### 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 “Par t 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 “Train ing Recommendations” to Task 7.

Appendix E Added Appendix E – Operations Cost Survey

Appendix F Added Appendix F – GA MA 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

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-3 TABLE OF CONTENTS

1. SUMMARY

....................................................................................................................... ........ 9
2. BACKGRO UND .................................................................................................................... . 10
3. Preamble Discussi on ........................................................................................................... .. 13 A) Subpart B Aspects (inc luding Autopilot) ................................................................................ 13 B) Summary Table of Subpart B part 23 Proposals versus part 25 propos als ...................... 22 C) Subpart B - Means of Co mpliance A ppendix O ................................................................... 33 D) Subpart B - Appendix C Ic e Accretio ns ................................................................................ 39 E) Powerplant Aspects ............................................................................................................ ... 44 F) Systems and Rela ted Aspects .............................................................................................. 47

4. RULEMAKING RECOMMENDATIONS .............................................................................. 52 A) Subpart B As pects ............................................................................................................. .... 52 B) Ice Accretions for showing complia nce to 14 CFR 23 Subpart B ....................................... 64 C) Powerplant Aspects ............................................................................................................ ... 70 D) Systems As pects

............................................................................................................... ..... 72

5. ADVISORY MA TERIAL S ...................................................................................................... 75 A) Sub-Part B Aspects ............................................................................................................ .... 75 B) Powerplant Aspects ............................................................................................................ ... 75 C) Systems As pects

............................................................................................................... ..... 82 D) AC 23- 17C ..................................................................................................................... ......... 82
6. ALTERNATIVES CONS IDERED ......................................................................................... 84

7. CERTIFICATION CO ST INPU T ........................................................................................... 92 A) Assumpti ons ................................................................................................................... ........ 92 B) Increased Cost Categori es .................................................................................................... 94 C) Increased Cost Summar y ...................................................................................................... 9 7 D) Costs for Certificat ion to a Portion ....................................................................................... 100 E) Reduced Costs Categori es ................................................................................................. 100 F) Summary ARC Posi tion on Costs ....................................................................................... 101
8. OPERATING COST ............................................................................................................ 103 A) Cost of Available Ce rtification Options ................................................................................ 103 B) Traini ng ......................................................................................................................

........... 104 C) Design Implic ations ...........................................................................................................

... 105 D) Airplane Manufac turing Industry

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

................................................................................................................... 105
9. BENEFIT SUMMARY

.......................................................................................................... 106 A) Icing Accident Da tabase Re view ........................................................................................ 106 B) Icing Incident Da tabase Re view .......................................................................................... 114
10. TRAINING RECO MENDATIO NS ...................................................................................... 116 A) Introduc tion ..................................................................................................................

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

........................................... 117 C) Focused Ice Training

............................................................................................................ 121 D) Changes to FAA training and testing ma terial .................................................................... 124

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-4 11. TASK 9 RECOME NDATION S ........................................................................................... 125 A) Backgr ound.....................................................................................................................

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

..... 125 C) Options .......................................................................................................................

........... 127 D) Applicability Of T he Proposed Rule .................................................................................... 132 E) Benefit Su mmary ...............................................................................................................

... 134 F) Cost Summary

...................................................................................................................... 136 G) Guidance

............................................................................................................................... 137

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-5 TABLE OF APPENDICES

APPENDIX A – PART 23 ICING ARC CHARTER

APPENDIX B – PART 23 ICING ARC MEMBERS

APPENDIX C – PART 23 AIRPLANE SEVER E ICING AIRWORTHINESS DIRECTIVES

APPENDIX D – RECOMMENDED R EVISION TO AC 23.1419-2D

APPENDIX E – OPERATIONS COST SURVEY

APPENDIX F – GAMA PART 23 ICING ACCIDENT SURVEY

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-6 TABLE OF TABLES

Table 1 - Comparison of Part 25 ve rsus Part 23 Re commendatio ns ............................ 22

Table 2 - Suspect ed SLD Ev ents .................................................................................. 35

Table 3 - Pre-Activation Ic e Accretions - Appendix C
Continuous Maximum Conditions ........................................................................... 43

Table 4 - Sec. 23.67 Applic able Ice Accr etions ............................................................. 56

Table 5 - "Sec. 23.1093 -Table 1" - Ic ing Conditions fo r Ground Te sts ......................... 71

Table 6 - Aircraft Certifi ed to § 23.1419 Am dt. 23- 43 .................................................... 85

Table 7 - Size Assumptions Used for Ce rtification Cost Estimates ............................... 93

Table 8 - Certification Approval Options with Respect to Ic ing Condit ions .................... 93

Table 9 - Regulatory Input - Airframe A nalysis .............................................................. 94

Table 10 - Regulatory Input – Flight Testi ng ................................................................. 96

Table 11 - Summary of Increased Certific ation Costs for Propos ed Rulemaking .......... 98

Table 12 – Detailed Medians for t he Aspects of Ce rtificat ion ........................................ 99

Table 13 – Events App licable to SLD .......................................................................... 106

Table 14 – International Ev ents Applicable to SLD ..................................................... 108

Table 15 – Events Applicable to ICTS Rule making ..................................................... 109

Table 16 – SLD Descrip tor Distri bution ....................................................................... 111

Table 17 – Phase of Fl ight Distrib ution........................................................................ 113

Table 18 – SLD Incident s ............................................................................................ 115

Table 19 – Events Applicable to Task 9 Pr oposed Ru le.............................................. 135

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-7 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 fo r 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

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-8 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 fo r 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

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-9 1. SUMMARY

The Part 23 Icing Aviation Rulemaking Commi ttee was formed in early 2010 by FAA
charter to consider the follo wing 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 ic e 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 contam inated tailplane stall (ICTS). Completed

3 Recommend revision to current § 23.1419 on airplane performance requirements in icing that require an exem ption to the 61 knot stall s peed requirement in icing. Completed

4 Determine applicable accidents a nd incidents that can be used for benefits in the economic analysis. Completed by Revision A

5 Summarize certification and operating co sts associated with the recommended regulations that can be used in the economic analysis. Completed by Revision A

6 Identify compliance guidance that will be requi red to facilitate showing compliance
with the recommendations above. Completed

7 Identify impact on operations in kn own 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 Safe ty Recommendation A-10-12 is feasible for part 23 airplanes for operations in icing conditions (tasking added Q3 2010). Completed

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-10 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 invest igation led to the conclusion that freezing drizzle conditions created a ridge of ice on the wing’s upper surfac e aft of the deicing
boots and forward of the ailerons. The NTSB c oncluded that the ridge of ice resulted in uncommanded roll of the airplane. The atmospher ic conditions (freezing drizzle) that may have contributed to the accident are out side the icing envelope specified in Appendix C of part 25 of t he Federal Aviation Regulati ons (14 CFR part 25) for certification of the airplane. Freezing rain is another atmo spheric 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 al so 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 prohi bit operations in supercooled large drop
conditions.

The NTSB issued various safety recommendat ions to the FAA following the Model
ATR72 accident. One of the recommendat ions, 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 t he limits for aircraft certification.

Another recommendation, A-96-54, states:

Revise the icing criteria published in 14 C ode of Federal Regulations (CFR), parts 23 and 25, in light of both rec ent research into aircraft ice accretion under varying conditions of liquid water content, drop size distribution, and tem perature, and recent developments in both the design and use of aircraft. Also, expand the appendix C icing certification envelope to include freezin g drizzle/freezing rain and mixed water/ice crystal conditions, as necessary.

The FAA tasked the Aviation Rulemaking Advi sory 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 condi tions. The ARAC was tasked to consider the need to define a mixed phase icing envir onment (supercooled liquid and ice crystals). They were also asked to study the effects icing r equirement changes could

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-11 have on pilot compartment view, airspeed indica ting 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 Rulemaki ng Advisory Committee’s (ARAC) Ice Protection Harmonization Working Group (H WG) completed their final report on recommended rulemaking and advisory materi al 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 Po werplant 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 reco mmendations addressing 14 CFR part 25 aircraft perfo rmance and handling qualities, engi ne installation effects, ice protection system require ments, and 14 CFR part 33 engi ne requirements. ARAC approved the report and sent it to the F AA in March 2006. The Ice Protection Harmonization Working Group has recently comp leted a review of available tools for compliance and revised the recommended guidanc e 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 (Docke t No. FAA–2010–0636) was published in the Federal Register on June 29, 2010.

An Aviation Rulemaking Commi ttee (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 t hey need to be modified for part 23. The charter is in Appendix A.

The ARC task was not to produce an SLD rule fr om scratch, but to review the proposed part 25 rule and compliance guidance alread y recommended by an ARAC Issue Group (Transport Airplane and Engine, TAEIG) fo r 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 el ectro-thermal, operator s of those part 23 airplanes or groups that represent operator s, 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 incorpor ation of AFM Limitations and procedures to recognize SLD and immediately exit severe ic ing. A list of the ADs is in Appendix C.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-12 The FAA also issued a generic issue paper “Rol l Control in Supercooled Large Droplet Conditions” in July 1997 t hat has been applied for new ce rtifications on aircraft equipped with reversible roll axis controls and pneumatic de-ici ng 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 evaporativ e wing anti-ice system. The issue paper can be found in the ARAC repor ts 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 becaus e they do not address the underlying safety concern of the unknown per formance 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 es tablished 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 lim itation on intentionally flying into SLD.

As documented in the ARAC report, ice cryst al conditions can affect engine operation and pitot probes. On part 23 airplanes, doc umented events of ice crystals affecting engine total temperature probes have been repor ted. 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 fo r part 23 airplanes in icing conditions
which states:

For all airplanes engaged in commercial op erations under 14 Code of Federal Regulations Parts 121, 135, and 91K, require the installa tion of low-airspeed alert systems that provide pilo ts 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.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-13 3. PREAMBLE DISCUSSION

A) S UBPART B A SPECTS ( INCLUDING A UTOPILOT )

The proposed part 23 regulation for showing sa fe 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 sa fely” 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 par t 25 Subpart B regulations with Appendix O ice accretions was reviewed. The part 23 ARC agreed with the ARAC recommendation that the regul ations required for Appendix C be also applicable for Appendix O, for those airplanes that are approved for Appendi x 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 differenc es 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 recomm ended 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 ici ng conditions and Part II of the proposed Appendix ice shapes that may occur in 14 CF R 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 re commendation that allow an option to certify an airplane to a portion of Appendix O. The Subpart B regul ations 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 certif ying to a portion of Appendix O in-flight wil l be difficult with current technology. Applicable guidance was added to the proposed advisory circul ar to address the concerns.

The part 25 proposed guidance has detail ed information on the limitations to accomplish such a certification. The ma terial 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 conditi ons is achievable. The ARC believes certifying to takeoff in Appendix O conditions would be the mo st 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 easie r to certify compared to the holding

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-14 phase. The guidance for takeoff in Appendi x O conditions assumes the airplane will not hold in Appendix O condition s, but for landing, certificat ion must consider a detect and exit holding ice shape. Guidance is incl uded in the draft part 23 advisory material.

The part 23 icing ARC discussed whether certif ication for takeoff (and/or landing) can be done to either freezing drizzle or freezing ra in. The majority an d 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 (current ly 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 t hem from reporting freezing drizzle. The ARC believes the average pilo t 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 discriminat ing between freezing drizzle and rain, and supports improvements in practices and tec hnology to improve reporting accuracy. However, the IPHWG judged that the conservati sm inherent in the ce rtification practices would result in safe operations. This c onservatism includes assuming a 12,000 foot vertical extent, 99% LWC and an engine out during the c limb (per § 25.111 requirements).

Another issue is after takeoff, one must a ssume 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. Tec hnology may be available in 5-7 years to determine the drop sizes aloft in terminal ar eas, 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 tak eoff (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 certif y an aircraft for either conditi on 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 tak eoff in freezing drizzle and light freezing
rain will accrete ice before li ft-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 ai rcraft meet published AFM/POH limitations and procedures. This may require prior manu facturer approval of Type II, III and IV ground deicing/anti-icing fluids.

The part 23 icing ARC took a slightly di fferent approach than the part 25 ARAC group
for “detect and exit”. For "operating safely after encount ering Appendix O conditions"

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-15 and "operating safely while exiting all ici ng conditions", the part 25 ARAC considered
that these are not failure cases and the te mptation 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 par t of any icing certification for Appendix C icing conditions i.e. if an Appendix C icing certif ication is sought, then "detect and exit" for Appendix O must also be addressed. The part 23 icing AR C 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 rec ognized 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 A ppendix 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, t he encounter with Appen dix 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 ic e 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 requi rements 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 address ed in the following paragraphs.

P ERFORMANCE AND HANDLING QUALITIES FOR " DETECT AND EXIT "

Regarding specifically handling qualities and performa nce, the discussions in the FTHWG addressed the following issues:

 Performance – The part 25 ARAC assu med that the take-off case need not be considered for a "detect and exit" airpl ane. 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 par t 23 icing ARC agreed, with the exception of a quantitative requirement for landing climb performance. The part 23 icing ARC decided that the airplane shoul d 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. T he ARC did not want a quantitative requirement in an environment the airplane is not approved for to possibly dictate design. Another factor wa s that the number of SLD events in a go-around was
small. Some ARC members raised t he 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 ex it because of the limited probability

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-16 of occurrence and prior history. No co mbinations of engine failures in SLD are
noted in the event database.

Various members of the ARC also ques tioned 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 appendi x C approval to require investigation with the specific SLD shape.

 Handling qualities – The part 25 ARAC proposed, with one exc eption, 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 V 2 . No justification for a relaxed standard of other handling qua lities 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 reco mmend that all Subpar t B controllability tests be accomplished for detect and exi t, but did recommend tests that address service history of airplanes in icing. These include susceptibility to roll control
anomalies and ice contami nated tailplane stall.

 Lateral controllability - The part 25 AR AC reviewed the JAA Interim Policy and the FAA ADs published to address roll controllability issues. Several manufacturers gave presentations of t heir experiences in addressing the FAA ADs during the part 25 rulemaking effort . The part 25 ARAC concluded that the existing requirement is adequate to addre ss 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. T he 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. T he ARC reviewed additional tests that were proposed by Transport Canada dur ing the part 25 ARAC group work. These included lateral control during 10° ban k 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 conduct ed to evaluate susceptibility to ice contaminated tailplane stall.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-17  Stall warning – The ARC bel ieved stall warning, provided by the same means as in non-icing, must be provided with critic al detect and exit ice shapes. The ARC adopted the three second after stall warn ing margin requirement proposed for part 25, in lieu of the five knot ma rgin 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, t he 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 se cond margin in Appendix O. The ARC believed a three second margin provi ded sufficient time to prevent stall, especially in the approach and landing phases of flight where t he majority of part
23 events occurred. Since detect and exit ice includes pre-detection ice, such a design would also provide stall warni ng 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 par t 25 as explained in the NP RM preamble, if a design with two icing stall warning schedules we re proposed, special conditions would be required.

 Approach speed – It is likely that stall s peeds 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 st all 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% thre shold proposed. The ARC was concerned with additional increases in approach s peed and resulting increases in landing distances, and the possibility of overr uns. The ARC proposed that the approach speed determined for Appendi x 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 susce ptibility to ice c ontaminated tailplane stall are evaluated with pre-activation ic e in Appendix C ici ng conditions, under current part 23 guidance and part 25 regulat ions. 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. Cu rrent part 23 guidance for A ppendix C ice accretion does not have the three second option. The ARC did not adopt the ARAC recommendation to apply the Appendix C pr e-activation ice stall warning requirements to Appendix O conditions. The ARC was concerned that applying the same requirements to Appendix O pr e-activation ice may have an overall adverse affect on safety by increas ing non-icing takeoff and landing speeds.

Current Part 23 advisory material (AC 23.1419-2D) specifies that stall warning margin with Appendix C pre-activati on ice be “positiv e...and adequate.” Compliance with this requirement is typica lly shown by decelerating the airplane
at 1 kt/sec and demonstrati ng 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 adjus tment to the stall warning schedule implemented for icing conditions is not ac tive. As a resul t, the airplane must meet this requirement with the non-icing stall warning schedule. Recent industry experience is that this r equirement 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 artifici ally high takeoff and landing speeds for all non-icing takeoffs and landings, which constitu te 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 warn ing than for Appendi x C pre-activation conditions which could in turn drive an even lower stall warning AOA setting which would further impact non-ic ing takeoff and landing speeds.

Testing ICTS susceptibility with pre-acti vation 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 fo r IPS activation based on 1) operation in conditions conducive to icing (temper ature and visible moisture), 2) first indication of ice accretion or 3) input fr om a primary ice detec tor are effective at minimizing unprotected exposure times in ic ing conditions. To further minimize risk of an event with pre-activation ice in Appendix O conditions, the ARC decided to require an Advisory or Primar y 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 c ontinue to be required to meet existing Appendix C pre-activation ic e 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 mitigati ng feature is installation of a Low Airspeed Alert, which will activate at ai rspeeds 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 sa me philosophy that stall warning and susceptibility to ICTS be evaluated with pr e-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 sc hedule for SLD conditions (as discussed above in the “Stall Warning” paragraph), or there is an autopilot limitation against operation after detection of SLD conditions.

A UTOPILOT A SPECTS

No regulation changes were pr oposed, 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 A ppendix C conditions listed as “normal conditions” for which the flight guidance system shoul d be designed. Similarly, the ARC believes the current guidance on testing autopilo ts in Appendix C c onditions 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 eval uating 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 cond itions, current part 23 certification practice is similar to airwor thiness action that was taken on most pneumatic boot equipped airplanes, with reversible late ral 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 cu es that indicate adverse changes in handling characteristics; therefore, t he 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 aut opilot 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 prohibi ted for flight in Appendix O conditions, particularly in t he single pilot, IMC environment, if adequate testing was accomplished. The current part 25 guidance and pr oposed 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 evaluatin g the autopilot in icing conditions. The ARC proposes to conso lidate the autopilot guidance for all icing conditions, Appendix C and Appendix O, into one section of the guidance for new type certificates. Appe ndix 3 of AC 23.1419-2D contains guidance on modified or new autopilots STC’s on airplanes approved fo r 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 opt ion 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 instal led and approved for flight in non-icing conditions, or required in non-icing flight for co mpliance to § 23.1523, it will be required for flight in icing cond itions based on operational requirements. Similarly, if an autopilot equipped airplane is appr oved 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 requirem ents for flight testing of ic e shapes simulating critical Appendix C, detect and exit (or pre-detection), and the ap proved portions of Appendix O. The guidance material retains the require ments to test the autopilot in natural Appendix C icing conditi ons. It is expected that the aut opilot 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 f light testing, the effect on autopilot performance and operation should be considered.

