critical icing 

conditions, and 

(b) Address drop size distributions. 

b. Section 23.1420 requires compliance with § 23.1420(a)(1), (a)(2), or (a)(3). 

(1) § 23.1420(a)(1). When complying with § 23.1420(a)(1), the applicant must provide a 

method for detecting that the airplane is operating in Appendix O icing conditions. Following 

detection, the airplane must be capable of operating safely while exiting all icing conditions. 
AC 23.1419-2E 

50 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

Certification for 23.1420(a)(1)) requires a means of alerting flightcrews when Appendix O 

conditions are encountered (§ 23.1420(a)(1)). 

(2) § 23.1420(a)(2). If the applicant seeks certification for safe operation in portions of 

Appendix O conditions, such as freezing drizzle only, or during specific phases of flight, § 

23.1420(a)(2) applies. If this option is chosen, following detection of conditions that exceed the 

selected portion of Appendix O, the airplane must be capable of operating safely while exiting all 

icing conditions. Certification for a portion of Appendix O (§ 23.1420(a)(2)) requires a means of 

alerting flightcrews when those portions of Appendix O are exceeded (§ 23.1420(a)(2)). 

(a) Initial certification for flight in a portion of Appendix O conditions will likely 

include all of freezing drizzle or all of freezing rain. Certification for flight in a portion of 

Appendix O conditions depends upon the applicant substantiating an acceptable way for the 

flightcrew to distinguish the portion of Appendix O conditions for which the airplane is certified 

from the portion of Appendix O conditions for which the aircraft is not approved. A 2009 review 

of engineering tool capabilities found that current technology does not support distinguishing 

between freezing drizzle and freezing rain in flight. Therefore certification for a portion of 

Appendix O will be challenging and will require close coordination with certifying authorities. 

Certification for a portion of Appendix O allows latitude for certification with a range of 

techniques and technology that may be available in the future. 

(b) However, initial certifications could be restricted to operation in Appendix O 

conditions by phase of flight. However, if certification is sought for takeoff/landing in freezing 

drizzle based solely on weather reporting provided by the airport, certification must also be done 

for freezing rain due to inaccuracies in current weather reports. 

(3) § 23.1420(a)(3). Section 23.1420(a)(3) applies when the applicant seeks certification 

for all of the icing conditions described in Appendix O. An airplane certified to § 23.1420(a)(3) 

must be capable of safely operating throughout the conditions described in Appendix O and does 

not need a means to detect Appendix O conditions. In effect, when § 23.1420(a)(3) is chosen, the 

airplane is certificated for flight in icing without any specific airplane flight manual procedures 

or limitations to exit icing conditions. 

 

c. Ice Accretions. 

(1) Some Areas of interest for Appendix O. The following are some areas of 

interest specific to supercooled large droplet conditions: 

(a) Ice shapes aft of protected areas of lifting surfaces. Appendix O 

icing conditions may result in a ridge of ice or ice roughness aft of the protected areas. On 

aircraft with reversible flight controls, a ridge of ice may cause uncommanded deflections of the 

control surfaces, which may result in an aircraft upset. Aircraft may also incur reduced 

maximum lift and stall at lower angles of attack, independent of the flight control system. 

Appendix O ice buildups can result in increases in stall speeds and potentially alter stall 

characteristics. 
AC 23.1419-2E 

51)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(b) Ice shapes on unprotected areas of lifting surfaces. Ice shapes 

resulting from Appendix O icing conditions can extend further aft on the airfoil than those from 

Appendix C icing conditions. When portions of the airfoil leading edge are unprotected, 

performance and handling qualities can potentially be affected. 

(c) Ice shapes on unprotected airframe regions. Areas of the airframe 

which do not accrete ice under Appendix C conditions should be examined for impingement and 

accretion in Appendix O conditions. The applicant should evaluate such issues as visibility 

through the windshield, ice accretion on fuel vents, locations of air data sensors, and potential 

airflow disturbance (for example on the airplane nose) from Appendix O accretions that could 

influence performance of the air data sensors. 

(d) Drag and power effects. Aircraft may exhibit reduced performance in 

Appendix C conditions because ice accretions cause increased drag and reduced lift. Such 

impacts can be increased in Appendix O conditions, since the accretions may extend further aft 

on protected areas, extend beyond protected areas, or occur in areas not typically protected 

(extended accretions on the fuselage and the lower wing surface, for example). Ice accretions 

may be rough and cause large local drag increases. 

(e) Engine considerations. Ice accumulation on the airframe and on air 

induction system components resulting from Appendix O icing conditions should be analyzed for 

potential ingestion of ice by the engine (relative to requirements of § 23.1093) and potential 

blockage effects. See AC 23-16B.

(2) Airframe Ice Accretions. 

(a) Pre-Detection Ice Accretion. This ice accretion, defined as pre-detection ice 

in 14 CFR 23, Appendix TBD, part II(b)(3), refers to the ice accretion existing at the time the 

flightcrew becomes aware that they are in Appendix O icing conditions and have taken action to 

begin exiting from all icing conditions. The time that the applicant should assume it will take to 

detect Appendix O icing conditions exceeding those for which the airplane is certified should be 

based on the means of detection. In general, we expect that the time to detect exceedance icing 

conditions may be significantly longer for a detection means relying on the flightcrew seeing and 

recognizing a visual icing cue than it is for an ice detection system that provides an attentiongetting alert to the flightcrew.

1. Visual Cues. See paragraph 15.e.(3) of this AC for time to detect 

Appendix O conditions 

 2. System. For Appendix O ice detection systems and Aerodynamic 

Performance Monitors that comply with the reliability requirements of § 23.1309, pre-detection 

ice is the maximum time the system was demonstrated to detect Appendix O conditions. If only 

freezing drizzle conditions are demonstrated by test, the applicant would need to show by 

analysis and design that the detection time for freezing rain would be equal or smaller., 
AC 23.1419-2E 

52 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(b) Aircraft Certified to Detect and Exit Appendix O Conditions (§ 

23.1420(a)(1) or § 23.1420(a)(2). Use the ice accretions in Table 6, below, to evaluate 

compliance with the applicable subpart B requirements for operating safely after encountering 

Appendix O atmospheric icing conditions for which the airplane is not approved, and then safely 

exiting all icing conditions. 

Table 6 Appendix O Detect and Exit Ice Accretion 

Flight 

Phase/Condition - 

Appendix O Detect-and-Exit Ice Accretion 

Part II , Paragraph (b) of Appendix TBD OF PART 23

Ground Roll No accretion 

Takeoff No accretion

1

Final Takeoff No accretion1

En Route No accretion 

Holding Exposure sequence: 

(1) Either Appendix C holding ice or Appendix O holding ice for 

which the airplane is approved, whichever is applicable, 

(2) Pre-detection ice, 

(3) Accretion from one standard cloud horizontal extent (17.4 nautical 

miles) in Appendix O conditions for which the airplane is not 

approved, followed by 

(4) Accretion from one standard cloud horizontal extent (17.4 nautical 

miles) in Appendix C continuous maximum icing conditions. 

The total time in icing conditions need not exceed 45 minutes. 

Appendix O conditions colder than -13°C are not required to be 

analyzed. 

 

1 Takeoff is not permitted when Appendix O conditions beyond those in which the airplane is certified to operate 

exist in the vicinity of the departure airport. 
AC 23.1419-2E 

53)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

Flight 

Phase/Condition - 

Appendix O Detect-and-Exit Ice Accretion 

Part II , Paragraph (b) of Appendix TBD OF PART 23

Approach The more critical of holding detect-and-exit ice and the combination 

of: 

(1) Ice accreted during a descent in the cruise configuration from the 

maximum vertical extent of the Appendix C maximum continuous 

icing conditions or the Appendix O icing environment for which the 

airplane is approved, whichever is applicable, to 2,000 feet above the 

landing surface, where transition to the approach configuration is 

made, 

(2) Pre-detection ice, and 

(3) Ice accreted at 2,000 feet above the landing surface while 

transiting one standard cloud horizontal extent (17.4 nautical miles) in 

Appendix O conditions for which the airplane is not approved and one 

standard cloud horizontal extent (17.4 nautical miles) in Appendix C 

continuous maximum icing conditions. 

Appendix O conditions colder than -13°C are not required to be 

analyzed. 

Landing No accretion 

Pre-activation Ice 

Accretion 

No accretion1

Pre-detection Ice 

Accretion 

Ice accreted on protected and unprotected surfaces during: 

 The time it takes to detect and identify Appendix O conditions 

(based on the method of detection) beyond those in which the 

airplane is certified to operate, and 

 The time it takes the flight crew to refer to and act on 

procedures, including coordinating with Air Traffic Control, to 

exit the icing conditions beyond those in which the airplane is 

certified to operate (minimum of two minutes). 

Failures of the Ice 

Protection System 

No accretion 
AC 23.1419-2E 

54 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(c) Aircraft Certified to a Portion or all of Appendix O Conditions (§ 

23.1420(a)(2) or § 23.1420(a)(3) Use the ice accretions in Table 7, below, to evaluate 

compliance with the applicable subpart B requirements for operating safely in Appendix O 

atmospheric icing conditions for which the airplane is approved.

Table 7 - Appendix O Ice Accretion 

Flight 

Phase/Condition - 

Appendix O Ice Accretion 

Part II , Paragraph (c) of Appendix TBD OF PART 23

Ground Roll No accretion if Type II, III or Type IV fluids are approved for the 

airplane. 

Takeoff Ice accretion occurring between lift-off and 400 feet above the takeoff 

surface assuming ice accretion starts at lift-off. No ice accretion prior 

to lift-off if Type II, III or Type IV fluids are approved for the 

airplane.

Final Takeoff Ice accretion occurring between 400 ft and the height at which the 

transition to the en-route configuration and speed is completed, or 

1500 ft above the take-off surface, whichever is higher, plus “Takeoff” 

ice accretion. No ice accretion prior to lift-off if Type II, III or Type 

IV fluids are approved for the airplane. 

Climb Ice accretion during the climb after takeoff. Ice accretion includes ice 

accreted during takeoff phase plus the most critical of climb through 

6,000 feet in freezing drizzle, or climb through 3,500 feet in freezing 

rain. 

En Route Ice accreted during the en-route phase of flight. 

Holding Ice accreted during a hold with no reduction for horizontal cloud 

extent (i.e., the hold is conducted entirely within the 17.4 nautical mile 

standard cloud extent). A hold of 45 minutes should be considered for 

OAT at and above -13°C, and the time required to transit 17.4 nm 

should be considered below -13°C. 

Approach Most critical ice accretion of: 

(1) Ice accreted during a descent in the cruise configuration from the 

maximum vertical extent of the Appendix O icing environment to 

2,000 feet above the landing surface, followed by transition to the 

approach configuration and maneuvering for 15 minutes at 2,000 feet 

above the landing surface; and 

(2) Holding ice (if the airplane is certified for holding in Appendix O 

conditions). 
AC 23.1419-2E 

55)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

Flight 

Phase/Condition - 

Appendix O Ice Accretion 

Part II , Paragraph (c) of Appendix TBD OF PART 23

Landing Most critical ice accretion of: 

(1) Approach ice plus 

descent from 2,000 feet above the landing surface to 200 feet above 

the landing surface with a transition to the landing configuration, 

followed by a go-around maneuver in accordance with Airplane Flight 

manual procedures from 200 feet to 2,000 feet above the landing 

surface, holding for 15 minutes at 2,000 feet above the landing surface 

in the approved maximum flap holding configuration, and a descent to 

the landing surface in the landing configuration; and 

(2) Holding ice (if the airplane is certified for holding in Appendix O 

conditions). 

Pre-activation Ice 

Accretion 

Ice accreted during the time for the flightcrew to recognize icing 

conditions and activate the ice protection system, plus the time for the 

ice protection system to perform its intended function. 

Pre-detection Ice 

Accretion 

Ice accreted during the time for the flightcrew to detect Appendix O 

conditions, refer to and initiate procedures, and any time for systems 

to perform their intended functions (if applicable). Pre-detection ice 

need not be considered if there are no specific crew actions or systems 

changes associated with flight in Appendix O conditions. 

Failures of the Ice 

Protection System 

Same criteria as for Appendix C, but in Appendix O conditions. 

(d) Shape and Texture of Simulated Ice. Ice shapes for Subpart B of part 25 

testing are typically based upon icing tunnel tests or CFD computations or both. Current CFD 

programs do not provide roughness information. Roughness levels and aft extent of roughness 

for Appendix O ice shapes should be determined from icing tunnels or tanker testing, if the 

capabilities exist. Characteristics of roughness, such as particle density and height of roughness 

elements, may be critical and should be simulated on the flight test airplane. However, when the 

empirical capabilities do not exist, the roughness levels (or equivalents) as defined in Table 8, 

below, may be used for Appendix O ice accretions. 
AC 23.1419-2E 

56 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

Table 8 Appendix O Ice Accretion Roughness 

Ice Type Roughness Height 

(mm)

Percent of 

Surface 

Covered

Notes

FZRA or FZDZ, 

thin accretions; 

thickness 

< 3mm (0.12 inch) 

1.5 to 2 mm (0.06 to 

0.08 inch) 

or 

16 to 20 grit sandpaper 

Particle 

density 

to cover 

50% to 70% 

of total area 

Use to simulate predetection, initial 

accretions, or 

roughness on 

computed ice 

shapes 

FZDZ thickness 

> 3 mm (0.12 inch) 

 3 to 6 mm (0.12 to 0.24 

inch) Mean particle size 

~4.5mm Intercycle, residual, 

unprotected 

surfaces 

FZRA thickness 

≥ 3 mm (0.12 inch) 

and ≤ 6 mm (0.24 

inch) 

FZRA 

thickness > 6 mm 

(0.24 inch) 

6 to 8 mm (0.24 to 0.31 

inch) 

Mean particle size ~7 

mm 

Notes: 

1. The simulated roughness elements should approximate roughness elements 

observed in icing tunnels or natural icing. Smooth and spherical elements should not 

be used because they may result in non-conservative aerodynamic results. 

2. For computed ice shapes, the roughness simulation should be extended aft to the 

limits of predicted accretion (where the ice accretion thickness is calculated as 

0.015"). 

(d) Ice Adhesion Inhibitors. The guidance for part 25, Appendix C icing 

conditions apply to part 25, Appendix O icing conditions. 

(e) Number of ice shapes for dry air flight testing. 

1. The ice accretion(s) used to show compliance should consider the speeds, 

configurations (including configuration changes), angles of attack, power or thrust settings, etc. 

for the flight phases and icing conditions that they are intended to cover. 

2. The ice accretion(s) used to show compliance should consider the entire 

Appendix O envelopes, including temperatures near freezing where runback may accrete behind 

mechanical ice protection systems. 
AC 23.1419-2E 

57)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

3. In determination of critical ice shapes for flight testing of Appendix O ice 

shapes, the following should be considered: 

 The critical freezing drizzle ice shape 

 The critical freezing rain ice shape. 

4. Any of the applicable ice accretions (or a composite accretion 

representing a combination of accretions) may be used to show compliance with a particular 

Subpart B requirement if that accretion is either the ice accretion identified in the requirement or 

is shown to be more conservative than the ice accretion identified in the requirement. 

5. The ice accretion that has the most adverse effect on stall angle of attack 

and handling characteristics may be used for compliance with the airplane performance 

requirements if any difference in performance is conservatively taken into account. 

6. An Appendix O ice shape may be used in lieu of Appendix C ice shape to 

show compliance if it can be shown to be more critical. 

7. The number of shapes may be reduced based on similarity to an airplane 

in which flight test data shows the critical ice shape configuration(s). 

(3) Propeller Icing. Stop frame video of recent flight testing of a part 23 aircraft in 

Super-Cooled Large Drop (SLD) conditions have shown ice accretions on the full span of the 

propeller blades. Propeller icing research (Paragraph 6.b., Reference 7) was able to duplicate 

this ice accretion and supports the propeller efficiency losses in Figure 2 in part 25, Appendix O 

icing conditions. 

(a) Propeller efficiency loss should be the value in Figure 2 to account for 

propeller runback ice and intercycle ice, unless data substantiates another amount. The applicant 

can assume there is zero efficiency loss at an airplane total temperature of 0 °C, and interpolate 

between this temperature and the static temperatures in Figure 2. 
AC 23.1419-2E 

58 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

SLD Propeller Efficiency Loss

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

0.6 0.7 0.8 0.9 1

Helical Tip Mach Number

Propeller Thrust Loss, %

-5 C OAT

-10 C OAT and colder

Figure 2 - SLD Propeller Thurst Loss 

(b) Testing, analyses or similarity should be conducted to verify the deice system 

minimizes intercycle and runback ice accretions. 

d. Engineering Tools. Appendix 7 of this AC provides guidance on the use of tools based on 

their state of development in 2009.

e. Subpart B Requirements. Section 23.21 (c) defines the Subpart B regulations that the 

airplane must be shown to be compliant with critical SLD ice shapes. 

(1) Detect and Exit SLD Conditions. Appendix 8 contains an example flight test 

program to show compliance to 23.21(c)(2). 

 

(2) Certification to all of Appendix O. The same regulations required for Appendix C 

ice accretion, with the addition of § 23.67(c)(1), are required for critical SLD conditions for 

which the airplane is to be certified. The guidance in Appendix 6 is applicable with the critical 

ice accretions in Appendix O for which the airplane is certified. 

(3) Certification to a portion of Appendix O. The following provides guidance to an 

applicant who chooses to approve their airplane for two specific phases of flight, takeoff and 

landing. 
AC 23.1419-2E 

59)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(a) Takeoff. Appendix 9 contains an example flight test program for an applicant 

who chooses to approve their airplane for operation in Appendix O for takeoff. 

(b) Landing. The critical ice accretions for showing compliance with applicable 

Subpart B regulations should consider the approach and landing phases. 

f. Natural Icing Flight Tests. Section 25.1420(a) requires that the airplane operate safely 

in the SLD icing conditions defined in Part 25, Appendix O. 

(1) Flight testing in measured, natural Appendix O icing conditions should be 

accomplished for: 

(a) Airplanes certified for unrestricted flight in Appendix O or a portion of 

Appendix O conditions should be flight tested in natural Appendix O icing conditions for each 

phase of flight for which approval is sought (i.e., compliance with § 23.1420(a)(3) or § 

23.1420(a)(2), or 

(b) Airplane derivatives whose ancestor airplanes have a service record that 

includes a pattern of accidents or incidents due to inflight encounters with Appendix O 

conditions. 

(c) For certification to 23.1420(a)(3), flight test encounters should include at least 

one freezing drizzle and one freezing rain encounter. 

(2) For airplanes certificated to detect Appendix O icing conditions and safely exit all 

icing conditions, flight testing in measured, natural Appendix O conditions should not be 

required to show compliance to § 23.1420(a)(1) if: 

(a) Design analyses show that the critical ice protection design points (i.e., heat 

loads) are adequate under the conditions of Appendix O and various airplane operational 

configurations; 

1. Certain angle of attack/stall warning sensors, such as wing mounted vane 

type, are empirically tested 

(b) For the Appendix O distributions where the capability exists, icing tunnel 

tests or icing tanker tests, and analytical codes are used to determine critical ice shapes on 

lifting surfaces. 

1. The simulated, critical ice shapes are flight tested to show compliance 

with applicable Subpart B regulations. 

(c) Appendix O detection method(s) are certified as described in section 15 of 

this advisory circular. 

(d) Subsequent designs may be able to use similarity to past certifications. 
AC 23.1419-2E 

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APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

15. Ice and Exceedance Icing Conditions Detection. Sections 23.1419(e) specifies 

requirements regarding activation of the IPS. These requirements are only applicable to Appendix 

C icing conditions. Section 23.1420(c) requires compliance with § 23.1419(e),(f) and (g) for the 

selected portion or all of Appendix O as applicable. Sections 23.1420 (a)(1) and (a)(2), 

respectively, require a means to alert the flightcrew that they are in Appendix O icing conditions 

or have reached Appendix O icing conditions from which they must exit. 

a. Compliance with § 23.1419(d). This section of the rule requires either a primary ice 

detection system, substantiated visual cues and an advisory ice detection system, or AFM 

procedures to activate the IPS based on visible moisture and temperature. A fourth option of 

AFM procedures based on visual cues is available for airplanes in the normal, acrobatic and 

utility category, 

(1) Primary ice detection system. A primary ice detector must either alert the 

flightcrew to operate the IPS using AFM procedures or automatically activate the IPS before an 

unsafe accumulation of ice on the airframe, engine components, or engine air inlets occurs. The 

primary ice detection system must perform its intended function for the airplane configurations, 

phases of flight, and within icing envelopes of Appendix C and Appendix O. Laboratory tests 

should demonstrate the ice detector’s ability to function properly within all of the required icing 

conditions and airplane operating envelope. If the ice detector cannot detect ice at low freezing 

fractions and ice accretes on the airplane in such icing conditions, the applicant should show that 

the airplane can be operated safely with the ice accretions. If safe operation cannot be 

substantiated, installation of an icing conditions detector may be required. Approval of the 

primary ice detector should include flight tests in measured natural icing conditions to verify 

analyses and laboratory test results, as well as to verify that the ice detector system performs its 

intended function. The primary automatic ice detection system should be designed to prevent 

continuous cycling of engine thrust in intermittent icing conditions. 

(2) Advisory ice detection system. The advisory ice detector, in conjunction with 

a primary cue, such as visible ice accretion on referenced or monitored surfaces, should advise 

the flightcrew to initiate operation of the IPS using AFM procedures. An advisory system is not 

the prime means used to determine if the IPS should be activated. The AFM must state the flight 

crew has primary responsibility for detecting icing conditions or ice accretions. Analyses and 

tests similar to those performed for a primary ice detector should be performed for an advisory 

ice detector to understand its characteristics, limitations, and installation. 

(3) Certification of an ice detection system 

(a) Certification plan. The applicant should present an icing certification plan 

to the cognizant aircraft certification office. This plan should include the method selected for 

demonstrating the ice detector system’s compliance with §§ 23.1301, 23.1309, 23.1419, 23.1420, 

and all other applicable sections. Advisory Circular 20-73 A, Appendix K, provides guidance on 

certification of ice detector systems. That appendix provides guidance regarding ice detection 

response times as the freezing fraction drops below 1. That guidance is equally applicable to 

advisory and primary ice detection systems. 
AC 23.1419-2E 

61)

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APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(b) Performance of the ice detector system when installed. In addition 

to the guidance in Advisory Circular 20-73 A, Appendix K, the following guidance applies. 

1. The applicant should conduct flow field and boundary-layer analyses of 

candidate installation positions to ensure that the ice detector sensor is not shielded from 

impinging Appendix C and Appendix O water drops. 

2. The ice detection system should be shown to operate in the range of 

conditions defined by Appendix C and the applicable portion of Appendix O. Sections 23.1419 

and 23.1420 also require a combination of tests and analysis to demonstrate performance of the 

ice detector and the system as installed on the airplane. This could include icing tunnel and icing 

tanker tests to evaluate ice detector performance. The applicant may use droplet impingement 

analysis to determine that the ice detector functions properly over the droplet range of Appendix 

C and the applicable portions of Appendix O when validated through natural or artificial icing 

tests (e.g. tanker, icing tunnel). 

3. The applicant should demonstrate that the airplane can be safely operated 

with the ice accretions formed at the time the ice protection system becomes effective, following 

activation by the ice detector. This includes low freezing fraction conditions. If an applicant 

provides a temperature vs. response time plot for an ice detector and demonstrates that no ice 

accretes on flight surfaces at temperatures where the response time is greater than 60 seconds 

then a 60 second pre-activation ice encounter may be used in developing the pre-activation ice 

shape.

4. Ice detectors typically have limitations with certain atmospheric 

phenomena, e.g. ice crystal conditions, outside of part 25, Appendix C, which the applicant must 

understand and not rely on the ice detection system to detect these conditions. 

5. The detector and its installation should minimize nuisance warnings. 

6. SAE AS5498 "Minimum Operational Performance Specification for 

Inflight Icing Detection Systems" provides a standard and qualification considerations for 

inflight ice detection systems. 

(c) Ice detector system safety considerations. The unannunciated failure 

of a primary ice detection system is assumed to be a catastrophic failure condition, unless 

characteristics of the airplane in icing conditions without activation of the airframe ice protection 

system(s) are demonstrated to result in a less severe hazard category. Ice detector reliability, 

hardware and software criticality requirements, for both primary and advisory systems, shall be 

consistent with the hazard classification for ice detectors resulting from a 1309 hazard analysis. 

If visual cues are the primary means of ice detection, the pilots retain responsibility to monitor 

and detect ice accretions when an advisory ice detection system is installed. However, the 

natural tendency of flightcrews to become accustomed to using the advisory ice detection system 

elevates the importance of the detector and increases the need to make flightcrews aware of an 

advisory ice detection system failure. Therefore, an undetected failure of the advisory ice 
AC 23.1419-2E 

62 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

detector should be considered a major hazard. 

(4) Visual cues. Visual cues can either be direct observation of ice accretions on the 

airplane’s protected surfaces or observation of ice accretions on reference surfaces. 

(a) The first indications of any of the following are examples of what could be 

used as visual cues. 

1. Accretions forming on the windshield wiper posts (bolt or blade). 

2. Accretions forming on propeller spinners. 

3. Accretions forming on an ice evidence probe. 

4. Accretions on the protected surfaces. 

(b) If accretions on protected surfaces cannot be observed, a reference system 

would be necessary if compliance with § 23.1419(d)(2) or (d)(4) is desired. The applicant 

should consider providing a reference surface that can be periodically de-iced to allow the 

flightcrew to determine if the airframe is continuing to accumulate ice. Without a means to deice 

the reference surface, compliance with § 23.1419(d)(2) or (d)(4) would require operation of the 

IPS as long are there is ice on the reference surface, even when additional ice is not 

accumulating. 

 

(c) Field of view. Visual cues should be developed with the following 

considerations. 

1. Visual cues should be within the flightcrew’s vision scan area while seated 

and performing their normal duties at various airplane attitudes. 

2. Visual cues should be visible during all modes of operation (day, night, 

and in cloud). 

(d) Verification. During the certification process, the applicant should verify the 

ability of the crew to observe visual cues or reference surfaces. The visual cues should be 

evaluated from the most adverse flightcrew seat locations in combination with the range of 

flightcrew heights, if available. For a single pilot airplane, the visual cue must be visible from 

the pilot seat. For airplanes certified with two flightcrew, a visual cue should be provided for 

both the left and right seats. Consideration should be given to the difficulty of observing clear 

ice, or accretions on painted surfaces, or the differentiating between characteristics and size of 

ice that should not require special knowledge or skills. The adequacy of the detection method 

should be evaluated in all expected flight conditions. The applicant can carry out night 

evaluations with simulated accretions to assess visibility in and out of cloud. Methods used to 

substantiate visual cues should be agreed to with appropriate certification authorities.. 
AC 23.1419-2E 

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APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(e) Airplane Flight Manual (AFM). The limitations section of the AFM must 

specify that the IPS must be operated when ice accretion is detected anywhere on the airplane 

and also must describe the visual cues verified in certification. 