The proposed guidance includes flight test ing symmetrical ice shapes, there is no proposal to flight test asymmetric ice sh apes. 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 mu st be addressed. This could include asymmetric lift due asymmetric wing ice sheddi ng, or possibly the autopilot operating near its authority limit due to ice accretion effect on contro l power or hinge moment. The ATR Roselawn accident is one example in which automatic autopilot disconnect after reaching authority limit re sulted in a loss of control. Although there are no such documented events in the part 23 fleet, this could be becaus e of current practice of prohibiting autopilot use in seve re icing, or it could be these events have occurred but
not documented due to the lack of flight data recorders in t he 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 befor e 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 hazar dous flight condition. A par agraph (i) is proposed to be added to Section 23.1329. This requirement w ould apply only if the autopilot is to be approved for use in Appendix O c onditions, 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 REPORTFEB 2012 - Revision BPage-22B) SUMMARYTABLE OFSUBPARTBPART23PROPOSALS VERSUS PART25PROPOSALSThe table below summarizes each Subpart B paragraph and the requirements proposed for part 23 detect and exitairplanes by the ARC versus proposed for part 25 by ARAC.Table 1 - Comparison of Part 25versus Part 23 RecommendationsSection Title ProposedPart 25Part 23 Proposed Part 23 ARCDetect &ExitDetect & Exit25.21 Proof of compliance23.2125.23 Load distribution limits23.2325.25 Weight limits23.2525.29 Empty weight andcorresponding CG23.2925.31 Removable ballast23.3125.33 Propeller speed and pitchlimits23.3325.101 General (performance) 23.4525.103 Stall speed 23.49 (a) and(b) only. Stall speed must bedefined to determine operating speeds andstall warning margin.Part 23 SLD ARC REPORTFEB 2012 - Revision BPage-23Section Title ProposedPart 25Part 23 Proposed Part 23 ARC25.105 Takeoff23.53NOTE 125.107 Takeoff speeds23.51NOTE 125.109 Accelerate-stop distance23.55NOTE 125.111 Takeoff path23.57NOTE 125.113 Takeoff distance and takeoffrun23.59NOTE 125.115 Takeoff flight path23.61NOTE 125.117 Climb: general 23.63NOTE 1Climb: AEO23.65NOTE 1Takeoff climb: OEI23.66NOTE 125.119 Landing climb AEO23.77Except in lieu of quantitative criteria climbmust be measurably positive.Climb OEI GW<6000 Normal23.67(a)NOTE 2Climb OEI GW>6000 Normal23.67(b)NOTE 225.121(a) Climb OEI TO GD Commuter23.67(c)(1)NOTE 225.121(b) Climb OEI TO GU Commuter23.67(c)(2)NOTE 2Part 23 SLD ARC REPORTFEB 2012 - Revision BPage-24Section Title ProposedPart 25Part 23 Proposed Part 23 ARC25.121(c) Climb OEI Final TOCommuter23.67(c)(3)NOTE 225.121(d) Climb OEI ApproachCommuter23.67(c)(4)NOTE 225.123(a) Enrouteflight path OEI23.69NOTE 225.123(b) Enrouteflight path OEI23.69NOTE 225.123(c) Enroute flight path 3-4 engineNANOTE 2Glide: Single engine airplanes23.71NOTE 225.125 Landing23.73 VrefApplicable. 1.3Vs or use App. C Vref aslong as maneuver margin tests OK Intentis to not bump SLD approach and landingspeed (runway overrun?) if App C speed isadequate.25.125 Landing23.75 Dist. Applicable if Vref defined for Appendix Odetect and exit greater than Appendix CVref. May be determined by analysis.Flight characteristics: General23.141Part 23 SLD ARC REPORTFEB 2012 - Revision BPage-25Section Title ProposedPart 25Part 23 Proposed Part 23 ARC25.143(a) Controllability andManeuverability23.143(a) Applicable forappropriate flight phases23.143(b) It must be possible to make a smoothtransition from one flight condition toanother (including turns and slips) withoutdanger of exceeding the limit load factor,under any probable operating condition.AEO only. May be evaluated concurrentlywith other flight tests.25.143(b)(1) Sudden failure of engine23.143(b)25.143(b)(2) Sudden failure of secondengine25.143(b)(3) Configuration changes25.143(c)(1) Control with OEI in icing TONOTE 225.143(c)(2) Control with OEI in icing Appr.& landNOTE 225.143(c)(3) Control with OEI in icing Appr.& GANOTE 225.143(d) Control force limits 23.143(c) Applicable25.143(e)-(g)Part 23 SLD ARC REPORTFEB 2012 - Revision BPage-26Section Title ProposedPart 25Part 23 Proposed Part 23 ARC25.143(h) Maneuver margin25.143(i) ICTS23.143(d)Not applicable.25.143(j) Control – pre-activation ice23.143(e)Applicable. Evaluated with 0.5g to 1.5g,low and high airspeed, idle and GAthrust/power.25.143(k) Control – pre-detection iceControl – detect & exit 23.143(f)Applicable. Evaluated with 0.5g to 1.5g,low and high airspeed, idle and GAthrust/power.Longitudinal and lateral control evaluatedwith sideslips expected during operations.Lateral control evaluation 23.143(g)Specific tests added to regulation.25.145(a) Pitch down capability 23.145(a)NOTE 325.145(b) Configuration changes 23.145(b)NOTE 325.145(c)&(d) GA w/complete flap retract– noloss of altitude23.145(b)(3)NOTE 31.5g capability aboveVmo/Mmo23.145(c)NOTE 3Part 23 SLD ARC REPORTFEB 2012 - Revision BPage-27Section Title ProposedPart 25Part 23 Proposed Part 23 ARCPower off glide gear and flapextended23.145(d)NOTE 3Landing with primary FCSfailure23.145(e)NOTE 425.145 Longitudinal control 23.145NOTE 325.147(a) Directional control – OEI 23.147(a)NOTE 225.147(b) Directional control – 2EI25.147(c) Lateral control – OEI25.147(d) Lateral control - 2EI25.147(e) Lateral control margin – AEOSudden engine failure – 2 secdelay23.147(b)NOTE 2Control with primary lateralFCS failure23.147(c)NOTE 425.149 Minimum control speed23.149NOTE 2Acrobatic maneuvers23.151NOTE 5Control during landings23.153NOTE 3Part 23 SLD ARC REPORTFEB 2012 - Revision BPage-28Section Title ProposedPart 25Part 23 Proposed Part 23 ARCElevator control force inmaneuvers23.155NOTE 3Rate of roll23.157Rate of roll evaluated qualitatively duringcompliance to 23.143(g).25.161 Trim23.161NOTE 325.171 General (stability) 23.171NOTE 325.173 Static longitudinal stability 23.173NOTE 325.175 Demonstrationof Static Long.Stab.23.175NOTE 325.177 Static lateral-directionalstability23.177Evaluated during sideslips conducted forICTS evaluation.25.181 Dynamic stability 23.181NOTE 325.201(a)(b)(d)(c)(1)23.201 &23.203Applicable. Use pass/fail criteria in AC23.1419-2D: Roll may slightly exceed15 degrees if characteristics qualitativelydetermined to be safe.25.201(c)(2) Turning stall 3 kt/sec23.203(a)(2)NOTE 5Part 23 SLD ARC REPORTFEB 2012 - Revision BPage-29Section Title ProposedPart 25Part 23 Proposed Part 23 ARC25.203 Stall characteristics23.201 &23.203Applicable except use pass/fail criteriafrom AC 23.1419-2D. One kt/sec wingslevel and turning stalls only. Noaccelerated turning stall.25.207(a) Stall warning23.207(a)Applicable.Means of stall warning23.207(b)Applicable.25.207(b) Means of stall warning same inicing23.207(i)Applicable plus means of stall warningsame as non-icing and Appendix C.25.207(c) 5 knot/5% margin to stall23.207(c)25.207(d) 3 knot/3% margin to Vsr23.207(c)See 25.143(h) Maneuver margin23.207(d)See 23.73Part 23 SLD ARC REPORTFEB 2012 - Revision BPage-30Section Title ProposedPart 25Part 23 Proposed Part 23 ARC25.207(e) 3 sec margin to stall in icing23.207(h)Adopt part 25 3 sec in lieu of part 23 fiveknot in icing. Reasons:3 sec is adequate time, particularly inapproach and landing phase where mostevents occurRelaxing margin in SLD may result in onlyone SW schedule for icing. How would aseparate SLD SW schedule beimplemented? A switch? We want toavoid that – workload issue or possibleintentional non-compliance.25.207(f) Stall warning 1.5g turns 2kt/sec23.207(e)Shouldn’t be required to be consistent withcurrent part 23 practice25.207(g) Abnormal configuration of highlift25.207(h) Stall warning pre-activation ice23.207(g)25.207(i) Stall warning pre-detection iceNot included in part 25 NPRM. NPRMpre-amble explains should be covered bydetect and exit ice shape.Acrobatic airplane stallwarning23.207(f)Spinning23.221Part 23 SLD ARC REPORTFEB 2012 - Revision BPage-31Section Title ProposedPart 25Part 23 Proposed Part 23 ARC25.231 Ground and water LongitudinalS&C23.231Applicable – no dedicated tests25.233 Ground and water DirectionalS&C23.233Applicable – no dedicated tests. Addguidance similar to App C to analyzesideslip data for x-wind capability25.235 Taxiing conditions23.235Not applicable25.237 Wind velocities23.233Operation on water23.237Applicable – no dedicated tests25.239 Spray characteristics23.23925.251(a) Vibration & buffeting23.251Applicable . Evaluation limited to 250,Vne, airspeed shown to have no iceaccretion, reduced speed limit published inthe AFM for SLD exit./*25.251(b) – (e) Vibration & buffeting23.25125.253(a) High speed characteristics &recovery23.25325.253(b) Maximum speed for S&C nonicing25.253(c) Maximum speed for S&C icingPart 23 SLD ARC REPORTFEB 2012 - Revision BPage-32Section Title ProposedPart 25Part 23 Proposed Part 23 ARC25.255 Out-of-trim characteristicsLegend and Notes:Not requiredRequired – specific language addedRequired – referenced in § 25.21(g)Redtext Not required in 23.1419 Amdt. 23-43NOTE 1: Airplane is assumed to takeoffclean and not takeoff into SLD conditions.NOTE 2: Service history shows part 23SLD accidents not due to engine failure.NOTE 3: No dedicated tests required. Controllability, trimand stability evaluated concurrently with other tests.NOTE 4: Service history shows part 23 SLDaccidents not due to flight control failure.NOTE 5: Not required or typically evaluatedcurrently for AppendixC icing conditions.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-33 C) S UBPART B

- M EANS OF C OMPLIANCE A PPENDIX O

The proposed part 23 guidance material for Appendix O was derived from the proposed part 25 proposed guidance. A descrip tion of the simulation tool limitations for Appendix O and guidance for airplane co mponents in the different Appendix O distributions are provided. Some of the details are omit ted 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 drizzl e 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 charte r did not intend to change the part I definitions, and ther e is no reason to, since the A RC 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, questi on the proposed liquid water content at the cold freezing drizzle condi tions as discussed below.

APPENDIX O ICE ACCRETIONS

The ARC reviewed the proposed ice accreti ons 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, A ppendix O, part I conditions, an d not reference part 25, Appendix O, part II, for the following reasons:

 Part 25, Appendix O, part II refe rences part 25 sections; and

 The ARC modified the detec t and exit ice accretions.

The ARC agreed with the part 25 proposal th at takeoff and failure ice shapes would not be required for a detect and exit airpl ane. 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 capabi lity 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 fo r means to limit the requirement to calculate enroute ice, sinc e 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 encounter ed 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 “detec t and exit” after a review of alternatives:

 The phases of flight required for analys is 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 cons idered by the ARC was simplif ication of detect and exit ice accretions. The ARC recognized that four different Appendix O distributions combined with four different flight phases would r equire 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. T he 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 ic ing events in suspected SLD conditions and
determined that most event s, 39%, occurred during the approach phase. So the ARC
determined that ice accret ed during the holding phase, wh ich may have preceded the events, and the approach phase, should be ev aluated. The landing phase had the next highest amount of events, 31%. Even though the majority of these events were hard landings and non-fatal, t he ARC believes the ice accr etion 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 la nding flaps versus approach flaps. If the design did develop substantial ice accret ion behind the protected area during the approach, it most likely would serve as an a ccretion 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 procedur es 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 phas e. The remaining part 23 SLD events occurred in climb, cruise, and descent (26% of events). The ARC believes the holding phase adequately addresse s 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 defin ition, which is included in the ARC
recommendations.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-35 Another alternative considered was evaluat ing 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 tem peratures above -10°C which suggests a reduced probability of occurrenc e with decreasing ambient te mperatures similar to Appendix C. An evaluation wa s presented to the ARC of the effects of the larger drops on a fluid based ice protection system is us ed on many part 23 aircraft. The cold temperature prolonged holding conditions becom e 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 probabili ty of the SLD conditions at the cold extremes. As such, it is recommended that the holding cr iterion in SLD, be limited to ambient temperatures above -13°C. The ARC was also concerned that an a ssumption of a hold in SLD icing conditions at the cold extr eme 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. T he review of the event history indicates that most in-flight events occur at a tota l 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 temperat ure is listed in Table 2.

Table 2 - Suspected SLD Events

Model Flight Altitude (ft) OAT (oF) KCAS Distance (nm) Time (min) KTAS T TOT (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 temper ature at the destination air port 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 materi al 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 propos ed for part 25 with three modifications:

The proposed part 23 regulation definition fo r hold will not include 45 minutes. The draft guidance will define 45 minutes for Ap pendix 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 t he enroute phase can be limited the time required to
transit 17.4 nm. See the discussion above fo r 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 minimu m balked landing climb gradient. The ARC proposes that the go-around may be accomplish ed 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 th e climb through a freezing drizzle or freezing rain layer which may extend higher than t he 1,500 feet AGL takeo ff phase. The ARC
believed the maximum vertical extents defined in proposed A ppendix O were too conservative (12.000 feet and 7,000 feet, re spectively for FZDZ and FZRA). The ARC analyzed data from “An Infe rred Climatology of Icing Conditions Aloft, Including Supercooled Large Drops. Part I: Canada and the Continent al United Stat es,” published in the November 2007 public ation of the Journal of Applied Meteorology and Climatology. For FZDZ and FZRA, 90% of vert ical 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 accreti on. A definition of climb wit h 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 ma y 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 condition s 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 (co mment 11.1 in docket FAA-2010-0636). This parameter is the mathematical product of 80V D (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 sm aller) and LWC (liquid water content in g/m 3 ). Icing conditions were encountered that re sulted in rapid increases in drag and stall speed beyond stall warning. The ice accret ion 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 gai n access to any documentation such as photographs. The severe icing encount ers 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 fr om several icing tunnel projects as follows (80VD calculated using calib ration 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 icin g research at an 80VD=20, OAT= -9.8°C (DOT/FAA/AR06/48)

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

5. Certification project (pr oprietary data reviewed by FAA only) at an 80VD=52,
OAT= -6.7°C

The roughness levels reviewed are associated with a range of tem peratures, airspeeds, freezing fractions as well as the drop size and liquid water content parameters. Many of the cases reviewed were well outside the propos ed Dow/Marwitz criter ia, but significant roughness effects are apparent. By inspection, it can be c oncluded that these cases outside the proposed criteria could produce adverse dr ag effects. Although an
exhaustive research effort was not performed, the roughne ss levels for point 4 are among the most benign of those reviewed ev en though it lies in t he center of the proposed "adverse" icing region. Roughness le vels for points 1 and 5 also lie in the “adverse” 80VD region and do not appear diffe rent than roughness documented outside the adverse region. Rough ness densities were varied and there were cases where roughness elements did not touc h each other. The review suggests that the proposed "adverse" icing criteria is an over-simplification of the comp lex icing physics that occur. In addition, the proposed criteria suggests that one type of icing conditions would be severe for all aircraft, regar dless of the type of ice pr otection system used, or the protected area extents. This simplisti c 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. T he Appendix O freezing drizzle (MVD>40) MVD is 110 μm. Using the NASA IRT calibrati on data, this corresponds to an 80VD of 249 μm. At -8°C, the Appendix O LWC for this distribution is 0.24 g/m 3 (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 adv erse region. The ARC does recognize
that the certification tunnel runs should document the de tails of roughness elements for simulated ice shape flight testing, and an appropriate note is added to the guidance
material.

N ATURAL SLD F LIGHT T EST

The part 23 ARC adopted the part 25 proposal regarding the requi rement to flight test in measured, natural ici ng conditions, which is r equired 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 c onditions 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 guidanc e that was specific on whether flight testing in natural Appendix O would be required. The ARC believed that if flight in any por tion of Appendix O was to be approved, (e.g. § 23.1420(a)(2) or (a)(3)) flight test in those portions s hould be conducted. The ARC believed that Appendix O conditions for which an airp lane 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 expo sed 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 al so 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 distributi ons where the capability exists 1 , icing tunnel tests or icing tanker tests and analytical c odes are used to determine critical ice shapes on lifting surfaces.

2. The simulated, critical ice shapes are flight test ed to show compliance with applicable Subpart B regulations.

1 Current icing tanker or icing tunnel simulation techni ques 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 met hod(s) are certified as described in the Advisory
Circular.

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

D) S UBPART B

- A PPENDIX C I CE A CCRETIONS

Task 2 & 3 - The part 23 icing ARC reviewed the current requirements for Appendix C which requires compliance to Subpart B per formance, stability, controllability, and maneuverability regulations with Appendix C ice accretions. The part 23 icing ARC proposes the following changes, which prov ides relief from the current rule:

S TALL SPEED (T ASK 3):

Section 23.1419, amendment 23- 43, required “...airplane performance...must not be less than that required in par t 23, subpart B.” The stall speed requirements of § 23.49 are included in subpart B performance. Fo r 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 boo t-equipped aircraft with simulated intercycle/residual ice has shown st all 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 ai rplane whose stall was defined by aerodynamic wing stall. This can represent a significant performance penalty for new aircraft if they had to be desi gned to meet the 61-knot stall speed requirement with ice on protected surfaces. Recently certificat ed 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. Pe rformance 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 t he 61-knot stall speed requirement with no major redesign.

In the notice of proposed rulemaking pub lished in the “Federal Register” on October 3, 1990 (55 FR 40598), for the prop osed rule that was to become amendment 23-43, the FAA stated the ba ckground 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 t he performance capability to exit the icing environment as readily as transport cat egory airplanes.” Normal category airplane airfoils, being smaller than those of trans port airplanes, are much more efficient collectors of ice and their perc entage drag increase in icing c onditions are larger than transport airplanes. The requirement to meet subpart B performance was added to guarantee there would be a given level of exce ss 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 m eet the 61-knot stall speed r equirement 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 s peed requirement of § 23.1419(a), amendment 23-43. The rationale was that an exemptio n with these compensating feat ures would not adversely affect safety since it is sa fer to make a forced landing at higher speed than it is to inadvertently stall the airplane. Ther e have been many fatal accidents in icing
conditions attributed to the latter.

1. The airplane with no ice accretions m eets the 61-knot stall speed requirement of § 23.49(c);

2. The airplane with critical ice accreti ons as defined in paragraph 13b of this AC complies with the stall warning requirement s of § 23.207. Stall warning means
with ice accretion should be t he same as in non-icing.

3. The AFM performance data in icing c onditions reflects the higher stall and operating speeds.

4. The airplane with critical ice accretions has acceptable stall characteristics and is safely controllable with normal piloti ng 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 f light 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 w ould have to include § 23.1091 at amendment 23-51 and § 23.1093 at amendment 23-51 to pr ovide the latest regulations for engine operation in icing conditions.

10. The airplane certification basis woul d 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 Rulema king 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 incorpor ate the regulations listed in the compensating features, the ARC dete rmined it was not necessary to incorporate the compensating features in the regul ations. The ARC recommended to keep a history of the issue in Advisory Circular 23.1419.

T AKEOFF ICE ACCRETION

The AC 23.1419-2D guidance on the perform ance 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:

S TALL WARNING

The ARC proposed amendments to 23.207 that would codify the AC 23.1419-2D guidance. These proposals wo uld require the means of stall warning and stall warning margin to be the same for ice protection syst em operation as in non-icing operation. It also proposes to codify the guidance on pre-activation ice.

I CE CONTAMINATED TAILPLANE STALL

The requirement to evaluate susceptibilit y with zero load factor push-overs and sideslips is codified.

L ATERAL CONTROL EVALUATION

The guidance in AC 23.1419-2D regarding latera l 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 c ontrol 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.

A CTIVATION OF ICE PROTECTION SYSTEM

The ARC adopted the proposed part 25 require ments, with the exception that the proposed part 23 rule would provide an option for imm ediate activation based on visual observation of first sign of ice a ccretion, for normal, utility and acrobatic airplanes approved for flight in icing. T he 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 beli eves the smaller scale of the part 23 noncommuter category airplanes allows easier obs ervation 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 vi sual cues are addressed in the definition of pre-activation ice used in stall warni ng and ICTS evaluations. The proposed part 25 rule requires either an ice det ection system, whose cost is relatively large compared to the airframe for a part 23 airplane, or ici ng 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 c an lead to a shorter system life.

D EFINITION OF PRE

- ACTIVATION ICE

As in part 25, current part 23 guidance addre sses stall warning and susceptibility to ICTS with pre-activation ice. Pre-activati on 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 harmoniz ed with Part 25. Large
Part 25 aircraft have moved toward Primar y 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 pr ograms with very large pre-ac tivation 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 t he NTSB “Most Wanted List”. Sinc e 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 char t provides an option that gives credit for an Advisory IDS and increases harmonization wi th 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 s hapes. 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 REPORTFEB 2012 - Revision BPage-43Table 3 - Pre-Activation Ice Accretions- Appendix C Continuous Maximum ConditionsIPS ActivationAC 25 Pre-activation IceAccretionPart 23 Pre-activation Ice AccretionThe left and right columns provide two approaches that maybe used. The right column provides typical values that maybe used in lieu of system specific data.Visual of FirstIndication ofAccretion on ReferenceSurfaceTime to detect(1)+30 seconds(2)+IPS response timeTime to detect(1)+30 seconds(2)+IPS response time2 minutes(2)Potential Icing Conditions(OAT and Visible Moisture)+30 seconds(2)+IPS response time+30 seconds(2)+IPS response time30 seconds(5)Primary IDS and Manual IPSActivationIDS response time+10 seconds(2)+IPS response timeIDS response time(3)+10 seconds+IPS response time30 seconds(3)(5)Primary IDS and AutomaticIPS ActivationIDS response time+IPS response timeIDS response time(3)+IPS response time20 seconds(3)(5)Advisory IDS No Credit IDS response time(4)+10 seconds(2)+IPS response time60 seconds(4)(5)Notes:(1) Total time not to exceed 2 minutes(2) Easily recognizable by the flight crew in allforeseeable 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 showthat detector will annunciate prior to ice accretion on critical surfaces. This maybe 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 reli ability. The concern is the possibility of a flight crew that has becom e dependent on the IDS that has failed (without annunciation of the failure), entering icing conditions and waiting for the no w 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 Performanc e Specification for Inflight Icing Detection System as possible specification to allow credit for t he Advisory IDS. One issue with the common vibrating probe ice detection system is the res ponse time at temperat ure near freezing.
Guidance material was added to the advisor y 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 flight crew. The ARC determined that any time reduction would be subjective and difficult to demonstrate.

Task 8 - The ARC was tasked to determine if usi ng 1-g stall speed criter ia in icing is an option to reduce approach speeds and landing distances in icing conditions. Part 25 already uses the 1-g stall speed require ment, 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 per formance, and 14 CFR part 36 noise requirements, was established for several past part 23 type certificati on projects. Pilot objectivity on stall identification has becom e a key factor in decisions on flying technique, especially where det errent buffet or excessive ly low load factors are developed during stalls to V SMIN . This can be especiall y true with ice accretion on protected surfaces (e.g., intercycle), in whic h the lift curve can flatten considerably as
CL MAX 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 V SMIN . 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 t he 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 guidanc e is needed for icing conditions.

E) P OWERPLANT A SPECTS

S EC

. 23.901 I NSTALLATION

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 capabilit y established for the engine itself under Sec. 23.903(a)(2) "

.

It was determined that the consideration of la rge 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 incl udes consideration of ice on "airframe components" similar to the part 25 proposal. As such, per the requ irements of § 23.901, no design feature of the installation should degrade the basic capability of the engine with respect to ice ingestion, but the i ngestion of airframe ice should be addressed under the more specific requirements of § 23.1093.

S EC

. 23.903 E NGINES

This language recommended for part 25 was revi ewed and it was determined that it was appropriate as drafted and s hould be recommended for incorporation into part 23. However, the ARC recommended advisory ma terial on how to determine acceptable service history.

S EC

. 23.905 P ROPELLERS

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 cond ition". It was determined that this requirement would not be affected by the addi tion of large drop conditions. However, the ARC recommends advisory material to clar ify the requirements with respect to large drop conditions and aircraft approved for flight into icing conditions.

S EC

. 23.929 E NGINE INSTALLATION ICE PROTECTION

Modifications to the requirement are recomm ended to incorporate reference to the large drop environment as well as clar ify 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 ai rcraft performance as defined in proposed 23.21(c). Since this requirement encompasse s the propeller and the engine installation, consideration of any applicable systems re quirements 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 t hat 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 t he scope of § 23.929 to propellers similar to part 25 and allowing § 23.1093 to be the fo cus 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 publis hed 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 su ch that the icing environment to be considered for propeller icing includes the SLD conditions wh ile exiting the environment, but for engine installations consideration of only the approved icing environm ents is acceptable.

S EC

. 23.1093 I NDUCTION SYSTEM ICING PROTECTION

The icing aspects of § 23.1093(a) Reciproc ating engines were reviewed and it was
determined that the cu rrent rule language was a cceptable 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 requi rement 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 prov ides for showing compliance with the defined icing conditions (Par t 25 Appendices C & O, Append ix D of part 33, and in falling and blowing snow) within the limitations established for the airplane for such operations. This relationship between t he aircraft limitations and compliance requirements was further clarified with reco mmended 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 t he requirements of § 23.1420(a)(1) or § 23.1420(a)(2).

In response to the part 25 NPRM, the Aeros pace Industries Association (AIA) submitted public comments that would m odify 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 tw o 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 incor porated into the ARC recommendations for part 23 as follows:

1) Recommend changes to idle speed langua ge 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 demonstrat ion 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 operati on of the engine at temperatures below the required test demonstrati on. If appropriate, no limitat ion 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 Appendi x 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 alo ft. 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 recomm endation in light of part 23 aircraft. Given that many part 23 aircraft already ha ve limitations on flight in SLD through FAA issued severe icing airworthiness dire ctives, 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 su ch conditions are expected to increase. As such, consideration of Appendix O exposures fo r 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 “sta ll, surge, or flameout or loss of engine controllability (for exampl e, rollback)” are redundant to the requirement for no unacceptable loss of power or thrust. The in clusion of “stall, surg e, or flameout or loss of engine controllability (f or example, rollback)” causes confusion. For example, as written, a rotating stall, which can c ause no noticeable impact to engine operation and would only be detectable by spec ial instrumentation could be found unacceptable. Therefore, deletion of t he stall, surge or flameout language is
recommended.

S EC

. 23.1521 P OWERPLANT L IMITATIONS

The proposed § 25.1251(f) would require limitat ions to be established for the minimum temperature as well as the duration, as discu ssed in item 2 above for § 25.1093(b)(2). Same rationale applies, and the requirement s were deleted from the recommendations for part 23.

F) S YSTEMS AND R ELATED A SPECTS

S EC

. 23.629 F LUTTER

. This section was reviewed with respect to changes that might be required due to unique aspects of SLD ice shapes. It was determi ned 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

FEB 2012 - Revision B Page-48 S EC

. 23.775 W INDSHIELD 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.

S EC

. 23.1323 A IRSPEED 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 reco mmended not to modify the regulati on or require flight testing in natural icing conditions for aircraft certif ied for IFR only (not approved for flight into icing conditions). AC20-73A already pr ovides guidance on usi ng 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 c onditions 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 airs peeds 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 hist ory revealed that issues invo lving ice crystals occurred at high true airspeeds and at altitudes typica lly above 29,000 ft. Although some incidents were reported at lower altitudes they all in volved aircraft capable of high cruise speeds above 29,000 ft. The 29,000 ft threshold wa s selected because of the typical performance and system complexity increas e 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 poli cy 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 po wer requirements at the low voltages of emergency bus operation. In addition, the probability of encount ering critical mixed phase or ice crystal conditions was considered sufficiently low t hat it should be considered remote (based on engineering judgment). Ai rcraft will still be protected against Appendix C icing conditions under the emergency power scenari os. 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 histor ical 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 conditi ons described by 14 CFR Part 25 Appendix O and 14 CFR Part 33 Appendix D provide for te sting in freezing rain beyond conditions currently evaluated. It is recommended that t hese additional freezing rain test conditions not be adopted, if later added to the Part 25 proposal.

S EC

. 23.1324 A NGLE 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 perform ance and system critic ality). It is acknowledged that the standard, trailing-vane-style angle of attack sensor should not be susceptible to mixed phase or ice crystal accr etions by design. However, the angle of attack probe designs that sense dynamic pre ssure for angle of attack (similar to pitot probes) can be expected to be susceptible to thes e conditions. Therefore, it is intended that this section uses the same icing c onditions 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 phenom ena of concern has been water entering mechanical parts that require free movem ent to operate correct ly, 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 functi on under any foreseeable operating condition. No regulatory changes are recommended. Suggested guidanc e material referencing
issues to be considered have been added to AC 23.1419. In addition the requirements of operation in the meteorological conditi ons described by 14 CFR Part 25 Appendix O and 14 CFR Part 33 Appendix D provide for te sting in freezing rain beyond conditions currently evaluated. It is recommended that t hese additional freezing rain test conditions not be adopted, if later added to the Part 25 proposal.

S EC

. 23.1325 S TATIC 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 al ready provides guidanc e on using Appendix C as the definition of icing conditions for por ts on IFR aircraft. It is recommended that wording be added to require the icing conditi ons 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 require ments for mixed phas e or ice crystal conditions was upheld here.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-50 S EC

. 23.1326 P ITOT HEAT INDICATION SYSTEMS

As part of the mixed phase icing requirem ents of §23.1323, higher heat probes will likely be required to compensate for the energy requi red 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 pr ior to takeoff to prot ect the equipment or composite structures. Since accurate ai rspeed information is only required for safe flight, there is no safety benefit to indica ting the pitot heat system is OFF for ground operations. These types of systems have ty pically required an ELOS to be compliant with the requirements of t he 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 reco mmend 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.

S ECTION 23.1329 A UTOMATIC P ILOT S YSTEM

See discussion under sub part B.

S EC

. 23.1403 I CING INSPECTION LIGHTS

. The current requirement for illumination of ice accumulations is provided by §23.1419(d). To address illumination requirem ents 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 dete ction system for system activation). The rule language was drafted to only require ic ing inspection lights if they are necessary and not to require wing inspection lights fo r aircraft where the wing cannot be viewed from the cockpit.

S EC

. 23.1416 P NEUMATIC DE

- ICER BOOT SYSTEM

. The requirements of §23.1416 are largely obsolete with the increased scope of §23.1309 and §23.1322. In additi on, 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 bot h dark cockpit and non dark cockpit types of indications as is consistent with the proposed cockpit philosophy.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-51 S EC

. 23.1419 I CE P ROTECTION

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 secti on §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 Operat ion - 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 protecti on system activation and ic e 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 follo wing 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 appen dix C natural icing encounters validating 3D ice accretion (o r impingement analysis) and 3D appendix O ice accretion analysis (or impingement anal ysis) satisfy the two method approach
described above.

Ice Detector Reliability Requirements – With respect to ice detector reliability and software criticality requirements, for bot h 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.

S EC

. 23.1420 S UPERCOOLED LARGE DROP ICING CONDITION

. The requirements of §23.1420 ar e 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 we ights of less than 60,000 lbs. The “approved portions” of 14 CFR Part 25, App endix O as used in the proposed regulations and guidance material is intended to refe r to aircraft that are certified against 23.1420(a)(2) or (a)(3). For aircraft cert ified against 23.1420(a)(1) the exposures in Appendix O are not approv ed 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 envir onmental conditions within the Appendix O environment, as well as the exposure du rations as defined in 23.1420 and the ice accretions recommended in section 3B of this report.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-52 4. RULEMAKING RECOMMENDATIONS

Rule language changes are denot ed 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 us ed by the FAA for publication in the NPRM).

A) S UBPART B A SPECTS

Added new 23.21(c)(1) to define the requirem ents of “capable of operating safely” in part 25, Appendix C conditions.

Added new 23.21(c)(2) to define the require ments for “capable of operating safely following detection and exit of Appendix O icing conditions.

Added new 23.21(c)(3) to define the require ments to show an airplane can operate safely in Appendix C, detect and exit A ppendix O, Appendix O or a portion of Appendix
O.

Added new (c)(4) to define requirement s in icing on weight and cg limits.

S EC

. 23.21 P ROOF OF COMPLIANCE

(c) The requirements of this subpart associ ated with icing conditions apply only if certification for flight in ic ing conditions is desired. If certification for flight in icing conditions is desired, the fo llowing 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 fa ilure 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 appendi x 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 operati ng limitations and operating procedures established by the applicant and provided in the Airplane Flight Manual.

(2) If the applicant does not seek certifica tion for flight in all icing conditions defined in Appendix O of part 25, complian ce with §§ 23.49(a) a nd (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 fo r which certification is not sought in
order to allow a safe exit from those cond itions. Compliance is only required at ambient temperatures of -13 degrees Cels ius and warmer in th e icing conditions

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-53 defined in part I of Appendix O of part 25. Compliance must be shown using the ice accretions for holding and approach ph ase as defined in part II(b) of Appendix TBD of this part, assuming normal operation of the airplane a nd 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 fo r flight in any por tion of the icing conditions of Appendix O of part 25, eac h requirement of this subpart, except for §§ 23.49(c), 23.77(d) and (e ), the sudden engine fa ilure requirements of § 23.143(b), 23.143(f), 23.145(c), (d), a nd (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 conditi ons 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 norma l operation of the airplane and its ice protection system in accordance with the operating limitat ions and operating procedures provided in th e 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 co mply are based on the light jet rule.

S EC

. 23.45 G ENERAL (P ERFORMANCE ).

* * * *

(i) If the applicant seeks certification for flight in icing conditions, performance must be determined with engine po wer losses associated with operating ice protection systems, except for takeoff pe rformance if operation of an ice protection system is prohibited for t akeoff by the Airplane Flight manual
Limitations section.

S EC

. 23.51 T AKEOFF SPEEDS

.

* * * *

(d) For normal, utility, and acrobatic cate gory 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 V S1 determined with the
most critical of th e takeoff ice accretions defined in Parts I and II of Appendix TBD of this part, as applicable in accord ance with § 23.21(c), if the stall speed

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-54 with takeoff ice accretion at maximum takeoff weight wi th takeoff flaps, gear retracted exceeds that in non-icing conditions by more than the greater of three (3) knots CAS or three (3) percent V S1
.
(e) In determining the takeoff speeds for f light in icing conditions, the values of
V MCG and V MC determined for non-icing conditions may be used.

S EC

. 23.53 T AKEOFF [ PERFORMANCE .] (a) For normal, utility, and acrobatic categor y airplanes, the takeoff distance must be
determined in accordance with paragraph (b) of this sect ion, using speeds determined in accordance with Sec. 23.51(a), [(b), (d) and (e)]

. (b) For normal, utility, and acr obatic category airplanes, the distance required to takeoff and climb to a height of 50 feet above the ta keoff surface must be determined for each weight, altitude, and temperat ure within the operational lim its 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, takeof f performance, as required by Secs. 23.55 through 23.59, must be determined with the operating engine(s) within approved operating limitations.

S EC

. 23.57 T AKEOFF 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 gr adient of climb determined in accordance with Sec. 23.67(c)(2) is greater than 0.4 percent, th e 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 app licable in accordance with § 23.21(c), from a height of 35 feet above the t akeoff surface up to the point where the airplane is 400 feet abo ve the takeoff surface; and

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-55 (ii) With the most critical of the final takeoff ice accr etions defined in Parts I and II of Appendix TBD of this part , as applicable in accordance with § 23.21(c), from the point wh ere the airplane is 400 feet above the takeoff surface to the end of the takeoff path.

S EC

. 23.65 C LIMB : ALL ENGINES OPERATING

.

* * * *

(c) For normal, utility, and acrobatic categor y 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 V S1 ; 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.

S EC

. 23.66 [T AKEOFF CLIMB : ONE ENGINE INOPERATIVE .]

* * * *

(g) For normal, utility, and acrobatic categor y 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.

S EC

. 23.67 C LIMB : ONE ENGINE INOPERATIVE

.

* * * *

(e) If the applicant is seeking certification for flight in icing conditions, the effect
of ice accretion as defined in the followi ng table, in accordance with applicable portions of § 23.21(c), must be determined if:

(1) V S1 with the appropriate ice accret ion 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 thr ee knots CAS or three percent V S1 ; and

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-56 (2) If commuter category, the degr adation of the gradient of climb
determined in accordance with Sec. 23.67(c)(2) is greater than 0.4 percent.

(3) If turbojet powered no rmal, 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

§ 23.67(b) Normal, utility, and acrobatic 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

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-57 S EC

. 23.69 [E NROUTE 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 V S1 ; or (2) if the service ceiling with “enrout e” ice is less than 22,000 MSL.

S EC

. 23.73 R EFERENCE LANDING APPROACH SPEED

.

* * * *

(d) If the applicant is seeking certification fo r flight in icing conditions, except as provided in paragraph (1), V REF 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 wi th § 23.21(c), if the stall speed with
critical ice at maximum la nding weight with landing flap s, gear down exceeds that in non-icing conditions by more than the greater of three (3) knots CAS or three (3) percent V S0
.

(1) V REF in the appendix O icing condition s for which certification is not sought may be the V REF determined in Sec. 23.73(d) with critical Appendix C ice accretions, if the airplane at that V REF 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.

S EC

. 23.77 B ALKED LANDING

. (a) Each normal, utility, and acrobatic cat egory reciprocating e ngine-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 V REF , as defined in Sec. 23.73(a) and Sec. 23.73(d)

. (b) Each normal, utility, and acrobatic cat egory reciprocating engine-powered of more than 6,000 pounds maximum weight and each no rmal, utility, and ac robatic 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)

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-58 (4) A climb speed equal to V REF , 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 V REF , as defined in Sec. 23.73(c) and Sec. 23.73(d)

. (d) For normal, utility, and acrobatic cat egory reciprocating engine-powered airplanes of 6,000 pounds or less maxi mum weight, if the applicant seeks certification for flight in icing conditions, the steady gr adient of climb at the landing field pressure altitude mu st be measurably positive with—

(1) Takeoff power on each engine; (2) The landing gear extended; (3) The wing flaps in the landing positi on 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 change s of angle of attack, they may be retracted; and (4) A climb speed equal to V REF as defined in Sec. 23.73(d) (5) The critical approach ice accretion de fined in Part II, paragraph (b), of Appendix TBD of this part.

(e) For normal, utility, and acrobatic cat egory reciprocating engine-powered airplanes of more than 6,000 pounds, tu rbine 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 th e 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 V REF as defined in Sec. 23.73(d)

(5) The critical approach ice accretion de fined in Part II, paragraph (b), of Appendix TBD of this part.

S ECTION 23.143 G ENERAL (C ONTROLLABILITY AND M ANEUVERABILITY )

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 complian ce with §23.143 in icing conditions—

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-59 (1) Controllability must be demonstrated with the ice accretion defined in Parts I and II of Appendix TBD of this part, as ap plicable 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 desi gn characteristic of the flight control system. It must be possible to prompt ly 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 mu st be steadily increasing with no force reversals, unless the change in control for ce is gradual and easily controllable by the pilot without using exceptional piloti ng skill, alertness, or strength.

(4) It must be possible to readily arr est and reverse roll rate using only lateral control input, and the late ral 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 f unction, it must be demonstrated in flight with the ice accretion de fined in part I(e), of Appe ndix 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 rever sal 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 accr etion defined in Part II, (b ) of Appendix TBD of this part as applicable in accordan ce 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 rever sal 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 mu st be steadily increasing with no force reversals, unless the change in control for ce is gradual and easily controllable by the pilot without using exceptional piloti ng skill, alertness, or strength. Additionally, lateral cont rol 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 late ral control force must not reverse with increase of
control deflection.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-60 S ECTION 23.207 S TALL 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 befo re the ice protection system has been activated and is performing its intended function, with the i ce 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 adver se flight characteristics when: (1) The speed is reduced at rat es not exceeding one knot per second; (2) The pilot performs the recovery maneu ver in the same way as for flight in nonicing conditions; and (3) The recovery maneuver is started no ear lier 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 turn ing flight must be suffici ent 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 afte r the onset of stall warning. When demonstrating compliance with this pa ragraph, the pilot must perform the recovery maneuver in the same way as for the airplane in no n-icing conditions. Compliance with this requirement must be demonstrated in flight with the speed reduced at rates not exceeding one knot pe r 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 m eans in icing conditions as for non-icing
conditions.

S ECTION 23.1329 A UTOMATIC P ILOT S YSTEM

...

(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.

S ECTION 23.1419 I CE PROTECTION

Amend 23.1419 by clarifying when compliance to 23.1419 is required. Amended rule would allow installation of ice pr otections systems, to facilitate exit from inadvertent icing encounters, without a requirement for comp liance to 23.1419. Capable of operating safely is re-defined. The activation of ic e protection system guidance in AC 23.1419-2D

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-61 and operation of ice protecti on system regulations recommended by ARAC for part 25
are added.

If certification with ice prot ection 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 est ablish, 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, te sts of the ice prot ection system must be conducted to demonstrate that the airplane is capable of operating safely in continuous maximum and intermittent maximum icing conditi ons, as described in appendix C of part 25 of this chapter. As used in this secti on, “Capable of operating safely,” means that airplane performance, controllability, maneuv erability, 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 dete rmining the formation of ice on the critical parts of the airpl ane. 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 operati on 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
reflectio n that would handicap crewmembers in the performance of their duties. The Airplane Flight Manual or ot her approved manual material must describe the means of determining ice formation and must contain in formation for the safe operation of the airplane in i cing conditions.

(d) One of the following methods of icing detection and activati on of the airframe ice protection system must be provided:

(1) A primary ice detection system that automatically activates or alerts the flightcrew to activat e the airframe ice pr otection system; or

(2) A definition of visual cues for rec ognition 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 i ce protection system; or

(3) Identification of conditions conducive to airframe icing as defined by an appropriate static or tota l air temperature and visibl e moisture for use by the flightcrew to activat e the airframe ice pr otection system; or

(4) For normal, utility and acrobatic categor y 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 ai rframe 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 acti vation 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 i ce protection system, including activation and deactivation, must be established a nd documented in the Airplane Flight
Manual.

23.1420

– S UPERCOOLED LARGE DROP ICING CONDITIONS

.

The proposed 23.1420 rule is similar to t he proposed 25.1420 rule. There is concern among some of the ARC members that the rule is vague on w hen natural icing in SLD is required.

(a) If certification for f light 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 th e 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 mu st be capable of operating safely while exiting all icing conditions. "Capable of operating safely," means that the airplane complies with the re quirements in § 23.21(c)(2).

(3) Operating safely in the icing condition s defined in Appendix O of part 25. "Capable of operating safely," means th at the airplane complies with the requirements in § 23.21(c)(3).

(b) To establish that the ai rplane can operate safely as required in paragraph (a) of this section, an analysis must be pe rformed 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 meth ods 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 ici ng tests, or a combin ation of both, of models of the airplane.

(3) Flight tests of the airplane or it s components in simulated icing conditions, measured as necessary to support the analysis.

(4) Flight tests of the airpla ne with simulated ice shapes.

(5) Flight tests of the airplane in na tural icing conditions, measured as necessary to support the analysis.

(c) For an airplane certifi ed in accordance with paragr aph (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 airpla ne is certified to operate.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-64 B) I CE A CCRETIONS FOR SHOWING COMPLIANCE TO 14 CFR 23 S UBPART B

The following definitions of ice accreti ons 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, Pa rt II. The definitions were modified to point to the appropriate part 23, subpart B referenc es and other changes recommended by the ARC to accommodate part 23 ai rcraft. 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 A PPENDIX TBD

- A IRFRAME I CE A CCRETIONS

(2) P ART I

- A IRFRAME I CE A CCRETIONS FOR S HOWING C OMPLIANCE W ITH 14 CFR
23 S UBPART B IN THE ICING CONDITIONS DEFINED IN 14 CFR 25 A PPENDIX C PART I.

(a) Ice accretions--General.

The most critical ice accret ion in terms of airplane performance and handling qualities for each flight phase must be used to show compliance with the applicable airplane performance and hand ling 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 a ppropriate to normal ice protection system operation, occurring between li ftoff and 400 feet above the takeoff surface, assuming accretion starts at liftoff in the takeo ff maximum icing conditions of part I, paragra ph (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 pr otected 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 tran sition 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, paragra ph (c) of 14 CFR 25, appendix C.

(3) En route ice is the critical i ce accretion on the unprotected surfaces, and any ice accretion on the protected surfaces a ppropriate to normal ice protection system operation, during the en route phase. Applicable only to airplanes that are not certified to op erate 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 appropria te 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 a ppropriate to normal ice protection system operation following exit from the hol ding 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 a ppropriate to normal ice protection system operation following exit from the a pproach flight phase and transition to the final landing configuration.

(b) In order to reduce th e number of ice accretions to be considered when demonstrating compliance with the require ments 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. Configur ation 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 pr ovided any difference in performance is conservatively taken into account.

(d) For both unprotected and protected part s, 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 app licable, propellers ar e 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 th e ice protection system is in accordance with a normal operating procedure provided in the Airp lane 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 protect ion 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) P ART II

- A IRFRAME I CE A CCRETIONS FOR S HOWING C OMPLIANCE W ITH 14 CFR
23 S UBPART B IN THE ICING CONDITIONS DEFINED IN 14 CFR 25 A PPENDIX O PART I

(a) General.

The most critical ice accretion in terms of airplane perform ance and handling qualities for each flight phase must be used to show compliance with the applicable airplane performance and handling qualitie s requirements for icing conditions as defined in § 23.21(c)(2) and (c)(3). Applicants must demons trate that the full range of atmospheric icing conditions specified in part I of 14 CFR 25, Appendix O hav e been considered, including drop diameter distributions, liqui d 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 accr etions defined in part II, par agraph (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 par t 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 wit h § 23.1420(a)(2), or defined by part I, paragraph (a)(4) of this appendix, for an airp lane 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 trans it of one cloud with a 17.4 nautical miles
horizontal extent in the most critical of the icing condit ions 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 cond itions need not exceed 45 minutes.

(2) Approach ice is the more critical of the ho lding ice defined by part II, paragraph (b)(1) of this appendix, or the ic e calculated in the applicable par agraph (b)(2)(i) or (ii) of part II of this appendix:

(i) For an airplane certified in accordanc e 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 abov e 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, paragr aph (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 accordanc e 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 ap pendix 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, paragr aph (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 fo r the flight crew to ta ke action to exit the icing conditions, including coordi nation with air traffic control.

(c) Ice accretions for airplanes certif ied 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 wh ich the airplane is capable of operating safely must be considered.

(1) Takeoff ice is the most critical ice accret ion 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 c onditions defined in part I of 14 CFR 25 appendix
O.

(2) Final takeoff ice is the most critical ice accr etion 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 fr om the takeoff to the en rout e configuration is completed and enroute climb speed is reached, whichever is higher. Ice accretion is assumed to
start at liftoff in the icin g conditions defined in part I of 14 CFR 25, appendix O.

(3) Climb ice is the critical ice accreti on on the unprotected surfaces, and any ice accretion on the protected surfaces appropria te 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 a pplicable only to airplanes that are not certified to operate above 30,000 feet. En route ice is the most critical ic e accretion on the unprotected surfaces, and any ice accretion on the prot ected surfaces appropriate to normal ice protection system operation, dur ing 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 hol ding phase of flight.

(6) Approach ice is the ice accretion on the unprotec ted 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 maximu m vertical extent of the ic ing 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 transiti on to the approach configuration and flying for 15 minutes at 2,000 feet above the l anding surface; or

(ii) Holding ice as defined by part II, paragr aph (c)(4) of this appendix.