(5) Temperature cue. The temperature cue used in combination with visible moisture 

should consider static temperature variations due to local pressure variations on the airframe. If 

the engine and airframe IPS are both activated based on visible moisture and temperature, a 

common conservative temperature for operation of both systems should be used. For example, if 

the engine IPS is activated at +5oC static air temperature or less, the airframe IPS should be 

activated at the same temperature, even if it is substantiated that the airframe will not accrete ice 

above +2oC static air temperature. This would ease the flightcrew workload and increase the 

probability of procedural compliance. 

(a) If this provision is used, the flightcrew should be able to easily determine the 

static air temperature. A display of static air temperature or a placard can be provided showing 

corrections for temperature vs. air speed to the nearest degree Centigrade in the region of interest 

(that is, around 0oC). 

(b) Airplane Flight Manual (AFM). The limitations section of the AFM should 

identify the specific static or total air temperature and visible moisture conditions that must be 

considered conditions conducive to airframe icing and should specify that the IPS must be 

operated when these conditions are encountered. 

b. Compliance With § 23.1419(e). This paragraph of § 23.1419 states that requirements 

of §§ 23.1419(d) are applicable to all phases of flight unless it can be shown that the IPS need 

not be operated. To substantiate that the IPS need not be operated during certain phases of flight, 

the applicant should consider ice accretions that form during these phases and establish that the 

airplane is able to safely operate in the continuous maximum and intermittent maximum icing 

conditions of Appendix C and the applicable portions of Appendix O. 

c. Compliance With § 23.1419(f). 

(1) This paragraph of § 23.1419 requires that after the initial activation of the IPS— 

(a) The IPS must operate continuously, or 

(b) The airplane must be equipped with a system that automatically cycles the 

IPS, or 

(c) An ice detection system must be provided to alert the flightcrew each time the 

IPS must be cycled. 

(2) Some examples of systems that automatically cycle the IPS are— 
AC 23.1419-2E 

64 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(a) A system that senses ice accretion on a detector and correlates it to ice 

accretion on a protected surface. This system then cycles the IPS at a predetermined condition. 

(b) A system that cycles the IPS based on the use of a timer. It should be 

substantiated that the airplane can safely operate with ice accretions that form between the time 

one deicing cycle is completed and the next cycle is initiated. If more than one cycling time (a 

choice of 1- or 3-minute intervals for example) is provided, it should be substantiated that the 

flightcrew is able to determine which cycle time is appropriate. 

(c) A system that directly senses the ice thickness on a protected surface and 

cycles the IPS. 

(d) A common attribute of the above systems is that the pilot is not required to 

manually cycle the IPS after initial activation. 

(3) Some types of ice detection systems that alert the flightcrew each time the IPS must 

be cycled could be the same as the automatic systems discussed above, except that the system 

alerts the crew each time the IPS must be manually cycled. Flightcrew workload associated with 

such a system should be evaluated. Because of flightcrew workload and human factors 

considerations, a timed system without an ice sensing capability should not be used to meet this 

requirement. The ice shedding effectiveness of the selected means for cycling the ice protection 

system should be evaluated during testing in natural icing conditions. 

d. Compliance With § 23.1403. Compliance with §23.1403 applies to aircraft certified 

for flight into icing conditions. The requirement is intended to address any visual ice 

accumulation requirements such as activating ice protection systems (§23.1419) or determining 

whether an exit from severe icing conditions (§23.1420(a)(1) or (a)(2)) is required. If the aircraft 

operating procedures do not depend on crew observation of ice accretions, an icing inspection 

light may not be required. An example of this would be installation of a primary ice detection 

system for activating ice protection system, rather than visual observation of icing. When 

considering whether visual cues are necessary, both AFM normal and abnormal procedures 

should be considered. Handheld flashlights are not an acceptable means of compliance. 

e. Compliance with § 23.1420(a)(1) or (a)(2). These paragraphs of § 23.1420 require 

that a means be provided to allow the flightcrew to detect when Appendix O conditions are 

encountered or when the selected portion of Appendix O conditions is exceeded. Means for 

determining when the selected portion of Appendix O icing conditions is exceeded may include 

visual means, ice detectors, or an airplane performance monitor. 

(1) Ice detectors. An ice detector system installed for compliance with 

§ 23.1420(a)(1) or (a)(2) is meant to determine when conditions have reached the boundary of 

the Appendix O icing conditions in which the airplane has been demonstrated to operate safely. 

The applicant should accomplish a droplet impingement analysis and/or tests to ensure that the 

ice detector is properly located to function during the aircraft operational conditions and in 

Appendix O icing conditions. The applicant may use analysis to determine that the ice detector 

is located properly for functioning throughout the droplet range of Appendix O conditions when 
AC 23.1419-2E 

65)

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APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

validated with methods described in SAE ARP 5903. The applicant should ensure that the 

system minimizes nuisance warnings when operating in icing conditions. 

(a) The low probability of finding conditions conducive to Appendix O ice 

accumulation may make natural icing flight tests a difficult means of demonstrating that the 

system functions in conditions exceeding Appendix C. The applicant may use flight tests of the 

airplane under simulated icing conditions (icing tanker). The applicant may also use icing wind 

tunnel tests of a representative airfoil section and ice detector to demonstrate proper functioning 

of the system and to correlate signals provided by the detectors with the actual ice accretion on 

the surface. 

(2) Aerodynamic performance monitor (APM). A crew alerting system using 

pressure probes and signal processors could be developed for quantifying pressure fluctuations in 

the flow field from contamination over the wing surface. This technology does exist, but full 

development is necessary before incorporating it into the crew warning system. 

(3) Visual Cues. Visual cues can range from direct observation of ice accretions aft of 

the airplane’s protected surfaces to observation of ice accretions on reference surfaces. 

Responding to a cue should not require the flightcrew to judge the ice to be a specific thickness 

or size. Examples of visual cues are— 

 Accretions forming on side windshields, 

 Accretions forming on sides of nacelles, 

 Accretions forming on propeller spinners aft of a reference point, 

 Accretions forming on radomes aft of a reference point, and/or 

 Accretions forming aft of protected surfaces. 

(a) Verification. See guidance for Appendix C conditions in paragraph 

15.a.(4).

(b) Time to detect conditions outside Appendix C. The amount of ice needed 

for reliable identification is a function of the distinguishing characteristics of the ice (for 

example, size, shape, contrast compared to the surface feature that it is adhered to), the distance 

from the pilots (for example, windshield vs. engine vs. wingtip), and the relative viewing angle 

(location with respect to the pilots’ primary fields of view). In the absence of specific studies or 

tests validating visual detection times, the following times should be used for visual detection of 

exceedance icing conditions following accumulation of enough ice to be reliably identified by 

either pilot in all atmospheric and lighting conditions: 

 1. For a visual reference located on or immediately outside a cockpit window 

(for example, ice accretions on side windows, windshield wipers, or icing 

probe near the windows) – 3 minutes. 
AC 23.1419-2E 

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Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

 2. For a visual reference located on a wing, wing mounted engine, or wing tip 

– 5 minutes. 

 

(c) Validation. Visual cues should be validated by two of the following methods, 

analysis, icing wind tunnel tests, measured natural icing tests, or icing tanker t tests. In the 

unique case of using two methods to validate visual cues on the windows of the cockpit, a 

combination of appendix C natural icing encounters validating 3D ice accretion or impingement 

analysis will satisfy the two method approach described above. The cues should consider the 

drop distributions of Appendix O, to establish that these cues would be appropriate in the 

restricted Appendix O icing conditions. If a reference surface is used, the applicant should 

validate that it correlates with ice accumulation on the critical surfaces. 

1. Icing Tunnel Tests. Icing tunnel tests should be used for surfaces that 

are practical to test, such as aft of protected area of wing leading edge. 

2. Hybrid airfoil models are often used in icing wind tunnels to match the 

flow and impingement characteristics of the leading edge of the airfoil. Models designed for 

testing over a wide range of AOAs may have limited fidelity in aft impingement regions of the 

airfoil (10% or 20% x/c). As such, models designed for a specific operating conditions may be 

used to confirm the CFD predictions of drop impingement for visual cues, and the CFD codes 

can then be used to further validate over a wider range of operating conditions 

3. Surfaces that are impractical to test in an icing tunnel. Except for 

validation of visually-based detect and exit cues of 14 CRF Part 25 Appendix O conditions, an 

acceptable method would be to compare the analytical results of impingement calculations 

(CFD) against observed impingement limits in Appendix C conditions. If the comparison 

provides sufficient correlation, it may be acceptable to use the CFD code to extend the results to 

predict the observation of larger drops required to detect and exit the Appendix O conditions for 

geometries where icing tunnel testing would be impractical, such as side windows. This would 

provide the comparison of two methods as discussed above. 

4. Natural Appendix O Flight Test. If a manufacture is using natural 

icing as a method of validating cues, the instrumentation should be appropriate for the conditions 

(e.g. if validating for large drops, the instrumentation should be capable of measuring large 

drops). 

16. Ice Shedding. Ice shed from forward airplane structure and components could result in 

damage or erode engine or powerplant components, as well as lifting, stabilizing, and flight 

control surface leading edges. Fan and compressor blades, impeller vanes, inlet screens and 

ducts, as well as propellers, are examples of powerplant components subject to damage from 

shedding ice. For pusher propellers that are very close to the fuselage and well back from the 

airplane's nose, ice shed from the forward fuselage and from the wings may cause significant 

propeller damage. Control surfaces such as elevators, ailerons, flaps, and spoilers are also 

subject to damage. 
AC 23.1419-2E 

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APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

Current trajectory and impingement analysis may not adequately predict such damage. 

Unpredicted ice shedding paths from forward areas such as radomes and forward wings 

(canards) have been found to negate the results of this analysis. For this reason, dedicated flight 

tests points should be conducted to evaluate ice shedding trajectories and damage to the airplane. 

The airplane should be exposed to an icing condition of magnitude and duration sufficient to 

create the expected worst-case ice accretion, including the 45-minute hold, and then flown into 

warmer temperatures to facilitate shedding. Flight test evaluation should also account for the 

critical, predicted trajectories in terms of normal operational angle of attack and sideslip. 

Trajectory and impingement analysis may be used to predict the critical trajectories and 

minimize the total number of test points required. One test point for each critical trajectory 

should be sufficient if the original ice accretion, shed trajectory, and any resultant damage is 

adequately documented. Video or motion pictures are excellent for documenting ice shedding 

trajectories and impingements, while still photography may be used to document the extent of 

damage. Any damage should be evaluated for acceptability. 

If flight tests are not conducted, an impact damage analysis should consider the worst-case ice 

shed event. The impact damage analysis may take conservative credit for the ice breaking up or 

shedding in pieces during the shedding event. Ice slabs consistent with those defined in AC20-

147A (draft) have been found to typically break up during engine ingestion events, and therefore 

the applicant’s analysis can assume slab-shaped ice sheds to break up to 1⁄2 of the original slab 

length. Ice that is not slab-shaped (e.g. double-horn shapes or radome “caps”) should not be 

assumed to break up during the shed event, however credit may be taken for smaller, thinner 

pieces (e.g. rivulets, nodules, feathers, small horns, etc.) shedding off the core ice shape prior to 

the shed event. The applicant may use different break up criteria if it can be substantiated with 

test data.

17. Autopilot. The accumulation of ice on the airplane wings and airframe can have an effect 

on airplane characteristics and autopilot performance. Autopilot operations may mask the onset 

of an icing condition/configuration that would present the pilot with handling difficulties when 

resuming manual aircraft control, particularly following any automatic disengagement of the 

autopilot. 

In general, it is not necessary to conduct an autopilot evaluation that encompasses all weights, 

center of gravity positions (including lateral asymmetry), altitudes, and deceleration device 

configurations. However, if the autopilot performance with ice accretion shows a significant 

difference from the non–contaminated airplane or testing indicates marginal performance, 

additional tests may be necessary. 

The proposed tests herein will approve autopilot operation in the icing conditions. A test 

program should assess the potential vulnerability on autopilot to icing conditions by evaluating 

autopilot performance during artificial ice shape tests and during natural icing tests. These tests 

will evaluate autopilot performance, autopilot low speed characteristics, and adequacy of 

autopilot alerts to warn the pilot of degrading aircraft handling qualities. Critical ice shapes must 

be chosen with the particular test purpose in mind. Tests might have to be performed with 
AC 23.1419-2E 

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APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

multiple configurations of ice shapes which address possible handling qualities/performance 

and/or control surface hinge moment issues. The applicant will need to discuss this topic with 

the administrator prior to final approval. If necessary, appropriate limitations and procedures 

should be established and presented in the AFM. 

a. Natural Icing Conditions Tests: 

(1) All autopilot modes should be evaluated in Appendix C natural icing conditions to 

validate the dry air ice shape test results. All autopilot modes should function properly in icing 

conditions. Airframe leading edge ice accretions could affect control power and control hinge 

moments resulting in incorrect autopilot gains. These evaluations should also show that 

autopilot actuators function properly and do not freeze up. The autopilot should be engaged for 

an extended period of time in natural icing conditions to check for unusual trimming and 

potential for ice to accrete in control surface gaps and jam controls. 

(2) In case flight in any portion of Appendix O will be approved with autopilot 

engaged, flight test evaluations of autopilot modes as for appendix C should be conducted. For 

SLD detect and exit approval, only artificial ice shapes tests should be accomplished. 

(3) De-icing. If the airplane is configured with a de-icing system, the autopilot should 

demonstrate satisfactory performance during the shedding of ice from the airplane. This can be 

demonstrated during autopilot evaluations in natural Appendix C icing conditions. 

b. Ice Shapes Tests. The following represents an acceptable test program for qualification 

of the autopilot in Appendix C and applicable Appendix O in addition to the tests in natural icing 

conditions: 

 Note: The autopilot should be evaluated during the course of the certification program with 

ice shapes. Appendix O ice shapes may degrade the performance of the flight guidance 

system, but should be safe for operation. 

Table 9 Autopilot Test Conditions 

Configuration Speed 

High lift devices retracted/gear up 

configuration: 

 Min speed in icing. 

 VMO/VNE or 250 KIAS, 

whichever is less or a speed at 

which it is demonstrated that the 

airframe will be free of ice 

accretion 

All approved approach configurations  VREF speed in icing 

(1) Autopilot Turns - In the configurations and speeds listed in Table 9, with critical ice 

shapes from appendix C and applicable appendix O (detect and exit and approved portions), 

conduct the following maneuver: autopilot maximum angle of bank turn in one direction and 
AC 23.1419-2E 

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APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

then rapid reversal of angle of bank in the other direction. Autopilot should smoothly roll into 

and out of turns without large overshoots in bank angle or during roll out on headings. 

(2) Approach - If the autopilot has the ability to fly a coupled instrument approach 

and/or go-around, conduct the following maneuvers per AFM procedures with the airplane 

configured as in item (1) above and: 

1. Coupled approach using all normal flap selections. 

2. Go-around using all normal flap selections. 

3. Glideslope capture from above the glidepath, if applicable. 

(3) Low Speed Characteristics. Low speed characteristics should also be evaluated 

when the airplane is stalled with the autopilot engaged, unless the design of the autopilot precludes 

its ability to operate beyond stall warning. For these designs the controllability at stall warning 

should be evaluated. 

(a) Critical ice shapes from appendix C and applicable appendix O (detect and 

exit and approved portions). 

(b) Most adverse weight and center of gravity position, symmetric fuel loading. 

(c) Autopilot servos set to minimum torque/authority. 

(d) In the configurations listed in Table 10, trim at the specified speeds and 

conduct the following maneuvers: 

1. Set the autopilot in altitude hold, reduce power/thrust to establish a 1 to 2 

kt/sec deceleration rate, until stall warning; 

2. Pilot recovery should be initiated 1 second after stall warning. 

3. For aircraft that have autopilots that do not have the capability to disconnect 

at stall warning, or autopilots with low airspeed protection, AFM procedures for autopilot should be 

followed (e.g., manual disconnect at stall warning). 

4. Recovery should be evaluated by applying manufacturers recommended 

procedures. 

5. Evaluate the aircraft response, need for directional/lateral control, airspeed 

increase, and altitude loss (assuming autopilot will disconnect as designed at stall warning). During 

the recovery, verify that no hazardous flight conditions develop. 

Table 10 Autopilot Low Airspeed Tests 

Aircraft Configuration Initial Test Speed Maneuver 

High lift devices retracted/gear 

up 

configuration: 

 Min holding speed in 

icing 

 Straight 

 Turning (maximum 

autopilot bank 

turns.) 

Highest lift landing 

configuration approved in 

icing conditions/gear down: 

 VREF speed in icing  Straight 

 Turning (maximum 

autopilot bank 

turns.) 
AC 23.1419-2E 

70 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(4) Autopilot Indications. If the autopilot is holding a sustained lateral control 

command, it could be indicative of an unusual operating condition for which the autopilot is 

compensating. Examples of such unusual operating conditions are asymmetric lift and/or drag 

due to asymmetric icing, fuel imbalance, or asymmetric thrust. In the worst case, the autopilot 

may be operating at or near its full authority in one direction. If the autopilot were to disengage 

while holding this lateral trim, the result would be that the airplane could undergo a rolling 

moment that could possibly take the pilot by surprise. Therefore, an indication will be required to 

permit the crew to manually disengage the autopilot and take control prior to any automatic 

autopilot disengagement. Unusual control position or bank angle may be shown to be an 

acceptable indication. 

18. Placarding and AFM. This AC provides guidance on airplanes for which the certification 

basis requires an AFM. Guidance for AFMs in this AC also applies to AFM supplements. 

Section 23.1581 states that an airplane flight manual (AFM) must be furnished with each 

airplane and must contain information necessary for safe operation because of design, operating, 

or handling characteristics. 

a. Placarding. Any placarding necessary for the safe operation of the airplane in an icing 

environment must be provided in accordance with § 23.1541. Examples of such placards are: 

(1) Kinds of operation not approved 

(a) If compliance to § 23.1419 not shown, “Flight Into Known Icing Conditions is 

Prohibited.” 

(b) If compliance to § 23.1420(a)(2) or (a)(3) not shown, “Flight in Freezing 

Drizzle, Freezing Rain, or Severe Icing Conditions Prohibited. ” 

(2) Fluid fillerinlets for fluid freezing point depressants should bear a placard 

showing approved fluid type and quantity. 

b. AFM Limitations Section. Section 23.1583 states the AFM must contain operating 

limitations determined under part 23. The AFM should provide the pilot with the information 

needed to operate the ice protection system while in icing conditions or prior to encountering 

icing conditions. The Limitations section of the AFM should include, as applicable, a statement 

similar to the following: “In icing conditions the airplane must be operated, and its ice 

protection systems used as described in the operating procedures section of this manual. Where 

specific operational speeds and performance information have been established for such 

conditions, this information must be used.” Information should also include: 

(1) Icing Conditions. For airplanes with a certification basis that includes § 23.1419 

amendment 23-14 or higher, the AFM should contain a statement similar to “This airplane is 

approved for flight in icing conditions as defined in part 25, Appendix C.” For these airplanes, 
AC 23.1419-2E 

71)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

there should not be references to operational terms such as “light” or “moderate” ice or “known 

icing.” Any airplane manufactured after 1973 that does not have § 23.1419 amendment 23-14 or 

higher in the certification basis must have a statement “This airplane is prohibited from flight 

into known icing conditions.” 

(2) Airspeed 

(a) Minimum airspeed limitations for each configuration approved for icing 

conditions. 

(b) Maximum airspeed limitation (if any) 

(2) Flap. Configuration limitations, if any (for example, a reduced flap setting for 

approach and landing, and flaps up for holding or extended operations in icing conditions). 

These limitations should reflect the configurations used to determine critical ice accretions for 

certification. 

(3) Autopilot. If an autopilot is installed and approved for flight in non-icing 

conditions, or required in non-icing flight for compliance to § 23.1523, it will be required for 

flight in icing conditions based on operational requirements. Similarly, if an autopilot equipped 

airplane is approved for any portion or phase of flight in Appendix O conditions, the autopilot 

will be required to operate in those Appendix O conditions. 

(a) Autopilot operation should be prohibited if any of the following are 

experienced in icing conditions: 

1. Mistrim indication or autopilot alert prior to disconnect 

2. Unusual control force or control deflection, or unusually large control 

forces to move flight controls when the autopilot is disconnected periodically; or 

3. Indications of frequent autopilot retrimming during straight and level 

flight. 

(b) If an autopilot was not shown to operate safely in Appendix O conditions in 

accordance with Section 17 of this AC or an applicant chooses to prohibit autopilot use in 

Appendix O conditions, autopilot operation should be prohibited if any of the following 

conditions in icing flight are experienced: 

1. Severe icing; 

2. Freezing drizzle or freezing rain 

(4) Performance. Performance limitations should be presented for flight in icing that 

reflect any effects on lift, drag, thrust, and operating speeds related to operating in icing 

conditions. These limitations may be presented in the Performance Information section of the 

AFM and included as limitations by specific reference in the Limitations section of the AFM. 
AC 23.1419-2E 

72 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(5) Takeoff. 

(a) Clean Wing Concept. The Limitations section should include a statement 

similar to “Takeoff is prohibited with any frost, ice, snow or slush adhering to the wings, 

horizontal stabilizer, control surfaces, propeller blades, or engine inlet.” Add any additional 

surfaces deemed critical. 

(b) Pre-Takeoff Contamination Check for Turbojet Powered Airplanes 

1. Turbojet airplanes without wing leading edge high lift devices. The 

AFM Limitations section should also require a pre-takeoff visual and tactile inspection of the 

wing leading edge and upper surface in ground icing conditions. In the case of the inability to 

ascertain if the fuel temperature is above freezing, the requirement to perform a visual/tactile 

check can be deleted if it can be shown that undetected ice accumulation does not occur on the 

wing upper surface due to cold soaked fuel. Ground icing conditions should be defined by the 

airplane manufacturer, but one example is defined as the Outside Air Temperature (OAT) below 

5 degrees C (41 degrees F), and one of the following conditions: 

(aa) Visible moisture (rain, drizzle, sleet, snow, fog, etc.) is present; 

or 

(bb) The airplane was exposed to visible moisture (rain, drizzle, sleet, 

snow, fog, etc.) since the previous landing; or 

(cc) The airplane experienced in-flight ice accretion since the 

previous takeoff; or 

(dd) The difference between the dew point temperature and the OAT 

is 3°C (5°F) or less; or 

(ee) Water is present on the wing 

2. Turbojet airplanes with engines mounted behind wing. The 

manufacturer should either show one of the three: 

(aa) Show that undetected ice accumulation does not occur on the 

wing upper surface due to cold soaked fuel (which may be accomplished by analysis of fuel 

system geometry); or 

(bb) Show that undetected ice accumulation on the wing upper 

surface caused by cold soaked fuel does not result in a hazard to the airplane due to engine ice 

ingestion; or 
AC 23.1419-2E 

73)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(cc) Add an AFM Limitation that requires a visual and tactile pretakeoff check if it cannot be ascertained that the wing fuel temperature is above 32 degrees F 

(0 degrees C), and the ground icing conditions listed above exist.

(6) Appendix O Conditions. 

(a) If compliance is based on §§ 23.1420(a)(1) or 23.1420(a)(2), the Limitations 

section must include a requirement that the flightcrew exit all (Appendix O and C) icing 

conditions immediately upon recognition that the Appendix O icing conditions exceed the 

certification boundary. Example language is provided below:

“Severe icing may result from environmental conditions outside of those for which the airplane 

is certified. Intentional flight into severe icing conditions may result in ice build-up on protected 

surfaces exceeding the capability of the ice protection system, or may result in ice forming aft of 

the protected surfaces. This ice may not be shed when using the ice protection systems, and may 

seriously degrade the performance and controllability of the airplane. 

Operations in icing conditions were evaluated as part of the certification process for this airplane. 

Freezing drizzle and freezing rain conditions were not evaluated and are considered severe icing 

conditions for this airplane. 

Intentional flight, including takeoff and landing, into freezing drizzle, freezing rain or other 

severe icing conditions is prohibited. A flight delay or diversion to an alternate airport is 

required if these conditions exist at the departure or destination airports. {Applicant should 

insert visual cue description here} is an indication of severe icing conditions that exceed those 

for which the airplane is certified. If severe icing, freezing drizzle, or freezing rain is 

encountered, immediately request priority handling or declare an emergency from air traffic 

control to facilitate a route, altitude change, diversion or immediate approach and landing as 

required to exit all icing conditions. Stay clear of all icing conditions for the remainder of the 

flight, including landing, unless it can be determined that ice accretions no longer remain on the 

airframe.” 

(b) For certification of detection and exit of Appendix O in accordance with § 

23.1420(a)(1) and §23.1420(a)(2) the Limitations section should contain appropriate limits that 

consider the certification assumptions with respect to portion (phase of flight, freezing drizzle, 

freezing rain, etc.) Example language for an airplane approved to takeoff and land in Appendix 

O is below:

““Severe icing may result from environmental conditions outside of those for which the airplane 

is certified. Intentional flight into severe icing conditions may result in ice build-up on protected 

surfaces exceeding the capability of the ice protection system, or may result in ice forming aft of 

the protected surfaces. This ice may not be shed when using the ice protection systems, and may 

seriously degrade the performance and controllability of the airplane. 
AC 23.1419-2E 

74 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

Operations in icing conditions were evaluated as part of the certification process for this airplane. 

Freezing drizzle and freezing rain conditions were not evaluated in any phase of flight except 

takeoff and landing. 

Except for takeoff and landing, intentional flight into freezing drizzle or freezing rain conditions 

is prohibited. If freezing drizzle or freezing rain conditions are encountered during a hold (in 

any airplane configuration) or in the en route phase of flight (climb, cruise, or descent with high 

lift devices and gear retracted), or if {Applicant should insert cue description here}, immediately 

request priority handling or declare an emergency from air traffic control to facilitate a route or 

altitude change to exit all icing conditions. Stay clear of all icing conditions for the remainder of 

the flight, including landing, unless it can be determined that ice accretions no longer remain on 

the airframe.” 

(c) The Limitations section must contain specific detection criteria – visual cues, 

specific to the aircraft that indicate flight is in appendix O icing conditions for which it is not 

approved. 

 (7) Equipment Limitations. 

(a) The Limitations section must contain the conditions for which all ice 

protection equipment must be activated. 

1. Section 23.1419 (e) requires one of three options. If compliance to 

23.1419(e)(2) is elected, the AFM should state that the IPS be activated at the first sign of ice 

accretion anywhere on the airplane. The procedures section can direct the pilot to look at 

specific location on the airplane. 

2. If an Advisory Ice Detection system is installed, the AFM must state that 

the pilot is responsible for detection of ice accretion, however AFM may state that ice protection 

must be activated “at first sign of ice accretion or ice detection annunciation, whichever occurs 

first.” 

(b) A list of all equipment required for flight in icing conditions. Section 

23.1583(h) (CAR § 3.778) requires that this list be included in the Kind of Equipment List 

(KOEL). 

(c) All icing inspection lights must be operative before flight into known or 

forecast icing conditions at night. The Master Minimum Equipment List (MMEL) must include 

functional icing inspection lights. 

(d) Environmental limitations for equipment operations as applicable (for 

example, minimum temperature for boot operation, maximum altitude for boot operation, and 

maximum outside air temperature for operation of thermal ice protection systems). 