(7) Landing ice is the ice accretion on the unprotec ted 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, paragr aph (c)(5)(i), of th is 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 su rface to a height of 200 feet above the landing surface with a transition to the l anding 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 t he landing surface in the maximum flap configuration approved for holding, and a descent to the l anding surface (touchdown) in the landing configuration; or

(ii) Holding ice as defined by part II paragr aph (c)(4) of this appendix.

(8) For both unprotected and protected parts, the ice accretion for the takeoff phase
must be determined for the ici ng conditions defined in part I of 14 CFR 25 appendix O, using the following assumptions:

(i) The airfoils, control surfaces, and, if app licable, 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 protec tion system is in accordance with a normal operating procedure provided in the Airplane F light Manual, except that after beginning the takeoff roll, it must be a ssumed 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 pr otection system has been activated and is performing its intended function is the critical ice accretion formed on the unprotected and normally protected surfaces before acti vation and effective operation of the ice protection system in the icing conditions def ined 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 ic e accretions to be considered when demonstrating compliance with t he 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 def ined for that flight phase. Configuration
differences and their effects on ice accr etions must be taken into account.

(f) The ice accretion that has the most adv erse effect on handling qualities may be used for airplane performance tests provided any di fference in performance is conservatively
taken into account.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-70 C) P OWERPLANT A SPECTS

S EC

. 23.903 E NGINES

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 th is 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 resu lted in an unsafe condition; or (iii) Section 33.68 of this chapter in eff ect 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 accumulati on service history in similar installation
locations which has not result ed in any unsafe conditions.

* * * * *

S EC

. 23.929 E NGINE INSTALLATION ICE PROTECTION Propellers (except woo den propellers) and other components of complete engine installations must be protect ed against the accumulation of ice as necessary to enable satisfactory functioning without appreciable loss of thrust when operated in the icing
conditions for which certi fication is requested.

If certification for flight in icing is requested: (a) P ropellers 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 co mplete engine installations must be protected against the accumulation of ice as necessary to comply with the applic able requirements of sub part E and F within 14 CFR 25 Appendi x C and the approved portions of 14 CFR 25 Appendix O.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-71 S EC

. 23.1093 I NDUCTION SYSTEM ICING PROTECTION

* * * * * (b) Turbine engines. Each engine, with all icing protection systems operating,

must: (1) Operate throughout its flight power ra nge, 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 blowin g snow within the limitations established for the airplane for such operation, with out 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 opera tion 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 de monstrated with the available air bleed for icing protection at its critical conditi on, 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 app licant must document the engine run-up procedure (including the m aximum time interval between run-ups from idle, runup power setting, and durat ion at power) and associ ated minimum ambient temperature, if any, the maximum time in terval, if any, and these conditions must be used in the analysis which establish es 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) Eac h turbine engine and its air inlet system mu st operate throughout the flight power range of the engine (including idling), without t he accumulation of ice on engine or inlet system components that would adversely a ffect 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 t he limitations established for the airplane for such operation. (2) Each turbine engine must i dle for 30 minutes on the ground, with the air bleed available for engine icing protecti on at its critical condition, without adverse effect, in an atmosphere that is at a temperat ure between 15° F and 30° F (between

- 9° and

- 1°C) and has a liquid water co ntent 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 peri odically to a moderate power or thrust setting in a manner acceptable to the Administrator.

* * * * *

S EC

. 23.1521 P OWERPLANT LIMITATIONS

.

* * * * *

(f) Maximum time interval between e ngine run-ups from idle, run-up power setting, duration at power and the associat ed minimum ambient temperature, if any, for ground operations in icing c onditions, as defined in § 23.1093(b)(2).

D) S YSTEMS A SPECTS

S EC

. 23.629 F LUTTER

. Unchanged.

S EC

. 23.775 W INDSHIELD AND WINDOWS

. (f) Unless operation in known or forecast icing conditions is prohibited by operating limitations, a means must be prov ide to prevent or to clear a ccumulations 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 atti tudes of the aircraft. Thi s includes taxi, takeoff, approach, landing and to perform an y 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.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-73 S EC

. 23.1323 A IRSPEED INDICATING SYSTEM

. (d) If certification for instrument flight rules is requested, or flight in icing conditions is requested, each airspeed system must have a heat ed pitot tube or an equivalent means of preventing malfunction due to icing. In addition, if certificat ion for flight in icing conditions is requested, the icing conditi ons 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 cond itions of Part 33, Appendix D, if the airspeed indicating system serves a critical functi on or the maximum certified ceiling is greater than 29,000 ft MSL and the M MO is greater than
Mach 0.75.

S EC

. 23.1324 A NGLE OF ATTACK SYSTEMS

. If an angle of attack system is provided for any instrument, device, or system required by the operating rules of this chap ter, 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 cond itions of Appendix D of Part 33, if the angle of attack system serves a cr itical function or the maximum certified ceiling is greater than 29,000 ft MSL and the M MO is greater than
Mach 0.75.

S EC

. 23.1325 S TATIC PRESSURE SYSTEM

. (b)(3) If a static pressure system is prov ided for any instrument, device, or system required by the operating rule s of this chapter, each stat ic pressure port must be designed or located in such manner that the correlation bet ween air pressure in the static pressure system and true ambient atmos pheric static pressure is not altered when the aircraft encounters icing conditions . If certification for f light 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 s ource 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 fr om 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

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-74 S EC

. 23.1326 P ITOT 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 operati ng. 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 temperatur e is greater than 5° C. (2) The pitot heating system is switched "on" and any pitot tube heating element is inoperative.

S EC

. 23.1403 ICING INSPECTION LIGHTS

. If certification for flight in icing conditions is desire d and aircraft procedures are dependent on visual observat ions of airframe ice accr etion, a means must be provided for illuminating the formation of i ce. Any illumination that is used must be of a type that will not cause gl are or reflection th at would handicap crewmembers in the performance of their duties.

S EC

. 23.1416 P NEUMATIC DE

- ICER BOOT SYSTEM

.

Delete this section.

S EC

. 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) S UB -P ART B A SPECTS

See Appendix D for recommended revisions to AC 23.1419-2D

B) P OWERPLANT A SPECTS

Note: The format of AC 23-16A has questi ons 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.

S EC

. 23.901 I NSTALLATION

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 installa tion compliance with § 23.901(d)?

Amendment 25-53 added require ments for ice, hail, and birds similar to those in part 33. Examples of installation issues normally not addressed by engine certification, but that s hould be addressed for installa tion compliance, include the following:

1. Ice build-up on areas where ice shed may be inges ted by the engines (for example, ice shed from wings and airfra me sources into aft mounted engines) should be addressed under the more sp ecific requirements of § 23.1093 (b); and

2. Consideration of items such as inlet sp litters, acoustic liners, and so forth, that may be damaged by impact with ice, hail, and birds.

S EC

. 23.903 E NGINES

AC 23-16A, reference Par agraph 23.903 - (added material)

What are some examples of how to show that "an ice accumulation service history in similar installation locati ons ... 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 forwar d 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 aircra ft installation certification.

S EC

. 23.905 E NGINES

AC 23-16A, reference Par agraph 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 fli ght 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 s hort durations during exit from all icing
conditions. For aircraft that will be a pproved 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 me thods for predicting break of ice shapes in flight. AC 20-147A contai ns some information on break-up as applicable to ice shapes used during pa rt 33 testing of turbofan engines. For shapes that have similar aspect ratios, similar breakup characteristics may be assumed.

S EC

. 23.929 E NGINE INSTALLATION ICE PROTECTION

AC 23-16A, reference Par agraph 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 fli ght 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 consis tent 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 cons idered. For aircraft certified to § 23.1420(a)(2) or (a)(3), considerat ion 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 t he engine or cooling inlets during icing encounters, then tests shoul d be performed with critical ice shapes, typically representing a 45 minute hol d, installed on these inlets, or evaluate the performance of such systems with tanker or natural icing te sts. Tests should consider the critical operating temperat ures and altitudes within Appendix C icing conditions. Tests of the generator cooli ng system with actual or simulated ice accumulation on the inlet should be perfo rmed with the maximum icing load on the electrical system at representative ambi ent temperatures. If data is analyzed in accordance with § 23.1043, the temper atures need to be corrected only to 32 degrees F, not a hot day.

Engine alternate induction air sources s hould remain functional in the required icing environments.

S EC

. 23.1093 I NDUCTION 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 induct ion 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 airpl ane 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, subp art 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 ic ing conditions should be addressed in a
similar manner to an aircraft not inte nded 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 expos ure times that are possible for an aircraft prohibited from fl ight 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 accret ion on the inboard wing of airplanes with aft fuselage mounted engines.

Applicants for basic (§ 23.1093) or de layed flight into icing certification (prior to §§ 23.1419, 23.1420) may sh ow compliance to §23.1093 with the following methods:

(a) Flight testing in measured natu ral icing or flight testing behind an airborne icing tanker, supplemented by analysis as described in paragraph 16 of AC 23.1419-2E, to sh ow the amount of ice that
accretes in five minutes at critical part 25, Appendix C continuous
maximum conditions does not sh ed 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 wi thout striking the inlet lip or engine spinner.

2. The ice shape on the wing leading edge does not break chordwise, i.e., the ice abo ve and below the stagnation line
should be considered.

3. In lieu of five minutes of ice accretion, credit can be used for operational ice prot ection systems, with the exception in paragraph (4). The most critical of the following
should be used:

(aa) Two minutes represe nting 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 th e graphite thermal deicing system.

Approval for the icing conditions of pa rt 33, Appendix D should similarly be
based on standard cloud extents and the al titude capabilities of the aircraft.

If the kinds of operation at the aircraft level change (for example flight into icing per § 23.1419 is sought), complian ce 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 consis tent 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 limit ations established for the airplane. For aircraft that will be approved fo r 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 requi rements 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 e ngine must be protected from ice with the throttle against the idle stop, wh ich may require an automatic increase in thrust when the engine ice protect ion system is activated. Natural icing flight tests should include evaluation of ice protection systems with bleed air from engines when the throttl e is at the flight idle stop.

For engine ice protection systems, wh ich for aft fuselage mounted engines can include the inboard wing ice protect ion system, a delay of two minutes in the continuous maximum icing conditi ons of appendix C to part 25 is
utilized to validate the ice sheddi ng 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 i ce 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 theproposed engine, ice shedding from the airframe should be readdressed. Data on ice shedding may be available from the airplane TC holder. Engine inlet lip i ce shedding should be addressed. The
amount of ice mass that could be shed should be compared to a similar, approved engine installati on or to part 33 engine compliance
data.

(b) Effects of Decreased Engine Power, Thrust or Bleed Air on Ice Protection System Operation. Bl eed air mass flows, pressures and temperatures of the proposed engine and of the existing, certified engine should be compared. If th ere is a reduction, the effectiveness of the ice protection system s 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 simula tion methods. Reliance on available
simulation methods combin ed with engineering judgment will be required for findings of compliance in the ici ng 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 fo r 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 in let 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 ph ase conditions for the air data sensors used for engine control may be acco mplished 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 mi xed-phase conditions. However, the local power density was higher around the stagnation area compared to purely liquid conditions due to the h eat required to melt the impacting particles that either fully or partially stick to the surface. For internal flow areas with considerable changes in ai rflow direction, and potential for trapping ice particles, the latent heat e ffect 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 s hould be accomplished. Some icing tunnel facilities have limited ice crystal capabilities that may be suitable for evaluating potential accumulations a nd/or shedding trends in such designs.

Compliance for pitot-style inlets (wit hout considerable changes in airflow direction) or for inlet designs usi ng inertial separation, may be shown through qualitative analysis of the desi gn and supported by similarity to previous designs that have show n 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 maximu m time interval would be required. For aircraft that complete a minimu m 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 eff ects or damage to the engine.
This shorter time interval would th en become an operating limitation.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-82 C) S YSTEMS A SPECTS

See Appendix D for recommended revisions to AC 23.1419-2D

D) AC 23-17C

Add additional materials for AC 23-17 ABC at end of the pertinent sections:

...

23.1323 Airspeed indicating system

...

Amendment 23-tbd and subsequent

This amendment added additional requirement s to address supercooled large drops and mixed phase/ice crystal requi rements. The regulation as applied to IFR aircraft is essentially unchanged from prio r amendments. For ai rcraft 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 requirement s of 23.1326 to alleviate the need for an ELOS for pitot systems that are not operat ed on the ground to protect equipment or composite structures or at high ambient temperatures in flight. For mo re discussion, see AC 23.1419-2E or subsequent revision.

...

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-83 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 c onsiders alternative ways to rulemaking to solve the safety issue under consideration. T he 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.

A LTERNATIVE 1: T ERMINAL A REA R ADAR AND S ENSORS

“The IPHWG considered the use of termi nal area radar and ground -based sensors to identify areas of SLDs so they can be avoi ded, rather than requi re certification for operations in SLD. Equipm ent 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 deve loped 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 airp lane is capable of safe operat ion in SLD conditions.”

A LTERNATIVE 2: I CING D IAGNOSTIC AND P REDICTIVE W EATHER T OOLS

“The IPHWG considered the use of icing di agnostic and predictive weather tools to avoid SLD rather than certify an airplane to operate in SLD conditions. Tools have been developed that can provide in formation on icing and SLD pot ential, but may not report all occurrences of SLD. These experimental tools are available on the Internet and can be used to provide flight planning informati on guidance for avoidance of SLD conditions. However, rulemaking would still be necessa ry to establish safety margins for inadvertent flight into such conditions and to provide an option for applicants to substantiate that the airp lane is capable of safe operat ion in SLD conditions.”

A LTERNATIVE 3: M AINTAIN C URRENT C ERTIFICATION M EANS OF C OMPLIANCE

The ARC considered the option of continui ng the current met hod of addressing SLD during certification of part 23 airplanes. One r eason for considering this is the fact that there are no icing related accident of airpl anes with the current par t 23 icing regulation (introduced at Amendment 23-43) in its certification basis. Table 6 lists these airplanes. It was also recognized that the icing a ccident 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

YearNumber 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 Associat ion (GAMA) review indicates that the proposed rule will not have a big impact on pa rt 23 airplane safety because it will only be applicable to new airplanes. The esti mated number of new aircraft manufactured and affected by the rulemaking will be small co mpared 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 certif ied 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 susc eptibility to roll cont rol anomalies in SLD and providing generic SLD cues and exit procedures in t he Airplane Flight Manuals (AFMs).

Adopting this alternative would obviously elim inate 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 performanc e and handling safety margins for airplanes operating in freezing drizzle or freezing ra in 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 perform ance, stall warning and characteristics, and handling qualities for fli ght in part 25, Appendix C icing conditions.

The current accepted means of determining t he 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.

A LTERNATIVE 4: P ILOT T RAINING

The ARC recognized that icing training for pilo ts 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 requi red by airworthiness directive (AD). The service history of these airplanes in ici ng 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 effectiv e (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 alte rnative was not chosen. However, the ARC will be proposing additi onal 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 lar ge percentage of event s) are recommended.

R ULEMAKING A LTERNATIVES C ONSIDERED OTHER THE A CTION P ROPOSED

The following are rulemaking alternatives (addi tional, reduced, or modified rules) that were considered by the ARC.

A LTERNATIVE 5: S IMPLIFY P ROPOSED S ECTION 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 prohib its flight in freezin g 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 woul d still be proposed as is. Adopting this alternative would delete the requirement to a nalyze and test “detect and exit” ice shapes and would be a large decrease in certification costs. It also addr esses one of the cons
described in alternative no. 3 above. Ho wever, 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 dr izzle or freezing rain, particularly stall warning, or a mixed phase, and therefore was rejected.

A LTERNATIVE 6: D ELETE P ROPOSED S ECTIONS 23.1420( A )(2) AND ( A )(3)

When alternative 5 was discussed, in additi on to simplifying paragraph (a)(1) of the proposed rule, deleting (a)(2) and (a)(3) wa s 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 adm inistrative expenses- issue papers, FAA/Applicant coordination). It was recogni zed that in some areas, th e proposed part 25 requirements would be more stringent (holdi ng for 45 minutes at extreme cold OAT; ice protection activation requirements) and less stringent in ot hers (certification for takeoff in freezing drizzle and not freezing rain, or vice versa). This alternative was not adopted for these

reasons.

A LTERNATIVE 7: T AKEOFF IN E ITHER F REEZING D RIZZLE OR L IGHT F REEZING R AIN

Operators of part 23 airplanes, particularly in commercial service, want the capability to takeoff and land in freezing drizzle and freezi ng rain. The ARC concurred with the part 25 ARAC IPHWG that certifying to a porti on should be permitted. In addition to proposing 23.1420(a)(2), the A RC 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 t hat would otherwise not be available. The latter is important because one of the ARC su rveys (Appendix TBD of this report) of operators showed a prohibition on freezing dr izzle 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 w ould not be uncommon to misidentify freezing drizzle and freezing rain. Because these ice accretions may have different effects on part 23 airplanes, the ARC decid ed that for now, takeoff cert ification in Appendix O would have to include all of Appendix O.

A LTERNATIVE 8: M ODIFY THE P ROPOSED P ART 25, A PPENDIX O I CING E NVIRONMENT

The ARC analyzed a common ice protection syst em on part 23 airplanes, the fluid antiice system, for compliance to the proposed par t 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 c ondition, requiring additio nal 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 appr opriate to propose SLD icing conditions different from that proposed for part 25. Alte rnatively, the ARC pr oposed rule language in 23.21(c)(2) to address the issue, and guid ance 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 wi thout undue penalty to part 23 aircraft.

A LTERNATIVE 9: R EDUCE N UMBER OF F LIGHT T ESTS OR A NALYSES R EQUIRED

The ARC asked itself, are we proposing re quirements for D&E airplanes for which service history shows no safety issue? Elimi nating tests that provide no safety benefit
would reduce certification cost. The ARC co uld not justify any revisions to what was proposed for certification for flight in Append ix O or an approved po rtion of it. Any
reduction would be a reduction of what is currently required for Appendix C icing
conditions.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-89 For a detect and exit airplane, the ARC decid ed at the beginning of their work to propose rules that address the safety concer n and not have icing conditions for which the airplane is not approved to dictate desig n. Compliance to t he 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 recor ders in the part 23 fleet could be one reason why, but also rationalized the following:

Section 23.77 - Icing research testi ng 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 severa l Appendix C condit ions, and therefore propeller performance could affect climb c apability 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 colle ction efficiency and therefore their performance does not change with drop size. Al so 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 forw ard 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 s hown 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 th at the ARC debated. Flutter experts from
some airframe manufacturers were c onsulted 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, servic e history shows no events due to flutter of SLD ice accretions. In addition, on unprotect ed 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 requir ed for detect and exit ice accretions.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-90 Ice crystal Requirements - Ic e crystal requirements for th e airspeed indicating system are proposed in § 23.1323. There are no docum ented ice crystal events of pitot probes on part 23 airplanes. The documented even ts 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.

A LTERNATIVE 10: R EDUCE N UMBER OF R EQUIRED I CE S HAPES

Similarly to alternative 9, the ARC asked itse lf if it could simplify the guidance on ice shapes to reduce the amount of analyses, ici ng 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 (elim inating landing, enroute, et c.) be used as a simplified approach that would provide most of the safe ty 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 c ould not rationalize doing the same for the portions of Appendix O for which the airplane is approved, for the
same reason as alternative 9.

A LTERNATIVE 11: A LLOW V ISUAL C UE FOR ALL P ART 23 A IRPLANES

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 in stalled. Adding an ice detection system
increases certification cost as well as the co st of the airplane (by at least $TBD). In reviewing the service history of part 23 airpl anes, 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 ad visory ice detection system to supplement visual cues for normal, utility, and acrobat ic 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-activa tion ice in SLD would not be required were
factors in the decision.

A LTERNATIVE 12: N ECESSITY TO F LIGHT T EST IN N ATURAL A PPENDIX O C ONDITIONS

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 whic h 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, maki ng natural icing one of the acceptable means of compliance, rather than an absol ute requirement. The ARC added specific guidance for a path for detect an d exit airplane in which natural icing flight tests in Appendix O would not be requir ed as one of the means of compliance. The ARC did not adopt this for an airplane approved to fl y 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 t hat position. The al ternative, not adopted,

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-91 would be to certify approved portions of Appendix O the same manner as detect and
exit.

A LTERNATIVE 13: A ERODYNAMIC P ERFORMANCE M ONITOR AS AN A LTERNATIVE TO § 23.1420

Similar to the first tw o alternatives, this alternative was not discussed in detail by the ARC but it is valid for part 23. The discu ssion 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 instab ilities 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 boundar y layer conditions had reached a safety threshold, regardless of what caused the boundary layer disturbance. Several attempts have been made to investigate t he feasibility of APMs on civil aircraft. Currently no
APMs are used on commercial aircraft and t here is little operational experience to establish confidence in the system’s capabili ties. 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 requir ed to obtain approval for installation on a Part 25 (23) airplane.”

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-92 7. CERTIFICATION COST INPUT

A) A SSUMPTIONS

As part of the Task 2, ARC members provided input on the estimate s on the cost of the proposed regulatory changes to assist the F AA in performing the regulatory analysis. Both the increase in costs and any potent ial for reduced costs were considered.

With the diverse range of aircraft within par t 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 certific ation options available to applicants.

The assumptions used for the certificati on 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 certificati on 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 antici pated 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 r equired (applicant’s discretion).

 For aircraft certified for tak eoff and landing (approved portion) per § 23.1420(a)(2), flight testi ng in natural large drop conditions would be required.

 For aircraft certified without restricti ons per § 23.1420(a)(3), flight testing in
natural SLD woul d be required.

 Costs estimates were to include total co sts, 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 hour s assuming that the FAA economist would use the appropriate $/hour rate for su ch technical engineering activity.

Some of the rulemaking recommendations w ould 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 certific ation costs within Appendix C certifications. ARC members were requested to provide an estimate of these costs to
be considered in the overall economic balance.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-93 Table 7 - Size Assumptions Used for Certification Cost Estimates

Aircraft Type Assumptions

Small part 23 aircraft Single reci procating 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 provi de guidance based on aircraft and certification complexity .

Table 8 - Certification Approval Opti ons 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 requirement s for aircraft certified for IFR/IMC operations.