(e) Limitations on operating time for ice protection equipment if these limitations 

are based on fluid anti-ice/deice systems capacities and flow rates. 

(f) Minimum engine speed if the airframe ice protection system does not function 

properly below this speed. 

(8) Placard. The AFM should contain a list of required placards.
AC 23.1419-2E 

75)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

c. AFM Normal Procedures Section. Section 23.1585(a) requires the pilot be provided 

with the necessary normal procedures for safe operation. The system components should be 

described with sufficient clarity and depth that the pilot can understand their function. Unless 

flight crew actions are accepted as normal airmanship, the appropriate procedures should be 

included in the FAA-approved AFM, AFM revision, or AFM supplement. These procedures 

should include use of the system(s) in a safe manner. 

(1) Preflight. Preflight action necessary to minimize the potential of enroute 

emergencies associated with the ice protection system should be included when a flight is 

planned in IMC at temperatures below freezing. 

(a) Ice protection systems should be checked by operating the systems and 

verifying proper cockpit annunciations. Mechanical systems such as pneumatic boots should be 

visually observed for operation. Fluid systems should be visually observed for evidence of fluid 

along the entire protected span. It may take several minutes for the entire panels to receive fluid, 

or the system may have air in it, particularly after a long period of inactivity. 

(b) The quantity of fluid in the reservoir tank, if a fluid ice protection system, 

should be checked. The AFM should specify the fluid types that are approved. 

(c) If two sources of electrical power or two pumps for fluid systems are 

provided, both should be checked during pre-flight. 

(2) In-flight. Procedures should be provided to optimize operation of the airplane 

during penetration of icing conditions, including all flight regimes. The AFM should include 

procedures that advise upon which conditions the ice protection equipment should be activated. 

(a) For fluid anti-ice/deice systems, information and method(s) for determining 

the remaining flight operation time should be provided. 

(b) Procedures for operation of the ice protection system, including activation and 

deactivation, must be established and documented in the Airplane Flight Manual, in accordance 

with § 23.1419(h). Information should be provided to indicate that a de-icing system should not 

be de-activated until the completion of an entire deicing cycle after leaving icing conditions. An 

anti-icing system should not be de-activated before leaving icing conditions. 

(c) The following statement should be included, including those airplanes 

approved for Appendix O conditions: “Convective clouds, above the freezing altitude, that are 

vigorously growing should be avoided since they may contain icing conditions exceeding those 

for which the aircraft has been certified.” 

(d) The recommended procedure for the various flight phases in icing conditions 

should be considered (e.g., whether flaps or landing gear extended, airspeed). AFM 
AC 23.1419-2E 

76 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

recommended procedures would include this operating information. These procedures should 

reflect the certification assumptions in critical ice shape determination. 

1. Holding 

2. Approach 

3. Landing 

4. Missed approach 

(e) Procedures for re-setting the stall warning system to the non-icing schedule if the 

design permits, after leaving icing conditions should be specified. Procedures should include 

pilot verification that airplane is free of ice accretion. 

d. AFM Abnormal or Emergency Procedures Section. . Section 23.1585(a) requires the 

pilot be provided with the necessary abnormal and emergency procedures for safe operation. 

The system components should be described with sufficient clarity and depth that the pilot can 

understand their function. These procedures should include proper pilot response to cockpit 

warnings and a means to diagnose system failures

(1) Procedures to be followed when ice protection systems fail and/or warning or 

monitor alerts occur, or suspected unannunciated failures occur, should be provided. 

Examples include minimum airspeeds to preclude wing stall and reduced flap deflection to 

preclude ice contaminated tailplane stall (ICTS). 

(2) Include any changes to other AFM abnormal or emergency procedures resulting 

from flight in icing conditions. 

(a) For compliance with §§ 25.1420(a)(1) or 25.1420(a)(2): 

1. The method used to determine when icing conditions must be exited, 

must be provided in the AFM abnormal/emergency procedures section, as well as appropriate 

failure indications and crew procedures. An example for a visual cue on the aircraft is: 

The following shall be used to identify freezing rain/freezing drizzle icing conditions and severe 

icing: 

“Accumulation of any ice on the wing aft of the protected area.” 

2. In addition to method certified by the applicant to exit icing conditions, 

the following should also be provided: 

“The following may be used to identify possible freezing rain/freezing 

drizzle conditions: 

(1) Visible rain at temperatures below plus five degrees C OAT. 

(2) Droplets that splash or splatter on impact at temperatures below plus 

five degrees C OAT. 
AC 23.1419-2E 

77)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(3) It is possible to experience severe ice accretions not visible to the flight 

crew, such as lower wing surface accretion on a low wing airplane or 

propeller blade accretion. Performance losses greater than the performance 

section of the AFM may be an indication of severe icing conditions.” 

Manufacturers may consider adding additional performance cues (e.g. XX 

knots speed loss, torque required) as indicators of severe icing. 

3. The abnormal/emergency procedures section should contain guidance 

relative to exiting the icing environment. Information should include recommended use of flight 

controls, minimum airspeeds, configuration of high lift devices, drag devices, automatic flight 

guidance system, engine power/propeller settings (as appropriate), and ice protection system 

operation. Flaps may be retracted following detection of Appendix O if applicant demonstrates 

retraction can be safely accomplished, critical ice shape determination accounted for ice 

accretion with flaps extended, testing to Subpart B used the appropriate flap, and applicant shows 

by analysis there will not be mechanical interference with leading edge flap ice accretion. 

(b) For certification of certain phases of flight to Appendix O, information 

defining these restricted phases should be provided. This information should include any aircraft 

configurations associated with the restricted phases of flight such as flap position, gear 

extension, or airspeed. 

(3) Stall warning and stall recovery procedure. Applicants should evaluate their 

recommended stall recovery procedures to assess its suitability in icing conditions and include in 

AFM. The procedure should consider basic airmanship techniques which establish the reattachment of the boundary layer (flow) of air over the aircraft’s wing surfaces. Such techniques 

should include a definite lowering or pushing forward of the aircraft’s nose/reduction of the 

wing’s angle of attack to ensure that the wing is again producing lift, with loss of altitude no 

more than necessary to achieve that objective. Procedures may include target pitch attitudes to 

achieve the reduction of angle of attack. 

(4) Ice Contaminated Tailplane Stall Recovery Procedure. Limitations and 

procedures for maximum flap deflection in icing conditions are sufficient to address ICTS for 

new airplanes. Training should emphasize flap limitations and not an ICTS recovery procedure. 

e. AFM Performance Section. Performance information, derived in accordance with 

subpart B of part 23, should be provided in the AFM for all relevant phases of flight in 

accordance with § 23.1587. Data are not required at outside air temperatures warmer than +5°C. 

(1) Stall speeds. Effect of critical ice accretions on stall speeds for all icing approved 

configurations should be provided. 
AC 23.1419-2E 

78 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(2) Takeoff performance. 

(a) Effects of ice protection system operation and/or ice accretions, if applicable, 

on takeoff distance and takeoff path, if applicable, should be presented in the same format as the 

basic non-icing data. 

(b) If airplane is approved for takeoff in Appendix O, separate data may be 

provided for “Freezing Drizzle and Freezing Rain” and “Icing Conditions Other Than Freezing 

Drizzle and Freezing Rain.” 

(3) Enroute climb performance. Enroute climb performance with critical ice 

accretions should be presented in the AFM in the same format as the basic non-icing data, if 

required by § 23.69. The critical ice accretion should be based on part 25, Appendix C for 

airplanes which are not approved for flight in Appendix O in the enroute or holding phase. 

(4) Cruise Performance. Not required for certification. The applicant may want to 

consider providing data based on critical, part 25 Appendix C icing conditions as an additional 

cue that the airplane is approaching the limits of certification. Examples may be airspeed at 

maximum power/thrust as a function of weight/altitude/temperature. 

 (5) Landing Performance 

(a) Balked landing climb data with critical ice accretions should be presented in the AFM in 

the same format as the basic non-icing data. 

(b) Approach climb data, if required to be determined, should be presented in the AFM in the 

same format as the basic non-icing data. 

(c) Landing distance, if required to be determined, should be presented in the AFM in the 

same format as the basic non-icing data. 

(d) The VREF in icing conditions, if different than non-icing, should be clear on the data 

charts. 

(e) If airplane is approved for landing in Appendix O, separate data may be provided for 

“Freezing Drizzle and Freezing Rain” and “Icing Conditions Other Than Freezing Drizzle and 

Freezing Rain.” 

 

(7) Appendix O Conditions for Which the Airplane is not Approved. A brief 

statement that freezing rain and freezing drizzle have not been tested. These icing environmental 

conditions outside the icing envelope of part 25, Appendix C, may exceed the capabilities of the 

ice protection system, and it may result in a serious degradation of performance or handling 

characteristics. 

(8) Maintenance Manual. The AFM should reference the maintenance manual for ice 

protection surface cleaning procedures, or application of ice adhesion inhibitors, if the flight 

crew can be expected to perform this function. The AFM should recommend application of ice 

adhesion inhibitors in accordance with the manufacturers instructions. 
AC 23.1419-2E 

79)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

19. Instructions for Continued Airworthiness. 

a. Requirements. Instructions for Continued Airworthiness (ICA) are required in 

accordance with 14 CFR 21.50(b) and 23.1529. ICA should be prepared in accordance with part 

23, Appendix G. As a minimum the following should be addressed: 

 (1) Basic description of the ice protection system operation, components, and 

installation 

(2) Servicing information, such as fluid type and quantities

(3) Location of panels used for inspection, and/or instructions to access components 

(4) Scheduling information for each applicable component including cleaning, 

inspecting, adjusting, testing and lubrication

(5) Overhaul or replacement periods for components, if any 

(6) Instructions for removing and replacing components 

(7) Precautions, such as toxicity of freezing point depressant fluid or flammability of 

some cements 

(8) Cleaning instructions, such as only soap and warm water for pneumatic deicing 

boots 

(9) Limitations on the materials that can be applied, such as ice adhesion inhibitors, 

rubber preservatives, cosmetic coatings 

(10) Recommendations on the frequency of use of ice adhesion inhibitors 

(11) Special equipment or materials, such solvents, cements, edge filler, conductive edge 

sealer, rollers for pneumatic boot installation. 

b. Fluid Ice Protection Systems. The tailcone, empennage and other areas aft of the TKS 

de-icing fluid flow should be inspected after each use of the ice protection system. This 

inspection should concentrate on extraneous fluid build-up on electrical contacts, flight control 

surface bearings, bellcranks, etc. The ice protection system fluid evaporates very slowly. 

Therefore, contaminates that collect in the fluid in areas of joints, skin laps, etc. may cause the 

acceleration of corrosive action. 

c. Repairs for Pneumatic Deicing Boots. Boot manufacturers have developed repair 

procedures for pinholes, cuts and tears. The repair process for these types of damage is critical 

because proper operation of the boots could be affected. If leaks or pinholes are not periodically 
AC 23.1419-2E 

80 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

repaired, the entire system could become inoperable if water, drawn in by the vacuum that holds 

the boots deflated, subsequently refreezes and blocks a pneumatic line. The performance of 

deicing boots is dependent on the height and speed of deicing boot inflation and of the 

composition of the surface ply and its ice adhesion characteristics. Repairs should not pinch off 

tubes and thereby reduce inflation height. With these concerns in mind, the following guidance 

represents a minimum that should be addressed for repair procedures (data may be provided by 

the deicer manufacturer’s to address the concerns by similarity to prior installations or testing): 

(1) Testing. The following tests should be accomplished:

(a) Boot Cycle Testing. The integrity of the repair should be evaluated via boot 

cycling at the maximum normal system operating pressure. Cycling should continue until the 

repair or boot fails. The normal deflation time may be shortened to speed up the test. For 

example, a 174-second deflation cycle can be reduced to 18 seconds while maintaining the 

six-second inflation time. Any material applied to the whole surface of the boot should also be 

evaluated in this test. 

(b) Cold Temperature Cycling. The testing in (1) (a) should be repeated at a 

temperature of 0 degrees F or colder.

(c) Hot Temperature. The boots may be exposed to hot temperatures, especially 

after on the ground on a hot, sunny day. The combination of high temperature and fluid 

exposure may cause deterioration and should be evaluated, see paragraph (e). 

(d) Proof and Burst Pressure Testing. This testing should be accomplished to 

show compliance to § 23.1438(b). When conducting the proof pressure test at 1.5 times 

maximum operating pressure, the repaired deicing boot should hold that pressure for 60 seconds 

and the repair should not fail. After the proof pressure test, the system should be inflated at 

maximum operating pressure, isolated, and the pressure drop verified not to exceed three Pounds 

Per Square Inch (PSI) in one minute. 

(e) Fluids Susceptibility. The repair should be exposed to various fluids for at 

least 24 hours in combination with a high temperature (160 degrees F) and the boots cycled at 

nominal pressure for at least 24 hours. Fluids to be evaluated include: fuels, oil, hydraulic fluids, 

glycol/water mixture, deicing boot age reduction, surface treatments and ice adhesion products, 

and ground deicing fluids. One method of accomplishing this test is to soak a rag with the fluid, 

place on the deicing boot over the repair, seal to prevent evaporation, and place in an oven at 

160 degrees F for 24 hours. Following this exposure the boot is removed, and cycled for 

24 hours. The deicing boot should inflate and hold air, and the repairs should remain in place 

and not leak air. 

(f) Sand and Rain Erosion. Sand and rain erosion testing should be 

accomplished to show that the repair does not erode at a greater rate than the boot. A typical 

sand erosion test is ASTM G-76-95. A typical rain erosion test is conducted on a whirling arm 
AC 23.1419-2E 

81)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

rig that exposes the boot to a rainfall rate of one inch per hour at 300 to 500 Miles Per Hour 

(MPH) (depending on the airplane maximum speed); using one to two Millimeter (mm) diameter 

drops. 

(g) The inflation height over the repaired area should be measured and compared 

against other unrepaired portions of the boot at temperatures covering the part 25, Appendix C 

envelope. 

(h) Ice Shedding. Ice shedding performance in the area of the repair, and of the 

whole boot if any material is applied to the whole boot, should be evaluated throughout the 

part 25, Appendix C continuous maximum and intermittent maximum icing conditions. It is 

particularly important to cover the range of temperatures and liquid water contents of part 25, 

Appendix C and the expected operational airspeeds. Simulated icing tests, such as an icing 

tunnel, may be used. 

(2) Materials Properties. Any material applied to the boots should be compatible with 

the deicing boot material. Use of brittle repair materials is not recommended. If the boot is 

completely resurfaced with a material, that material should be electrically conductive to allow 

bleeding of static charge from the deicing boot. 

(3) Repair Process Limitations. The repair process should contain limitations and 

quality control procedures such as: 

(a) Size of repairs. The maximum allowed repair size should be established and 

tested. Another consideration is the effect of the repair failure on the airplane. 

(b) Location and depth of repairs. Can structural elements such as tube fabric 

or stitches be damaged or can the wrong internal layers, such as tube fabric, be bonded together? 

It is recommended that boot manufacturers limits be used. 

(c) Density of repairs. The maximum density of repairs (number per area) 

should be tested. It is recommended that boot manufacturers limits be used. 

(d) Application of solvents and other chemicals. The application of solvents 

and other chemicals used in the repair process that can disbond the boot should be controlled so 

that they cannot penetrate internal layers of the boot. 

(e) Applicability of the repair procedure. Broken stitches represent a structural 

failure of the boot and should not be repaired. There should also be guidelines as to when 

severely worn boots should be replaced. 

d. Repairs for Electrothermal Propeller and Engine Inlet Deicing Boots. Boot 

manufacturers historically have not developed repair procedures for electrothermal deicing boots 

because the thermal mass characteristics of the repaired location will change and affect ice 
AC 23.1419-2E 

82 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

shedding. The following guidance is a minimum that should be addressed for electrothermal 

boot repairs: 

(1) Testing. The following tests should be accomplished:

(a) Fluids Susceptibility. The repair should be exposed to various fluids and the 

boots operated. Fluids to be evaluated include: fuels, oil, hydraulic fluids, glycol/water mixture, 

deicing boot age, appearance and ice adhesion products, and ground deicing fluids. 

(b) Sand and Rain Erosion. Sand and rain erosion testing should be 

accomplished to show that the repair does not erode at a greater rate than the boot. 

(c) Thermal Characteristics. The thermal conductivity of the repair should be 

evaluated to insure that it does not provide a “cold spot” on the deicing boot, resulting from 

either a higher thermal mass or lower thermal conductivity of the repair material. 

(d) Ice Shedding. Ice shedding performance in the area of the repair, and of the 

whole boot if any material is applied to the whole boot, should be evaluated throughout the 

part 25, Appendix C, continuous maximum and intermittent maximum icing conditions. 

Simulated icing tests, such as an icing tanker, may be used. 

(e) Vibration. The airplane should be tested in icing conditions to verify the 

repair on one blade does not directly or indirectly (due to ice shedding) cause unacceptable 

propeller vibration. 

(2) Materials Properties. Any material applied to the boots should be compatible with 

the deicing boot material. Use of brittle repair materials is not recommended. The material 

should be electrically non-conductive and should have similar thermal conductivity of the 

deicing boot material. The effect of the chemicals on the electrical wires or foil should be 

evaluated. 

(3) Repair Process Limitations. The repair process should contain limitations and 

quality control procedures such as: 

(a) Size of repairs. The maximum allowed repair size should be established and 

tested. Another consideration is the effect of the repair failure on the airplane. 

(b) Location and depth of repairs. Can heating elements such as wires or 

etched foil be damaged or can the resistance of the wire or foil be altered by the repair 

procedure? 

(c) Density of repairs. The maximum density of repairs (number per area) 

should be tested. 
AC 23.1419-2E 

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APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(d) Application of chemicals. Can the application of too much chemicals 

penetrate the boot and cause internal debonding of the boot? 

(e) Applicability of the repair procedure. Can the repair be accomplished on 

severely worn boots? 

20. Ground Deicing Fluids. 

a. Background. Notices (Flight Standards Information Bulletins for Air Transportation, 

FSAT, prior to 2006) are published yearly by the FAA, containing the latest deicing and antiicing fluid holdover time guidelines and the most recent information available on operating in 

ground icing conditions. Airplane operators use this information to develop aircraft ground 

deicing and anti-icing programs required by 14 CFR §§ 121.629(c) and 135.227(b) (3). 

Operators who operate under § 135.227(b) (1) or (2) may still utilize the Notice information as 

guidance in their ground deicing plan. AC 20-117, AC 135-16, AC 135-17, AC 120-58, and AC 

120-60B provide additional information on deicing and anti-icing of aircraft before takeoff. 

(1) Why use ground deicing fluids? Aircraft are deiced before takeoff and, as 

required, anti-iced using thickened pseudo-plastic fluids. This procedure provides temporary 

protection from ice adhering to the aircraft’s surfaces before takeoff. The thicker fluids (Type II, 

IV) provide considerably higher holdover times than the Type I fluids.

b. Potential Issues. The following have occurred in service resulting in re-designs and 

modified takeoff procedures and limitations when certain ground deicing fluids are applied 

before takeoff. 

(1) Performance. The presence of thickened fluid may affect the airplane’s 

performance because the fluids may not completely flow off the aircraft wing and lift devices 

before liftoff. 

(2) Longitudinal Control. Fluid residue may cause increased pilot control forces 

during takeoff rotation and climb for airplanes with reversible control surfaces.

(3) Vibration and Controllability. The fluid may also collect in the balance bays of 

aerodynamically or weight balanced control surfaces, due to inadequate drainage. This may 

result in unbalanced control surfaces, unexpected changes in control forces, and control surface 

vibrations. Additionally, there has been one turbojet airplane in which the elevator tab was 

found to be aerodynamically sensitive to accumulation of foreign materials on its surface, in this 

case ground anti-icing fluid, causing severe vibration and limit cycle oscillations.

(4) Freezing of Controls. Anti-icing fluid may collect and evaporate in quiet cove 

areas, like those along control surface hinge lines. When the residue of the evaporated anti-icing 

fluid is re-hydrated by humidity, rain or during washing of the airplane, it may freeze and lock 

the control surface when the airplane climbs to altitudes with subfreezing temperatures. The 

residue does not contain a freezing point depressant, usually a glycol compound, which 

evaporates when the anti-icing fluid dries. Rehydrated fluid has been found in and around gaps 
AC 23.1419-2E 

84 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

between stabilizers, elevators, tabs, and hinge areas. This especially can be a problem with nonpowered controls. Some pilots reported that they have had to reduce altitude until the frozen 

residue melted, which restored flight control movement. This phenomenon has not been 

experienced when a two-step deicing/anti-icing procedure is used. The first step is generally a 

hot Type I fluid mixture which flushes out residue. 

c. When Should These Issues Be Addressed? The evaluations of the above issues are not 

required for showing compliance to 14 CFR § 23.1419. Typically the effect of fluids on the 

airplane are evaluated by the airframe manufacturer, after type certification, at the request of an 

operator that is seeking approval of a ground deicing and anti-icing program incorporating Type 

II or Type IV fluid. However, there are design features, analyses and tests that an airplane 

manufacturer may want to consider during certification to prevent re-designs after type 

certification if it is anticipated operators will use ground deicing/anti-icing fluids. This 

information is provided in this AC at the request of several airplane manufacturers. 

d. How Should These Issues Be Addressed? Some issues can be addressed by design. 

There is currently no requirement to test for airplane performance or controllability after the 

application of deice/anti-ice fluids. The aerodynamics working group of the SAE G-12 Aircraft 

Ground Deicing Committee has been tasked to develop a SAE recommended practice for 

approving the use of fluids on airplanes. This recommended practice will be considered for part 

23 guidance in a subsequent revision to this AC. The following paragraphs summarize methods 

that have been used by manufacturers in previous projects to address these issues. They are 

provided to assist airplane manufacturers in evaluating fluids for their specific designs. 

(1) Design.

(a) The airplane design should be analyzed for possible collection sites. 

(b) The design should incorporate drain holes, particularly in control surface 

balance bays. 

(2) Airplane Performance. There have been various methods to evaluate

performance. Typically the lowest takeoff gross weight and maximum flap position approved 

for takeoff is considered critical because of the lower scheduled takeoff rotation speed. Three 

methods that have been used by airplane manufacturers: 

 (a) Takeoff parameters such as time to rotate/lift-off and rotate/lift-off airspeeds 

have been compared during takeoffs with and without fluids. Flow-off of fluids from the wing 

was simultaneously documented during takeoff roll and rotation. Stall speeds have been checked 

at altitude with 1 knot/sec decelerations. 

 (b) Takeoffs with and without fluids have been performed back to back and the 

lift loss decrement at liftoff determined. The flight test measured lift loss was then corrected by 

computational fluid dynamics (CFD) to determine the lift loss decrement at stall. A maximum 

5.24% difference in stall lift coefficient between the clean airplane and airplane with fluid has 
AC 23.1419-2E 

85)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

been considered acceptable for jet powered airplanes, and an 8% decrement has been considered 

acceptable for propeller powered airplanes. 

 (c) Takeoffs at fixed pitch angles are performed with and without fluid. Several 

pitch angles representing the range of pitch angles at liftoff are tested. A 6% decrement in lift 

coefficient at liftoff has been considered significant.

(3) Controllability. 

(a) The following has been evaluated at minimum practical gross weight, and 

maximum takeoff gross weight for airplanes with reversible longitudinal control, with minimum 

approved and maximum approved takeoff flap position, with all engines operating: 

1. Control power and control force during rotation at the scheduled VR. 

2. Controllability during takeoff with rotation at 10 knots or 7%, whichever 

is less, below the scheduled VR. 

3. Controllability tests (± 40o bank angle changes, ± 0.5g or stall warning) 

with takeoff flaps, as soon as practical after liftoff, either at V2 +10 or the speed at 50 feet + 10 

KIAS, depending on airplane category. 

4. Vibration/buffet at Vne or Vmo. 

(b) The following has been evaluated for multi-engine airplanes at minimum 

practical gross weight, with maximum approved takeoff flap position, with simulated one engine 

inoperative: 

1. Control power and control force during rotation at VR

2. Controllability tests (± 30o bank angle changes, +1.3/-0.8g or stall 

warning) with takeoff flaps, as soon as practical after liftoff, either at V2 or the speed at 50 feet, 

depending on airplane category. 

(4) Fluids. 

(a) Number of Fluids. The airplane manufacturer should evaluate the type and 

brand of fluids to be approved for the airplane. A representative Type II fluid, and a Type IV 

fluid if approved in the AFM, should be tested. The viscosity of the fluid should be considered 

when determining the brand of fluid to test. Type III fluid need not be tested if Type II or IV 

fluid is tested and showed acceptable lift loss. If the Type II and IV testing showed takeoff 

procedures needed to be modified, than Type III fluid may not need to be tested if the takeoff 

procedures for Type III are similarly modified. 
AC 23.1419-2E 

86 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(b) Fluid Application. 

1. Type II, III, and IV fluids should be applied undiluted. 

2. Procedures for de-icing and anti-icing should follow the proposed 

recommended procedures. All applicable surfaces (including the horizontal stabilizer) should be 

treated. Slats/flaps should be in the recommended position for fluid application. 

3. Takeoff tests should be conducted as soon as possible following antiicing fluid application. 

(c) It is preferable to test at the coldest outside air temperature at which the fluid 

can be used undiluted. 

(5) Airplane Systems. Any adverse effect on aircraft systems should be noted (e.g. 

ECS, APU inlet, vent blocking)

(6) Post Flight Inspections. Several flights should be conducted after one step 

applications of the thickened pseudo-plastic fluids to be approved for the airplane. Post flight 

inspections should be conducted to determine if fluid residue is present on the airplane in areas 

that may cause one of the problems discussed in paragraph 17.b. 

e. Airplane Flight Manual 

(1) Fluids. The type and brands of fluid approved, along with any minimum outside 

air temperature limitation, should be in the Limitations section. 

(2) Limitations. Procedures modified as a result of ground fluids should be in the 

Limitations section. Examples for part 23 airplanes are an increase in takeoff speeds and use of 

flaps. 

(3) Procedures. Pre-flight or post-flight inspection and cleaning of areas in which 

fluid residue is shown to occur. 

(4) Performance. Any increases in takeoff distance due to takeoff speeds increased 

above the established threshold should be presented in the Performance section. It should be 

noted that the takeoff testing is not required to be conducted on contaminated runways. Since 

runways may be contaminated in conditions in which these fluids will be used in operation, there 

should be a CAUTION that states the takeoff distance data is based on a dry runway, and that 

takeoff distances will be increased on contaminated runways.

f. Instructions for Continued Airworthiness. The following, if applicable, should be 

addressed in maintenance manual: 
AC 23.1419-2E 

87)

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(1) Inspection.

 (a) Drain holes. 

(b) Control balance bays. 

(c) Identified aerodynamically quiet areas. 

(2) Cleaning. High-pressure washing with a hot Type I fluid/water mix in areas where 

fluid could accumulate. For those locations equipped with Type III fluids, in lieu of Type I 

fluids, it is suggested that a high pressure washing with a heated Type III/water mix be 

employed. Such a procedure may require subsequent lubrication. 

g. Runway Deicing Fluids. Airplane manufacturers should be aware that since 1997 a 

problem of catalytic oxidation has been occurring on aircraft using carbon brakes. In 1997, 

airports started using more environmentally friendly fluids to deice runways. This resulted in the 

use of potassium formates and/or acetates. These chemicals (organic salts) attack the carbon in 

the brake and create a catalytic oxidation which softens the carbon, causing it to flake and 

crumble undetected and unpredictably over time thus reducing the life and long-term efficiency 

of the brakes themselves. SAE G-12F, among other industry working groups, has been working 

for some time to try and reduce these effects from runway de-icers. These runway fluids are now 

being found to adversely affect anti-icing fluid applied to aircraft and also to promote the 

formation of anti-icing fluid residue gel in aerodynamically quiet areas of the aircraft. 

AC 23.1419-2E 

Appendix 1 

A1-1 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

APPENDIX 1. DEFINITIONS 

1. DEFINITION OF TERMS. For the purposes of this AC, the following definitions should 

be used. 

a. Anti-Ice. The prevention of ice formation or accumulation on a protection surface, either 

by evaporating the impinging water or by allowing it to run back and off the surface or freeze on 

non-critical areas. 

b. Part 25, Appendix C Icing Conditions. The part 25, Appendix C certification icing 

condition standard for approving ice protection provisions on aircraft. The conditions are 

specified in terms of altitude, temperature, LWC, representative droplet size (MED), and cloud 

horizontal extent. 

NOTE 6: In part 25, Appendix C, the term “mean effective diameter” refers 

to what is now called the “Median Volume Diameter (MVD),” determined using 

rotating multi-cylinders and assuming a Langmuir distribution.

c. Artificial Ice. A structure formed from material other than frozen water, but intended to 

represent an ice accretion. See “simulated ice shapes.” 

d. Critical Ice. The aircraft surface ice shape formed within required icing conditions 

results in the most adverse effects for specific flight safety requirements. For an aircraft surface, 

the critical ice shape may differ for different flight safety requirements, e.g., stall speed, climb, 

aircraft controllability, control surface movement, control forces, air data system performance, 

dynamic pressure probes for control force “feel” adjustment, ingestion and structural damage 

from shed ice, engine thrust, engine control, and aeroelastic stability. 

e. Deice or Deicing. The periodic shedding or removal of ice accumulations from a 

surface. This occurs by destroying the bond between the ice and the protection surface. 

f. Exceedance Icing Conditions. Icing conditions for which the airplane is not approved. 

g. Freezing Drizzle. Drizzle is precipitation on the ground or aloft in the form of liquid 

water drops that have diameters less than 0.5 mm and greater than 0.05 mm (100 μm to 500 μm). 

Freezing drizzle exists at air temperatures less than zero degrees C (supercooled), remains in 

liquid form, and freezes upon contact with objects on the surface or airborne. 

h. Freezing Precipitation. Freezing rain or drizzle falling through or outside a visible 

cloud. 

i. Freezing Rain. Rain is precipitation on the ground or aloft in the form of liquid water 

drops which have diameters greater than 0.5 mm. Freezing rain is rain that exists at air 
AC 23.1419-2E 

Appendix 1 

A1-2 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

temperatures less than zero degrees C (supercooled), remains in liquid form, and freezes upon 

contact with objects on the surface or airborne. 

j. Ice Crystals. Any one of a number of macroscopic, crystalline forms in which ice 

appears. 

k. Icing Conditions. The presence of atmospheric moisture and temperature conducive to 

airplane icing. 

l. Intercycle Ice. Ice that builds up on a deiced surface and exists immediately before 

actuation of the deice system. 

m. Liquid Water Content (LWC). The total mass of water contained in liquid drops 

within a unit volume or mass of air, usually given in units of grams of water per cubic meter 

(g/m3) or kilogram of dry air (g/kg). 

n. Mean Effective Diameter (MED). The calculated drop diameter that divides the total 

liquid water content present in the drop size distribution in half, i.e., half the water volume will 

be in larger drops and half the volume in smaller drops. The value is calculated, based on an 

assumed droplet size distribution, (e.g. Langmuir distribution) which is how it differs from 

median volume diameter. 

o. Median Volume Diameter (MVD). The drop diameter that divides the total liquid water 

content present in the drop distribution in half, i.e., half the water volume will be in larger drops 

and half the volume in smaller drops. The value is obtained by actual drop size measurements. 

p. Mixed Phase Icing Conditions. Partially glaciated clouds at an ambient temperature 

below 0°C. The clouds contain ice crystals and supercooled liquid water drops. 

q. Monitored Surface. The surface of concern regarding the ice hazard, (e.g., the leading 

edge of a wing). Ice accretion on the monitored surface may be measured directly or correlated 

to ice accretion on a reference surface. 

r. Pre-Activation Ice. Protected surface ice accretion prior to the full effectiveness of the 

ice protection system.

s. Protected Surface. A surface containing ice protection, typically located at the surface’s 

leading edge. 

t. Protection Surface. Active surface of an ice protection system, for example, the surface 

of a deicing boot or thermal ice protection system.
AC 23.1419-2E 

Appendix 1 

A1-3 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

u. Reference Surface. The observed (directly or indirectly) surface used as a reference for 

the presence of ice on the monitored surface. The presence of ice on the reference surface must 

occur prior to – or coincidentally with – the presence of ice on the monitored surface. Examples 

of reference surfaces include windshield wiper blades or bolts, windshield posts, ice evidence 

probes, propeller spinner ice, and the surface of ice detectors. The reference surface may also be 

the monitored surface. 

v. Residual Ice. Ice that remains on a protected surface immediately following the 

actuation of a deicing system.

w. Reversible Flight Controls. The flight deck controls that are connected to the pitch, 

roll, or yaw control surfaces by direct mechanical linkages, cables, or push-pull rods such that 

pilot effort produces motion or force about the control surface hinge line. Conversely, force or 

motion originating at the control surface (through aerodynamic loads, static imbalance, or trim 

tab inputs, for example) is transmitted back to flight deck controls. 

(1) Aerodynamically Boosted Flight Controls: Reversible flight control systems that 

employ a movable tab on the trailing edge of the main control surface linked to the pilot's 

controls or to the structure in such a way as to produce aerodynamic forces that move, or help to 

move, the surface. Among the various forms are flying tabs, geared or servo tabs, and spring 

tabs. 

(2) Power-Assisted Flight Controls: Reversible flight control systems in which some 

means is provided, usually a hydraulic actuator, to apply force to a control surface in addition to 

that supplied by the pilot to enable large surface deflections to be obtained at high speeds. 

x. Runback Ice. Ice formed from the freezing or refreezing of water leaving an area on an 

aircraft surface that is above freezing and flowing downwind to an area that is sufficiently cooled 

for freezing to take place. This ice type is frequently a byproduct of partially evaporative 

(running wet) ice protection systems, thermal deicing systems, and can occur on airfoils near 

freezing temperature. 

y. Simulated Ice. Ice shapes that are fabricated from wood, epoxy, or other materials by 

any construction technique. 

z. Supercooled Large Drops (SLD). Supercooled liquid water that includes freezing rain 

or freezing drizzle. 

aa. Supercooled Drops. Water drops that remain unfrozen at temperatures below 0°C. 

Supercooled drops exist in clouds, freezing drizzle, and freezing rain in the atmosphere. These 

drops may impinge and freeze after contact on aircraft surfaces 
AC 23.1419-2E 

Appendix 1 

A1-4 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

2. DEFINITION OF ACRONYMS. 

Acronym Definition 

AC Advisory Circular 

ACO Aircraft Certification Office 

AFM Airplane Flight Manual 

AIR Aerospace Information Report 

AOA Angle of Attack 

APU Auxiliary Power Unit 

ARP Aerospace Recommended Practice 

AS Aerospace Standard 

ATC Air Traffic Control 

C Centigrade 

CAR Civil Air Regulations 

CFR Code of Federal Regulations 

CG Center of Gravity 

CS Certification Specification (EASA) 

ELOS Equivalent Level of Safety 

F Fahrenheit 

FAA Federal Aviation Administration 

FPM Feet Per Minute 

FSAT Flight Standards Information Bulletins for Air Transportation 

EASA European Aviation Safety Agency 

EFIS Electronic Flight Information Systems 

FIDS Flight Ice Detection Systems 

ICA Instructions for Continued Airworthiness 

ICTS Ice Contaminated Tailplane Stall 

IMC Instrument Meteorological Conditions 

IPS Ice Protection System 

KCAS Knots Calibrated Airspeed 

KIAS Knots Indicated Airspeed 

KOEL Kind of Equipment List 

LOUT Lowest Operational Use Temperature 

LWC Liquid Water Content 

MDI Magnetic Direction Indicator 

MED Mean Effective Diameter 

MFC Maximum Mach number for stability characteristics 

MMEL Master Minimum Equipment List 
AC 23.1419-2E 

Appendix 1 

A1-5 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

Acronym Definition 

MOC Means Of Compliance 

MSL Mean Sea Level 

MVD Median Volume Diameter 

NASA National Aeronautics and Space Administration 

NTSB National Transportation Safety Board 

OAT Outside Air Temperature 

PFIDS Primary Flight Ice Detection Systems 

PMA Parts Manufacturing Approval 

POH Pilot's Operating Handbook 

PSI Pounds Per Square Inch 

PSIG Pounds Per Square Inch Gauge 

RGL Regulatory and Guidance Library 

RPM Revolutions Per Minute 

SAE Society of Automotive Engineers 

SLD Supercooled Large Drops 

STC Supplemental Type Certificate 

TC Type Certificate 

TCDS Type Certificate Data Sheet 

TEU Trailing Edge Up 

TSO Technical Standard Order 

VFE Flaps Extended Speed 

VIT Variable Incidence Tailplane 

VLE Landing Gear Extended Speed 

VMC Minimum Control Airspeed 

VMO Maximum Operating Airspeed 

MMO Maximum Operating Mach Number 

VNE Never Exceed Airspeed 

VR Takeoff rotation speed 

VS1 Stall speed in a specific configuration 

VREF Reference Landing Approach Airspeed 

V2 Takeoff safety speed 

 AC 23.1419-2E 

Appendix 2 

A2-1 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

APPENDIX 2. GUIDELINES FOR DETERMINING CERTIFICATION BASIS ON 

FLIGHT IN ICING APPROVAL STCS AND AMENDED TCS 

1. My CAR 3 (or earlier certification basis) aircraft has ice protection systems installed 

and is not placarded against flight into known icing. Am I approved for flight in icing 

conditions? 

These CAR 3 airplanes are permitted to fly in icing conditions if: 

 the ice protection systems are installed per type design data of the same model in the 

Type Certificate Data Sheet (TCDS); 

 the Pilot’s Operating Handbook (POH), AFM, or AFM supplement associated with the 

ice protection systems do not prohibit it; 

 the equipment listed in the KOEL is installed and functioning; and 

 the airplane complies with the equipment requirements of § 91.527 or § 135.227, if 

applicable. 

2. What if I have a CAR 3 (or earlier certification basis) airplane that is permitted to fly in 

icing conditions but I replace the ice protection system with another system? 

It depends on what is meant by another system. If it is replacement parts, such as replacing 

pneumatic deicing boots with those from another manufacturer, the certification basis can remain 

unchanged; see Appendix 5 of this AC for more information. If it is another type of system, for 

example replacing a pneumatic deicing system with a freezing point depressant system or 

electrothermal system, compliance to § 23.1419, amendment 23-14 must be shown. Section 

23.1419, amendment 23-43 would not be required since a modification to an ice protection 

system is considered “not significant” under the Changed Product Rule. 

3. As a follow-up to the last question, suppose I change my mind and want to re-install my 

ice protection systems. Will my aircraft be approved for flight in icing? 

Yes, as long as the systems are installed per type design data and the POH, AFM, or AFM 

supplement associated with the ice protection systems do not prohibit flight in icing conditions 

(or “flight into known icing”). Retroactive removal of flight into known icing approval can only 

be accomplished by the airworthiness directive process. 

4. I have a CAR 3 (or earlier certification basis) airplane that has no ice protection system 

installed and the type design data does not contain flight in icing approval. What is the 

certification basis if I add ice protection systems? 

Under the Changed Product Rule, adding approval for flight in icing conditions is considered a 

significant change (AC 21.101-1) and compliance should be shown to the latest amendment. In 
AC 23.1419-2E 

Appendix 2 

A2-2 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

addition, § 91.527 or § 135.227, if applicable, has a minimum requirement of equipment. The 

applicable regulations for an icing certification are: 

 23.603 23.1093 23.1301 23.1327 23.1501 23.1581 

 23.773 23.1095 23.1309 23.1351 23.1525 23.1583 

 23.775 23.1097 23.1323 23.1357 23.1529 

 23.905 23.1099 23.1325 23.1547 

 23.929 23.1101 23.1326 23.1419 23.1559 

It is recognized that compliance to § 23.1419(a), which requires that the airplane meet Subpart B 

performance in icing conditions, may be impractical for some CAR 3 airplanes. The Changed 

Product Rule allows the applicant to elect compliance to amendment 23-14 for that particular 

paragraph of § 23.1419. In this case the performance regulations are used as guidelines as 

discussed in paragraph 13a (2) of this AC. 

5. My airplane has some ice protection systems installed but is not certified for flight in 

icing. A later model of my airplane, which is on the same TCDS, is certified for flight in 

icing in accordance with § 23.1419. The later model does have a different engine installed 

with higher horsepower and a different ice protection system. Can I install the exact same 

ice protection systems as the later model, install a new engine with at least the same 

horsepower, and be certified for flight in icing? 

Yes, and similarity may be used to show compliance to the applicable regulations. However, 

there may be some testing required. The current method of compliance to § 23.1419 includes 

tests (susceptibility to ice contaminated tailplane stall, for example) that may not have been 

accomplished during certification of the later model. 
AC 23.1419-2E 

Appendix 3 

A3-1 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

APPENDIX 3. GUIDELINES FOR SUPPLEMENTAL TYPE CERTIFICATES (STC) 

AND AMENDED TYPE CERTIFICATES ON AIRPLANES 

1. APPLICATION. 

a. As stated in the “APPLICABILITY” section, the guidance in this AC applies to any 

STC or amended TC on an airplane for which the applicant wants approval under the 

provisions of § 23.1419. Increase in gross weight, changes in engine power, and propeller 

changes could affect approval in icing and these areas would have to be evaluated using AC 

23.1419-2D as the method of compliance. An applicant wishing to use an alternate Means of 

Compliance (MOC) needs to consult the Standards Office. Whether the certification basis for 

the STC or amended TC includes 14 CFR, § 23.1419 at amendment 23-14 or 23-43 is 

irrelevant as far as the tests that should be accomplished. The difference in the certification 

basis does not change the tests that must be accomplished, only their pass/fail criteria. 

b. Compliance to icing regulations has been either an afterthought or totally disregarded 

on many modification programs on aircraft certified for flight in icing conditions. In some 

cases, the rationale used was that since the ice protection systems were not modified, icing 

regulations do not need to be addressed. This may be an incorrect assumption. Icing 

regulations may need to be addressed for any modification that could affect the following in 

icing conditions: 

(1) Aircraft performance 

(2) Flying qualities, 

(3) Engine operation 

(4) Essential system operation. 

c. If it is desired to retain flight in icing approval of the modified airplane, the following 

examples are modifications in which compliance to icing regulations need to be revisited: 

(1) Engine changes 

(2) APU 

(3) Propeller changes 

(4) Engine inlet or accessory inlet changes 

(5) Antennae installations or other external modifications 

(6) Gross weight increases 

(7) CG envelope increase 
AC 23.1419-2E 

Appendix 3 

A3-2 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(8) Flight envelope increase

(9) Turboprop conversion 

(10) Modifications to lifting surfaces 

(11) Installation of vortex generators 

(12) Modifications to ice protection systems 

(13) Addition of/or re-location of fuel vents 

(14) Addition of/or autopilot replacement. 

d. The icing regulations that are addressed in this appendix are: 

(1) § 23.929 

(2) § 23.1093 

(3) § 23.1301 

(4) § 23.1309 

(5) § 23.1419 

e. The following guidance address some specific, common modifications: 

(1) Engine Changes. 

(a) Effects of increased engine power or thrust: 

1. On airplanes with a certification basis at amendment 23-14 or higher, 

any degradation in stall characteristics, stability or control, or marginal characteristics, due to 

increased engine power or thrust, will require re-evaluation with ice accretions. Since the 

pass/fail criteria are qualitative, testing (original airplane and modified airplane) should be 

accomplished back to back by the same test pilot. Stall warning should also be evaluated. 

Although the margins are not a concern at high power, they need to evaluate if higher power 

masks any stall warning cues. The following tests should be accomplished: 

(aa) Stall characteristics and stability of minimum weight and 

maximum weight, aft CG limit 

(bb) Controllability at forward CG limit and critical weight. 
AC 23.1419-2E 

Appendix 3 

A3-3 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

2. Susceptibility to ice contaminated tailplane stall should be addressed for 

airplanes in which the engine thrust increase is greater than 10 percent or the airplane has a 

service history of ICTS susceptibility. Maximum power is usually more critical than idle. This 

cannot be done with analysis on a propeller airplane with reversible controls due to second order 

effects. Flight testing should be accomplished with 40-grit sandpaper and intercycle/residual ice 

on horizontal tailplane, intercycle/residual ice on vertical stabilizer, and 45-minute ice accretions 

on unprotected leading edge tail surfaces. 

 Engine Induction Icing. Refer to AC 23-16A for guidance. 

(c) Ice Shedding. Engine compliance data to § 33.77 should be compared 

between the currently installed engine and the proposed engine. If the ice slab used to show 

compliance is smaller for the proposed engine, ice shedding from the airframe should be readdressed. Data on ice shedding may be available from the airplane TC holder. Engine inlet 

lip ice shedding should be addressed. The amount of ice mass that could be shed should be 

compared to a similar, approved engine installation or to part 33 engine compliance data. 

(d) Effects of Decreased Engine Power, Thrust or Bleed Air. 

1. Ice Protection System Operation. Bleed air mass flows, pressures 

and temperatures of the proposed engine and of the existing, certified engine should be 

compared. If there is a reduction, the effectiveness of the ice protection systems must be 

substantiated. 

2. Airplane Performance. Airplane performance in icing conditions 

should be re-evaluated. 

(2) Essential APU. When an essential APU is modified or added, operation in icing 

conditions should be addressed similarly to engines since essential APUs are covered by 

§ 23.1093. 

(3) Propeller Changes. 

(a) Section 23.929 states that propellers (except wooden propellers) and other 

engine installations must be protected against the accumulation of ice as necessary to enable 

satisfactory functioning without appreciable loss of thrust when operated in the icing conditions 

for which certification is requested. 

(b) If the deicing system is listed on the propeller TCDS, it does not indicate that 

compliance to § 23.929 was shown. It means that the deicing system was shown to function 

properly, the deicing system complies with propeller structural and vibration regulations, and 

deicing system failure modes, as discussed in § 23.929 of AC 23-16, cannot cause an unairworthy condition. 
AC 23.1419-2E 

Appendix 3 

A3-4 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(c) The typical analysis report from the deicing boot manufacturer is not 

sufficient by itself to show compliance to § 23.929. The typical report calculates intercycle ice 

thickness for various flight and icing conditions, but does not calculate the effect on propeller 

efficiency, which must be done to show no appreciable loss of thrust. For STCs, it would be 

acceptable to show that intercycle ice is equal to or less than the accretions obtained on the same 

propeller on an airplane that was flight tested in icing conditions and shown to have no 

appreciable loss in thrust. 

(d) The typical deicing boot manufacturer report also contains a caveat that it 

does not address propeller runback ice. Similarity to another propeller that was flight tested in 

icing conditions is usually done to address runback. Similarity would include propeller and 

deicing boot aerodynamic and thermal similarity, deicing cycle time, propeller RPM, and flight 

conditions. Note that metal and composite propellers have different thermal masses. 

(e) As a final qualitative check for both intercycle and runback ice on new 

airplane programs, airplane performance is checked during flight tests in icing conditions. A test 

point as close to minus 22 degrees F as possible should be included in the flight tests. 

(f) The propeller installation, including spinner and cowl geometry, must be 

compared to previously tested installations in icing conditions. Changes that could allow 

moisture to reach the brush blocks must be avoided. 

(g) If the proposed propeller is calculated to have higher efficiency than the 

existing, approved propeller, the guidance in paragraph 1e (1) (a) of this appendix should be 

followed. 

(h) If the proposed propeller(s) and/or deicing system are predicted to increase the 

size of intercycle ice, the effects of propeller ice shed onto other parts of the airplane should be 

addressed. 

(i) For New Propeller Deice Electrical Power Systems: 

1. The surface temperature characteristics of the propeller boots should be 

shown to be the same as original certified system. 

(aa) If the temperature characteristics and deice timing cycle are shown 

to be changed, flight testing in measured natural icing conditions are required to evaluate 

propeller deicing and airplane performance 

(bb) If the temperature characteristics and deice timing cycle are shown 

to be unchanged, a demonstration of propeller deicing and airplane performance in natural icing 

conditions should be performed. 

(cc) Flight testing should be accomplished as close to –22 degrees F as 

possible. 
AC 23.1419-2E 

Appendix 3 

A3-5 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

2. A rational analysis of the heat generated by the system should be made 

and compared to the existing system if the system is located in areas where ice accretion and 

runback could be affected, such as the spinner. 

(4) Engine Inlet or Accessory Inlet Changes. Guidance is provided in the “engine 

changes” section above. It should be noted that § 23.1093 applies to engine oil and accessory 

cooling inlets as well as induction inlets. 

(5) Antennas, Installations or Other External Modifications. 

(a) When antennas, cameras, fairings for such installations, or other external 

installations such as drain masts are installed on aircraft, the installer should show the following: 

1. The predicted ice accretion does not contribute significantly to drag; 

2. There is no ice-shedding hazard due to impact or ingestion on 

downstream structure, engines or propellers. See paragraph 14 of the AC for guidance on ice 

shedding. 

3. There is no ice related performance reduction of lifting surfaces; 

4. There is no ice related effect on downstream air data sensors or ice 

detectors. 

(b) A very conservative, simple analysis may be accomplished first to show the 

objectives (a) 1 and (a) 2. If the conservative analysis fails, the analysis can be refined to 

determine if the initial analysis was overly conservative. The conservative analysis can assume 

the following: 

1. The water catch area is the full frontal area of the installation; 

2. Collection efficiency is one. 

3. No runback or evaporation of impinging water.

4. Assume the shape on blade antenna will be similar to airfoils and the 

shape on low profile antennae will be single horn shapes. 

(c) The installer should determine the critical icing condition, and the 45-minute 

hold in continuous maximum conditions needs to be included. If the analysis shows a problem, 

then one or more of the following can be accomplished: 

1. Determine realistic collection efficiency either with an ice accretion code 

or with the “FAA Icing Handbook”; 
AC 23.1419-2E 

Appendix 3 

A3-6 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

2. Determine the real impingement limits by using an icing code, which may 

reduce the collection area; 

3. Run the full configuration in an icing code to determine if the installation 

is in a shadow zone. 

4. If drag is a problem, run an ice accretion code to determine a more 

realistic ice shape. 

(d) Flight tests in measured natural icing or with simulated ice shapes should be 

accomplished to determine if there are any detrimental effects due to the ice accretions if: 

1. The installation is upstream of air data sensors or an ice detector; or 

2. The installation is on a lifting surface or 

3. The installation could create a wake on a lifting surface. As an example, 

if an external modification is large enough (e.g. dish antenna), it may interfere with the flow field 

around the tail and the susceptibility to ICTS may need to be addressed. 

(e) The one exception to (d) 2 is fairings. An analysis to show the impact on 

maximum lift coefficient, in combination with flight tests with no ice accretions, may be 

acceptable. 

(6) Gross Weight Increases. 

(a) At the increased angle of attack for a given airspeed, the impingement limits 

will change. An impingement analysis needs to be accomplished to show the ice protection 

coverage remains adequate. 

(b) The impingement analysis should also evaluate unprotected areas such as fuel 

vents. 

(c) If the following flight testing with no ice show no degradation from the 

unmodified aircraft, and no marginal characteristics, flight testing with ice (or simulated ice 

accretions) are not required: 

1. Stall warning, stall characteristics, and stability at maximum weight, aft 

CG limit

2. Stall speeds and controllability at maximum weight, forward CG limit. 

(d) Operational speeds and AFM/POH performance data in icing conditions need 

to reflect higher stall speeds. 
AC 23.1419-2E 

Appendix 3 

A3-7 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(e) Climb performance in icing conditions should be evaluated to determine if the 

airplane is capable of operating safely. 

(f) An analysis should show increased weight makes the airplane equal or less 

susceptible to tailplane stall. The analysis should evaluate tail trim requirements and tail ice 

accretion at the higher airplane angle of attack. 

(g) The service history of the airplane should be reviewed to determine if stall 

warning and low airspeed awareness should be addressed. 

(7) CG Envelope Increase. Generally, the same guidance used for gross weight 

increases can be used for CG envelope increases. The one exception is when an increase of 

forward center of gravity limit on airplanes makes an airplane more susceptible to ice 

contaminated tailplane stall. This should be addressed by flight testing for airplanes with 

unpowered, reversible elevators or with propellers. An analysis may be acceptable for other 

configurations. 

(8) Flight Envelope or Operating Procedure Changes. 

(a) If an increase in maximum operating altitude is applied for, the applicant 

should demonstrate: 

1. The ice protection system operating pressures (for pneumatic 

systems) or temperatures (for hot air systems) by dry air testing; and 

2. The stall speeds and stall characteristics associated with ice accretions 

if these are shown to be influenced by Mach number. 

(b) The effect of increased cruise airspeeds and increased altitudes that could 

affect windshield ice accretion, and adequacy of the windshield heat, should be addressed. 

 

(c) The effect of different operating airspeeds and altitudes that could affect 

critical ice accretions. 

(9) Turboprop Conversion. 

(a) If the ice protection systems utilize engine bleed air for operation, the 

pneumatic lines may accumulate more water than the current unmodified type design. This 

water can subsequently refreeze and block the pneumatic lines, resulting in failure of some or all 

zones of the pneumatic system. The applicant needs to show that the pneumatic deicing system 

will continue to function in icing conditions. 
AC 23.1419-2E 

Appendix 3 

A3-8 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(b) The pneumatic deicer operating pressure may also decrease at lower engine 

RPMs. A minimum engine RPM for acceptable pneumatic operating pressure, which should 

allow for descent, should be established and published in the AFM/POH. 

(10) Modifications to Lifting Surfaces. 

(a) Critical ice accretions (including pre-activation, intercycle, residual, and 

runback) may have to be re-defined, especially if the changes affect wing angle of attack. Stall 

strips are good collectors of ice and are an example where leading edge ice accretions should be 

re-defined. If ice accretions are changed or the modifications could affect control power or 

control surface hinge moments, flight testing with simulated ice accretions should be 

accomplished to evaluate one or more of the following: 

1. Stall warning, stall characteristics, and stability at maximum weight, aft 

CG limit; 

2. Stall speeds, stall warning, controllability and performance at maximum 

weight, forward CG limit; 

3. ICTS susceptibility at light weight, forward CG limit if the aircraft has 

unpowered, reversible elevators or propellers. 