 Includes any ice protection equipment installed on a “non-hazard” basis as there are no additional icing ru le 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.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-94 B) I NCREASED C OST C ATEGORIES

The increased costs were further divided to a ccount 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 system s and the effect of t he airframe ice shapes on the performance and handling qua lities of the aircraft (not including actual flight testing). This type of ac tivity 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 performa nce 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 s hapes, 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 ce rtification efforts.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-95 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 installati on 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 architec ture and integration, system safety assessments, SLD ice detector qualification and installation certification, any modifications to windshield heat levels, angl e of attack and pitot pr obe requirements, as well as any supporting analysis for the above.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-96 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 s hapes 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 hav e 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 shed ding, 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 instrumentati on for SLD (rental if required)

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-97 C) I NCREASED C OST S UMMARY

The estimates reflect the increased costs for applicants for the different types of
certification. The differences in bids refl ect different approaches towards certification As an example, some applicants may us e more analysis, and less icing and wind tunnel tests, not all applicants have a ccess to icing tankers and consequently may have more effort expended in ic ing and/or flight te sts. As such, the bid pairs (labor and non-recurring costs) should not be sp lit between different estimates.

The bids reflect the best estimates availa ble at this point in time, but did have
considerable variance between t he different estimates. This is likely a reflection of the uncertainties in the certification proce ss (applicants won’t know the full extent of work required until a full certification pl an is completed and approved), as well as
what facilities/simulation methods are availabl e to the various applicants. As such, it is recommended to use a median approach to the regulatory analysis to more accurately reflect the true co sts associated with the rule.

Table 11 provides a summary of the total labor hours and the non-recurring costs that
would occur for each certificat ion program. It is assum ed that the APO will determine the appropriate engineering labor rate for use in the analysis.

For reference on detect and exit certificat ion, most manufacturers assumed one Appendix O ice shape confi guration for flight test evaluation, although one manufacturer assumed three ice shapes.Part 23 SLD ARC REPORTFEB 2012 - Revision BPage-98Table 11 - Summary of Increased Certification Costs for Proposed RulemakingSummarySmall Large Small Large Small Large Small Large Small Large Small LargeEstimate Anone none 2700 hrs 4890 hrs 6020 hrs 10465 hrs none none 343,000$ 427,500$ 997,000$ 1,740,500$Estimate Bnone none no bid 15300 hrs no bid 32300 hrs none none no bid 2,340,000$ no bid 3,620,000$Estimate Cnone none 1900 hrs no bid 4440 hrs no bid none none 188,000$ no bid 453,000$ no bidEstimate Dnone 100 hrs 4096 hrs 4106 hrs 10124 hrs 10074 hrs none 2,000$ 233,500$ 480,500$ 542,000$ 1,029,000$Estimate Enone none 3324 hrs 5283 hrs 11214.5 hrs 15728 hrs none none 108,231$ 635,762$ 520,154$ 2,528,646$Summary Mediannone 100 hrs 3012 hrs 5087 hrs 8072 hrs 13097 hrs none 2,000$ 210,750$ 558,131$ 531,077$ 2,134,573$UnrestrictedHours Non-recurring costsBasic FIKI Basic FIKI(non-FIKI) Detect and Exit Unrestricted (non-FIKI) Detect and ExitTable 12 provides a summary of the total labor hours and the non-recurring costs that would occur for each aspect ofcertification considered. As discussed above, separation ofthe bid pairs (labor and non-recurring) is not recommended.Part 23 SLD ARC REPORTFEB 2012 - Revision BPage-99Table 12 – Detailed Medians forthe Aspects of CertificationSmall Large Small Large Small Large Small Large Small Large Small LargeMedian of all bids received, by category:Airframe Analysis none 0 hrs 810 hrs 1158 hrs 1847 hrs 2342 hrs none -$ -$ -$ -$ -$Wind Tunnels none 0 hrs 80 hrs 614 hrs 160 hrs 1217 hrs none -$ 27,500$ 90,250$ 90,500$ 164,300$Icing Wind Tunnels - Airframe Aspects none 0 hrs 208 hrs 296 hrs 434 hrs 768 hrs none -$ 50,000$ 137,994$ 88,518$ 384,982$Icing Wind Tunnels - Engine Aspects none 0 hrs 89 hrs 258 hrs 147 hrs 574 hrs none -$ 8,003$ 83,997$ 21,884$ 247,741$Engine Installation none 100 hrs 225 hrs 325 hrs 390 hrs 750 hrs none 2,000$ 1,000$ 1,000$ 1,000$ 6,000$Misc - Systems none 0 hrs 364 hrs 740 hrs 804 hrs 1336 hrs none -$ 7,500$ 27,500$ 7,500$ 32,500$Flight Test - Dry Air Testing none 0 hrs 463 hrs 1190 hrs 1416 hrs 4274 hrs none -$ 23,500$ 106,250$ 62,500$ 248,750$Flight Test - Tanker Testing none 0 hrs 380 hrs 255 hrs 740 hrs 415 hrs none -$ 48,000$ 77,750$ 113,825$ 76,750$Flight Test - Natural SLD Testing none 0 hrs 0 hrs 0 hrs 924 hrs 1752 hrs none -$ -$ -$ 141,000$ 346,500$UnrestrictedHours Non-recurring costsBasic FIKI Basic FIKI(non-FIKI) Detect and Exit Unrestricted (non-FIKI) Detect and Exit

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-100 D) C OSTS FOR C ERTIFICATION TO A P ORTION

The guidance material recommen dations provide guidance for certification to a portion of the large drop environment in the context of approving tak eoff and landings in such conditions. The feedback from the operators wit hin the ARC, indicated that this could become a significant operating restricti on, and as such market demand may be
sufficient for a manufacturer to seek such an approval.

The advisory material recommends addition al ice shape scenar ios that require consideration, and also advises that flight testing in natural large drop icing would be required. Additionally, sinc e the certification would stil l be restricted during certain phases of flight, development of exit ic ing cues and ice shapes would be required.

The consensus opinion of the ARC was that t he certification for approval for takeoff and landing is that the costs would be 70% of the difference bet ween a detect and exit
certification and a full unrestrict ed certification as noted below.

Portion Costs Takeoff & Landing ൌ



## ∑ Detect & Exit Costs ൅70%* 

# ሾ ∑ Unrestricted Costs ‐ 

## ∑ Detect & Exit Costs 

# ሿ

E) R EDUCED C OSTS C ATEGORIES

An effort was made to identify the reduc ed 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 (Analysi s, 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 A ppendix 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 certific ation to § 23.1419 is reduced.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-101 Examples of potential reduc ed 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 associat ed with writing and working on an exemption request is eliminated.

Takeoff Determination of takeoff speeds or takeo ff performance due to takeoff ice accretions is proposed not to be required for reciprocati ng or turboprop powered normal category airplanes. Therefore the cost to determine ta keoff 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 t he potential for roll control anomalies in SLD conditions for aircraft with non-powered roll control surfaces.

The ARC members reviewed the request and c ould not identify a significant reduced cost. It was the opinion of the ARC mem bers, that the magnit ude of any reduced costs are well within the uncertainty of the increas ed cost estimates shown above. As such, it is recommended that the potential for reduced costs be acknowledged as a conservative factor in the regulatory anal ysis rather than an exp licit calculation.

F) S UMMARY ARC P OSITION ON C OSTS

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 respec t to the overall safety benefit on icing safety for the part 23 fleet. The GAMA pr esentation included in A ppendix F illustrates
the limited effect on the cu rrent 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 fli ght in icing. As fli ght in icing systems are optional equipment on many part 23 aircra ft, this trend will not be altered by the
introduction of new certification rules. A dditionally, 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 occu rred on aircraft built prior to increased icing
certification standards a ssociated with § 23.1419, Amendm ent 43 which was introduced in 1993. This rule change only considers Ap pendix 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 l anguage to be added to the AFMs with generic identification cues. The lack of safety ev ents associated the amended icing rules, begs the question of whether increased standards of § 23.1419, Amendment 43 provides sufficient protection for exiting severe ici ng conditions, including exposures to part 25, Appendix O. Another unint ended 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 manu facturers/customers ma y opt for a no-hazard system due to the certificati on requirements and increased f light 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 sc ale, limited power, and reversible flight controls makes it technically challenging to ce rtified 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 limitati ons which will limit the aircraft exposure to conditions when forecast or reported. Signifi cant certification cost reduction could be realized by reducing the scope for detect and ex it aircraft to determining and validating exit cues. The exit procedures for an inope rative ice protection system could be used to provide the safety margins desired for a sa fe 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 woul d not be assessed, a level of safety commensurate with the ex posure risk could be achieved.

Alternately, it may be possible to reduc e the certification requirements, while maintaining the level of safety, based on t he accident history review with focus on the
certification areas t hat are affected. Using this type of bottoms up approach would provide the maximum value fo r the certification costs.

While there is a desire to maintain an equiva lent 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 operat ional 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.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-103 8. OPERATING COST

A) C OST OF A VAILABLE C ERTIFICATION O PTIONS

On the operators’ side for non-recurring co sts, a breakdown divided into three categories can be envisaged.

(1) A IRPLANES C ERTIFIED TO § 23.1420( A )(1) “D ETECT AND E XIT ”

It is envisioned that most part 23 airplanes, par ticularly the airplane s marketed more for part 91 operations versus part 135 cargo 2 operations, will be certified to “detect and exit.” These airplanes will be prohibited fr om operating in Appendix O conditions, for example taking off at an airpor t 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 thes e conditions. Based on NATA and RACCA surveys, it can be assumed t hat 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 wh o 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 cost s associated with the following:

 Cancelled flight (due to Appendix O conditions at the departure airport)

 Cancelled flight (due to Appendix O c onditions 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 AF M Limitation. Appendix O conditions would cause severe icing on many part 23 airplanes.

(2) A IRPLANES C ERTIFIED TO § 23.1420( A )(2) “A PPROVED TO O PERATE IN A PORTION

OF A PPENDIX 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 c onditions. There are additional certification costs for landing. The surveys showed t he operators want these capabilities for new

2 The operating rules for cargo versus passenger op erations 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.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-104 airplanes. The only effe ct 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 wi ll have costs associated with the following:

 Impact on dispatch (performance limit ed 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 sma ll as discussed in § 23.1420(a)(1).

(3) A IRPLANES C ERTIFIED TO § 23.1420( A )(3) “A PPROVED TO O PERATE IN ALL OF A PPENDIX O”

It is not anticipated that a part 23 airplane wil l be certified to this rule due to the small scale effects and capabilities of ice prot ection systems common on these airplanes. However, it should not be ruled out comp letely 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 operati ng costs associated with this option are:

 Impact on dispatch (performance limit ed take-offs or landings and payload decrease)

B) T RAINING

Costs due to any increase in training should be considered for t he 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 informa tion published by the manufacturer, within the AFM, that is specific to the type of aircraft;..”

The increased cost would involve training the limitations, any pr ocedure in Appendix O different than in Appendix C, and Appendix O recognition c ues. 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 a ssumed this was included in the part 25 rulemaking effort.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-105 C) D ESIGN I MPLICATIONS

Compliance to the new rules may result in des ign changes which will affect operators. Modifications in the ice protection system s 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) A IRPLANE M ANUFACTURING I NDUSTRY

The new rule will not affect the current flee t. New airplanes with a prohibition on taking off and landing in Appendix O will compete with t he existing fleet. Except for some very recent certifications which adopted recommended language in AC 23.1419-2D, the current fleet has no such prohibi tion. 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 m any 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 s uppliers. Regarding the RACCA survey, the question was “presuming you’re considering a new aircraft”. The NATA representative, a part 135 cargo operator, comment ed that they usually buy used airplanes anyway, so the impact due to these operat ors may not be large.

E) A CTUAL C OST D ATA

This discussion is meant to guide the FAA econom ist to the types of recurring costs that should be considered. The surveys in A ppendix E of this r eport contain limited quantitative data which may be useful to the economist.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-106 9. BENEFIT SUMMARY

A) I CING A CCIDENT D ATABASE R EVIEW

The ARC examined incidents and accidents to identify those which may be considered in the benefit analysis of the regulatory evaluat ion. The ARC would like to acknowledge the work of Steve Green, a consultant hire d by the FAA to help assemble the part 23 icing database and identify applicable accidents. Much of the nar rative in this section of the report was extracted from a draft of Mr. Gr een’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 projec t 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 consider ed, however several of these were reexamined to determine if SLD wa s present. Four events were rejected from the current work following additional examination of thei r relevance. An additional 7 events were determined to present inade quate data for evaluation. Although these 7 events had been evaluated for the previous study, it wa s 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 st udy 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 dat abase, 1 from the F AA 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 robu st “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 ear lier, including Civil Air Regu lations (CAR) 3. No
aircraft in the events database were ce rtificated 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

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-107 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-2 08B 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

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-108 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 incide nt 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

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-109 There exist 16 events known to the FAA of thru st 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 alti tude of 28,000 to 41,000 f eet. Blockage of the heated total temperature probe causing erron eous data to the FADEC is suspected. These events are not available publicly and are not listed. T here are 6 documented events on part 23 airplanes of possible ic e 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 prom ulgate guidance on ice cont aminated tailplane stall (ICTS). The following events are suspected ICTS events t hat are not included in the
SLD tables above:

Table 15 – Events Applicab le 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 Pa sco, 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 protec tion system was inoperative.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-110 T HE U SE OF NTSB P UBLIC D OCKETS

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 pres ent, and in some of those cases, it is not complete. Some dockets are thorough, containing original written statements and police reports. They almost always contai n a statement from t he pilot-in command, should he/she have survived, as well as witness statements and ATC transcripts where appropriate. The docket also contains phot ographic evidence, although there is no standard for the photographic evidence.

FAA AIDS reports are not suppor ted 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.

W AS A IRPLANE E QUIPPED WITH I CE P ROTECTION S YSTEMS ?

A common issue with the NTSB dockets for part 23 airplane events is the lack of documentation of the ice prot ection systems and certification, even when the accident clearly involves airframe icing. At one poi nt, during the mid eighties, the Board used a
field documentation form that contained c heck boxes for icing equipage and icing certification. In many ca ses, these checkboxes, even th ough present, were not used.
Later Board field documentation forms have no provision for the indication of ice protection equipment or certif ication. 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 ce rtification data indicates that, for that airplane serial number, icing certification was not an option.

There were also a number of cases in whic h the Board documentation did not formally mention icing equipage. In some case s, the icing equip age could be determined through the wreckage documentation. In some events it was determined by obtaining a marketing photograph available of that particu lar 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 configurati on in use at the time of the event.

A IRPLANE C ERTIFICATION B ASIS

There are 85 reports generat ed by the NTSB which make no reference to icing
certification at all in either the factual reports or docket ma terials. Because of the wide irregularity in the NTSB data, certificati on has been assumed when the TCDS allows it and the aircraft is evidently equipped. If the serial number was available, either through

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-111 the report or through a lookup of the registration, the Ty pe Certificate Data Sheet
information could be accessed to determine w hether the serial number fell within the range of aircraft that were icing certificated if pr operly equipped.

All the aircraft in event database that were cert ificated 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 Je tstream 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 t he events. This is significant and suggests traini ng 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 discusse d ice accretion. In one case, the TKS system was believed to be active; in the ot her, the operation of t he TKS could not be determined. In one case, thunderstorms were in close proximity. No other recent “nonhazard” certifications were noted.

S UPERCOOLED L ARGE D ROPLET AND G LACIATED C ONDITIONS A NALYSIS

Descriptors such as severe ice, freezing ra in, 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, ic e pellets on the ground. There were limited
references to “SLD” since most of thes e accidents occurred prior to the 10/31/94
Roselawn accident and SLD is a term that wa s coined after that accident. For many of the part 23 events with no surviv ors, prior to 1994, the onl y 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

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-112 Snow events appearing in approximately in 20% of the events, and suggests another training subject. In some ci rcles, it was believed the pr esence of snow indicated all water was glaciated (therefore no airframe ic e 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.

W AS THE E VENT A PPLICABLE TO THE P ROPOSED SLD R ULE ?

The presence of SLD alone does not make the event applicable to the proposed SLD
rule. There must also be evi dence that the SLD was a factor in the accident. Examples include lift/drag degradation, stall and controlla bility. A lift/drag degradation appears in some form in nearly all of t he reports for which detailed info rmation is available, with the exception of ICTS events. It is likely that an early and aggressive response to these degradations may prevent more severe outco mes. 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 si nk 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 ov er gross weight limit

W INDSHIELD I CING

The presence of windshield icing was a disq ualifying condition if no other aerodynamic event was found, since the detect and exit r equirement will not addre ss windshield icing. Windshield icing was exhibited in 29 of 214 part 23 airplane events; however windshield icing alone is typically a non-fatal event.

P ILOT A WARENESS OF I CING

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 aw are 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

FEB 2012 - Revision B Page-113 A CTIVATION AND O PERATION OF I CE P ROTECTION S YSTEM

A great deal of information about the operati on of the IPS is not available from the reports, dockets or statements. Qualitatively, a substa ntial number of events are associated with a failure to oper ate the IPS. Since part 23 airplanes typically are not equipped with a flight data recorder or voic e recorder, these events involve at least one
survivor.

P HASE OF F LIGHT

Most part 23 SLD events occurred during appr oach and landing. Many of these events were non-fatal hard landings. Approximatel y two thirds of t he SLD events on approach and missed approach were fatal. An SLD ev ent 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

O PERATING R EGULATION

There does not appear to be a relationshi p between operating rule and number of events. Part 135 aircraft were ju st 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.

R ECOMMENDATIONS FOR A CCIDENT INVESTIGATION

The investigation of an accident that may in volve icing could be greatly enhanced if the following steps were taken:

 Document the ice protection equipment

 Document the ice protection s witch positions, if not destroyed

 Include the aircraft serial number (NTSB does; FAA does not)

 Document the status of the ice pr otection systems (switch positions, pilot statements, etc.)

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-114  Determine if the airplane was certificat ed 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 edg e, antenna, landing gear,

etc.

 In general, greater care with dates and registration numbers would be useful.

B) I CING I NCIDENT D ATABASE R EVIEW

The three sources of data for this project represent three different thresholds of data reporting. The first, report ed accidents, is a set of dat a that must meet a defined criteria. Because of the severity of t hese events, it is unlikely that any have been unreported. The second source of data, reported incident s, 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 wit hout 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 aware ness of the program, wh ich is not large in general aviation pilot community. An ASRS r eport 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 evaluati on is limited if not impossible. What is
valuable is the identific ation of precursor characteristics. In many, if not most, Part 23
accidents there is almost no data available r egarding 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 thos e accidents from which no survivor information can be obtained probably looked similar, at least initially.

The icing incidents support the propos ed rulemaking to show adequate climb performance and an evaluation of ice contaminated tailplane st all in detect and exit SLD
conditions. The incidents also show winds hield 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 possi ble FZDZ was misreported as FZRA. Limiting
detect and exit encounters to outside air te mperatures of -10°C and warmer is also supported. The following table cont ains 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

FEB 2012 - Revision B Page-116 10. TRAINING RECOMENDATIONS

A) I NTRODUCTION

The Part 23 icing ARC undertook a detailed eval uation of all Part 23 aircraft accidents in which icing was a causal factor. The acci dent 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 know n icing or that have any ice pr otection equipment. In order to have the greatest impact on icing accident rate, the ARC recommends an integrated approach be taken that encompasses not only enhanc ements in the certification of Part
23 aircraft but also an educational initiative fo r all operators. This educational initiative needs to include all pilots, not only pilots of ai rcraft certificated for flight into known icing
conditions.

The ARC is not recommending training m andated through regulation, but instead a focused training initiative / marketing campai gn similar to the effective training initiative recently administered to improve runway safe ty. The FAA recently led an effort to improve runway safety in the United Stat es (U.S.) by decreasing the number and severity of surface incidents and runway incu rsions. To achieve this end, the FAA’s Office of Runway Safety launched a multi-pronged educational initiative with
collaboration between the F AA and its stakeholders in the aviation community. Together with industry, the FAA develop ed and delivered updated advisory material, brochures and interactive programs to a broad audi ence of pilots and flight instructors.
The results of this educational initiative ar e irrefutable. The runway incursion rate dropped 50% two years in a row. This achiev ement is the result of a focused message being effectively communicated to the pilot popul ation. For future initiatives such as training for intentional or uni ntentional 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 a ccidents 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 statem ent that “flight into known ice is prohibited”. Therefore, pilots faced with an inadvertent encounter with ice have no guidance from the manuf acturer on exit procedures, approach configuration or speed considerations. Adding to this la ck of knowledge is t he misconception among pilots that all aircraft are aerodynamically te sted to some level of ice regardless of the
certification of the aircraft. Fo r aircraft that are certified for f light into known ice, there is great misunderstanding as to how much ice that aircraft is “certi fied” to carry and when the pilot must begin the exit from icing c onditions. It doesn’t hel p 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 p ilots. Secondly, there are many, deeply ingrained misconceptions am ong the pilot population with respect to

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-117 best procedures and practices to follow in ici ng conditions. Despite greater scientific understanding of flight charac teristics 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 trai ning 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 hel pful if training topics were developed and final training mate rial promoted by the FAA as in the model of runway safety. This would ensure that a focused message is deliv ered that encompasses all of the areas of training recommended by the A RC and that the message is delivered to all operators of part 23 aircraft.

In the evaluation of icing accidents, se veral topics emerged that requires focused training in order to reduce t he icing accident rate. Those training topics are listed below. In order to have the greates t impact on learning, all the training should be given in practical terms. For example, give real wo rld, practical guidance for determining if an aircraft is certified for flight into know n ice and knowing the limitations of that certification; real world, practical guidanc e of how a wing stall feels and technique for recovery versus a tail stall feel and recovery.

B) D ISCONNECTS BETWEEN THE C ERTIFICATION AND O PERATIONS WORLD

As was discovered in the recent Part 23 Ce rtification 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) T HE DIFFERENCE BETWEEN STALL WA RNING AND AERODYNAMIC STALL

Pilots need to be made aware of the fa ct 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 in to effect). The first warning of an impending stall may be an aerodynamic buffe t or increasing sloppiness of the flight controls rather that the stall warning horn, light, stick shaker, etc.

(2) T HE 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. P ilots should be aware that approach and landing with partial flaps will most likel y preclude an ice cont aminated 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.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-118 (3) T HE MEANING OF “ APPROVED FOR FLIGHT INTO KNOWN ICE ”

The ARC recommends that the FAA emphasi ze the conditions and visual cues
that define aircraft certification level and emphasize that operat ionally, no matter what the certification, no aircraft has the capability for unlimited safe flight in all icing conditions. Training should emphasiz e 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”, “for ecast icing conditions”, “known icing conditions” and “potential icing conditio ns” as well as information from the FAA legal interpretation dated January 16, 2009. That legal interpretation states: “"Known icing conditions" involve circumstance s 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 repor ts 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 k nown icing conditions. Such forecasts may cover a large geographic area or repr esent too long a span of time to be particularly useful to a pilot.” A pilo t, and his or her proper analysis of that information in evaluating the risk of encount ering known icing conditions during a particular operation. The pilot should consid er 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 informa tion relevant to a proposed flight, including appl icable surface observations, temperatures aloft, terminal and area forecasts, AIRMETs, SIGM ETs, and pilot reports (PlREPs). As new technology becomes available, pilo ts should incorporate the use of that technology into their decision making pr ocess. If the composite information indicates to a reasonable and prudent pilo t 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) T HE DIFFERENT CATEGORIES OF CERTIFICATION FOR “ FLIGHT INTO KNOWN ICE ”

Pilot training should include the level of pr otection the certificat ion 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 conv ey that depending on cert ification level and
when the aircraft certification was obt ained there is a wide range of conditions
that were tested or not te sted as the case may be.

In general, aircraft can be classified into three areas:

1. Airplanes not equipped nor approved for f light in icing cond itions. Education and training should emphasize the following:

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-119 a. In-flight icing accidents and incide nts involving these airplanes have outnumbered those on icing certificat ed airplanes in recent years. b. No flight testing is conducted to show the airplane can safely exit an inadvertent encounter - pilots of t hese airplanes should be aware that these airplanes are not tested fo r “inadvertent” icing encounters. c. There are only requirements for engine induction icing, and for IFR approved airplanes, ice protection fo r 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 descri bed in Advisory Circular 20-73A.

2. Airplanes with ice protec tion but prohibited from fli ght in known icing. AOPA Safety Advisor No.22 at http://www.aopa.org/asf/publications/sa22.pdf addresses the subject. a. “Non-hazard” systems ar e meant simply to buy time for a pilot to escape from unexpected icing conditions. b. Non-hazard systems have no require ment to demonstrate that they can protect your airplane during icing conditions.

3. Airplanes certified for flight in ic ing conditions. These airplanes can be subdivided further by when they were certified: a. The earliest certifications were “appr oved” for flight in icing conditions if they were properly equipped. T here was no real requirement for testing of these systems. b. Testing of ice protection systems in itially tested for stall buffet only and had no icing climb gradient requirements. c. New aircraft certified today must meet climb gradi ent 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 r equiring 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 fr om one exposure to another as can it’s affect on aircraft performance.

 No aircraft, regardless of certification le vel, will be able to indefinitely maintain flight in all icing conditions.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-120  Ice protection is primarily used to prot ect aircraft during transient encounters in icing conditions. Always plan to exit icing conditions.

(5) H OW 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 pr otection systems are to be operated, and their actual performance. For exam ple, fluid systems are designed and tested as anti-ice systems. Certif ication testing assumes t here 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 bef ore 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 ai rplane is in severe icing and must exit immediately.

For pneumatic deicing boots, pilots s hould understand t hat there may be conditions in which ice may not shed complete ly 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 inhi bitors, for example the product “ICEX” for Goodrich boots, greatly improv e shedding performance (AIAA-2007-1090, “Residual and Intercycle Ice for Lower-S peed Aircraft with Pneumatic Boots”). Products not approved by the boot manufactu rer or airplane manufacturer should not be applied to boots.

(6) G ROUND DE

- ICE PROCEDURES ``

Training should focus on the importanc e 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 us ing fluids / methods to remove ice or snow and reasons why it’s important to only use methods and fluids approved by the manufacturer (materials co mpatibility, pooling of fl uids in flight control surfaces, etc).

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-121 C) F OCUSED I CE T RAINING

Previous attempts to educate the pilot population on the dangers associated with icing conditions went into great detail on areas t hat were not necessary or simply added to confusion regarding airframe ic e. 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 airc raft control, for example. The training recommendations below should focus on the practical, real world application of t he following subjects.

(1) I NTERPRETING 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 ident ify the presence and location of such conditions. Recently developed NOAA “Java tools” av ailable online can pr ovide forecasts of temperatures aloft, air mass water c ontent, and icing probability in map form, easily adjustable for various MSL altitudes.

(2) I DENTIFY AND ADHERE TO PERSONAL MINIMUMS

FAA and Industry emphasize the use and adherence to personal minimums for any flight. Weather rela ted personal minimums used in FAA-Industry Training Standards (FITS) usually focuses on wi nds, ceiling and visibility. The ARC recommends FITS increase emphasis on ic ing related personal minimums which
include “find and avoid” as well as ex it 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) H OW 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 protecti on systems’ capability, or require an immediate exit from the icing region. The rate of ice accretion is an important factor in effe ctiveness of ice protection systems. The ice-carrying characteristics of individual airpla nes may be significantly different.

(4) D EICE 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 us ing 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,

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-122 etc). Training should include weather re lated factors in maintaining the clean aircraft for takeoff (example: freezing precipitation falling prior to takeoff but not adhering to wing).

(5) D EMONSTRATE 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 ev en 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 incr eases 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 wit h pneumatic deicing boots under most
conditions.

Another myth floating around is that high speed laminar flow airfoils are more susceptible to ice than “thicker,” convent ional 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. Go ing back to report DO T/FAA/AR-06/48, one can see that at the angle of attack fo r 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 angl e of attack. The result is a rapid loss of lift as airspeed is reduced below a ce rtain threshold. This explains the high number of hard landings in the accident database.

(6) D EMONSTRATE HOW RAPID ACCUMULATION AFFECTS TIME AVAILABLE FOR EXIT / E XIT S TRATEGIES

Tests conducted at NASA Glenn Research Center on several modern airfoils demonstrated that in some instances, exposur e to clear icing fo r just two minutes could double the drag, r educe the maximum lift by 25%-30% and reduce the critical angle of attack by 8 degrees (whi ch would correspond to a substantially higher stall speed). Training should emphasize that in ic ing conditions with rapid accumulation, there is very little time ava ilable for exit. Exit strategies should be
considered before enteri ng 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 imm ediate assistance from ATC and declaring an emergency and teach pilots that rejectin g 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 PI REP or other information regarding

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-123 enroute icing conditions. Do not hesit ate to request assistance from ATC. However, as pilot in command, it is im portant 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 responsiv e, the pilot must advise ATC that if the course or altitude requested is unavai lable, an emergency will be declared and required changes will be made.

(8) L AST RESORT CHOICE

An off airport landing may be emba rrassing but is a better option than uncontrolled flight into terrain.

(9) A UTOPILOT 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) S INK 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 literat ure. Although ther e is almost always some type of lift/drag degradat ion which precedes a cata strophic event, the most
common event in which it manifests itse lf is hard landing. Out of 137 part 23 airplane icing accidents in the period st udied, 37% were hard landings or landing short of the runway. A pproximately one third of t he part 23 accidents identified as applicable to the SLD rule are hard l andings 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. Traini ng should emphasize a slow reduction in power during the flare, and the fact t he higher drag due to ice will require more power to maintain the same sink rate as in non-icing.

(11) C ONFIGURATION AND SPEED CONSIDERAT IONS AFTER FLIGHT IN KNOWN ICE FOR

APPROACH AND LANDING

Approximately 51% of ici ng 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 reco mmends increased training emphasis on

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-124 approach and landing strategies after ic ing encounters. Specifically, train operational tactics with ice adhering to t he aircraft such as delayed descent, avoiding prolonged approach vectors, keeping speed up, and delaying/limiting flap configuration changes.

D) C HANGES TO FAA TRAINING AND TESTING MATERIAL

(1) R EVIEW 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) R EVIEW 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) D EVELOP 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). E XAMPLES :

o Severe icing recognition- photos

o Minimum airspeed for flaps up op eration and appr oach 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 ce rtain older airplanes)

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-125 11. TASK 9 RECOMENDATIONS

A) B ACKGROUND

The following task was added in the third quarte r 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 im pending 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 ce rtificates, amended type certificates, and supplemental type certificates.

The ARC reviewed the NTSB safety recomm endation letter and noted that the NTSB is recommending a system in addition to the sta ll warning system and an aural indication to complement existing visual low airspeed aw areness 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 st ick 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 t he onset of the stick shaker.”

The ARC reviewed icing accidents for which t here is flight data recorder data. The common scenario is a reduction of airspeed, typica lly 1 – 2 kt/sec leading to a stall. The autopilot is engaged in altitude hol d or vertical speed mode in a climb, and the flightcrew is unaware of the airspeed decay. The flightcr ew 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) P ROPOSED R ULE

The ARC decided that a low airspeed alert syst em 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, r equires 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 certifi ed 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 traini ng emphasis items. One single engine, reciprocating engine airplane certified to th e latest amendment requires biennial icing

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-126 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 warn ing in applicable SLD conditions for new airplanes. Therefore, for new airplanes t hat 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) F LIGHT IN I CING VERSUS N ON

- ICING C ONDITIONS

The ARC discussed rule language that would not distinguish icin g flight from nonicing flight in consideration of t he NTSB recommendation that a low airspeed alert would increase safety in non-ic ing 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 determi ne recommendations for flight in icing conditions

o The ARC did not have a database of ev ent history for no n-icing flights and therefore did not have sufficient information to assess the potential
benefits of a broad action to addr ess operations in non-icing
conditions.

o A system to address non- icing flight may be more complicated and costly than icing flight. For exam ple, 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 associat ed with tying the system to a system such as airframe, propelle r, or engine ice protections system.

(2) A IRPLANES C ERTIFIED FOR F LIGHT IN I CING V ERSUS N OT C ERTIFIED FOR F LIGHT

IN I CING

The ARC also discussed applicability to an airpla ne 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 cert ified under CAR 3 or Part 23 ). This indicates such airplanes inadvertently enc ountering icing is a larger safety issue than icing certified airplanes. However, the ARC dec ided to apply the rule only to airplanes certified for flight in ic ing 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 st arting to be certified on part 23 airplanes. These systems activate at a factor of 1.2 of the non-icing

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-127 stall speeds, which should provid e protection with inadvertent ice
accretions.

o Limiting applicability of t he rule reduces its cost,

o Older part 23 airplanes not certified for icing typically do not have glass cockpits and therefore appl icability of the rule (if 23.1311) would be limited anyway.

(3) A UTOPILOT

The ARC discussed whether a new rule s hould apply only when the autopilot is engaged. Analysis of events indicated 4 out of 69 in wh ich there is evidence of no autopilot, or no autopilot upon airplane deliv ery. All four of these airplanes were not certified for flight in icing. Mo st part 25 icing events with flight recorder data and cockpit voice recorder data indicate airspeed decay with autopilot engaged. However, document ed 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 b een 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 airs peed 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. Ther e was no consensus reached on which rule would be more appropriate.

C) O PTIONS

(1) O PTION #1

- R ECOMMENDED R ULE L ANGUAGE 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 fr om 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.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-128 Proposed paragraph (h)(1) prevents an applicant complying with proposed (h)(2) by a prohibition of autopilot use in ici ng. 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 ici ng conditions. The ARC consensus is that the use of an autopilot, even in ic ing, 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 autopilo t 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 t heir safety recommendation letter are mitigated by a means to indicate an uns afe 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 A ppendix C ice accretions on protected and unprotected surfaces. Additional ev idence is AD 2007-10-15 on the Cessna Caravan which required a Low Airspeed Aw areness 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 p ilot system is installed:

(xx) The automatic pilot system mu st 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 pr otection system operati on” the ARC noted that applicable icing events were only with airplanes in which ice is present on protected surfaces in normal system operati on (e.g. intercycle or residual ice on pneumatic boots). The ARC noted that ai rplanes equipped with fluid freezing point depressant systems and thermal anti- ice systems are not in the accident list. The intent of this languag e 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 ai rspeed. A stall warning system that complies with § 23.207 with critical part 25, Appendix C ice accretions is an acceptable means. Airplanes with a cert ification basis that includes § 23.1419 at
Amendment 23-43 or later will have a stall warning system that is compliant.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-129 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 spee d, 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 fligh t, and the AFM Supplement must require the “bug” speed to be set in icing for all flight phases.

The ARC recognized that icing stall spee d may not be available to modifiers of older airplanes, and the icing operating s peeds 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 val ue of a 20% increase in stall speed due to critical Appendix C ice accretions ma y be used by applicants to schedule a low airspeed annunciation. Another value ma y be used if substantiated by the applicant. The ARC recognized the 20% val ue 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 annun ciation 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 angl e of attack based. However, the absence of nuisance warning is expected to be demonstrated, and if a nuisance occurs, the annunciation threshold can be r educed closer to 1.2Vs, but not below
1.2Vs.

Since a non-icing operating s peed that is at least 1.3 times non-icing stall speed is not expected to cause nuisance, t he ARC expects in many applications an increase in icing operati ng 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 la nding 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 ai rspeed 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 des igns, it would be difficult to avoid a nuisance warning during flare. The A RC 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

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-130 icing as a result if ice contaminated ta ilplane stall susceptibility testing or analyses, then an annunciation would not be required for full flaps.

An envelope protection that prevents the airplane from st alling in icing would be an acceptable means of compliance. The modifier in these projects would not have icing stall speed data. Howe ver, using the generic guidance for annunciations, a system that prevents t he 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 event s show that the flightcrew are not adequately monitoring the airspeed indicator. The NTSB noted in their safety recommendation letter for A-10-12, that di straction 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 c ue), so a redundant aural al ert might have provided them with an effective warning about the decreasing airspeed.

The means required in (h)(2) does not hav e 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 acti on to take control of the airplane and manually disengage the autopilo t. If the autopilot dise ngages without warning, an upset may be experienced. In eit her case, the means and AFM procedures should be demonstrated in flight test.

A DVANTAGES 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 applic able to more modifi cation 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 pr oposed 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 incor poration of new avionics, which may reduce pilot workload and safety. Glass cockpits by themselves may be a safety enhancement and are not a fa ctor in icing accidents..

 A § 23.1311 is targeting new glass cockpits because implementation of a low airspeed alert is much less co stly compared to only an autopilot installation, but the safety improvem ent targets autopilot use in icing and

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-131 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) O PTION #2

- R ECOMMENDED R ULE L ANGUAGE FOR 23.1311

Add new language to § 23.1311 Electronic Dis play Instrument Systems:

(8) If the applicant is seeking certific ation for flight in icing conditions, incorporate visual cues, and either an aur al or tactile warning, to provide awareness to the pilot that the airs peed is below the reference operating speed for the airplane configuration,

This rule already incorporates language r egarding visual display of instrument markings in paragraphs (a)(6) and (a)(7).

A DVANTAGES OF § 23.1311 VERSUS § 23.1419:

 Rule Consistency – There is conc ern about consistency with previous ARC recommendations, which were to specific Subpart B rules and not
23.1419.

 Visibility – STC applicants may no t be aware of requirements embedded within § 23.1419

 Scope of § 23.1419 – Section 23.1419 out lines certification requirements for aircraft ice protection system s (IPS). Although § 23.1419 can apply when changes are made to the aircraft t hat do not directly affect the IPS, these are usually changes to the exteri or of the aircraft which can affect how ice accretes. An applicant w ould 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 a llow an operator to install and/or upgrade autopilots wit hout 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 incorporat ing 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 t he low airspeed event.

 Practicality on older models - The pr acticality 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 coul d 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 descen t, but this simply means they are holding to a desired rate such as 500 ft/min. Even more advanced systems have flight envelope protection c apabilities. This means that as the aircraft approaches stall or over speed, 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 § 23.1 303(e) (specifically aural warnings) if an electronic display is replacing that instrument.

D) A PPLICABILITY O F T HE P ROPOSED R ULE

(1) T YPES 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 aut opilot is being certified for the first time on that particular icing certifi ed model. One member agreed only if the modification also included a glass cockpit, which would make compliance less costly. One other me mber disagreed entirely and felt the rule should not be applied to autopilots but to new avionics. The issue was not only cost to comply, particula rly 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 Ne w Modes, Features or Performance

If the modification involved replac ing 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 M odes, Features or Performance

If the replacement autopilot incor porated new modes, features, or performance differences, the ARC was al most evenly split as to whether the proposed new rule should apply. Three members stat ed 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 airp lane 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 un der the Changed Product Rule and would require assessment per AC 21. 101 to determine applicability of the proposed 23.1419 rule change. Cons ideration 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 belie ved 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 r egulation 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 ce rtification basis to be inadequate – that is, the change includes characteri stics that were not foreseen during the initial (or previously approved) ty pe certification. The ARC believed that this may not be universally inte rpreted and the AC should be revised.

### Part 23 SLD ARC REPORT

FEB 2012 - Revision B Page-134 E) B ENEFIT S UMMARY

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 ce rtified 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 evidenc e of a loss of control at low airspeed. Examples include witnesses observing the airplane descending out of clouds in an uncontrolled state, or r adar that indicated a loss of airs peed. An example is “"aircraft slowed from 270 to 150 ground speed in 4 minut es, 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 a ssumed. 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-208B 1 Bellevue, ID 2 0 Yes

10/29/2003 CE-208B 1 Cody, WY 1 0 Yes

11/8/2002 CE-208B 1 Parks, AZ 4 0 Yes

5/5/2001 CE-208B 1 Steamboat Springs, CO 1 0 Yes

4/4/1999 PA-46-350 2 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-46-310P 2 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-60 1 Putnam, TX 5 0 Yes

9/2/1981 MU-2B-25 1 McLeod, TX 5 0 Yes

12/6/1980 MU-2B-40 1 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 requ ired 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 Am endment 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 fo r part 23 icing certification).

The ARC noted that all but th ree of the airplanes in the list had takeoff gross weight above 6,000 lb., and 12 out of the 20 were tu rboprops. The majority of the ARC believes that restricting the rule to ai rplanes above 6,000 lb. may be an option to be evaluated during the economic a nalysis 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 airp lanes above 6,000 lb. gross weight. One technical rationale that supports using the power plant type criteria is that reciprocating powered airplanes have shorter spool up times for airspeed recovery, however one observation was that stall recovery with ic e accretion is effected by angle of attack reduction. If either were pur sued, the ARC noted that all t he 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 app licability as discussed may potentially reduce the rule cost and burden on small airplane owners while protec ting the majority of the flying public. The above analysis was based on SPAS data from May, 2011.

The ARC made an interesting observation on airpla ne not certified for icing. Before the airplanes not certified for ic ing were excluded from the applicable Task 9 list, they made up 71% of the events. The ARC believes ed ucation 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 protec tion systems activate at a nominal 1.2 times non-icing stall speed.)

F) C OST S UMMARY

(1) D ESIGN AND C ERTIFICATION

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 informat ion is already available, however the glass cockpit software would have to be dev eloped 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 manufac turers. These modifi cations, in addition to software and display modifications, woul d require a signal to indicate an ice protection system is activated (to indicate t he airplane is in icing conditions) and a flap position signal. The average estimate provi ded by airframe manufacturers on the ARC is 140 man-hours. The requir ed 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 s hapes and the flight test evaluat ions piggy-back evaluations of the autopilot or glass cockpit.

(2) R ECURRING C OSTS

The unit cost increase of an autopilot instal lation 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) G UIDANCE

Since there was no consensus on whether a proposed new rule should be in § 23.1311 versus § 23.1419, the ARC did not draft re commended guidance as it did for SLD and ice crystals. The ARC believes the follo wing should be addressed in the guidance:

Acceptable means of compliance (the discussi ons in section B Proposed Rule) should be included)

Applicability (the discussions in section C A pplicability 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 Spe ed and High Speed Awareness Cues.”