4. For unprotected winglets, flutter margins needs to be addressed. 

(b) Susceptibility to ICTS should be addressed for either horizontal or vertical tail 

modifications or wing modifications that are predicted to increase ICTS susceptibility. ICTS 

susceptibility may be addressed by analysis on jet-powered aircraft with irreversible elevator 

controls. 

(11) Installation of Vortex Generators. 

For vortex generators that are installed near the leading edge, the applicant should 

provide data on expected ice accretions. Flight conditions to consider are the 45-minute hold, 

descent, and approach. Substantiation of the effects on stall speeds, stall characteristics, and 

stability and control should be provided. 

(12) Modifications to Ice Protection Systems. 

(a) Critical ice accretions may have to be re-defined. If ice accretions are 

changed or the modifications could affect control power or control surface hinge moments, flight 

testing with simulated ice accretions should be accomplished to evaluate one or more of the 

following: 

1. Stall warning, stall characteristics, and stability at maximum weight, aft 

CG limit; 
AC 23.1419-2E 

Appendix 3 

A3-9 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

2. Stall speeds; stall warning and controllability at maximum weight, forward 

CG limit; 

3. ICTS susceptibility at light weight, forward CG limit if the aircraft has 

unpowered, reversible elevators or propellers. 

(13) Addition of or Relocation of Fuel Vent. 

As a minimum an impingement analysis and/or similarity should be used to show that 

ice does not obstruct the fuel vents. 

(14) Replacement of Autopilot 

Guidance in this AC, paragraphs 17 for autopilots should be consulted. Similarity to the 

previously approved autopilot through analysis or testing may be acceptable. There are specific 

scenarios in which autopilots can get the pilot into trouble in an airplane approved for flight into 

known icing. Those scenarios resulted in accidents and are factual. Based on our service 

experience, even though there are no regulatory requirements addressing autopilots in airplanes 

approved for known icing, applicants are strongly encouraged to include features that mitigate 

these autopilot induced accident scenarios. Where it would be impractical to add such a feature, 

the design should include adequate trim in motion cues. For replacement autopilots, the design 

of the original and replacement autopilots should be compared. 

(15) Erosion Strips for Deicing Boots 

The guidance in Appendix 5 for replacement deicing boots is applicable. 

AC 23.1419-2E 

Appendix 4 

A4-1 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

APPENDIX 4. GUIDELINES FOR CERTIFYING ICE PROTECTION SYSTEMS 

ON AIRPLANES NOT CERTIFICATED FOR FLIGHT IN ICING 

1. APPLICABILITY. There may be times when applicants may want to certificate an ice 

protection system installation on an airplane that is to remain not certificated for flight in icing. 

This used to be called a “non-hazard” basis. This means that the aircraft is prohibited from flight 

in icing conditions but there is some ice protection to facilitate an exit from an inadvertent icing 

encounter. The following guidance provides a reference; novel systems may require additional 

considerations. 

2. SUBPART B – FLIGHT.

a. The applicant must show that installation of the system (not operating) does not affect 

performance, stalls, controllability, maneuverability, stability, trim, ground/water handling, 

vibration and buffet, and, if applicable, high speed characteristics. If any of these are affected, it 

should be shown that applicable regulations are still complied with and place the appropriate 

information in the AFM. Compliance should be accomplished with dry air flight tests. If the 

system is being evaluated as an amended TC or STC, it is not necessary to investigate all weight 

and CG combinations and flight conditions when results from the airplane certification testing 

clearly indicate the most critical combination to be tested. 

b. In some cases the effect of system operation may need to be evaluated. For pneumatic 

deicing boots, the operation of the boots (inflation) should have no hazardous affect on airplane 

performance and handling qualities. The effect of pneumatic boot operation on stall speed and 

stall warning should be evaluated and appropriate information placed in the AFM. Freezing 

point depressant systems when operating have been shown to increase drag. 

3. SUBPART D – DESIGN AND CONSTRUCTION. 

a. The ice protection systems should be evaluated to determine the impact to the airframe 

structure per the applicable regulations in subpart D. The load conditions determined from 

Subpart C should be used in this evaluation. The individual ice protection system components 

should also be evaluated to determine that they would withstand the load conditions from 

Subpart C if their failure can cause a hazard. Thermal effects on structure of thermal ice 

protection systems and fluid/structure compatibility of freezing point depressant systems should 

be evaluated. 

b. An evaluation of flutter characteristics to account for the added mass of the ice protection 

systems should be made per § 23.629. 

c. If a thermal windshield ice protection system is installed, an evaluation of the visibility 

due to distortion effects through the protected area should be made. In accordance with 

§ 23.775(g), a probable single failure of a transparency heating system should not adversely 

affect the integrity of the airplane cabin or create a potential danger of fire. 
AC 23.1419-2E 

Appendix 4 

A4-2 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

d. For wing and empennage electrical deicing systems, the indirect effects of lightning 

maybe an issue. The airplane must be shown to be protected against catastrophic effects from 

lightning in accordance with § 23.867. As a minimum the effect of the ice protection system 

installation should be addressed by analysis and design. 

4. SUBPART E – POWERPLANT. For an airplane not certificated for flight in icing, 

compliance to § 23.929 is not required but compliance to § 23.1093 is required. 

5. SUBPART F – EQUIPMENT.

a. On airplanes with a certification basis of amendments 23-20 and higher, compliance to 

§ 23.1301 must be shown. Compliance to § 23.1301 would entail showing the airplane can 

safely exit inadvertent icing encounters by providing the data in paragraphs (1) through (5). 

Subsequent installations on other aircraft models can be based upon similarity to the natural icing 

tests that were conducted provided that the installations can be shown to be sufficiently similar 

(ref. paragraph 10.f.). Airfoil size, shape, operating envelope, and airplane ice accretion sites 

should be included in the similarity analysis: 

(1) A functional flight test in dry air 

(2) Icing tunnel tests in part 25, Appendix C icing conditions 

(a) Evaluate the ice protection system operation 

(b) Determine protected area ice accretion such as runback, intercycle ice 

(3) Empirical flight test data (natural icing or tanker) 

(a) Validate ice accretions for ice shape flight testing 

(b) Evaluate and document susceptibility of movable control surfaces to fixed 

surface bridging/freezing and subsequent lockup of controls 

(c) Evaluation of autopilot operation and recommended operation in icing 

(d) Qualitatively evaluate climb performance 

(e) Evaluate degradation in windshield visibility 

(4) Dry air ice shape flight tests 

(a) Ice shapes 

1. Five minute accretions on unprotected areas 

2. Protected area ice accretions 
AC 23.1419-2E 

Appendix 4 

A4-3 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(b) Objectives 

1. Evaluate stability and controllability 

2. Evaluate increase in stall speed. 

b. Compliance to the latest applicable amendment of § 23.1309 should be shown. See AC 

23.1309-1D for additional guidance. To show compliance to § 23.1309 the following would 

apply: 

(1) Show that installation of the system, and normal operation of the system, does not 

affect operation of essential equipment. Examples are: 

 

(a) Electromagnetic interference testing 

(b) Operation of the stall warning system. 

(2) Show that hazards are minimized on single engine airplanes and prevented for 

multi-engine airplanes in the event of a probable failure. Examples of failures that should be 

addressed: 

(a) Auto inflation of deicing boots 

(b) Failures that could cause an asymmetric wing condition 

(c) Bleed air leaks of thermal systems 

(d) Electrical shorts in electrothermal systems. 

(3) Compliance can be by analysis or test or a combination. The loss of the ice 

protection system would not have to be considered since the airplane is not approved for flight in 

icing. For the purposes of the current regulation, the system would not be an essential load. 

(4) Show that the system when operating normally does not create a greater hazard than 

operating with no ice protection system. For example, on systems where there is runback the 

applicant should show that the runback ice does not cause a greater hazard than the ice accretion 

with no ice protection. Hazards to address would be stalls, tailplane stalls, and engine operation 

if applicable. 

c. To show compliance to § 23.1351 an electrical load analysis should be done if the ice 

protection system utilizes the airplane’s primary electrical power system. If the ice protection 

system utilizes its own alternator/generator, other regulations in § 23.1351 may be applicable. 

d. Compliance to § 23.1419 or § 23.1420 are not required. 
AC 23.1419-2E 

Appendix 4 

A4-4 

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

6. SUBPART G – OPERATING LIMITATIONS AND INFORMATION. 

a. A cockpit placard in view of the pilot and the AFM should state that the airplane is 

prohibited from flight in icing conditions. 

b. A description of all ice protection system controls and annunciations should be in the 

AFM. 

c. The AFM should contain a WARNING that stall warning in icing conditions may not be 

reliable and must not be relied upon in icing conditions, even with a heated stall warning sensor. 

d. Stall speeds with the system installed or system operating, if increased from the baseline 

airplane, should be published in the AFM. An incremental delta increase may be used for all 

configurations, if appropriate. 

e. Procedures to mitigate locked controls due to ice accretion, if applicable. 

f. Autopilot operation procedures. 

(1) For aircraft equipped with an autopilot, the autopilot should be disconnected 

periodically to check for unusual control force or deflection, and to move the flight controls to 

check for evidence of ice accreting in control surface gaps or frozen actuators. 

(2) There should be a WARNING that the autopilot will NOT maintain airspeed if ice 

accretes on the airplane. MONITOR airspeed closely. 

g. Instructions for continued airworthiness in accordance with § 23.1529 should be 

provided. 
AC 23 1419-2E 

Appendix 5 

A5-1

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

APPENDIX 5. GUIDELINES FOR APPROVAL OF REPLACEMENT 

PARTS FOR AIRFRAME DEICING SYSTEMS 

1. The requirements leading to approval of replacement airframe deicing systems (propellerdeicing systems will be addressed in a revision) or airframe thermal deicing or anti-icing systems 

are functions of the project certification basis and similarity with the original part(s), as 

summarized in Table 5-1 and discussed in the following paragraphs: 

TABLE 5-1. SUMMARY OF TEST REQUIREMENTS FOR REPLACEMENT AIRFRAME 

DEICING COMPONENTS 

Aircraft 

Approved for 

Flight in Icing 

Conditions? 

Certification 

Basis 

Approval 

Process 

Required 

Tests to Show 

Safe Operation 

throughout Part 

25, Appendix C 

Icing Conditions 

Natural Icing Flight 

Tests 

 

No PMA Not required Not required 

Yes CAR § 3.712 STC See paragraph b. See paragraph b. 

Yes 23-0 to 23-13 STC See paragraph b. See paragraph b. 

Yes 23-14 to 23-42 STC Required See paragraph c. 

Yes 23-43 or higher STC Required Required 

a. For aircraft whose certification basis does not include CAR § 3.712 or § 23.1419, the 

deicing system is optional equipment and not required. In this case, the replacement parts can be 

approved via the Parts Manufacturer Approval (PMA) process in 14 CFR, part 21, subpart K. 

The replacement parts must be shown to function properly, remove ice or prevent ice accretion 

as well as the previously installed equipment, not introduce additional failure modes that could 

prevent continued safe flight and landing, and not affect stall characteristics, stability or control 

of the airplane in dry air. Comparative tests of the original versus the replacement parts are 

acceptable to show how the part removes or prevents ice accretion. 

b. For aircraft whose certification basis is CAR § 3.712 or an original issue under 

§ 23.1419, an STC is required. Original certification of these aircraft only required that 

pneumatic deicers be installed per approved data and that they have a positive means of 

deflation. No icing flight tests were required, and airplanes were considered “approved for flight 

into known icing” when the airplane was equipped with a complement of certificated deicing or 

anti-icing equipment spelled out in operational requirements. For replacement parts in these 

aircraft it is advisable for the Aircraft Certification Office (ACO) to contact the ACO 

maintaining the original type design data to determine factors such as variance with the original 

design, the original certification requirements, and the service history of the original product. 
AC 23.1419-2E 

Appendix 5 

A6-2

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

The replacement parts must be shown to function properly, remove ice or prevent ice 

accretion as well as the previously installed equipment, and not introduce additional failure 

modes that could prevent continued safe flight and landing. Comparative tests of the original 

versus the replacement parts may be acceptable. If the original certification basis is to be 

utilized, it is highly recommended that an entry in the AFM supplement limitations section, or a 

placard, with the following wording be required: “This airplane has not demonstrated 

compliance with the icing environment requirements of 14 CFR, part 25, Appendix C. 

c. For replacement parts on an aircraft whose certification basis is § 23.1419, 

amendments 23-14 through 23-42, an STC is required. Flight testing in measured, natural icing 

conditions should be accomplished if the replacement parts are of different materials or have 

different design characteristics. Supplemental testing in artificial icing conditions (icing tunnel, 

tanker) should also be accomplished to cover the complete part 25, Appendix C envelope. The 

replacement parts must be shown to function properly, remove ice or prevent ice accretion as 

well as the previously installed equipment, and not introduce additional failure modes that could 

prevent continued safe flight and landing. A matrix of performance and flying qualities as 

discussed in paragraph 13a (2) of this AC should be accomplished. The Standards Office should 

be contacted since the requirement to flight test in measured, natural icing conditions is 

dependent on a number factors such as whether AFM performance in icing conditions is based 

on protected surface ice accretions, the service history of the airplane, and flight testing 

accomplished during the original certification with protected surface ice accretions. Follow-on 

applications of the new parts in aircraft other than the initial certification may then be approved 

through similarity provided the conditions in § 23.1419(c) are met. There may be cases where 

minor modifications would not require additional measured, natural flight tests. 

d. For replacement parts on an aircraft whose certification basis is § 23.1419, 

amendment 23-43 or higher or those aircraft where the applicant wants to add “flight in icing 

conditions” operational approval, an STC is required. Flight testing in measured, natural icing 

conditions is required if the replacement parts are of different materials or have different design 

characteristics. Supplemental testing in simulated icing conditions (icing tunnel, tanker) may 

also be required to cover the complete part 25, Appendix C envelope. The replacement parts 

must be shown to function properly, remove ice or prevent ice accretion as well as the previously 

installed equipment, and not introduce failure modes that could prevent continued safe flight and 

landing. A matrix of performance and flying qualities as discussed in paragraph 13a (1) of this 

AC should be accomplished. Follow-on applications of the new parts in aircraft other than the 

initial certification may then be approved through similarity provided the conditions in 

§ 23.1419(c) are met. There may be cases where minor modifications would not require 

additional measured, natural flight tests. 

3. Engineering judgment must be used to determine that the modifications would not affect 

the effectiveness of the ice protection in natural icing conditions. If there is any question 

as to the need for a particular design to be subject to natural icing tests, the ACO should 

contact the Standards Office as well as the ACO that performed the original certification 

and the national resource specialist for aircraft icing. Again, seemingly benign 

differences can have significant negative effects on an aircraft's ice protection capability. 
AC 23.1419-2E 

Appendix 6 

A6-1

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

APPENDIX 6. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT 

AMENDMENT 23-XX 

1. In accordance with § 23.1419, Amendment 23-XX, "capable of operating safely" in icing 

conditions means that the airplane must comply with § 23.21(c)(1) with critical Appendix C ice 

accretions. Section 23.21(c)(1) defines all of Subpart B but lists the exceptions. Guidance for 

each subpart B regulation, as related to icing, is in the following Table 6-1. 

2. In accordance with § 23.1420, Amendment 23-XX, "capable of operating safely" in icing 

conditions means that the airplane must comply with § 23.21(c)(3) with critical ice accretions in 

the portions of Appendix O for which the airplane is certified. Section 23.21(c)(3) defines all of 

Subpart B but lists the exceptions. Table 6-1 can also be used for compliance guidance, with the 

exception of takeoff. For takeoff guidance in Appendix O, see Appendix 9. 

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 

AT AMENDMENT 23-XX 

Regulation 14 CFR 

Section 

Guidance 

Proof of 

compliance 

23.21 Only critical weight and CG loadings, as determined during the noncontaminated airplane tests, are required. Natural icing flight tests 

may be accomplished at a nominal CG. 

Load 

distribution 

limits 

23.23 Only critical weight and CG loadings, as determined during the noncontaminated airplane tests, are required. Tests in which lateral 

load is critical, such as stall characteristics, should include tests with 

maximum allowable fuel asymmetry. 

 There should not be different load, weight, and CG limits for flight 

in icing. Operation in icing conditions should be essentially 

transparent to the flightcrew in that no icing-specific methods of 

operation (other than activating ice protection systems) should be 

required. This philosophy is also based on human factors issues to 

reduce operational complexity and flightcrew workload. 

General 

(Performance) 

23.45 Must comply, except performance should be determined up to a 

temperature of standard plus five degrees C instead of plus 

30 degrees C. It can be assumed that ice accretion will not be 

present on the airframe at temperatures warmer than plus five 

degrees C. For deicing systems, the average drag increment and 

propeller efficiency determined over the deicing cycle may be used 

for performance calculations. Propeller deicing codes do not 

address propeller runback icing. Similarity to previously flighttested configurations or qualitative performance evaluations in 

natural icing should be accomplished. 

Stall speed 23.49 

(a)(b) 

Must comply with critical ice accretions. Stall speeds with critical 

ice accretions must be determined and published in the AFM. 
AC 23.1419-2E 

Appendix 6 

A6-2

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 

AT AMENDMENT 23-XX 

Regulation 14 CFR 

Section 

Guidance 

Takeoff speeds 23.51 Takeoff speeds must be based on stall speed with Appendix C 

takeoff ice accretions for normal, utility, and acrobatic category 

turbojet powered airplanes without a wing leading edge high lift 

device and commuter category airplanes, if the applicant seeks 

certification for flight in icing conditions, if the stall speed with 

takeoff ice accretion exceed the threshold defined in § 23.51(d). 

If applicable, when determining the takeoff speeds V1, VR, and V2

for flight in icing conditions, the values of VMCG and VMC

determined for non-icing conditions may be used. 

Takeoff 

performance 

23.53 The effect of operating ice protection systems on engine 

performance must be accounted for. Must be based on takeoff icing 

speeds if different than non-icing in accordance with § 23.51(d). It 

can be assumed there is no ice accretion prior to lift-off for those 

airplanes in which takeoff ice accretion must be considered. 

Accelerate-stop 

distance 

23.55 The effect of any increase due to takeoff in icing conditions may be 

determined by analysis. 

Takeoff path 23.57 

Takeoff 

distance and 

takeoff run 

23.59 May be calculated by a suitable analysis. 

Takeoff flight 

path 

23.61 

Climb: general 23.63 For the regulations defined in § 23.21(c)(1), must be compliant with 

critical Appendix C ice accretions, except ambient temperatures 

above 41-degrees F do not need to be addressed. 
AC 23.1419-2E 

Appendix 6 

A6-3

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 

AT AMENDMENT 23-XX 

Regulation 14 CFR 

Section 

Guidance 

Climb: all 

engine 

operating 

23.65 Must be shown to be compliant with engine power losses associated 

with operating ice protection equipment that are not prohibited for 

takeoff. 

The effect of ice accretion on climb performance (lift, drag and 

climb speed) must be accounted for if not excepted per § 23.65(c). 

For example, accounting for takeoff ice accretion in Appendix C 

conditions is not required for normal category reciprocating or 

turboprop powered airplanes. The effect of Appendix C takeoff ice 

accretion must be accounted for on normal category turbojets if the 

stall speed increase or climb performance degradation are above the 

thresholds defined in § 23.65(c). Flight testing of the takeoff ice 

accretion should be accomplished to evaluate stall speed and climb 

performance. 

*Takeoff 

climb: one 

engine 

inoperative 

23.66 Applicable for multiengine airplanes if compliance to § 23.65(c) is 

required. 

Climb: one 

engine 

inoperative 

23.67 The effect of operating ice protection systems on engine 

performance must be accounted for. The effect of ice accretion on 

climb performance (lift, drag and climb speed) must be accounted 

for if not excepted per § 23.67(e). For example, accounting for 

takeoff ice accretion in Appendix C conditions is not required for 

normal category reciprocating or turboprop powered airplanes. The 

effect of Appendix C takeoff ice accretion must be accounted for 

(except for § 23.67(c)(1) on commuter category airplanes and 

turbojets without a wing leading edge high lift device, such as slats, 

if the stall speed increase or climb performance degradation are 

above the thresholds defined in § 23.67(e). Flight testing of the 

takeoff ice accretion should be accomplished to evaluate stall speed 

and climb performance. 

Enroute 

climb/descent 

23.69 Must be determined with “Enroute” ice if the enroute climb speed 

selected in icing is more than the non-icing speed by the greatest of 

three KCAS or three percent VS1, or if the service ceiling with 

“Enroute” ice is less than 22,000 ft. MSL. The enroute climb speed 

must be at least the minimum airspeed specified in the AFM 

limitations section. 
AC 23.1419-2E 

Appendix 6 

A6-4

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 

AT AMENDMENT 23-XX 

Regulation 14 CFR 

Section 

Guidance 

Glide: single 

engines 

airplanes 

23.71 If applicable and if ice protection systems become inoperative with 

engine out, the best glide speed in icing must be determined if 

different from the non-icing speed by more than three KCAS. May 

be determined analytically. 

Reference 

landing 

approach speed 

23.73 Must be based on stall speed with critical Appendix C ice accretion 

if the stall speed with critical ice at maximum landing weight with 

landing flaps, gear down exceeds that in non-icing conditions by 

more than the greater of three (3) knots CAS or three (3) percent 

VS0. The VMC determined for non-icing conditions may be used if 

the vertical tail does not have ice accretion in normal system 

operation. If based on the non-ice VREF , the airplane with critical 

ice accretions must still comply with the stall warning and 

maneuver margin requirements of § 23.207.

Landing 

distance 

23.75 Must be determined with critical ice accretion if VREF in icing 

conditions is greater than VREF in non-icing conditions. The effect 

of landing speed increase on the landing distance may be 

determined by analysis. 

Balked landing 23.77 

(a)(b)(c) 

Must be compliant with critical ice accretions, all ice protection 

systems operational, all landing flap settings, at an ambient 

temperature of 41 degrees F. 

General 

(control) 

23.141 Must be shown to be compliant with the regulations defined in § 

23.21(c)(1) with critical ice accretions. 

Controllability 

and 

maneuverabilit

y (General) 

23.143 

(a)(b) 

Controllability is evaluated concurrently with other tests, and during 

the flight, when conducting ice shape and natural Appendix C flight 

testing. In lieu of the evaluation of sudden engine failures for multiengine airplanes, the following is accomplished: 

If the non-icing VMC is used for takeoff speeds, it must be shown 

that the airplane is safely controllable and maneuverable at the 

minimum V2 for takeoff with the critical engine inoperative and 

with “takeoff” ice accretion. 

If the non-icing VMC is used for VREF, it must be shown that the 

airplane is safely controllable and maneuverable during a go-around 

starting at the minimum VREF with the critical engine inoperative 

and with critical ice accretion. 

 23.143 

(c) 

Maximum control forces are applicable. 
AC 23.1419-2E 

Appendix 6 

A6-5

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 

AT AMENDMENT 23-XX 

Regulation 14 CFR 

Section 

Guidance 

` 23.143 

(d)(1) 

Controllability is evaluated concurrently with other tests, and during 

the flight, when conducting ice shape and natural Appendix C flight 

testing. 

 23.143 

(d)(2)& 

(d)(3) 

Susceptibility to ICTS should be evaluated with critical ice 

accretions, sandpaper ice and pre-activation ice as discussed in 

paragraph 13.e. of this AC. 

 23.143 

(d)(4) 

Aileron hinge moment reversal and other lateral control anomalies 

have been identified as causal factors in icing accidents and incidents. 

The following maneuver, along with the evaluation of lateral 

controllability during a deceleration to the stall warning speed during 

the tests to show compliance to §§ 23.201 and 23.203, and the 

evaluation of static lateral-directional stability for compliance to § 

23.177, is intended to determine the susceptibility of the airplanes to 

aileron hinge moment reversals or other adverse effects on lateral 

control characteristics due to ice accretion. 

(a) Holding configuration, holding ice accretion, maximum landing 

weight, forward center-of-gravity position, minimum holding speed 

(highest expected holding angle-of-attack); and 

(b) Landing configuration, holding ice accretion, medium to light 

weight, forward center-of-gravity position, VREF (highest expected 

landing approach angle-of-attack). 

1. Establish a 30-degree banked level turn in one direction. 

2. Using a step input of approximately 1/3 full lateral control 

deflection, roll the airplane in the other direction. 

3. Maintain the control input as the airplane passes through a wings 

level attitude. 

4. At approximately 20 degrees of bank in the other direction, apply a 

step input in the opposite direction to approximately 1/3 full lateral 

control deflection. 

5. Release the control input as the airplane passes through a wings 

level attitude. 

6. Repeat this test procedure with 2/3 and up to full lateral control 

deflection unless the roll rate or structural loading is judged excessive. 

It should be possible to readily arrest and reverse the roll rate using 

only lateral control input, and the lateral control force must not reverse 

with increasing control deflection.

 23.143 

(e) 

Susceptibility to ICTS must be evaluated with pre-activation ice 

accretions as defined in Table 2. A 0.5g pushover and 1.5g pull-up 

are required for pre-activation ice in lieu of the 0g pushover. 
AC 23.1419-2E 

Appendix 6 

A6-6

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 

AT AMENDMENT 23-XX 

Regulation 14 CFR 

Section 

Guidance 

Longitudinal 

control 

23.145 

(a)(b) 

Must be shown to be compliant with critical ice accretions. 

Susceptibility to ICTS should be evaluated during flap extension 

tests. 

 23.145 

(c) 

Not required. Flight tests above VMO/MMO are not conducted for 

icing certification. 

 23.145 

(d) 

Not required. 

 23.145 

(e) 

Evaluation of failure of primary longitudinal flight control system 

not required for icing certification. 

Directional and 

lateral control 

23.147 

(a)(b) 

Critical configuration(s) determined from the non-contaminated 

airplane tests must be evaluated. 

 23.147 

(c) 

Evaluation of failure of primary lateral flight control system not 

required for icing certification. 

Minimum 

control speed 

23.149 

(a) 

Definition of VMC, applicable to landing phase in icing conditions. 

 23.149 

(b) 

Not required for takeoff phase in Appendix C icing conditions. 

 23.149 

(c) 

If the vertical tail is unprotected or has intercycle/residual/runback 

ice during ice protection system normal operation, VMC speeds with 

critical ice must be evaluated to determine if the proposed VREF

speed in icing complies with § 23.73. Static VMC tests may be used. 

 23.149 

(d) 

Not required. 

 23.149 

(e) 

Applicable to landing phase in icing conditions. 

 23.149 

(f) 

Not required in Appendix C icing conditions. 

Acrobatic 

maneuvers 

23.151 Not applicable for icing certification. 

Control during 

landings 

23.153 Must be shown to be compliant with critical ice accretions. 

Elevator 

control force in 

maneuvers 

23.155 Critical configuration(s) determined from the non-contaminated 

airplane tests must be evaluated. 