 This section should reference the proposed ru le 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 protecti on 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 ic ing, it is good practi ce 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

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..Part 23 SLD ARC REPORTAPPENDIX B – PART 23 ICING ARC MEMBERSFEB 2012 - Revision BPage B-1Point of Contact Company PhoneKarl Berg Honda Aircraft 336-662-0246 x1022Tom Bond FAA Icing Chief Scientist & Technical Advisor 216-433-3900Greg Bowles GAMA 202-393-1500Pedro Fernando Almeida Di Donato* ANAC 55-12-37972614Marcelo Leao Domingos Embraer 55-12-3927-6610Jim Duncan Piper Aircraft 772-299-2684Chuck Enders FAA Flight Standards, Air Transportation 202-493-1422John Fisher FAA Engine & Propeller Directorate 781-238-7149Michael H Grossmann NATA 330-498-9333Kristine Hartzell AOPA 301-695-2086John Hazlet RACCA 818 847 0000 x300Garrett Homan Cirrus Design 218-788-3490Jim Hoppins Cessna Aircraft 316-517-8926David Johns* Transport Canada 613-941-8384Jerry Jordan CAV Aerospace 913-706-6460Kurt Laurie Cessna Aircraft 316-517-1984Mário Celso dos Anjos Oliveira Leite ANAC 55-12-37972434Jim Martin* Transport Canada 613-952-4311Jason Nickel Hawker Beech 316-676-0297Jerry Ostronic FAA Flight Standards, Air Transportation 412-886-2580 x332David Parkins Designated Engineering Representative 607-269-0702 x223Paul Pellicano FAA Small Airplane Directorate 404-474-5558Andy Pierce FAA Flight Standards, Air Transportation (Part 135) 202-267-8238Everett Rochon FAA Flight Standards, General Aviation & Commercial 202-267-7413David Schwartz Piper Aircraft 772-299-2682Dennis van de Laar National Air Transportation Association 703-575-2041Gary Welsh Hawker Beech 316-676-6923* Non voting - foreign airworthiness authorityPart 23 SLD ARC REPORTAPPENDIX C – PART 23 AIRPLANE SEVERE ICING AIRWORTHINESS DIRECTIVESFEB 2012 - Revision BPage C-1Airplane ModelDocket Final RuleAerostar Aircraft Corporation Models PA-60-600, PA-60-601, PA-60-601P, PA-60-602P, and PA-60-700P Airplanes 97-CE-56-AD 98-04-23Pilatus Britten-Norman Ltd., Models BN-2A, BN-2B, and BN-2T Airplanes 97-CE-54-AD 98-04-21Pilatus Aircraft Ltd., Models PC-12 and PC-12/45 Airplanes 97-CE-53-AD 98-20-28Partenavia Costruzioni Aeronauticas,S.p.A. Model P68, AP68TP 300, AP68TP 600 Airplanes 97-CE-51-AD 98-04-20Mitsubishi Heavy Industries, Ltd., MU-2B Series Airplanes 96-CE-61-AD 96-25-02Harbin Aircraft Manufacturing Corp., Model Y12 IV Airplanes 97-CE-50-AD 98-04-19Empresa Brasileira de Aeronautica S.A. Airplanes. (Embraer) Models EMB-110P1 and EMB-110P2 Airplanes 96-CE-02-AD 96-09-12Dornier Luftfahrt GmbH,228 Series Airplanes96-CE-04-AD 96-09-14De Havilland, Inc., DHC-6 Series Airplanes96-CE-01-AD 96-09-11The Cessna Aircraft Company, 208 Series96-CE-05-AD 96-09-15The Cessna Aircraft Company, Model T210R Airplane 98-CE-19-AD 98-20-33The Cessna Aircraft Company, Models T210, P210, P210R Airplanes 97-CE-62-AD 98-05-14 R1The Cessna Aircraft Company Models T303, 310R, T310R, 335, 340A, 402B, 402C, 404, F406, 414, 414A, 421B,421C, 425, and 441 Airplanes97-CE-63-AD 98-04-28Jetstream Aircraft Limited Models 3101 and 3201 Airplanes 96-CE-07-AD 96-09-17The New Piper Aircraft PA-23, PA-30, PA-31, PA-34, PA-39,PA-40, and PA-42 Series Airplanes 98-CE-77-AD 99-14-01The New Piper Aircraft Corporation Models PA-46-310P and PA-46-350P Airplanes 97-CE-60-AD 98-04-26Beech Aircraft Corporation Models 99, 99A, A99A, B99, C99, B200, B200C, 1900, 1900C, and 1900D Airplanes 96-CE-03-AD 96-09-13Raytheon Aircraft Company 200 Series Airplanes98-CE-17-AD 98-20-38Raytheon 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 Airplanes97-CE-58-AD 98-04-24Raytheon Aircraft Company Model 2000 Airplanes97-CE-59-AD 98-04-25AeroSpace Technologies Of Australia Pty Ltd., Models N22B and N24A. 97-CE-49-AD 98-04-18SIAI Marchetti, S.r.1 Models SF600 andSF600A Airplanes 97-CE-64-AD 98-05-15SOCATA--Groupe AEROSPATIALE, Model TBM 700 Airplanes. 97-CE-55-AD 98-04-22Twin 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 Airplanes97-CE-57-AD 98-20-34Fairchild Aircraft Corporation, SA226 and SA227 Series Airplanes 96-CE-06-AD 96-09-16

### Part 23 SLD ARC REPORT
APPENDIX D – RECOMMENDED RE VISION TO AC 23.1419-2D

U.S. Department
of Transportation

Federal Aviation

Administration 

# A dvisory 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) se ts 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 RE VISION 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 Cert ification 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 Appr oval (“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 T ools for Compliance to § 23.1420 .............. A7-1 Appendix 8 Example Flight Test Progra m for Compliance to § 23.21(c)(1) A8-1 Appendix 9 Example Flight Test Prog ram for Compliance to § 23.21(c)(2) - Takeoff in part 25, Appendix O Icing Conditions A9-1AC 23.1419-2E

iv 

### Part 23 SLD ARC REPORT
APPENDIX D – RECOMMENDED RE VISION 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 Ex it 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 Requi rements for Replacement of Airframe Deicing Components ....................................................... A5-1 6-1 Part 23 Subpart B Tests for S ection 23.1419 at Amendment 23-XX .. A6-1AC 23.1419-2E

5 ) 

### Part 23 SLD ARC REPORT
APPENDIX D – RECOMMENDED RE VISION 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 demons trating compliance with the ice protection requirements in Title 14 of the Code of Federa l 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 manufact urers, modifiers, foreign regula tory authorities, and FAA small airplane type certification engine ers, and their designees. This AC applies to airplane ice protection systems in any normal, utility, acroba tic 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 polic y related to th e certification of ice protection systems on part 23 airplanes, issu ed prior to this AC, and is superseded by this

AC.

4. Applicability. The guidance provided here applies to the approval of airp lane ice protection systems for operating in the icing environment de fined 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 pred ecessor 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 ap plicable to a part 23 airplane icing certification program regardless of the certifica tion basis for the basic airplane; however, for those airplanes certificated in accordance with pa rt 3 of the CAR or ear lier, and through part 23 at amendment 23-13, the application of these se ctions may be limited to the equipment being used for ice protection. Some sy stems that were previously appr oved 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, controllabilit y, 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 equi valent 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 RE VISION TO AC 23.1419-2D

(2) Prior to the adoption of amendment 23-43, so me part 23 airplanes were certificated for flight in icing using § 25.1419.

(3) In addition to the previously me ntioned requirements (§§ 23.929, 23.1309, and 23.1419), other sections must be applied depend ing 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 requiremen t 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 propell ers in § 23.929, windshields in § 23.775, and static ports in § 23.1325.

(b) Added SLD and ice crystal requir ements for engines in § 23.1093(b)

(c) Added SLD and ice crystal requirem ents 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 ac tivation and operation guidance in § 23.1419

(f) Deleted § 23.1416 because the requi rements are addressed in §§ 23.1309 and

23.1322.

(g) Replaced the requirement for illu mination of ice accumulations provided by §23.1419(d) with a new §23.1403.

b. ACs. Copies of current editions of the follo wing 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 Dist ribution 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 Commissi on for Aeronautic, Inc. Document RTCA/DO-178B,” January 11, 1993.

AC 20-117 “Hazards Following Ground De icing and Ground Operations in

Conditions Conducive to Airc raft Icing,” December 3, 1982.AC 23.1419-2E

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APPENDIX D – RECOMMENDED RE VISION TO AC 23.1419-2D

AC 20-147 “Turbojet, Turboprop, and Turbof an 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 S upplemental Type Certification,” September 27, 2007.

AC 21.101-1 “Change 1, Establishing th e Certification Basis of Changed

Aeronautical Produc ts,” April 28, 2003.

AC 23-16A “Powerplant Guide for Certif ication 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 Titl e 14 CFR, Part 23, § 23.629, Flutter,” September 28, 2004.

AC 23.1309-1D “System Safety Analysis a nd 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 Gr ound Deicing (pocket),” December 14,

1994.

Copies of the current AC may be purchased fr om 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 Certif ication of Part 23 Airplanes,” August 14,

2003.AC 23.1419-2E

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APPENDIX D – RECOMMENDED RE VISION TO AC 23.1419-2D

6. Related Reading Material.

a. FAA Orders.

FAA Order 8110.4C, “Type Certif ication,” October 26, 2005.

b. FAA Technical Reports. The following FAA technical reports can be obtained from

the National Technical Information Serv ice in Springfield, Virginia 22161:

(1) FAA Technical Report DOT/FAA/CT-88/ 8, "Aircraft Icing Handbook" (March 1991), includes reference material on ground and ai rborne icing facilities , simulation procedures, and analytical techniques. This document repres ents 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, "Engineeri ng Summary of Powerplant Icing Technical Data," provide technical information on airframe and engine icing conditions, and methods of detecting, preventing, and removi ng ice accretion on airframes and engines in flight. Although

most of the information contained in ADS-4 a nd 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 F AA Rules for Operating in Icing Conditions" (November 2001), provides a good reference fo r understanding icing operational rules.

(4) FAA Technical Report DOT/FAA/AR-02/68, "Effe ct of Residual and Intercycle Ice Accretions on Airfoil Performance" (May 2002), details icing tunnel te sting 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 Prog ram: Flight Test Report” (M arch 2000), provides reference information on Ice Contaminated Tailplane Sta ll (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 availa ble at the NASA Glenn Research Center Icing Branch website: icebox.grc.nasa.gov.

(7) FAA Technical Report DOT/FAA/06-60, “Pr opeller Icing Tunnel Tests on a FullScale Turboprop Engine,” March 2010AC 23.1419-2E

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### Part 23 SLD ARC REPORT
APPENDIX D – RECOMMENDED RE VISION TO AC 23.1419-2D

(8) FAA Technical Report DOT/FAA/AR-09/10, “Dat a and Analysis for the Development of an Engineering Standard for Superc ooled Large Drop Conditions,” March 2009

(9) FAA Technical Report DOT/FAA/AR-09/13, "T echnical 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 Av iation Administration, Ai rcraft Certification Service, Aircraft Engineering Division, Tec hnical 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 (Elect rically 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 Co mmonwealth Drive, Warrendale, PA 15096-0001 or from their website at www.sae.org:

ARP4761 “Guidelines and Me thods for Conducting the Safe ty 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 Ic ing 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

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APPENDIX D – RECOMMENDED RE VISION TO AC 23.1419-2D

The SAE and a working group for Task 11A of th e FAA Inflight Aircra ft Icing Plan have developed the following documents:

ARP5903 “Droplet Impingeme nt 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, “Specifi cation for Electrically -Heated Pitot and Pitotstatic Pressure Heads,” 1967.

(2) American Society for Testing and Mate rials (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 regula tions for part 23 airplanes.

8. Planning.

a. Flight in Icing Approval. The applicant should submit a cer tification plan in accordance

with FAA Order 8110.4C and AC 20-73A. The cer tification plan should describe all of the applicant's efforts intended to lead to certification. This pl an should identify, by item to be certificated, the certificat ion methods that the app licant intends to use. It should provide for a certification checklist. Regarding § 23.1419, it shoul d clearly identify analyses and tests, or references to similarity of desi gns that the applicant intends for certification of the ice protection system. These methods of showing complian ce should be agreed upon between the applicant and the FAA early in the type certification pr ogram. 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 concu rrence prior to conducting certification tests.

b. Installations without Flig ht 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 th ese systems have been called “n on-hazard” installations. This means that the aircraft is prohibited from fli ght in icing conditions but there is some ice protection to facilitate an exit from an inadvertent icing encount er. Guidance for the approval of these types of ice protection systems can be found in Appendix 4 of this AC.AC 23.1419-2E

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APPENDIX D – RECOMMENDED RE VISION 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 demonstrat e by analyses and tests that the airplane is capable of safely operating thr oughout the icing envelope of part 25, Appendix C. The envelope can be reduced for airplane s certificated for operation where systems or performance limitations (e.g., altit ude), not related to ice protec tion, exist. Airplanes must also be able to safely opera te in or exit the icing cond itions defined by part 25 Appendix

O.

The applicant, however, has several certificat ion 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 th at 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 ai rframe 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 airc raft 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 ex posures 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 Appendi x O for part 23 aircraft.

10. Analyses and Ground Testing. The applicant normally prepares analyses to

substantiate decisions involvi ng application of selected i ce protection equipment and to substantiate decisions to leave normally prot ected areas and component s unprotected. Such analyses should clearly state the basic pr otection required, the assumptions made, and delineate the methods of analysis used. All an alyses should be validated either by tests or by methods agreed to by the FAA. This subs tantiation should include a discussion of the assumptions made in the analyses and the design provisions include d to compensate for these assumptions. Analyses are normally used for the following:

a. Areas and Components to be Protected. The applicant should ex amine the areas listed in AC 20-73A to determine the degree of protection required.AC 23.1419-2E

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APPENDIX D – RECOMMENDED RE VISION TO AC 23.1419-2D

An applicant may find that protection is not re quired 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 demonstr ate that allowing them to go unprotected does not adversely affect the ha ndling 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 a nd vertical stabilizers, propellers, and any other leading edges or protuberances such as antennas that may requi re 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 formati on limit and the extent of the protection surface coverage needed. The applicant should consul t AC 20-73A, “Aircraft Ic e Protection” for more

detailed information.

(2) Critical Ice Accretions. The critical ice accretions for which operational

characteristics are to be evaluated should be de termined for each flight phase as discussed in paragraph 13.b. of this AC. The parameters to be considered are th e flight conditions (e.g., airplane configuration, airspeed, angle of attac k, altitude) and the ici ng conditions of part 25, Appendix C (temperature, liquid water content, m ean 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 cri tical 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 whic h the operational characteristics of the overall airplane are to be analyzed. S ee AC 20-73A for more information.

(a) A mean effective droplet diameter of 22 microns and a liquid water content of 0.5 gm/m 3 with no horizontal extent co rrection are normally used for this analysis; however, the applicant should substantiate the specific values used, including temperature, which represent the critical conditions for the airpla ne's performance and handling quali ties. Critical flight conditions

should be considered such as we ight and speed for critical angl e of attack, a nd airspeed and altitude for maximum water catch. For exampl e, 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 des cent, approach) to establish the most critical simulated ice shapes to be used during dry air flight tests.AC 23.1419-2E

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### Part 23 SLD ARC REPORT
APPENDIX D – RECOMMENDED RE VISION TO AC 23.1419-2D

c. Airframe.

(1) Structural Analyses.

(a) The structural analyses should include analyses which establ ish that critical ice build-ups on antennas, masts, and other compone nts 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 struct ural analyses; however similarity to previous approved designs is a common method of compliance.

(b) Determine that the temperature gradie nt produced on heated windshields does not adversely affect windshi eld structural integrity.

(2) Flutter Analyses. AC 23.629-1B, “Means of Compliance with Title 14 CFR, Part 23, §23.629, Flutter,” provides guidance for show ing compliance with §23.629. Aeroelastic stability analyses should use the mass distri butions 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 include s any accretions that could develop on control surfaces. The analyses need not consider the aerodynamic effect s 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 in spection, or visually observed from the ground. Part 23 airplanes ma y operate into airports without any ground equipment. For these airplanes, the design shoul d incorporate provisions to allow the flightcrew close access to the wing upper surf ace to facilitate a pre-take off contamination inspection. Recessed steps and handles in the fuselage, in pr oximity to the wing leading edge, would be one example.

d. Power Sources.

(1) Power Source Analysis. The applicants should evalua te the power sources in their ice protection system design. Elec trical, 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 th e ice protection system, plus a ll other essential loads throughout the airplane flight envelope under conditions requiring operati on 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. Tw o 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

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APPENDIX D – RECOMMENDED RE VISION TO AC 23.1419-2D

(a) Two-Engine Airplanes require two sources in a ccordance with § 23.1309(c). All power sources that affect engine or engine ice protection systems for multi-engine airplanes must comply with the engine is olation requirements of § 23.903(c).

(b) Single-Engine Airplanes . Section 23.1309(a) require s that the ice protection system be designed to minimize hazards to the ai rplane in the event of a probable malfunction or

failure. Failure condition clas sifications of “major”, “haz ardous” or “catastrophic” are considered hazards. Complete loss of the airfra me 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 tw o sources of electrical power. This is also consistent with past project sp ecific 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 so urce system is planned.

(c) Load Shedding. Determine if load sheddi ng can be accomplished after a partial failure condition. If app licable, a load shedding sequence should be provided so the pilot may assure that adequate power is available to the ice protection equipm ent 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 Direct ion 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 a nd information for an acceptable means, but not the only means, for showing co mpliance with the requir ements of § 23.1309(a) and (b) (amendment 23-49) for equipment, syst ems, and installations in 14 CFR, part 23 airplanes. The regulatory requirements ar e in § 23.1309. Substant iation of the hazard classification of ice protecti on system failure conditions is typically accomplished through analyses and/or testing. It has been standa rd industry practice to assign a probability of encountering part 25, Appendix C icing conditions of “one” for an airplane ce rtificated for flight in icing.

(1) During the analyses, each identifiable failu re 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

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(a) Those that allow an ice shap e to accrete in size greater than design levels , to accrete asymmetrically, or accrete in ar eas 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 a ny 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 experi ence 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 ex it icing conditions would not be acceptable after any failure

condition that would become catas trophic within the av erage exposure time it takes to exit icing

conditions.

(3) Power Source Failure. Assure that no probable fa ilure or malfunction of any power source (electrical, fluid, bl eed 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 appropria te corrective action in accordance with § 23.1309(b)(3).

(a) The requirement for warning informa tion in § 23.1309(b)(3) is dependent on the severity of the failure, not depend ent 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 norma lly. Annunciation would not be required for obvious, inherent failures, such as fa ilure of a fluid windshield system.

1. Pneumatic deicing boots should be sh own to operate at the pressure
threshold of the annunciation.

2. Annunciation when the boots are receiv ing adequate pressure has been used in previous certifications . For boots that cycle automati cally, annunciation lights may be provided when the boots are not r eceiving adequate pressure when commanded, in lieu of lights that illuminate during each inflation cycle. Th is 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

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APPENDIX D – RECOMMENDED RE VISION 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 overloa d 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 e ssential circuits and should be provided sepa rate protection).

(c) Ice protection monitor and warning circuits should be considered separate from control circuits and each should pr ovide 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 prot ection system is not acceptable.

(6) Windshield Heat Systems. . For detect and exit aircraft, failures of the windshield system need not be considered in co mbination 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 cr eate a potential danger of fire.

(7) Appendix O Icing Conditions.

(a) Airplanes Certificated to Opera te 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 fli ght 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 proba bility should not be reduced based on phase of flight.

3. Flight testing of failure ice shap es 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

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1. It is not necessary to conduct system safety assessments for flight in the icing conditions defined in appe ndix 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 th e 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 conditi ons while the ice protection system is
activated is hazardous , in accordance with AC 23.1309-1D, pr ovided 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 bei ng considered for certification.

2. If an aircraft is not similar to a previ ous design, an assessment of the hazard classification may require more analysis or te sting. 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 sh apes could be evaluated with wind tunnel testing or, potentiall y, 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 avai lable to reduce the ha zard classification.

3. Visual Cues. Typical system safety analyses do not address the probability of crew actions, such as observi ng a visual cue before performing a specified action. As advised in AC 23.1309-1D, quantitative assess ments of crew errors are not considered feas ible. When

visual cues are to be the method for detecti ng Appendix O conditions and determining when to exit them, the applicant should asse ss the appropriateness and reasona bleness of the specific cues (see section 15 of this AC for additional guidance).

f. Similarity Analyses.

(1) In the case of certification based on similari ties to other type ce rtificated airplanes previously approved for flight in icing conditions, the applican t should specify the reference airplane model and the component to which the refe rence applies. Specific similarities should be shown for physical, functional, thermodynamic, pneumatic, aerodynamic, and environmental areas. Analyses should be conducted to show th at the component installation and operation is equivalent to the previous ly approved installation.AC 23.1419-2E

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APPENDIX D – RECOMMENDED RE VISION TO AC 23.1419-2D

(2) Similarity requires an evaluation of both th e 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. Similar ity 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 in stallation to be certificated; and

(b) The previously certificated system a nd installation have no unresolved icing related service history problems.

(3) FAA Order 8110.4C should be consulted rega rding the use of pr eviously 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 accordan ce with § 23.1093. See AC 23-16C for more
information.

h. Propeller Ice Protection.

(1) An analysis should be provided for pa rt 25, Appendix C icing conditions that:

(a) Substantiates the chordwise and spanwise ice protection coverage

(b) Substantiates the ice protection sy stem power density or fluid rate

(c) Calculates intercycle ice accretions and resulting efficiency losses.

(2) See AC 20-73A for additional gui dance on propeller analysis.

i. Pitot Probe Ice Protection. Section 23.1323(d)(1) requires the airspeed indicating system on aircraft certificated for flight in ici ng 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 cer tificated 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 upstr eam 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 accordan ce with 23.1420(a)(1), (a)(2) or (a)(3).AC 23.1419-2E

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(2) TSO Authorizations. Compliance with the techni cal standard order (TSO) qualification standard for electrically heated pito t 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 Automotiv e Engineers (SAE) Aeronautical Standard AS8006 and supplements the icing requirements with spec ific part 25, Appendix C icing conditions and specific liquid water content tests from Br itish Specification (BS) 2G.135 “Specification for Electrically-Heated pitot and Pitot-Static Pressu re Heads.” However it does not contain tests for Appendix O icing conditions. The applicant is responsib le 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 ma y 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. Recen t cloud characterization research has indicated that appr oximately 40 percent of icing c ondition events consist of liquid water drops and ice crystals (mixed phase ic ing conditions). Also, glaciated atmospheric conditions, which consist solely of ice crystals , are encountered during aircraft operations. The operating rules do not prohibit operations in mixe d 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 opera tion at high altitude and high airspeed. Pitot tubes are mounted such that they typically are high efficiency collectors of ice crystals. Encountering high conc entrations 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 substan tial 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 sa fe flight and landing of the airp lane.” Potential examples of this include fly-by-wire ai rcraft or aircraft with airspeed-depe ndant control schedu les. 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 cr ystal conditions define d by Part 33, Appendix D.

(b) British Specification 2G.135, “Specifica tion for Electrically-Heated Pitot
and Pitot-Static Pressure Heads.” Some pitot tube manufacturer s 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, wi th simulated mixed-phase and glaciated icing, isAC 23.1419-2E

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an acceptable way to demonstrate complian ce 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 hi gh probability of occurrence for mixed phase icing conditions. There are no acc epted standard data for the pr obability of mixed phase icing conditions, or for the probability of total water content levels w ithin such conditions. However,
the total water content of such conditions is a di stributed probability similar to Appendix C. The most probable mixed phase icing co nditions are at relatively low total water contents, with the highest total water contents bei ng least probable. In addition, th e 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, complia nce with Appendix C icing conditions should be shown over the duration of the emergency. Fo r 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 draina ge should be evaluated as
installed on the aircraft. Mete orological conditions that may need to be considered include flight through drizzle or rain prior to cold soaking the aircra ft. 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 sw itched OFF during takeoff or in flight if the potential for ici ng conditions exist. The indica tion may be presented using the electronic flight instrument system, crew alerti ng 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 st atus and indications to the fli ght crew. When the pitot heat system is commanded to the OFF state by the flig ht crew and the potentia l 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 thres hold 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 inst alled for the angle of attack system mustAC 23.1419-2E

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have a means to prevent malfunction from icing conditions. This include s any sensor (such as
lift detector or lift tran sducer) that is used in the stall warning system s. Section 23.1324 requires a heated angle-of-attack system sensor or equi valent means to prevent malfunction due to icing
conditions.

(1) Icing Approval. For aircraft approved for flight in to icing, the angle of attack and stall warning ice protection must be designe d 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 a ttack sensors are not likely to be susceptible to ice crystals. A qualitative analys is based on the service hi story on vane angle-ofattack sensors is an accept able 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 locat ion that may affect the sensor's operation.

(4) TSO Authorizations. Compliance to the TSO qualification standard for stall warning instruments (TSO-C54) is not sufficien t 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-ici ng capability, but only temperatur e and airspeed are specified. The precipitation test conditions of AS403A in clude 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 appropria te icing conditions. If this proof of compliance is not obtained in flight tests, anal ysis and/or icing tunnel test data should be
submitted.

(5) Water Contamination. Consideration should be give n for the impingement or runback of water that may freeze within sensing devi ces that require the free movement of components as part of their sensing functionality. Meteorological co nditions 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 icingAC 23.1419-2E

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conditions. For aircraft certified for flight into known icing, the app licable icing conditions are defined by Part 25, Appendix C and the applicable portio ns of Part 25, Appendix O (in accordance with 23.1420(a)). Mixed phase icing and ice crystals have not been shown to cause i ssues 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 heat ed, a thermal evaluation should be conducted to demonstrate that the ice protection is adequate. Cons ideration 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 depr essant fluid systems have been successfully certificated on part 23 airplanes. However, th is 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 system s in DOT/FAA/CT-TN 86/11. Certification highlights from this publication are repeated below.