Rate of roll 23.157 Airplane must comply with “takeoff” ice accretions for paragraph 

(a) and critical ice accretions for paragraph (b). Controllability may 

be degraded from the non-iced airplane but must still be compliant. 
AC 23.1419-2E 

Appendix 6 

A6-7

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 

AT AMENDMENT 23-XX 

Regulation 14 CFR 

Section 

Guidance 

Trim 23.161 The results from the non-contaminated airplane tests should be 

reviewed to determine whether there are any cases where there was 

marginal compliance. If so, or if qualitative evaluations with ice 

accretions show any control anomalies, these cases should be 

repeated with ice. Otherwise, no dedicated tests with ice accretions 

required, qualitative evaluations can be accomplished concurrently 

with other tests. 

General 

(stability) 

23.171 Must be shown to be compliant with critical ice accretions. 

Static 

longitudinal 

stability 

23.173 Stability may be degraded from the non-iced airplane but must still 

be compliant. 

Demonstration 

of static 

longitudinal 

stability 

23.175 Critical configuration(s) determined from the non-contaminated 

airplane tests must be evaluated. 

Static 

directional and 

lateral stability 

23.177 Must evaluate steady heading sideslips in accordance with 

paragraph (d). These tests should check for hinge moment reversals 

about the lateral and directional axis up to full rudder deflection. 

The results from the non-contaminated airplane tests to show 

compliance with paragraphs (a) and (b) should be reviewed to 

determine whether there are any cases where there was marginal 

compliance. If so, these cases should be repeated with ice. Stability 

may be degraded from the non-iced airplane but must still be 

compliant. 

Dynamic 

stability 

23.181 Critical configuration(s) determined from the non-contaminated 

airplane tests must be evaluated with critical ice accretions. 
AC 23.1419-2E 

Appendix 6 

A6-8

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 

AT AMENDMENT 23-XX 

Regulation 14 CFR 

Section 

Guidance 

Wings level 

stall 

23.201 As a minimum wings level stalls with cruise, approach and landing 

flaps, power off and on, should be evaluated with critical ice 

accretions. Roll may slightly exceed 15 degrees if characteristics 

qualitatively determined to be safe. Stall characteristics should also 

be evaluated when the airplane is stalled with the autopilot engaged, 

unless the design of the autopilot precludes its ability to operate 

beyond stall warning. For these designs the controllability at stall 

warning should be evaluated. Recovery at stall warning should also 

be evaluated by only applying engine power or thrust. Evaluations 

should be accomplished by trimming at minimum AFM icing 

airspeed, setting the autopilot in altitude hold (for turns commanding 

a heading change), reducing power/thrust to establish a 1 kt/sec 

deceleration rate, and at stall warning apply power/thrust. Evaluate 

the aircraft response, need for directional/lateral control, airspeed 

increase, and altitude loss (assuming autopilot will disconnect as 

designed at stall warning). 

If a stick pusher system with anticipation logic installed, 

deceleration rates slower than 1 kt/sec may need to be conducted to 

evaluate the highest angle of attack activation of the stick pusher. 

Turning flight 

stalls 

23.203 Turning stalls should be evaluated with critical ice accretions 

similarly to wings level stalls. Stall characteristics should also be 

evaluated when the airplane is stalled with the autopilot engaged, 

unless the design of the autopilot precludes its ability to operate 

beyond stall warning. For these designs the autopilot operation up 

to stall warning and controllability at stall warning should be 

evaluated. 

Accelerated 

turning stalls 

23.203 

(a)(2) 

Accelerated turning stalls not required unless tests with no ice show 

marginal compliance````` 
AC 23.1419-2E 

Appendix 6 

A6-9

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 

AT AMENDMENT 23-XX 

Regulation 14 CFR 

Section 

Guidance 

Stall warning 23.207 

(a)-(c) 

Should be evaluated concurrently with stall speed and stall 

characteristics tests. The stall warning margin with critical ice 

accretions must be compliant. 

 

If the stall warning system incorporates anticipation, deceleration 

rates slower than 1 kt/sec may need to be conducted to evaluate the 

highest angle of attack activation of the stall warning system. 

In addition to the standard stall tests conducted in natural icing and 

with artificial ice shapes required to show compliance to § 

23.1419(b), recovery at stall warning should also be evaluated by 

applying the manufacturer recommended stall recovery procedures. 

The following three aircraft configurations should be performed: 

1. Flaps up, gear up (wings level) 

2. Approach configuration (turn using bank angle of 15 to 30o) 

3. Landing configuration approved for icing (wings level) 

Evaluations should be accomplished as follows: 

1. Trim at minimum AFM or VREF icing airspeed 

2. Set power/thrust to establish a reasonable deceleration rate 

that will allow the pilot to reach stall warning while 

maintaining constant altitude. 

Note: Vary stall entry rate as required to hold constant 

altitude during stall entry. 
AC 23.1419-2E 

Appendix 6 

A6-10

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 

AT AMENDMENT 23-XX 

Regulation 14 CFR 

Section 

Guidance 

Stall warning 

(continued) 

23.207 

(a-c) 

3. Recover at onset of stall warning + 1 second using 

appropriate aircraft procedures. 

Note: Evaluate the aircraft response, need for 

directional/lateral control, airspeed increase, and altitude 

loss during recovery maneuver. The aircraft shall exhibit 

positive control and demonstrate that a pilot of average 

skill can execute the procedure as defined. 

4. The same conditions should be evaluated with the autopilot 

engaged in altitude hold mode. 

Note: If autopilot design is such that it does not automatically 

disconnect at stall warning, then per the requirements of 

AC23.1419-2C evaluations should be conducted with autopilot 

engaged until aircraft begins to lose altitude. At which point 

disengage autopilot and initiate stall recovery by utilizing 

appropriate aircraft procedures. 

Maneuver 

margin 

23.207 

(d) 

40-degree bank level altitude turns and 30 degree/30 degrees bankto-bank rolls at the flight conditions specified in the regulation 

should be accomplished to demonstrate the airplane is free of buffet 

and stall warning with critical ice accretions. All takeoff and 

approach flap settings should be evaluated. For one-engine 

inoperative evaluations, only a 30-degree turn is necessary, and the 

appropriate thrust may be simulated with all engines operating at a 

reduced power/thrust. 

Accelerated 

stall warning 

margin 

23.207 

(e) 

Not required. 

Acrobatic 

airplane stall 

warning 

23.207(f) Applicable for acrobatic airplanes. 
AC 23.1419-2E 

Appendix 6 

A6-11

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 

AT AMENDMENT 23-XX 

Regulation 14 CFR 

Section 

Guidance 

Stall warning 

with preactivation ice 

23.207(g) Must be shown with pre-activation ice that a stall and adverse flight 

characteristics, such as a large or abrupt roll or yaw excursion, can 

be prevented in a one knot/sec deceleration after waiting at least one 

second after stall warning. The pre-activation ice is defined in Table 

2 of this Advisory Circular. Recovery at stall warning should also 

be evaluated by applying the manufacturer recommended stall 

recovery procedures. The following three aircraft configurations 

should be performed: 

1. Clean (wings level) 

2. Approach (turn using bank angle of 15 to 30o) 

3. Landing (wings level) 

Evaluations should be accomplished as follows: 

1. Trim at minimum AFM or VREF icing airspeed 

2. Set power/thrust to establish a reasonable deceleration rate 

that will allow the pilot to reach stall warning while 

maintaining constant altitude. 

Note: Vary stall entry rate as required to hold constant altitude 

during stall entry. 

Means of stall 

warning in 

icing 

conditions 

23.207(i) The type of stall warning with critical ice accretions representing 

normal operation of the IPS and pre-activation must be the same as 

with the non-contaminated airplane. Biasing of the stall warning 

(resetting schedule to lower angles of attack when ice protection is 

initiated) may be required to achieve acceptable margins to stall. 

The method of biasing should be evaluated. It is acceptable to 

return to the non-icing schedule when the critical wing surfaces are 

free of ice accretions. The applicant should validate that the means 

used to determine when the critical wing surfaces are free of ice 

accretions is reliable under all expected operating conditions. 

Spinning 23.221 Not required. 

Longitudinal 

stability and 

control 

23.231 Must be shown to be compliant. 
AC 23.1419-2E 

Appendix 6 

A6-12

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 

AT AMENDMENT 23-XX 

Regulation 14 CFR 

Section 

Guidance 

Directional 

stability and 

control 

23.233 Must be shown to be compliant with critical ice accretions. The 

results of the steady heading sideslip tests with critical ice may be 

used to establish the safe cross wind component. If the flight test 

data show that the maximum sideslip angle demonstrated is similar 

to that demonstrated with the non-contaminated airplane, and the 

flight characteristics (e.g., control forces and deflections, bank 

angle) are similar, then the non-contaminated airplane crosswind 

component is considered valid. 

If the results of the comparison discussed above are not clearly 

similar, and in the absence of a more rational analysis, a 

conservative analysis based on the results of the steady heading 

sideslip tests may be used to establish the safe crosswind 

component. The crosswind value may be estimated from: 

VCW = VREF * sin (sideslip angle) /1.5 where: 

VCW is the crosswind component, 

VREF is the landing reference speed appropriate to a minimum 

landing weight, and sideslip angle is that demonstrated at VREF

Operation on 

unpaved 

surfaces 

23.235 Not required.

Operation on 

water 

23.237 Required only for seaplanes and amphibians certified for flight in 

icing conditions.. 

Spray 

characteristics 

23.239 Not required. 

Vibration and 

buffet 

23.251 The non-icing tests should be accomplished with the ice protection 

systems installed. 

Should be qualitatively evaluated in conjunction with other dry air 

ice shape flight tests up to the lower of: 

250 KCAS 

VMO/MMO/VNE

A speed at which it is demonstrated that the airframe will be free of 

ice accretion. 

Vibration due to propeller icing/de-icing should be evaluated during 

the natural icing testing. 

High speed 

characteristics 

23.253 If applicable, compliance should be shown with airframe ice 

protection systems installed. Not required with ice accretions. 
AC 23.1419-2E 

Appendix 7 

A7-1

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

APPENDIX 7. CAPABILITY OF ENGINEERING TOOLS FOR COMPLIANCE TO 

§ 23.1420 

Table 7-1 graphically illustrates results of a 2009 assessment of the capabilities of 

engineering icing tools. This assessment is described in detail in AC 25-XX. As described in the 

legend to that table, the capability of each tool for the various applications is classified as green, 

yellow, or orange, Reliance upon available simulation methods combined with engineering 

judgment will be required for finding compliance with § 23.1420. Even though a simulation tool 

type may be classified as green, an applicant must ensure that the specific tool is appropriate for 

its application and is used in a conservative manner, including consideration of critical-case icing 

conditions. General and specific concerns that should be considered are discussed in this section 

of the AC. While Table 7-1 illustrates the current state of simulation capabilities, we expect that 

capabilities will improve in the future. We encourage applicants and research agencies to 

develop and validate the engineering tools currently classified in Table 7-1 as yellow and 

orange. 

Table 7-1 illustrates that, for some Appendix O conditions, few of the engineering tools are 

classified as green or yellow for use as a means of compliance. Radomes, for example, have no 

engineering tools classified as green. In other cases, such as areas aft of protected areas, there is 

only one simulation tool that is classified as green. 
AC 23.1419-2E 

Appendix 7 

A7-2

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(1) Capabilities & Limitations of Engineering Tools and Measurement 

Instrumentation for Appendix O Icing Conditions

(a) Icing Tunnel. A tunnel that uses a single pressure source for spray bars 

cannot simultaneously produce the large and small drop distributions (bi-model distributions) 

defined in Appendix O. However, NASA has developed a technique called “sequencing” that 

alternates large and small drop sprays to simulate Appendix O conditions. When icing tunnels 

are used as an element of the means of compliance: 

1. Scale effects must be considered for tunnel blockage effects. 

2. For FZDZ with a median-volume diameter (MVD)<40μm, the cloud drop 

distributions in the IRT are similar to existing Appendix C calibrations. 

 3. A simulation of freezing drizzle may be acceptable without an exact 

simulation of the drop size distributions defined in part 25, Appendix O. Standard icing tunnel 

drop distributions may be acceptable to use in lieu of the Appendix O distributions if the water 

content at the higher drop sizes are conservative. Superposition of the effects on the stagnation 

region versus any effects aft of the protected areas may be required to represent the local water 

catch in these locations. 

4. If there are concerns about the bi-modal distribution affecting performance 

of ice protection systems, sequencing should be considered. Sequencing2 of freezing drizzle 

conditions has been demonstrated in the IRT for unprotected surfaces. The sequencing technique 

approximates drop distributions found in natural conditions, however, it results in rougher 

textures than Appendix C ice shapes. 

5. Ice shapes in unprotected areas are generally considered critical from the 

perspective of producing the largest disruption to the airflow. With a large ice shape, details on 

the impingement limit characteristics, which may have a less critical effect, may not be 

essential. However, sequencing between large and small drop conditions may be necessary if 

standard sprays do not produce the drop distribution appropriate for simulation of the conditions 

desired. (The phrase “standard spray” method refers to using the IRT nozzles in off-design 

conditions to generate larger drops for SLD conditions.) In cases where the impingement limit 

characteristics are important, sequencing may be necessary. 

6. In general, sequencing produces rougher textures than a standard spray. 

 

2 Simulation of a Bi‐modal Large Droplet Icing Cloud in the NASA Icing Research Tunnel, M. Potapczuk

and D. Miller, R. Ide, and J. Oldenburg, 43rd AIAA ASM, Reno, NV, Jan. 2005
AC 23.1419-2E 

Appendix 7 

A7-3

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

7. Sequencing may not be an appropriate way to test thermal systems because 

the rate of mass flow per unit area (i.e. mass flux) of the incoming water is not the same for the 

small and large drop sprays. 

8. If sequencing is used to test deicing systems, the ratio of sequencing time to 

shed cycles should be evaluated to ensure that sequencing does not inappropriately affect the ice 

shape. 

9. The tunnel model should be a full scale model if the tunnel test objective 

is the definition of ice accretion. A hybrid model may be used provided the more aft 

impingement of the SLD, compared to Appendix C drops, is accounted for. Experimental tests 

of methods for designing subscale hybrid airfoils with full-scale leading edges to determine 

leading edge ice shapes for large-chord airfoil sections has been accomplished in icing wind 

tunnels (References TBD). These techniques have been used successfully for Appendix C icing 

conditions. Adapting them to icing tests for SLD conditions requires an evaluation of the areas 

of interest for impingement analysis and analysis of the flow-field to determine if scale 

conditions aft of the leading edge can be met considering the compromises necessary in design 

variables on circulation, velocity distribution and impingement characteristics. Although we 

anticipate that the hybrid airfoil design technique would be applicable for SLD conditions, such 

use has not been tested and validated to date. 

10. Scale models may be used, with appropriate scaling corrections, to 

examine impingement limits relative to fuselages or windscreens with scale models. While 

scaling icing shapes and roughness is still an emerging area of technology, scaling of droplet 

inertia effects and impingement limits are in a more mature state. This technique may be used to 

examine visual icing cues, validate location of detection devices, and determine total accretion 

areas that could be used in drag estimates (if required). 

11. The tunnel model should incorporate geometry features such as spanwise 

gaps or steps.

(b) Computational Fluid Dynamic Tools. Computational fluid dynamic (CFD) 

tools—the “codes” referred to in the table—are used extensively in certification for Appendix C 

conditions. CFD tools can provide valuable information on impingement limits, icing limits, ice 

size, ice shape, and ice thickness for Appendix O conditions. Some validation of collection 

efficiency and ice shapes has been accomplished for FZDZ; there have been no validation 

exercises for FZRA. CFD tools have been devised to predict, using mathematical calculation, 

ice accretion on an airplane in SLD conditions and the behavior of various types of ice 

protection systems as a result of those accretions. Besides being useful for assessing effects on 

protected surfaces, these tools can also account for the possibility of SLD ice impingement 

beyond the ice protection system limits, as well as for possible water runback. No current CFD 

method, however, can identify the breakup of water into rivulets, roughness formation, ice 

sliding that may occur under these circumstances, the shape or location of runback ice, or any 

effect of spanwise features such as steps and gaps.. Thus analysis of the regions behind those 

that are protected by ice protection systems requires some combination of CFD results, 
AC 23.1419-2E 

Appendix 7 

A7-4

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

empirical data and test results (if available), and engineering judgment. This usually consists of 

determining the extent of possible ice formation using some criteria from the computational 

analysis, such as ice extent, impingement limits, or some minimum ice thickness level. The 

resulting ice shape would include intercycle or residual ice on the protected region and ice 

formed aft of the protected region. This result is then combined with guidance on ice roughness 

levels, such as described elsewhere in this document, to produce a rough ice region that can be 

evaluated in wind tunnel testing or flight tests. 

1. Information can be calculated for drop trajectories for evaluating sensor 

locations and potential visual cues. 

2. Many non-lifting surfaces require testing with 3-D computer codes. At the 

current time, many 3-D codes do not have large drop effects (such as splashing and break-up). 

Even without large drop effects, however, 3-D codes can offer information on impingement 

limits. Although 3-D codes may generate physical models and correlations that can support 

analysis of large drop icing, the capabilities of performing analyses with 3-D SLD CFD tools 

have not yet been evaluated. There are codes that may have this potential, but no guidance can 

be offered at this time for their use. 

3. Some codes have limited capabilities with short-chord geometries (e.g., 

antennas or struts) for Appendix C icing conditions. These limitations are expected to be similar 

for large drop icing and are typically addressed with empirical methods or icing tunnels. 

However, for non-lifting surfaces, conservative assessments may be acceptable, such as 

assuming drop impingement on the full frontal area, assuming the collection efficiency is one, 

and approximating the shapes appropriate for the temperature (glaze, rime, etc.). 

(c) Icing Tankers 

1. Icing tankers have been used extensively by some manufacturers for 

Appendix C icing certifications. Icing tankers typically have a limited plume size and have been 

used primarily for localized icing effects, such as ice shedding, and for assessing the thermal 

performance of anti-ice systems. 

2. Current tankers do have some limited capabilities to produce freezingdrizzle-sized drops, but they cannot produce the distribution effects. Current tankers do not 

produce freezing rain distributions either, and the feasibility of producing such conditions is 

likely limited by drop break-up (due to deceleration effects) and the ability to sub-cool the large 

drops within a workable flight envelope. Additionally, drop sorting effects are likely, because of 

higher fall rates of large drops within an Appendix O distribution. 

(d) Instrumentation. When making in-situ measurements of Appendix O 

conditions, it is important to note that technology to make such measurements is rapidly 

changing. It is essential to consult experts in all phases of the measurement program, including 

those aware of the latest problems and strengths of each probe. You should use instrumentation 

suited to the task. 
AC 23.1419-2E 

Appendix 7 

A7-5

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

1. Instrumentation must be mounted in appropriate locations on the aircraft, 

where the measurements are not affected by the airflow. 

2. For certification purposes, the instrumentation must be calibrated. An 

often-overlooked aspect of a measurement program is the need to calibrate the instruments. 

3. Appropriate software and analysis techniques are also essential, because 

complicated algorithms are often needed in the analysis. 

4. Instruments are required to measure particle concentrations as a function 

of size over the complete size range—2 μm to at least 1,500 μm—including cloud drops and 

precipitation drops. This may require more than one probe. 

5. Liquid water content and ice water content (IWC) measurements obtained 

by integrating 2-D images from spectral measurements generally have larger errors than those 

obtained from probes specifically designed to make such measurements. Consequently, it is 

recommended that probes designed to measure LWC and, if necessary, IWC, directly be used, 

recognizing that some hot-wire devices detect larger drops (>50μm) with reduced efficiency. 

Mixed-phase clouds can occur frequently, so it is necessary to be able to discriminate between 

ice and liquid particles, especially for sizes larger than 50μm, so that ice particles are not 

incorrectly identified as SLDs. 

6. For detect-and-exit airplanes (those certifying to §23.1420(a)(1)), it may 

not be necessary to measure IWC; but for airplanes using natural icing SLD flight tests to certify 

for a portion of Appendix O (§23.1420(a)(2)) or for unrestricted operations (§23.1420(a)(3)), 

IWC must be determined in order to assess the SLD conditions. 

(1) Component Evaluations 

(a) Lifting surfaces. This paragraph is applicable to anti-icing systems aft of 

protected areas and to deicing systems both on and aft of protected areas. 

For detect-and-exit airplanes (§ 23.1420(a)(1)) in freezing drizzle conditions, icing 

tunnels alone may be used to develop ice shapes, provided that the model appropriately 

represents the airfoil beyond the FZDZ icing limit. Roughness may be evaluated in icing tunnel 

testing and replicated on the ice shapes for flight testing. The standard spray2

 method should be 

used for anti-icing systems because of the varying mass flux of incoming water associated with 

sequencing. For deicing systems, it is acceptable to use either the standard spray or the 

sequencing technique. 

(b) Radomes .

Most radomes are too large to fit into existing icing wind tunnels. Additionally, 

computational analysis of radomes typically would require 3-D codes. Many 3-D codes do not 

have large drop effects and if they do not, freezing drizzle ice shapes cannot be simulated. (All 3-

D codes have capabilities for testing impingement limits, however.) Radome ice shapes have been 
AC 23.1419-2E 

Appendix 7 

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Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

developed in the past for Appendix C icing conditions using analysis and observed ice shapes 

from Appendix C flight tests (typically holding ice shapes). 

For detect-and-exit airplanes (§ 23.1420(a)(1)) in freezing drizzle conditions, one 

method of compliance would be to modify Appendix C ice shapes to account for the larger 

impingement regions produced in FZDZ as predicted by the 3-D codes. You may use CFD codes 

to predict ice thickness. Ice roughness should be in accordance with the section headed Standard 

Roughness Levels for Appendix O Ice Shapes later in this appendix. The radome ice tested 

should reflect the total mass associated with the icing exposures for § 23.1420(a)(1) airplanes, 

which are defined in 14 CFR 23, Appendix TBD, part II. 

(c) Non-Lifting Surfaces (Antennas, Enhanced Vision Cameras, Struts, 

Auxiliary Inlets) 

For non-lifting surfaces that do not require use of 3-D codes, 2-D codes in 

combination with icing tunnels are available as a means of compliance. However, many nonlifting surfaces require the use of 3-D codes. At the current time, many 3-D codes do not have 

large drop effects, although some codes may have this potential. 

For detect-and-exit airplanes (§ 23.1420(a)(1)), if the non-lifting surface is not 

critical from an engine ingestion or airframe damage perspective, 3-D codes may provide 

sufficient information for compliance. However, for more critical surfaces, until large drop 

effects in 3-D codes are validated, icing tunnels alone may be used to develop ice shapes. 

(d) Ice Detection Methods 

Different types of ice detection require assessment of their capabilities in large drop 

conditions, based upon their sensing technology. Vibrating probe type ice detectors which detect 

ice accretion on a probe through a decrease in the probe’s vibration frequency, may experience 

increased response time in large drop exposures because splashing and aerodynamic forces, 

particularly in near freezing temperatures, can cause water to shed from sensing surfaces. This 

physical behavior may also occur with other types of probes. 

While CFD can determine whether the large drops impact the ice detection surface, 

available CFD codes cannot accurately predict aerodynamic forces that cause drop shedding, or 

freezing fraction effects which may delay freezing. Therefore, use of CFD alone is not 

acceptable for showing that ice detectors function in large drop conditions. When possible, 

effects of installation position should be evaluated with a combination of codes and icing 

tunnels. Devices mounted on smaller surfaces could be assessed in an icing tunnel. However, if 

the device is mounted on the fuselage, and tunnel blockage effects would preclude a meaningful 

icing tunnel test, then CFD codes that adequately predict the shadowing and concentration 

effects may be used to verify that the equipment is properly located. 

Because of the lack of engineering tools for FZRA, primary and advisory ice 

detectors used for compliance with § 23.1420(c) will require validation in natural large drop 

conditions to substantiate that the detectors function in all Appendix O conditions, unless ground 

testing with both FZDZ and FZRA drops representative of Appendix O distributions and 

temperatures can be substantiated. However, if visual cues are certificated as the primary means 

of compliance with § 23.1420(a)(1)(i) and the airplane is equipped with an ice detector system 

that is not required for compliance with § 23.1420(a)(1)(i) or § 23.1420(c), then the ice detector 

need not be tested in natural Appendix O conditions. Certification of visual cues for detect-and-
AC 23.1419-2E 

Appendix 7 

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Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

exit airplanes is discussed later in this appendix under the heading Certification for Detect and 

Exit - § 23.1420(a)(1). 

(e) Air Data Sensors 

1. Air Data Sensor Position Installation Effects. When possible, you 

should evaluate the effects of installation position with a combination of CFD codes and icing 

tunnels. Devices mounted on smaller surfaces could be assessed in an icing tunnel. However, if 

the device is mounted on the fuselage and tunnel blockage effects would preclude a meaningful 

icing tunnel test, then codes that adequately predict the shadowing and concentration effects are 

acceptable as the only method for compliance with installation location requirements. 

2. Air Data Sensor Performance Effects. Icing tunnels alone may be used to 

determine the performance of air-data sensors in Appendix O icing conditions in compliance 

with §§ 23.1323, 23.1324, and 23.1325. For sensors with collection efficiencies approaching "1," 

if performance has been shown in FZDZ conditions, then a qualitative analysis based upon 

water-catch ratios may be used for extrapolation to FZRA conditions. If the Appendix C or 

mixed-phase or ice crystal conditions are shown to be more critical for air-data sensors than the 

SLD environment, the number of tests may be reduced. However, the test methods should be 

validated until confidence is provided. In some cases, such as that of wing leading-edge-mounted 

lift transducers, icing tunnel tests may still be necessary. 

(2) Means of compliance to § 23.1420 

(a) Certification for Detect and Exit - § 23.1420(a)(1) 

1. Freezing Drizzle (FZDZ)<40μm. FZDZ conditions with an MVD less 

than 40μm are similar to existing Appendix C distributions with the exception of a small 

percentage of the mass in drops larger than typical Appendix C conditions. As a result, many of 

the current Appendix C simulation methods can support compliance. The small percentage of 

large drops in this distribution can affect the impingement limits and increase the water catch. If 

visual cues are used for compliance with § 23.1420(a)(1)(i), it may be possible to use codes in 

combination with icing tunnels to verify the visual cues. Visual cues should not be based on only 

one engineering method; a second, correlating method should be used. 

2. Freezing Drizzle FZDZ>40μm. Where the capabilities of the tools 

available for FZDZ>40μm are the same as for FZDZ<40μm, the applicant may use similar 

means of compliance that are adjusted for the FZDZ>40μm icing conditions. The tool 

capabilities are different for mechanical deicing system protected areas and areas aft of the 

protected areas.

Note: Icing tunnels are classified as yellow when used for testing for FZDZ 

>40μm because use of the tunnels appears feasible but has not been demonstrated. Icing tunnel 

tests alone are acceptable for the development of ice shapes for deicing system protected areas 
AC 23.1419-2E 

Appendix 7 

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Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

and areas aft of the mechanically protected areas. Sequencing or standard distributions are 

acceptable, but the ratio of sequencing time to shed cycles should be examined. 

3. Freezing Rain (FZRA) (MVD<40μm & MVD>40μm). The capabilities 

of the tools for FZRA are limited. To simulate accretions on unprotected surfaces and aft of 

protected areas, CFD codes may be used to determine the difference in impingement region 

between FZRA and FZDZ. The increase in impingement area can then be simulated using a 

standard roughness in that region. For areas where a ridge of ice may form, a simulated ridge 

may be developed using a height developed analytically based upon local water catch. Ridge 

location could be developed from FZDZ tunnel tests, and the height would be modified based 

upon the ratio of local water catch (determined with CFD) between FZDZ and FZRA. Other 

concerns: 

Thermal Ice Protection Systems—Analyses to assess water catch and 

melting/evaporation rates are acceptable for determining the capabilities of thermal systems in 

FZRA, provided that the analyses are based upon the validated results of the system capabilities 

performed for Appendix C and FZDZ. Any additional ice that may form on runback ice shapes 

in freezing rain should be accounted for by analysis of the runback volume. Potential roughness 

effects ahead of the runback should be addressed. 

Mechanical Ice Protection Systems — For assessing mechanical ice protection 

system performance in FZRA, it is acceptable to use the same pre-activation and intercycle and 

residual ice shapes as for FZDZ. The limits of accretion should be determined using CFD tools. 

Validation of Visual Cues — Use of qualitative analysis is acceptable for 

assessing whether visual cues used for FZDZ will function in FZRA conditions. 

(b) Certification for a Portion of Appendix O - § 23.1420(a)(2) 

Current technology does not support distinguishing between FZDZ and FZRA in 

flight. Because of this, airplanes should not be certificated for compliance with § 23.1420(a)(2) 

based upon the boundaries between FZDZ and FZRA. Certification to § 23.1420(a)(2) is 

discussed in the main body of this AC; however, there are concerns about the ability of 

applicants to define ice shapes which distinguish between the approved portions and the 

unapproved portions of Appendix O with the current simulation tools. As a result, certification 

for a portion of Appendix O will be challenging and will require close coordination with 

certifying authorities. 

Certification for a portion of Appendix O that considers phase of flight (e.g., 

takeoff, holding), as discussed in the body of this AC in paragraph 8(b), may be feasible. Any 

method of certification for a portion of Appendix O should be included as part of the certification 

planning and will require approval from the cognizant certifying authority. 
AC 23.1419-2E 

Appendix 7 

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Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

(c) Certification for Unrestricted Operations - § 23.1420(a)(3) 

The use of simulation tools as described for detect-and-exit airplanes is also 

acceptable for showing compliance for airplanes certificated in accordance with § 23.1420(a)(3). 

However, the means of compliance should include flight tests in measured Appendix O icing 

conditions. 

AC 23.1419-2E 

Appendix 8 

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Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

APPENDIX 8. EXAMPLE FLIGHT TEST PROGRAM FOR COMPLIANCE TO § 

23.21(C)(2) “SLD DETECT AND EXIT” 

1. Stall Speed (§ 23.49). 

Stall speeds must be defined with all flap positions approved for flight in icing. There is no 

requirement to show compliance with the maximum stall speed requirements of § 23.49 (c). The 

ice shapes to be flown are those determined to be critical “detect and exit” shapes. . 

2. Reference landing approach speed (§ 23.73). 

There is no requirement for the approach speed to be 1.3 times the stall speed determined with 

detect and exit ice shapes. The approach speed determined for Appendix C ice accretions may 

be used, but compliance with these shapes must be shown to the maneuver margin requirements 

of § 23.207(d). The approach speed with detect and exit shapes must be increased if required for 

compliance to the maneuver margin requirements. 

3. Landing distance (§ 23.75). The landing distances determined for Appendix C operations 

may be used if the Appendix C approach speed is used following detect and exit of Appendix O 

icing conditions. If the approach speed must be increased for detect and exit, the increase in 

landing distance may be determined by analysis. 

4. Landing Climb: All-engines-operating (§ 23.77). 

When showing compliance with 23.1420(a)(1), in lieu of a specific climb gradient requirement 

for each aircraft category, the gradient of climb at the landing field pressure altitude must be 

measurably positive for all aircraft following an SLD icing encounter. For normal category, 

meeting the positive gradient is required at all field elevations and weights. Guidance shall be 

included in the AFM that, in the case of an SLD icing encounter, provides the appropriate actions 

and limitations of the aircraft following the encounter. 

Acceptable Test Program. The following represents an acceptable test program:

a. Critical detect and exit ice shape 

b. Forward centre of gravity position appropriate to the configuration. 

c. Highest lift landing configuration, landing climb speed no greater than VREF. 

d. Stabilize at the specified speed and conduct 2 climbs or drag polar checks 

as agreed with the Authority. For propeller airplanes, the torque or power should be reduced to 

simulate the applicable propeller efficiency loss in Figure TBD. 

5. Controllability and Maneuverability - General ((§ 23.143). 

A qualitative and quantitative evaluation is usually necessary to evaluate 

the airplane's controllability and maneuverability. In the case of marginal 

compliance, or the force limits of§ 23.143(c) being approached, additional substantiation may be 

necessary to establish compliance. 
AC 23.1419-2E 

Appendix 8 

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Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

Acceptable Test Program. The following represents an acceptable test program for general 

controllability and maneuverability, subject to the provisions outlined above: 

a. Critical detect and exit ice shape 

b. Medium to light weight, aft centre of gravity position, symmetric fuel loading. 

c. For all flight phases except takeoff, evaluate controllability (no dedicated test points required, 

accomplished concurrently during other tests). 

d. Deploy and retract deceleration devices at the following conditions: 

Configuration Trim Speed 

High lift devices retracted 

configuration: 

Minimum Holding Speed 

• VMO or 250 KIAS, whichever is less 

Highest lift landing configuration: VREF, and 

• VFE or 250 KIAS, whichever is less 

e. Conduct an approach and go-around with all engines operating using the 

recommended procedure. 

f. Conduct an approach and landing using the recommended procedure. These tests should be 

done at heavy weight and forward centre of 

gravity. 

a. Controllability for Appendix O “Detect and Exit” icing conditions (§ 23.143(f)) 

Use the critical detect and exit ice shape. For airplanes with unpowered elevators, these tests 

should also be performed with roughness due to SLD impingement at locations where ice may 

accrete in normal IPS operation. 

b. Pushovers/Pull-ups and Sideslips (§ 23.143(f)(1)(2)(3)(4)) 

Conduct a pull up to 1.5g and a pushover to 0.5g without longitudinal control force reversal. 

Changes in longitudinal control force to maintain speed with increasing sideslip should be 

progressive, with no reversals or unacceptable discontinuities. Additionally, lateral control 

movements and forces must not reverse and there should be no lateral control snatching (i.e. 

sudden, sharp oscillations or reversals in control force) with increasing angle of sideslip . 

Acceptable Test Program. 

a. The most critical weight, the most critical of aft or forward center of gravity position, 

symmetric fuel loading. 

b. In the configurations listed below, trim the airplane at the specified speed. Conduct pull up to 

1.5g and pushover to 0.5g without longitudinal control force reversal. 
AC 23.1419-2E 

Appendix 8 

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Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

Configuration Trim Speed 

High lift devices retracted, power or 

thrust for level flight 

Minimum Holding Speed 

Highest lift landing configuration, 

idle and go-around power or thrust 

VREF-5 and 

VFE-minimum margin required to avoid 

exceeding VFE during maneuver 

c. Conduct steady heading sideslips to the sideslip appropriate for crosswind approach 

and landing with thrust or power for approach at VREF. 

c. Lateral control evaluation (§ 23.143(f)(5)) 

Aileron hinge moment reversal and other lateral anomalies have been identified as a causal factor 

in icing accidents and incidents. The lateral control evaluation is applicable to airplanes 

equipped with spoilers as well as ailerons. It is applicable to reversible and irreversible lateral 

control configurations since the effects of the following are being evaluated: 

Hinge moment reversal and other lateral anomalies 

Stall or partially stall of the outer wing 

It should be possible to readily arrest and reverse the roll rate using only lateral control input and 

the lateral control force should not reverse with increasing control deflection. There is no 

quantitative requirement for roll rate but roll rate capability should be qualitatively evaluated and 

shown to be adequate. 

Acceptable Test Program. The following represents an acceptable test program for general 

controllability and maneuverability, subject to the provisions outlined above: 

a. Maximum landing weight, forward center of gravity position, symmetric fuel loading. 

b. In the configurations listed in the table below, trim at the specified speeds in level flight and 

conduct the following maneuvers: 

i. establish a 30° bank level turn; 

ii. Using a step input of approximately 1/3 full lateral control deflection, roll the airplane in the 

other direction; 

iii. When the airplane reaches approximately 20° bank in the opposite direction, apply the same 

lateral control input in the opposite direction. 

iv. Release input and recover as the airplane passes a wings level attitude. 

v. Repeat the test procedure with 2/3 and then full lateral control deflection unless the roll rate is 

judged to be excessive. 
AC 23.1419-2E 

Appendix 8 

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Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

Configuration Trim Speed 

Holding configuration: minimum holding 

speed (highest expected holding angle-ofattack) 

Approach configuration VREF 

Highest lift landing configuration: VREF 

6. Stall Demonstration (§§ 23.201 and 23.203). 

Sufficient stall testing should be conducted to demonstrate that the stall characteristics comply 

with the requirements. In general, it is not necessary to conduct a stall program which 

encompasses all weights, centre of gravity positions (including lateral asymmetry), altitudes, 

deceleration device configurations. Compliance to the quantitative roll excursion requirements 

of § 23.201(d) and 23.203(b)(4) is not required. Roll excursions should not exceed the values in 

§ 23.201(d) and 23.203(b)(4) by a large amount, and roll characteristics should be qualitatively 

determined to be safe. 

Based on a review of the stall characteristics of the non-contaminated airplane, a reduced test 

matrix can be established. However, additional testing may be necessary if: 

• the stall characteristics with ice accretion show a significant difference from the noncontaminated airplane, 

• testing indicates marginal compliance, or 

• a stall identification system (e.g. stick pusher) is required to be reset for icing conditions. 

Acceptable Test Program. The following represents an acceptable test program subject to the 

provisions outlined above. Turning flight stalls at decelerations greater than 1 knot/sec are not 

required. 

a. Critical detect and exit ice shapes. Unless the applicant can substantiate one ice shape is 

critical for stall speed and angle of attack, the critical freezing drizzle ice shape, a freezing 

drizzle ice accretion of short duration that only results in roughness, and the critical freezing rain 

ice shape should be flight tested. The number of these shapes can be reduced if similarity can be 

shown to an airplane in which flight test data is available. 

b. Medium to light weight, aft centre of gravity position, symmetric fuel loading. 

c. Normal stall test altitude. 

d. In the configurations listed below, trim the airplane at the same initial stall speed factor used 

for stall speed determination. For power-on stalls, use the power setting as defined in § 

23.201(e)(4) but with ice accretions on the airplane. 

Decrease speed at up to 1 knot/sec to stall identification and recover using the same test 

technique as for the non-contaminated airplane. 

i. High lift devices retracted configuration: Straight/Power Off, Straight/Power 

On, Turning/Power Off, Turning/Power On. 

ii. Approach configuration: Straight/Power Off, Straight/Power On, 

Turning/Power Off, Turning/Power On.. 

iii. Highest lift landing configuration approved for icing: Straight/Power Off, Straight/Power On, 

Turning/Power Off, Turning/Power On. 
AC 23.1419-2E 

Appendix 8 

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Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

e. For at least one straight/power off stall in each configuration, during the deceleration 

and at speeds down to stall warning, roll aircraft left and right up to 10 degrees bank using lateral 

control. It must be possible to produce and correct roll by unreversed use of lateral control. 

There should be no snatching (i.e. sudden, sharp oscillations or reversals in control force) of the 

pilot’s lateral control. 

7. Stall Warning (§ 23.207). As stated in paragraph (i) of the rule, the means for stall warning 

with Appendix C ice accretion, Appendix O detect and exit and pre-detection, must be the same 

as in non-icing. 

a. Normal Ice Protection System Operation (§ 23.207(h)). The detect and exit ice shape 

represents ice accretion after the pilot has detected Appendix O conditions and has exited icing 

conditions. The stall warning margin with detect and exit ice shapes is reduced from Appendix 

C with the intent that the stall warning schedule designed for Appendix C ice accretions can 

comply with § 23.207(j). The intent is to avoid designs that require pilot action to implement an 

Appendix O stall warning schedule. It is assumed that Appendix C stall warning schedules are 

implemented automatically following activation of the engine or airframe ice protection system. 

Acceptable Test Program. The following represents an acceptable test program: 

a. In the configurations listed below, trim the airplane at 1.5 VS1. 

i. High lift devices retracted configuration: Straight/Power Off, Straight/Power 

On, Turning/Power Off, Turning/Power On 

ii. Approach configuration: Straight/Power Off, Straight/Power 

On, Turning/Power Off, Turning/Power On 

iii. Landing configuration: Straight/Power Off 

b. At decelerations of up to 1 knot per second, reduce the speed to stall warning 

plus 3 seconds, and demonstrate that stalling can be prevented using the same test 

technique as for the non-contaminated airplane, without encountering any adverse 

characteristics (e.g., a rapid roll-off). Recovery at stall warning should also be evaluated by 

applying the manufacturer’s procedures. 

b. Ice Accretion Prior to Detection of Appendix O icing conditions (for airplanes not 

certified for flight throughout the icing conditions of Appendix O) (§ 23.207(h)). For 

assessing compliance with the ice accretion prior to detection of Appendix O icing conditions, it 

is assumed that the airplane has been in icing conditions long enough for the ice protection 

system to have been activated. Therefore, any changes to stall warning or stall identification 

system settings resulting from activation of the ice protection system are assumed to have taken 

place. The stall warning requirements for pre-detection Appendix O (visual cues) are the same 

as detect and exit. Therefore if one stall warning schedule is utilized for icing (Appendix C and 

detect and exit), in most applications the stall warning tests with detect and exit (§ 23.207(j)) can 

be used to show compliance with (§ 23.207(i). 
AC 23.1419-2E 

Appendix 8 

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Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

If the AFM will prohibit autopilot use following detection of Appendix O conditions, safe 

operation with autopilot engaged should be shown prior to detection of Appendix O conditions. 

Approaches to stall warning with pre-detection ice should be accomplished to evaluate airplane 

response and verify acceptable stall warning margin . 

8. Maneuver Margin (§ 23.207(d)). The airplane should be shown to be free of buffet and stall 

warning in 40° bank turns at approach speed in all approach flap configurations. Tests should be 

conducted with thrust/power for a 3° glide slope, and with thrust/power to maintain altitude. 

9. Wind Velocities (§ 23.233). 

Crosswind landings with detect and exit ice should be evaluated on an opportunity basis. 

The results of the steady heading sideslip tests with detect and exit ice may be used to establish 

the safe cross wind component. If the flight test data show that the maximum sideslip angle 

demonstrated is similar to that demonstrated with the noncontaminated airplane, and the flight 

characteristics (e.g. control forces and deflections) are similar, then the non-contaminated 

airplane crosswind component is considered valid. 

If the results of the comparison discussed in paragraph TBD, above, are not clearly similar, and 

in the absence of a more rational analysis, a conservative analysis based on the results of the 

steady heading sideslip tests may be used to establish the safe crosswind component, similar to 

the method for Appendix C. 

10. Ground and Water Handling Characteristics – Longitudinal stability and control (§ 

23.231). No dedicated tests required, can be evaluated during landings. 

11. Ground and Water Handling Characteristics – Directional stability and control (§ 

23.233). No dedicated tests required, can be evaluated during landings. 

12. Operation on water (§ 23.237). Applicable for amphibians and seaplanes approved for 

flight in icing conditions. 

13. Vibration and Buffeting (§ 23.251). 

Qualitative evaluations should be combined with the other testing. Evaluation can be limited to 

250 KCAS, Vne, an airspeed shown to have no ice accretion, or a reduced speed limit published 

in the AFM for SLD exit procedures. 

14. Definition of Sideslip Angle Appropriate to the Type of the Airplane.

For the purpose of showing compliance the requirements presented in this guidance material, the 

sideslip angle appropriate to the type of the airplane may be defined considering one of the 

options below: 

 The sideslip angle that cover conservatively crosswind operation, engine failure 

scenarios, and other conditions where sideslip may be experienced within the approved 

normal flight envelope. 
AC 23.1419-2E 

Appendix 8 

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Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

 In the absence of appropriate data, a conservative approach is the adoption of: 

o A value of 15 deg as a conservative approach provided that this value can be 

considered appropriate for the type of aircraft based on the review of sideslip 

angle obtained during the demonstration of lateral and directional static stability 

with landing configuration at Vref. 

o A value based in the following equation based on the theoretical sideslip value 

for a 30 knots crosswind derived for transport category airplanes. This equation 

has been shown to conservatively represent (i.e., exceed) the sideslip angles 

achieved in maximum crosswind takeoffs and landings and minimum static and 

dynamic control speed testing for a variety of transport category airplanes. 

V Airspeed   kcas

Where sideslip angle

V









 



 





:

30 arcsin

The results obtained from the use of this equation should be compared with the 

range of sideslip angles obtained during the steady heading sideslip maneuvers to 

avoid the adoption of a value greater than the airplane capacity to generate 

sideslip at operational speeds representative of takeoff and landing. 

Note: The equation above maybe modified based on the experience of applicant 

by changing the constant value by the demonstrated crosswind component 

obtained during the no-icing tests. 

 Any other value agreed with the certification authority. 

AC 23.1419-2D 

Appendix 9 

A9-1

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

APPENDIX 9. EXAMPLE FLIGHT TEST PROGRAM FOR COMPLIANCE TO § 

23.21(C)(3) FOR APPROVAL TO TAKEOFF IN FREEZING DRIZZLE AND LIGHT 

FREEZING RAIN 

1. General. Approval for takeoff in freezing drizzle and light freezing rain can be accomplished 

in three phases: 

a. Dry air flight tests with ice shapes simulating accretion in the takeoff and initial 

climb out of freezing drizzle and freezing rain 

b. Dry air flight tests with ice shapes simulating residual takeoff and climb ice 

accretion 

c. Takeoff demonstrations in natural Appendix O conditions 

2. Takeoff and climb in Appendix O conditions. 

a. Ice shape definitions. The ice shapes flown are defined as follows: 

1. Takeoff: As defined in table XXX. 

2. Final Takeoff: As defined in table XXX. 

3. Climb: As defined in table XXX. 

b. Number of ice shapes to flight test. The number of ice shapes can be reduced as 

follows: 

1. “Final takeoff ice” may be used for “takeoff ice” if shown to be more critical 

(chord location of ice due to high flap deflection may have to be addressed). 

2. The “enroute ice” accretion may be used for “final takeoff” or “takeoff” if 

shown to be more critical (chord location of ice due to high flap deflection may have to be 

addressed). 

3. The ice accretion(s) that has the most adverse effect on stall and handling 

qualities may be used for airplane performance tests provided any difference in performance is 

conservatively taken into account. 

4. The applicant should evaluate the proposed cold weather operations 

procedures and determine if any untreated surfaces can accrete ice, such as upper fuselage. The 

drag due to ice accretion on these surfaces may be analytically calculated. 

5. Either the critical freezing drizzle or freezing rain may be tested, if 

substantiated to be more critical. Note that the vertical extent of FZDZ is larger than FZRA. 

c. Assumptions. For both unprotected and protected parts, the ice accretion for the 

takeoff phase must be determined for the icing conditions defined in paragraph 2.a. above, using 

the following assumptions: 

1. The airfoils, control surfaces, and, if applicable, propellers are free from frost, 

snow, or ice at the start of takeoff; 

2. The test program assumes Type II, III or IV fluids are approved for the 

airplane and these fluids keep the lifting surfaces clean until lift-off; 
AC 23.1419-2E 

Appendix 9 

A9-2

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

3. The ice accretion begins at liftoff; 

4. The critical ratio of thrust/power-to-weight; 

5. Failure of the critical engine occurs at VEF; and 

6. Crew activation of the ice protection system is in accordance with a normal 

operating procedure provided in the Airplane Flight Manual, except that after beginning the 

takeoff roll, it must be assumed that the crew takes no action to activate the ice protection system 

until the airplane is at least 400 feet above the takeoff surface. 

7. FAA approved takeoff performance data assumes a clean, dry runway. 

d. Flight tests. The table below provides guidance for each of the applicable Subpart 

B regulations. 

23.45 General 

(performance) 

Applicable. 

23.49(a) 

and (b) 

Stall speed Tested in same manner as Appendix C ice shapes in 

following configurations: 

High lift devices retracted configuration, "Final Takeoff Ice." 

High lift devices retracted configuration, "En-route 

Ice." 

Holding configuration, "Holding Ice." 

Lowest lift take-off configuration, "Holding Ice." 

Highest lift take-off configuration, "Take-off Ice." 

23.51 Takeoff speeds The values of VMCG and VMC determined for non-icing 

conditions may be used. The value of VS1 must be 

based on “Takeoff Ice”, if required per the rule. 

23.53 Takeoff performance Takeoff performance is determined with engine power 

losses associated with ice protection equipment that is 

not prohibited for takeoff. 

23.55 Accelerate-stop 

distance 

The effect of any increase in V1 due 

to take-off in icing conditions may be determined by a 

suitable analysis. 

23.57 Takeoff path The effect of the take-off speed increase, thrust loss, 

and drag increase on the take-off path may be 

determined by a suitable analysis. 

23.59 Takeoff distance and 

takeoff run 

The effect of the take-off speed increase, thrust loss, 

and drag increase on the take-off distance and run may 

be determined by a suitable analysis. 

23.61 Takeoff flight path The effect of the speed increase for icing, thrust loss, 

and drag increase on the take-off flight path may be 

determined by a suitable analysis. 

23.63 Climb: general Climb speeds are based on VS1 determined with 

applicable ice accretion. 
AC 23.1419-2D 

Appendix 9 

A9-3

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

23.45 General 

(performance) 

Applicable. 

23.65 Climb: AEO Approved take-off lift configurations, "Takeoff Ice." 

Not applicable if stall speed and climb requirement 

icing/non-icing differences comply with regulation. 

23.66 Takeoff climb: OEI Approved take-off lift configurations, "Takeoff Ice." 

23.67 Climb: One engine 

inoperative 

Not applicable if stall speed and climb requirements of 

regulation are complied with. 

23.67(a) GW<6000 Normal, 

Utility, & Acro 

High lift devices retracted configuration, "Final 

Takeoff Ice." 

23.67(b)(1) GW>6000 Normal, 

Utility, & Acro 

Lowest lift take-off configuration, "Takeoff Ice." 

23.67(b)(2) GW>6000 Normal, 

Utility, & Acro 

High lift devices retracted configuration, "Final 

Takeoff Ice." 

23.67(c)(1) TO GD Commuter Highest lift take-off configuration, landing gear 

extended, "Takeoff Ice." 

23.67(c)(2) TO GU Commuter Lowest lift take-off configuration, landing gear 

retracted, "Takeoff Ice." 

23.67(c)(3) Climb OEI Final TO 

Commuter 

High lift devices retracted configuration, "Final 

Takeoff Ice." 

23.67(c)(4) Climb OEI Approach 

Commuter 

NOTE 2 

23.69(a) Enroute flight path 

AEO 

Evaluated with “Enroute Ice.” Climb speeds are based 

on VS1 determined with “Enroute Ice.” Not applicable 

if climb speed and service ceiling icing/non-icing 

comply with regulation. 

23.69(b) Enroute flight path OEI Evaluated with “Enroute Ice.” Climb speeds are based 

on VS1 determined with “Enroute Ice.” 

23.71 Glide: Single engine 

airplanes 

Evaluated with “Enroute Ice.” 

23.73 Reference landing 

approach speed 

Not applicable. 

23.75 Landing distances Not applicable. 

23.77 Landing climb AEO Not applicable. 

23.141 Flight characteristics: 

General 

Applicable as defined in guidance for following 

sections. 

23.143(a) Safely controllable & 

maneuverable 

Applicable for appropriate flight phases 
AC 23.1419-2E 

Appendix 9 

A9-4

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

23.45 General 

(performance) 

Applicable. 

23.143(b) Smooth transitions in 

conditions 

It must be possible to make a smooth transition from 

one flight condition to another (including turns and 

slips) without danger of exceeding the limit load 

factor, under any probable operating condition. AEO 

only. May be evaluated concurrently with other flight 

tests. 

23.143(b) Sudden failure of 

engine 

Not applicable. 

23.143(c) Control force limits Applicable 

23.143(d) ICTS Zero g pushovers and sideslip evaluated at: 

Approved take-off lift configurations, V50 or V2, 

"Takeoff Ice." 

Lowest lift take-off configuration, all-enginesoperating initial climb speed, “Final Takeoff Ice” 

High lift devices retracted configuration, enroute 

climb speed, “Enroute Ice” 

23.143(e) Control – preactivation ice Not applicable. 

23.143(f) Control – detect & exit Not applicable. 

23.143(g) Lateral control 

evaluation 

Approved take-off lift configurations, V50 V2, 

"Takeoff Ice." 

 

Lowest lift take-off configuration, all-enginesoperating initial climb speed, “Final Takeoff Ice” 

 

High lift devices retracted configuration, enroute 

climb speed, “Enroute Ice” 

23.145(a) Pitch down capability Highest lift take-off configuration, "Takeoff Ice." 

 

Highest lift take-off configuration, "Final takeoff Ice." 

 

High lift devices retracted configuration, “Enroute 

Ice” 

23.145(b)(1) Flap extension Not applicable. 

23.145(b)(2) Go-around Not applicable. 
AC 23.1419-2D 

Appendix 9 

A9-5

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

23.45 General 

(performance) 

Applicable. 

23.145(b)(3) GA w/complete flap 

retract– no loss of 

altitude 

Not applicable. 

23.145(b)(4) TO power Not applicable. 

23.145(b)(5) Control power w/flaps 

extended 

Not applicable. 

23.145(b)(6) Flap retraction Highest lift take-off configuration, "Takeoff Ice." 

Highest lift take-off configuration, "Final takeoff Ice." 

23.145(c) 1.5g capability above 

Vmo/Mmo 

Not required. 

23.145(d) Power off glide gear 

and flap extended 

Not required. 

23.145(e) Landing with primary 

FCS failure 

Not required. 

23.147(a) Directional control - 

OEI 

Evaluated with “Enroute Ice.” 

23.147(b) Sudden engine failure – 

2 sec delay 

Evaluated with “Enroute Ice.” 

23.147(c) Control with primary 

lateral FCS failure 

Not required. 

23.149 Minimum control 

speed 

Compliance to paragraph (b) can be shown by 

showing simulated engine failures at V2 are 

controllable with all approved takeoff high lift 

configurations with “Takeoff Ice.” 

23.151 Acrobatic maneuvers Required for acrobatic and utility airplanes if such 

maneuvers are not prohibited in Appendix O 

conditions. 

23.153 Control during landings Not applicable. 

23.155 Elevator control force 

in maneuvers 

Applicable with “Enroute Ice. Evaluation limited to 

250 KCAS, Vne, or an airspeed shown to have no ice 

accretion. 

23.157 Rate of roll Approved take-off lift configurations, 1.2VS or 

1.1VMC, whichever is higher, "Final Takeoff Ice." 

23.161 Trim Evaluated concurrently with other tests. 

23.171 General (stability) Applicable. 

23.173 Static longitudinal 

stability 

Applicable. 
AC 23.1419-2E 

Appendix 9 

A9-6

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

23.45 General 

(performance) 

Applicable. 

23.175 Demonstration of Static 

Long. Stab. 

Only paragraph (a) is applicable, evaluated with 

“Enroute Ice”. 

23.177 Static lateraldirectional stability Approved take-off lift configurations, V50 or V2, 

"Takeoff Ice." 

Lowest lift take-off configuration, all-enginesoperating initial climb speed, Final Takeoff Ice” 

High lift devices retracted configuration, enroute 

climb speed, “Enroute Ice” 

23.181 Dynamic stability Provided that there are no marginal 

compliance aspects with the 

non-contaminated airplane, it is not necessary to 

demonstrate dynamic stability in specific tests. 

Qualitative evaluations should be combined with the 

other testing. Any tendency to sustain oscillations in 

turbulence or difficulty in achieving precise attitude 

control should be investigated. 

23.201 & 

23.203 

Stall characteristics Applicable. One kt/sec wings level and turning stalls 

only. No accelerated turning stall. Configurations 

evaluated: 

 

All approved take-off lift configurations, "Takeoff 

Ice." 

 

Lowest lift take-off configuration, “Final Takeoff Ice” 

 

High lift devices retracted configuration, “Enroute 

Ice” 

23.207(a) Stall warning clear & 

distinctive 

Applicable. 

23.207(b) Stall warning means Applicable. 

23.207(c) Stall warning margin 5 

KCAS 

Stall warning should be assessed in conjunction with 

stall speed testing and stall characteristics testing. 
AC 23.1419-2D 

Appendix 9 

A9-7

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

23.45 General 

(performance) 

Applicable. 

23.207(d) Maneuver margin Airplane should be free of buffet and stall warning in 

following level altitude turns at specified bank: 

 

Approved take-off lift configurations, V50 or V2, 40° 

bank, "Takeoff Ice." 

 

Approved take-off lift configurations, V50 or V2, 30° 

bank, simulated thrust for OEI, "Takeoff Ice." 

 

Lowest lift take-off configuration, all-enginesoperating initial climb speed, 40° bank, Final Takeoff 

Ice” 

 

High lift devices retracted configuration, minimum 

enroute climb speed, “Enroute Ice” 

23.207(e) Stall warning in 

accelerated turning 

stalls 

Not required. 

23.207(f) Stall warning - 

acrobatic 

Applicable if acrobatic category. 

23.207(g) Stall warning – preactivation ice Not applicable. 

23.207(h) Stall warning – detect 

and exit 

Not required. 

23.207(i) Means of stall warning 

same in icing 

Applicable. Means of stall warning in Appendix O 

same as non-icing and Appendix C. 

23.207(e) Stall warning 1.5g 

turns 2 kt/sec 

Shouldn’t be required to be consistent with current 

part 23 practice 

23.207(f) Acrobatic airplane stall 

warning 

 

23.221 Spinning Not required. 

23.231 Ground and water 

Longitudinal S&C 

Applicable – no dedicated tests 

23.233 Ground and water 

Directional S&C 

Applicable – no dedicated tests. Crosswind capability 

can be determined similar to Appendix C. 

23.235 Operation on unpaved 

surfaces 

Not required. 

23.237 Operation on water Applicable – no dedicated tests 
AC 23.1419-2E 

Appendix 9 

A9-8

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

23.45 General 

(performance) 

Applicable. 

23.239 Spray characteristics Not required. 

23.251 Vibration & buffeting Applicable. Evaluation limited to 250 KCAS, Vne, or 

an airspeed shown to have no ice accretion. 

23.253 High speed 

characteristics 

Not required. 

3. Flight tests with Ice shapes simulating residual takeoff and climb ice accretion. 

a. After takeoff into freezing drizzle or freezing rain conditions, several scenarios that 

result in additional ice accretions are possible: 

1. The airplane has to immediately return and land; or 

2. The airplane subsequently encounters Appendix C icing conditions; for which 

it is approved for flight in and is not required to exit; 

3. The airplane encounters Appendix O conditions in a subsequent flight phase 

and must exit. 

b. In the last two scenarios, ice may or may not sublimate off, depending on the flight 

and ambient conditions. It is possible that freezing rain ice accretions may be removed, if one 

assumes that a warm layer exists above the freezing rain. For an airplane that has to return and 

land, there is a high probability that not only will the takeoff ice accretions remain on the 

airplane, but additional ice will accrete. To address these scenarios, the applicant should show 

that: 

1. The additional Subpart B requirements associated with holding, approach and 

landing phases are shown with the “Enroute” ice calculated for takeoff in Appendix O; and 

2. Unless the applicant can empirically substantiate that Appendix O takeoff ice 

accretion will always shed under any foreseeable scenario, the applicant should conduct the 

flight tests in 1. above with Appendix C or Appendix O detect and exit ice shapes that are 

empirically determined by combining the critical Appendix O takeoff ice accretion (“Enroute”) 

followed by the respective Appendix C or Appendix O detect and exit ice accretion (critical of 

approach or landing, as defined in Table XX of this AC, but holding need not be considered). 
AC 23.1419-2D 

Appendix 9 

A9-9

Part 23 SLD ARC REPORT 

APPENDIX D – RECOMMENDED REVISION TO AC 23.1419-2D 

4. Natural icing flight tests 

a. Appendix O Conditions. Takeoffs should be accomplished in Appendix O 

conditions to demonstrate that the airplane can safely takeoff in Appendix O conditions. 

1. Appendix O Conditions. It is not necessary to quantify the conditions with 

airplane mounted equipment. Airport observations are sufficient. The following conditions 

should be demonstrated as a minimum: 

(a) Moderate freezing drizzle 

(b) Light freezing rain 

2. Airplane Configuration 

(a) Nominal weight and CG. 

b. Ground Deicing/Anti-Icing Fluids. Type II and Type IV fluids have resulted in 

modifications of takeoff procedures due to changes in lift losses, control forces, or rotation 

characteristics. Assessment of the fluids prior to testing in natural freezing drizzle or freezing 

rain should be considered. 

c. Demonstration Objectives. The following should be evaluated 

1. Takeoff performance 

2. Longitudinal controllability at rotation and during climb 

3. Lateral/directional controllability during climb 

4. Flap and gear operation 

Part 23 SLD ARC REPORT 

APPENDIX E – OPERATIONS COST SURVEY 

FEB 2012 - Revision B Page E-1

This appendix provides information received by the ARC relative to surveys 

distributed by the operations sub-group. 

Regional Air Cargo Carriers Association (RACCA) Survey

With respect to operation in ground icing conditions Yes No extra

if the appropriate anti‐icing procedures and time

limits are followed, is your operation currently

approved to takeoff in freezing drizzle? 1 4   

if the appropriate anti‐icing procedures and time

limits are followed, is your operation currently

approved to takeoff in light freezing rain? 2 3   

Presuming that you're considering a new aircraft Yes No extra

would a newly certificated airplane in which takeoff

or flight in freezing drizzle was prohibited by an

operating limitation have a significantly negative

effect on the airplane's viability in your operation? 3 2   

would a newly certificated airplane in which takeoff

or flight in freezing rain was prohibited by an

operating limitation have a significantly negative

effect on the airplane's viability in your operation? 3 2   

would a newly certificated airplane in which takeoff

or flight in freezing drizzle was prohibited by an

operating limitation bias you against purchasing it? 4 1   

would a newly certificated airplane in which takeoff

or flight in light freezing rain was prohibited by an

operating limitation bias you against purchasing it? 3 1

not so much as

freezing drizzle
Part 23 SLD ARC REPORT 

APPENDIX E – OPERATIONS COST SURVEY 

FEB 2012 - Revision B Page E-2

Aircraft Owner and Pilots Association (AOPA) Survey

1.  Is your aircraft equipped with a de‐ice/anti‐ice system?

# Answer Response %

1 Yes 25 78% 

2 No     7 22% 

Total 32 100%

2.  Is your aircraft certified for flight into known icing conditions?

# Answer Response %

1 Yes 21 88% 

2 No     3 13% 

Total 24 100%

3.  What type of operations do you use your aircraft for?

# Answer Response %

1 Personal 2 10% 

2 Business     4 19% 

3 Both Personal and 

Business 15 71% 

Total 21 100%
Part 23 SLD ARC REPORT 

APPENDIX E – OPERATIONS COST SURVEY 

FEB 2012 - Revision B Page E-3

4.  Do you utilize de‐ice/anti‐ice fluid and hold‐over times in your

winter operations?

# Answer Response %

1 Yes 11 52% 

2 No     9 43% 

3 Not Sure 1 5% 

Total 21 100%

5.  Do your operations allow for takeoff in freezing drizzle/light

freezing rain?

# Answer Response %

1 Yes 6 50% 

2 No     5 42% 

3 Not Sure 1 8% 

Total 12 100%
Part 23 SLD ARC REPORT 

APPENDIX E – OPERATIONS COST SURVEY 

FEB 2012 - Revision B Page E-4

6.  Approximately how many times does this occur per year?

# Answer Response %

1 0 0 0% 

2 1     2 33% 

3 2 2 33% 

4 3-5     1 17% 

5 6-10 0 0% 

6 More than 10     1 17% 

Total 6 100% 

7.  On average, what is the cost (in dollars) of a canceled flight to

you or your company?

Text Response

1000.00 

3 TO 5 THOUSAND $ 
Part 23 SLD ARC REPORT 

APPENDIX E – OPERATIONS COST SURVEY 

FEB 2012 - Revision B Page E-5

8.  During winter operations, do your operations allow for landing

in freezing drizzle/light freezing rain?

# Answer Response %

1 Yes 9 45% 

2 No     8 40% 

3 Not Sure 3 15% 

Total 20 100%

9.  Approximately how many times does this occur per year?

# Answer Response %

1 0 1 11% 

2 1     2 22% 

3 2 3 33% 

4 3-5     2 22% 

5 6-10 0 0% 

6 More than 10     1 11% 

Total 9 100% 
Part 23 SLD ARC REPORT 

APPENDIX E – OPERATIONS COST SURVEY 

FEB 2012 - Revision B Page E-6

10.  If a divert is required, what is your average distance to an

alternate airport?

# Answer Response %

1 0-50 nm 5 26% 

2 51-100 nm     12 63% 

3 101-150 nm 1 5% 

4 More than 150 nm   0 0% 

5 Not sure 1 5% 

Total 19 100% 
Part 23 SLD ARC REPORT 

APPENDIX E – OPERATIONS COST SURVEY 

FEB 2012 - Revision B Page E-7

11.  What is your average total fuel flow per hour in gallons?

Text Response

85 

45 

70 

40 

60 

75 

75 

85 

200 

78 

75 gph 

90 

65 GAL JET A 

100 

63 

160 

65 

80 

70 
Part 23 SLD ARC REPORT 

APPENDIX E – OPERATIONS COST SURVEY 

FEB 2012 - Revision B Page E-8

12.      If you were in the market for a new aircraft, would you

reconsider the purchase if that aircraft (certified for FIKI) carried a

limitation that takeoffs and landings in freezing drizzle or freezing

rain were prohibited?

# Answer Response %

1 Yes 16 55% 

2 No     6 21% 

3 Not Sure 7 24% 

Total 29 100%
Part 23 SLD ARC REPORT 

APPENDIX E – OPERATIONS COST SURVEY 

FEB 2012 - Revision B Page E-9

National Air Transportation Association (NATA) Survey

Do you operate FAR Part 23 airplanes under Part 135? 

Answer Options Response 

Percent 

Response 

Count 

Yes 100.0% 6 

No 0.0% 0 

answered question 6 

skipped question 0 

What type(s) of Part 23 certificated airplanes do you operate? (Please check all that 

apply.) 

Answer Options Response 

Percent 

Response 

Count 

Single-Engine Piston 0.0% 0 

Multi-Engine Piston 66.7% 2 

Single-Engine Turboprop 66.7% 2 

Multi-Engine Turboprop 33.3% 1 

Turbojet 33.3% 1 

answered question 3 

skipped question 3 
Part 23 SLD ARC REPORT 

APPENDIX E – OPERATIONS COST SURVEY 

FEB 2012 - Revision B Page E-10

Are any your Part 23 aircraft airplanes with a de-ice or anti-ice system certified for 

flight into known icing conditions? 

Answer Options Response 

Percent 

Response 

Count 

Yes 100.0% 3 

No 0.0% 0 

answered question 3 

skipped question 3 

Do you utilize de-ice / anti-ice fluid on your Part 23 airplanes? 

Answer Options Response 

Percent 

Response 

Count 

Yes 100.0% 3 

No 0.0% 0 

answered question 3 

skipped question 3 

Do you have OpsSpec authority to use an approved deicing/anti-icing program that 

complies with 121.629(c)? 

Answer Options Response 

Percent 

Response 

Count 

Yes 33.3% 1 

No 66.7% 2 

answered question 3 

skipped question 3 
Part 23 SLD ARC REPORT 

APPENDIX E – OPERATIONS COST SURVEY 

FEB 2012 - Revision B Page E-11

Does your operation allow for takeoff in (check all that apply): 

Answer Options Response 

Percent 

Response 

Count 

Light freezing drizzle 66.7% 2 

Freezing drizzle 66.7% 2 

Light freezing rain 66.7% 2 

Freezing rain 66.7% 2 

None of the above 33.3% 1 

answered question 3 

skipped question 3 

When utilizing your Part 23 airplane(s), how often on average, during the past five 

winter seasons, have takeoffs in freezing precipitation occurred? 

Answer Options Response 

Percent 

Response 

Count 

0-3 0.0% 0 

4-6 0.0% 0 

7-10 0.0% 0 

11-15 0.0% 0 

More than 15 100.0% 2 

answered question 2 

skipped question 4 
Part 23 SLD ARC REPORT 

APPENDIX E – OPERATIONS COST SURVEY 

FEB 2012 - Revision B Page E-12

When utilizing your Part 23 airplane(s), how often on average, during the past five 

winter seasons, have you been unable to dispatch those airplane(s) because of 

freezing precipitation? 

Answer Options Response 

Percent 

Response 

Count 

0-3 0.0% 0 

4-6 50.0% 1 

7-10 0.0% 0 

11-15 0.0% 0 

More than 15 50.0% 1 

answered question 2 

skipped question 4 

How often on average, during the past five winter seasons, did you have to divert 

your Part 23 airplane(s) because of freezing precipitation at the destination? 

Answer Options Response 

Percent 

Response 

Count 

0-3 50.0% 1 

4-6 0.0% 0 

7-10 50.0% 1 

11-15 0.0% 0 

More than 15 0.0% 0 

answered question 2 

skipped question 4 
Part 23 SLD ARC REPORT 

APPENDIX E – OPERATIONS COST SURVEY 

FEB 2012 - Revision B Page E-13

How often on average, during the past five winter seasons, did your Part 23 

airplane(s) divert because of icing conditions encountered en-route? 

Answer Options Response 

Percent 

Response 

Count 

0-3 50.0% 1 

4-6 50.0% 1 

7-10 0.0% 0 

11-15 0.0% 0 

More than 15 0.0% 0 

answered question 2 

skipped question 4 

How often on average, during the past five winter seasons, have you been unable to 

dispatch your Part 23 airplane because of freezing precipitation? 

Answer Options Response 

Percent 

Response 

Count 

0-3 100.0% 2 

4-6 0.0% 0 

7-10 0.0% 0 

11-15 0.0% 0 

More than 15 0.0% 0 

answered question 2 

skipped question 4 
Part 23 SLD ARC REPORT 

APPENDIX E – OPERATIONS COST SURVEY 

FEB 2012 - Revision B Page E-14

How often on average, during the past five winter seasons did you have to divert your 

Part 23 aircraft because of freezing precipitation at the destination? 

Answer Options Response 

Percent 

Response 

Count 

0-3 50.0% 1 

4-6 50.0% 1 

7-10 0.0% 0 

11-15 0.0% 0 

More than 15 0.0% 0 

answered question 2 

skipped question 4 

How often on average, during the past five winter seasons did your Part 23 aircraft 

divert because of icing conditions encountered en-route? 

Answer Options Response 

Percent 

Response 

Count 

0-3 50.0% 1 

4-6 50.0% 1 

7-10 0.0% 0 

11-15 0.0% 0 

More than 15 0.0% 0 

answered question 2 

skipped question 4 
Part 23 SLD ARC REPORT 

APPENDIX E – OPERATIONS COST SURVEY 

FEB 2012 - Revision B Page E-15

In what FAA region do you conduct most of your operations? 

Answer Options Response 

Percent 

Response 

Count 

Alaska 0.0% 0 

Southwest 0.0% 0 

Northwest Mountain 0.0% 0 

New England 0.0% 0 

Western Pacific 0.0% 0 

Eastern 0.0% 0 

Great Lakes 66.7% 2 

Southern 33.3% 1 

Central 0.0% 0 

Hawaii 0.0% 0 

answered question 3 

skipped question 3 

Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

Part 23 Icing Accident Survey 

FAA-SAD P-231cingARC 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

Differences Between P23 & P2

• Part 23 has many times more accidents each year whe

compared to part 25 

+ Training grounds for new pilots + Less regulation on pri vate use + Fewer professional flight crews + Fewer type rating required aircraft + Etc. 

• Number of accidents allows for statistically relevant ana

not possible in part 25 

FMSPD P-23lcingPRC 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

U.S. Active Aircraft 

• Piston Turboprop • Turb

Rotorcraft _ Gliders _ light

Active Aircraft Experimental Light Sport 

• 320,000 Worldwide • 228,000 US 

• 163,103U.S. Piston 

• 145,497 US Single Piston • 17.515 US Twin Piston 

FAA-SAD P-23 1cingARC 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

Piston Airplanes Manufactured Annu

u.s. Active 

Piston Flee

163,103 

Airplanes 

L{) 0 L{) 0 L{) 0 L.() 0 L{) 0 L() <.D <.D I'--- I'--- OJ OJ a:> 0) 0 

0) 0) 0) 0) 0) 0) 0) 0) 0) 0 

...--- ...--- ...--- ...--- ...--- ...--- ...--- ...--- ...--- C"J 

Gil""" Stati .. ; . .. Dat. 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

2008 U.S. Active Piston Fleet Hours 

• Single Engine §91 Twin Engine §91 • Single Engine §135 Twin Engine §135 

292,000 404,000 

2,328,000 r--...... -. 

12,746,000 

FAA-SAD P-231cingARC 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

Population of Data 

• NTSB Icing Accidents 1990 - 2009 

+ Data set provided to GAO during 201 0 independent review o

accidents 

+ NTSB data from 1988+ is standardized 

o Common accident themes 

o Frequency of events 

• 457 "Icing Accidents" from 1990 - 2009 

+ Fatal- 212 + Serious Injury - 51 + Minor Injury - 48 

+ No Injury - 146 

FMSPD P-23lcingPRC 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

1:DJ 

1[(() 

Total GA Accidents to P-23 Ici

Accidents 

GA Acc idents to P-23 lcing Acc idents (1990 - 2009 NTSB Data) r---------"""- 0 GA Acc idents _ P-23 lcing Acc idents 

P.231dng accktllflts al1l124% ofGA acddentI ov .. last:20 yeaT1 (1990-2009 HTSS Data) 

P·23tctng aCddentl hawdedlNdby abou: 3 tlm ... lnceth. earty 1990, (1m· 2009NTSB Data) 

__ 

-r 

__ 

--

______ 

-'--

__ ______ 

-

1999 1991 199219931 994 1995 1995 1997 1995 1999 = 2001 2002 2003 2004 = = 2007 

FMSPD P-23lcingPRC 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

400 

100 

Fatal GA Accidents to Fatal P-

Icin Accidents 

GA Fatal Accidents to P-23 Fatal Icing Accidents (1990 - 2009 NTSB Data) 

\----., 

• GA FatalAccidents _ P-23 Icing FatalAccidents 

Fml P-23 Icing Icddenbllre2.94% offabil GA Icddenbl OVIf Int20 YUfW (1990- 2009NTS8 Data) 

F ltal P·23 Icing .. cddMtl havededlned by Ibcti: hatf since the arty 1990. (1990 -2009 NTSB Data) 

1999 1991 1992 1993 1994 1995 1995 1997 1995 1999 = 2001 = 2003 2004 = = 2007 

FMSPD P-23lcingPRC 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

Common Themes 

• Major Themes: 

+ Non-FI K I aircraft into forecast icing condition+ Attempted flight with ground ice & frost + Loss of forward visibility + Stall on Landing to Some Accumulations + Induction System Icing + SLD overwhelms de/anti-Ice systems 

FMSPD P-23lcingPRC 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

"Other" Icing Accidents 

• Stall on Approach Due to Some Ice • Frozen Pitot/Static • Anti/De-Ice System Failures • Didn't Use Anti-Ice System • Loss of Traction on Landing • Didn't Maintain Minimum Icing Airspeed • Unknown 

FMSPD P-23lcingPRC 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

1990·2001 §23 Icing Accident Ca

TnT" 

• Icing wiNo Eqpt. Gnd. Ice/Frost • SLD (w/FIKI) 

Induction Ice (FIKI) . Windshield Icing Other 

15% 

20% 

FAA-SAD P-231cingARC 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

1990·2001 §23 Fatal Icing Accid

Causes 109 Total 

• Icing wiNo Eqpt. Gnd. Ice/Frost • SLD (w/FIKI) 

Induction Ice (FIKI) . Windshield Icing Other 

1% 19% 

3% 

5% 

13% 

FAA-SAD P-231cingARC 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

"Other" Icing Accidents 

• Stall on Approach Due to Some Ice • Frozen Pitot/Static • Anti/De-Ice System Failures • Didn't Use Anti-Ice System • Loss of Traction on Landing • Didn't Maintain Minimum Icing Airspeed • Unknown 

FMSPD P-23lcingPRC 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

1990·2001 §23 FIKIlcing Accide

Causes 51 Total 

_ Windshield Icing Stall on Flare _ SLD (w/FIKI) 

Ground Ice _ Failed System Skid on Runway 

_ Other 

4% 

12% 

12% 

FAA-SAD P-231cingARC 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

1990·2001 §23 Fatal FIKI Approv

lci Accident Causes Tota

• Windshield Icing Didn't Use 

Ground Ice • Failed System 

17% 

13% 

22% 

FAA-SAD P-231cingARC 

. SLD 

Other 

18% 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

Operational Rule Effectivenes

• Operational Issues 

• Large Safety Benefit (Existing Fleet so Large) • More Difficult to Control than Design 

oAssume 30% Effective Peak (Ramp Up/Ramp Down) 

• Majority of Accidents are Operational Issues 

. 53% Flight into icing wino equipment 

o Education Campaign (30% Effective) = 15% Reduction in 

Accidents Immediately 

. 20% Ground icing takeoffs 

o EducationCampaign (30% Effective) = 6% Reduction in 

Accidents Immediately 

FMSPD P-23lcingPRC 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

Design Rule Effectiveness 

• Design Rule Effectiveness 

+ Smaller Safety Benefit + More Definite Results + Slower Benefit (New Models to Existing Models) 

o Existing Fleet 228,000 Airplanes 

0 1% retiremenUyear 

o New Non-F I K 1- 1333/year o New FIKI (SLD Proof) -1616 per year o New Designs Adopted @ 1 O%/year to year 

FMSPD P-23IcingPRC 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

Design Rule Effectiveness 

• SLD Represents 6% of Accidents Today 

+ "Bulletproof' Design (100% effective, Typical Productio

Rates, 10% New Design AdoptionfY ear) 

5 

10 

15 

20 

FMSPD P-23lcingPRC 

Total Icing 

Accident 

Reduction 

0% 0% 

0.2% 0.4% 

0.6% 

Fatal Icing 

Accident 

Reduction 

0% 0% 

0.1 % 

0.3% 

0.5% 

FIKllcing 

Accident 

Reduction 

0% 

0.1 % 

0.4% 

0.9% 

1. 3% 

Fatal FIKI 

Accident 

Reduction 

0% 

0.1 % 

0.7% 

1. 6% 

2.5% 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

Suggested Direction 

• Auto Ice Detection Represents 18% of Fatal FI K I 

Accidents Today 

+ "Bulletproof' Design (100% effective, Typical Productio

Rates, 10% New Design AdoptionfY ear) 

FMSPD P-23lcingPRC 

Fatal FIKI 

Accident 

Reduction 

0% 

5 0.1 % 

10 .5% 

15 1.1 % 

20 1. 7% 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

Design Rule Effectiveness 

• Failure Detection Represents 12% of FI K I Equippe

Accidents Today 

+ "Bulletproof' Design (100% effective, Typical Productio

Rates, 10% New Design AdoptionfY ear) 

5 

10 15 

20 

FMSPD P-23lcingPRC 

FIKllcing 

Accident 

Reduction 

0% 

0.1 % 

0.3% 0.7% 

1.1 % 

Fatal FIKI 

Accident 

Reduction 

0% 

0.1 % 

0.3% 0.7% 

1.1 % 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

Summary Chart 

• Reductions in T otallcing Accidents (23 per year) 

5 

10 15 

20 

Total20yr 

Flight into 

Icingwlo Equip. 

5% 

10% 

15% 

10% 

5% 

47 

Takeoff 

wlGround 

Frost 

2% 

4% 

6% 

4% 

2% 

19 

SLD Icing 

0% 0% 

0.2% 0.4% 0.6% 

- = Operational Changes - = Design Changes 

FMSPD P-23lcingPRC 

WIS Icing 

0% 

0.1 % 

0.7% 

1. 6% 

2.5% 

4 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

Summary Chart 

• Reductions in F atallcing Accidents (10 per year) 

5 

10 15 

20 

Total20yr 

Flight into 

Icingwlo Equip. 

6% 

12% 

18% 

12% 

6% 

24 

Takeoff 

wlGround 

Frost 

1% 

2% 

4% 

2% 

1% 

4 

SLD Icing 

0% 0% 

0.1 % 

0.3% 

0.5% 

0 

- = Operational Changes - = Design Changes 

FMSPD P-23lcingPRC 

W/S Icing 

0% 

0.0% 0.0% 

0.1 % 

0.1 % 

0 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

Summary Chart 

• Reductions in FI K I Approved Icing Accidents (5 pe

0% 0% 0% 1% 0% 

5 0.1 % 0.1 % 0.1 % 2% 0.1 % 

10 0.5% 0.5% 0.4% 4% 0.3% 15 1. 2% 1.1 % 0.9% 2% 0.7% 

20 1. 8% 1. 7% 1. 3% 1% 1.1 % 

Total20yr 1 0 2 0 

- = Operational Changes - = Design Changes 

FMSPD P-23lcingPRC 
Part 23 SLD ARC REPORT 

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY 

FEB 2012 - Revision B 

Summary Chart 

• Reductions in Fatal FIKI Approved Icing Accidents (2 per 

year) 

0% 0% 0% 2% 0% 

5 0.1 % 0.1 % 0.1 % 4% 0% 

10 .5% 0.3% 0.7% 7% 0.1 % 15 1.1 % 0.7% 1. 6% 4% 0.2% 

20 1. 7% 1.1 % 2.5% 0.4 1.1 % 

Total20yr 0 0 0 2 0 

- = Operational Changes - = Design Changes 

FMSPD P-23lcingPRC