(1) Analyses. The two critical analyses required ar e the fluid flow rate required and an evaluation of the operational a ngles 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 provid ed can be effectively read.

(b) If it is desired that the airplane be di spatched 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 critic al continuous maximum icing conditions, correctin g for cloud horizontal content.AC 23.1419-2E

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2. 45 minutes based on the flow rate required in critic al continuous maximum icing conditions, with no co rrection 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 reser voir, 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 th e protection required by § 23.853(d) (prior to amendment 23-34) or § 23.853(e) (after amendm ent 23-34). An accessible shutoff should be provided in systems usi ng flammable fluids.

(c) The effect of fluid ingestion into engi nes, 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 contam ination do not occur, or are prevented through inspect ion or other measures

(d) The effect of fluid compatibility with electrical contacts and with airframe components, particularly composite materials, sh ould be evaluated. The applicant should verify
that adverse reactions such as corrosion or c ontamination do not occur, or are prevented through inspection or other measures (for example, if et hylene glycol is a component fluid, then silver and silver-plated electrica l switch contacts and terminals shoul d 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 per cent mono-ethylene glycol, which is considered extremely toxic.

(f) Another freezing point de pressant fluid, TKS80, is available. Icing tunnel
tests of TKS80 and AL5 fluids have shown that they perform differentl y. 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 ta nk cap should be distinguishable from other caps such as fuel and a placard stating a pproved 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 windshie ld or propellers are protected with a freezing point depressant system. On ma ny of the approved inst allations the windshield system is turned off just prior to landing.AC 23.1419-2E

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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 sta ll warning is on the icing schedule.

n. Windshield Heat Systems For certification in the icing c onditions specified in Appendix O, the time increment for the

windshield should be consistent with the a pproved portions per 23.1420(a)(2) or (a)(3). Acceptable methods of compliance include analysis validated by na tural 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 expecte d. The primary purposes for flight testing an airplane equipped for flight in ic ing conditions is to evaluate su ch degradation, determining that the flying qualities remain adequate, and that pe rformance levels are accep table for this flight environment. For airplanes w ith a certification basis of 23- 43 or higher, § 23.1419(a) requires that an airplane comply with the performance, stability, controllabili ty and maneuverability regulations of part 23, Subpart B. Flight testing in measured, na tural icing conditions is required by § 23.1419(b) unless similarity is used as th e method of compliance. In addition, unless similarity can be used, § 23.1419(b) requires at least tunnel testi ng, dry air testing, or airborne tanker testing.

a. Flight tests for a typical pa rt 23 airplane icing certifica tion are generally conducted in three stages:

(1) Initial Dry Air Tests With Ice Protect ion Equipment Installed And Operating. Initial dry air tests are usually the first steps c onducted to extend the basi c airplane certification to evaluate the airplane with th e ice protection system installed and operating. The initial dry air tests are conducted to verify that the ice protectio n 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 bl eed demands on the engine s and other installed
systems.

(2) Dry Air Tests With Predicted Simulated Ice Shapes Installed. Dry air tests with predicted, simulated critical ice shapes installe d are usually the second step for certification for flight in icing. Airplane performance and ha ndling characteristics are evaluated with these simulated ice shapes.AC 23.1419-2E

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(3) Flight Tests in Icing Conditions. Flight tests in icing conditions, which may include artificial icing tests such as flight behind an airborne ic ing tanker aircraft, are normally employed to demonstrate that the ice protection system performs under flight conditions as the analysis or ground test indicated. These demons trations 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 ve rify the airplane's ability to safely operate throughout that icing envelope.

b. Flight Test Safety. FAA Order 4040.26A “Aircraft Certific ation 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 accr etions, are considered high risk. Many applicants have equipped their ice shape flight te st airplane with a stall/spin chute.

12. Flight Tests. The following sections cover the major f light 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, so me 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 rate s and flow patterns on liqui d 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 th e certification requirements when all ice protection system components are installed and functioni ng. 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 ill ustrate typical flight test prac tices. Other types of equipment

should be evaluated as thei r 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 al titude band of part 25, Appendix C—Mean Sea Level (MSL) to 22,000 feet above MSL—unless perfor mance constraints or aircraft limitations unrelated to the ice protection system in the AFM restrict the airpla ne 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 appropria te speed and temperature (if any) limitation on

activation of boots should be included in the AFM.AC 23.1419-2E

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(c) Effect of Inflated Boots. The operation of the boot s (inflation) should have no hazardous effect on airplane performance and hand ling qualities. An example of an unacceptable

hazardous effect is that some boot inflation sequencing schemes re sult 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 sh own by inflating the boots at several speeds in the flight envelope from stall speed to (V NE + V D )/2 or (V MO + V D )/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 pneum atic and boot arrangement should be examined for low points, which may collect water, and consid eration should be given to the installation of water drainage points. Period ic inspection and drainage proc edure 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 eval uation of the effectiveness of water/air separators and/or drainage holes should be accomplished by flying through precipitation followed by a verification of pr oper 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 sugg ested that system current, brush block voltage (between each input brush and the ground brush), a nd 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 dur ing dry air tests. These surface temperature measurements are useful for correlating analyt ically 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 Mi nute (RPM) and propeller cyclic pitch range expected during icing flights. Any significant vi brations 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

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Service difficulty reports have indicated prope ller damage during de-ice/anti-ice system activation during maintenance without the engines running.

(c) Precipitation. The system should be monitore d to confirm proper function in precipitation. There have been designs that allo wed water to reach the electrical brush blocks and prevent their operation.

(3) Electric Windshield Anti-Ice.

(a) Thermal Analysis Validation. Dry air flight test s 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 therma l analyses. Thermal analysis

should substantiate that the surf ace 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 windshie ld, inside and out, may also be needed, particularly with pressurized airplanes.

(b) Cockpit Visibility. An evaluation of the visi bility, 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 visi bility 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 dist ribution over the protected surfaces is achieved.

Colored fluid or colored water with camera docum entation 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 operat ing since drag increases have been documented on previous certification programs.

(c) Temperature. The system should be functiona lly tested at the minimum part 25, Appendix C ambient temperatures.

(d) Windshield. The fluid anti-ice/deice sy stems may be used to protect propellers and windshields, as well as leading edges of airfo ils. The fluid for windshield fluidAC 23.1419-2E

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systems, and for propeller fluid systems forw ard of the windshield, should be tested to

demonstrate that it does not beco me opaque at low temperature.

(e) Cockpit Annunciations. Means of indicating fluid flow rates, quantity remaining, and so forth, should be evaluated to dete rmine that the indicators are plainly visible to the pilot and that the indications pr ovided 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 eval uation 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 th at is made of composite mate rial, a thermal analysis/survey

should be conducted to assure ther e is no engine cowl delaminati on or other structural failure.

(5) Ice Inspection Light(s). The installation should be ev aluated for both in and out of clouds during night flights to dete rmine that adequate illumination exists in the required areas (activation of ice protection systems and/or id entification of severe icing cues), and that excessive glare, reflections or ot her distractions to the flight cr ew do not exist. The evaluation should consider flight both in and out of cl oud, but may be accomplished without flight into actual icing conditions. The Airp lane 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 performan ce 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). Dr y air flight tests with simulated ice shapes installed al so result in a considerable re duction in the amount of flight testing that would otherwise be required to accumula te the test ice shapes, and then evaluate their effects on airplane performance and handli ng characteristics in stable air.

(2) Flight Test Safety. Dry air tests with simulated i ce 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 hybr id), and the most adverse ice conditions (shape or shapes, texture, locati on, and thickness) for the relevant aerodynamic characteristics for the following, as appropriate: pre-activation ice, in tercycle ice, failureAC 23.1419-2E

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conditions, runback ice, and residu al ice. Consideration should also be given to unprotected areas. See paragraph 13b for more inform ation. These predictive methods should be

conservative and should address th e conditions associated with th e 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 operati onal envelope, including climb, crui se, descent, holding pattern, approach, and landing. Ice shapes critical for pe rformance 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 te st 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 ic e detection and annunciation. These delays may

include slow ice detector res ponse at temperatures near free zing (low freezing fraction as discussed in AC 20-73A) and the number of pr obe heat cycles utilized for annunciation or automatic ice protection activation. An applican t should provide a temperature versus response time plot for their installed ice detector and s how that, at temperatures for which runback ice

occurs on critical surfaces that ei ther the response time is less than 60 seconds or runback ice has not yet formed during the respons e time. Runback ice should be evaluated empirically and should be evaluated using the same means of comp liance 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 wa rning margins and mane uvering capability should also be evaluated. Operating speeds, stall wa rning speeds, and AFM performance information should be adjusted, if necessary, to provide a cceptable 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 ar e expected to degrade in icing conditions and should be investigated to determine that the “airplane is capable of operating safely.” For cer tification 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 ma y be used in preparing specific AFM operating procedures and limitations for flight in icing conditions.

(c) Air Data Calibrations. If ice accretion is predicte d to alter the position error of the production air data system (e.g. radome ice accretion), the position error would need to beAC 23.1419-2E

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determined using air data calibration flight test s (i.e. tower fly-by, trai ling 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 ici ng tankers and icing wi nd 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 exampl e, ice detectors) and ice shap es and, in the case of natural icing tests, to confirm the conclusions reached in flight tests conduc ted with simulated ice shapes. Testing should be accomplished at vari ous 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 a nd component parameters, and icing conditions encountered. Analysis should be accomplished to show that the location of the instrumentation will allow measurement of freestream conditions (o r appropriate correction factors). See AC 20- 73A for guidance on measuring the icing conditions. The location of all ex ternal instrumentation installed for icing flight tests, including cameras and visual devices, should be analyzed to verify that ice-shedding haza rds are not introduced.

(2) Documentation of Ice Accretion. Ic e 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 ch ase 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 vi sual dimensional analysis of ice

accretions. Care should be taken since some measuring devices may accrete ice and alter analysis of accretions on a surf ace 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 instru mentation packages may

have an effect on the aircraft handling characteristics, or the ice thickness maybe the significant variable. Comparison of ice thickness and ge neral correlations to prior measured icing conditions may be sufficient fo r some types of testing.

(2) Artificial Icing.

(a) Why Do Artificial Icing Tests? Testing in artificial icing environments such as icing tunnels or behind airbor ne icing tankers represents one way to predict the ice protection capabilities of individual elemen ts of the ice protection equipment. The high liquid water content and large drop size conditio ns of Appendix C are easily simulated and not frequently

encountered in natural ic ing flight tests. Due to the usuall y small dimensions of the artificialAC 23.1419-2E

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icing environment, testing is usually limited to s ections of lifting surfaces, to components having small exposed surfaces such as heated pitot tube s, 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 comp onent 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 inst rumentation 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 i ce 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 mo re information on scaling test parameters.

2

. Conformity. The test article must be conformed. Although parts of the ice protection system may be si mulated, critical system parameters must be conformed. An example would be deicing boot steady state pressu re, 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 pr oduce the required LWC, spray times can be adjusted to provide the equivalent water catch for part 25, A ppendix C cloud lengths. If large ice shapes or runback ice is expected, test ambient temperat ure may have to be adjusted to provide an equivalent freezi ng fraction. Temperatures can change the ice adhesion/shed

characteristics and this should be taken into acco unt 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 featur es, such as stall strips mounted on deicing boots, may not readily shed i ce 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 aerodyn amic degradations due to the re duced scale rela tive to the wing root (on wings incorporating significant taper rati os). 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 sy stems, the outboard sections also represent the extremities of the bleed air system where temperat ure and pressure losses are the greatest, whichAC 23.1419-2E

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can be critical for runback accretions. The dist ribution 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 co nditions. Flight tests in natural icing conditions are necessary to demonstrate the acc eptability of the airplane and ice protection system for flight in icing conditions. AC 20-73A provides additi onal information that would be useful when establishing a natural ici ng 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 stabilizati on in brief exposures. Additiona l exposures may be required to allow extrapolation to the envelope critical c onditions by analysis. Te st 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 anal yses show that the critical ic e protection design points (that is, heat loads, critical shapes, accumulation, and acc umulation 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 de termined to be in general correlation with those found in dry air testing. Refer to Tabl e 3. for performance, stability, control and maneuverability requirements.AC 23.1419-2E

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(aa) Holding. A target accretion thic kness equivalent to the 45- minute duration encounter in Appendix C Cont inuous 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 an alyses and § 33.77 ice slab test results. To minimize flight testing, an appl icant has the op tion 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 pr otection systems with bleed air fr om 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 st all or handling qualities tests should be accomplished in daytime visual meteorol ogical conditions, afte r accreting ice.

5. Performance, Stability, Controllability. See paragraph 13.c.

6

. Ice detection cues or ice detectio n system operation. See paragraph

15 of this AC.AC 23.1419-2E

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APPENDIX D – RECOMMENDED RE VISION 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 ob jectionable 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 pr ovided, 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 e xposure to icing conditions. Ev aluations should confirm that aerodynamic balance surfaces are not subject to ici ng 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 contro l 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 c onditions should be evaluated when showing compliance to § 23.1523. Ice de tection, ice protection system operation and monitoring, and autopilo t operation and monitoring (includi ng 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 accumulati ons in various ways depending upon type, shape, size, and locat ion of these accumulations.

a. Flight Tests

(1) Section 23.1419 at Amendment 23-XX or Later. Airplane performance, controllability, maneuvera bility, 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 ap plicable 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 th e no ice testing (basic aircraft certification). However, as a minimum, stability and cont rollability should be evaluated at minimum holding speed in holding configuration and V REF in all approved approach and landingAC 23.1419-2E

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configurations. It is not require d to test at high airspeeds. In stead, the maximum airspeed defined in the guidance for 23.251 may be used. It is not re quired 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 i ce accretions in terms of handling characteristics and/or performance for each flight phase should be determined. The parameters to be considered are the flight cond itions (e.g., airplane configuration, airspeed, angle of attack. altitude) and the ic ing conditions of part 25, Appendix C (temperature, liquid water content, mean effective drop diameter). Table 2 summarize the ice accreti ons defined in part 23, Appendix TBD, part I. .AC 23.1419-2E

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TABLE 2. ICE ACCRETION DE FINITIONS, 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 hi gh lift devices Commuter Category or Turbojet Airplanes with a takeoff configuration that does not include leading edge high
lift devices

Takeoff Not required. Ice accretio n occurring between liftoff and 400 feet above the takeoff surface, assuming accretion starts at liftoff in the
“takeoff maximum ici ng’ 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/m 3 ;

 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

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TABLE 2. ICE ACCRETION DE FINITIONS, 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 hi gh 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 surf aces, and any ice accretion on the protected surfaces appropriate to normal ice protect ion system operation, during the en route phase, in part 25, Appendix C, continuous or intermittent maximum icing
conditions.

Holding Ice accretion on the unprotected surf aces, and any ice accretion on the protected surfaces appropriate to normal ice prot ection 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 surf aces prior to activa tion 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

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TABLE 2. ICE ACCRETION DE FINITIONS, 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 fr eezing fractions of one is
less than stated time. (4) In low freezing fractions conditi ons, applicant should show that detector will annunciate prior
to ice accretion on critical surfaces. This ma y 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 fo r definition. For airspeeds below 160 KCAS, empirical data should substantiate that de icing systems shed ice at each cycle.

Residual See Appendix 1 of this AC for definition.

Runback See Appendix 1 of this AC for defin ition. This ice type is frequently a byproduct of partially evaporative (running wet) i ce protection systems and thermal deicing systems, but can also occur on mechanical ice protection systems at a small temperature band near freezing. Empiri cal 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 condi tions, 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 hi gh 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 con tinuous maximum cloud of up to 55 nm, correcting liquid water conten t for horizontal extent.

Thin, rough A thin layer of ice that may occu r 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

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TABLE 2. ICE ACCRETION DE FINITIONS, 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. Fo r 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 wh en demonstrating compliance:

(1) The more critical of takeoff ice a nd 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 substantia ted 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 th an 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 determin ed in the various flight phases and flight conditions may be “enveloped” into one critical shape.AC 23.1419-2E

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(b) Shape and Texture of Simulated Ice. The shape and texture of the simulated ice should be developed, and substantia ted by agreed methods. The ice shapes should be agreed to by the FAA prior to ice shape flight testing.

1. Common practices for deve loping 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 artifici al icing cloud (e.g. airborne icing tanker).

2. Natural icing or airborne tanker test ing may show ice sh apes 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 appl ication of any ice a dhesion inhibitor such as ICEX is not permitted for natura l 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 clea ned at the start of a natural ici ng or artificial ic ing test program per recommended maintenance procedures.

(2) Propeller Icing. Deicing boot manufacturer’s analys es show that intercycle ice does exist with propeller deici ng systems and their analyses do not account for ice runback. Propeller icing research (Parag raph 6.b., Reference 7) shows that propeller icing efficiency in icing conditions varies greatly with icing condi tions and deicing system design. The research results support the assumption of a nomi nal thrust penalty shown in Figure 1.

(a) Airplane performance in icing condi tions should include the propeller efficiency losses caused by propeller inte rcycle 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 lo ss at an airplane total temperature of 0 °C, and interpol ate between this temperature and the - 5°C static temperatures in Figure 1.AC 23.1419-2E

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(c) Airplane performance during natural icing flight testing should be quantitatively compared with performan ce during ice shape flight tests. On reciprocating and turbopr op powered airplanes, if there is degradation in performance compared to the ice shape re sults, 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 NumberPropeller 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 ic e shapes representing failures not shown to be extremely improbable should be conducted to validate h azard 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 Ta ble 2 for unprotected surfaces; and

2

. For protected surfaces, one-half the accretion specified for unprotected surfaces (22.5 minutes) if the associated AFM opera ting 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

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3. For failure conditions that are: (a) not annunciated to th e flight crew, or (b) annunciated to the flight crew , but the associated AFM proce dure 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 realis tic exit scenario in lieu of

the 22.5 minutes ice accretion. This failure s cenario should account for the time it takes:

1

. For the system to annunciate the failure (e.g., one de icing 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-deg ree standard rate turn and transiting a 17.4-nautical mile, part 25, Appendix C c ontinuous maximum cloud. Besides the design

standard 17.4 nautical mile hori zontal cloud extent, a cloud extent of 46-nautical miles (adjusted for liquid water content per part 25, Appendix C), which is exp ected for 10 percent of icing encounters, should also be consider ed in the safety analysis. The exit scenario shall include the possibility that the airplane may have to climb 4,000 feet out of ic ing 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 sh ould 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 fli ght 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 exiti ng 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

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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 ro lls, 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 V REF • Level, 40-degree banked turns;

• Bank-to-bank rapid ro lls, 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 ro lls, 30 degrees – 30 degrees at 1.2 V S1 ;

• 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 sta ll 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 ro lls, 30 degrees – 30 degrees at 1.2 V S1 ;

• 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 du ring flight testing in natural icing conditions. Examples areAC 23.1419-2E

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provided in Table 4. Stall spee d 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 e dge 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 maximu m 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 tailp lane 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 a nd 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 a nd landing gear should be tested beginning with zero flaps up to the maximum flap setting to be approved for landing followingAC 23.1419-2E

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an icing encounter. Since increased flap extens ion will increase the pote ntial for ICTS, flight testing should proceed cautiously as the flaps are further extended

.

(bb) Critical weight and CG position (n ormally full forward at light weight).

(cc) Speeds from 1.2 VS 1 or Reference Landing Approach Airspeed (V REF )-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 wi ll not result in exceeding Flaps Extended Speed (V FE ) or Landing Gear Extended Speed (V LE ), as applicable, during the maneuver. The speeds VS 1 and V REF may have to be redefine d with critical ice shapes.

(dd) Power or thrust: flight idle to maximum go-around.

2. Ice Shapes: The applicant specifies th e critical ice case(s) for investigation in terms of locat ion, shape, thickness, and texture, and obtains FAA concurrence for the ice shape(s) to be investigated.

(aa) The critical shape(s) should c ontribute 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 A ngle-of-Attack (AOA) on th e horizontal tail, ice shapes on the wing should be removed. The cri tical ice accretion case( s) should include an allowance for the ice shape accreted during any ti me delays in activati on of the ice protection system associated with ice dete ction or observation systems, inte rcycle and residual ice, runback ice, or the accretion that may be reasonably expected in service.

(cc) It should be noted that ice accret ed with the flaps retracted might
result in a more critical conditi on than ice accreted with the fl aps extended. Ice accretion shape and thickness need not be greate r than that resulting from expo sure to the icing conditions defined in Appendix C to Part 25 or the 45-minut e 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 eval uated with pre-ac tivation ice. In many cases the pre-activation ice may be si mulated by sandpaper ice. A thin ice layer simulated by sandpaper has been found to be criti cal on some aircraft and should be evaluated along with critical ice accretions on airplanes with a reversible longi tudinal control system.

(ff) Failure conditions of the ice pr otection system should also be addressed. Maximum landing flap ex tension with a failed ice prot ection system may be defined at an intermediate position. This should b ecome an airplane limitation for a failure.AC 23.1419-2E

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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 hor izontal stabilizer. Before the maneuver, the test pilot determines in itial entry speeds and pitc h attitudes to achieve the target load factor and target airspeed as the airplane pi tches through approximately level flight. (aa) The objective of the pushover mane uver 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. Begi n the maneuver with the airplane trimmed or trimmed as nearly as possible at the test power , configuration, and te st (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 requi red control force or force reversal. Continue the test points incrementally by increasing the amplitude of forward c ontrol 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 longit udinal force required. During the pitch down maneuver, the test pilot should not change the ra te of longitudinal cont rol 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 procedur es 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 fo rce 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 demonstrat e suitable controllability and maneuverability throughout the maneuver, includ ing recovery, with no tendency to diverge in pitch or other indications of a st alled 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 di rection disqualifies that test point.AC 23.1419-2E

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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 cont rollability and maneuvera bility throughout the maneuver with no tendency to diverge in pitch



(c) Other Parameters that May I ndicate a Stalled Tailplane. If the test aircraft is instrumented, the following pa rameters may indicate a stalled tailplane:



  The relationship of pitch rate ( q ) versus elevator deflection ( δ E ) 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 app ears as reduced elevator effectiveness, C m δ E

.

  If the elevator stalls, th e aircraft will continue toward zero-g regardless of the force applied by the pilot to return to on e-g flight. This may be determined by examining the slope of the plot of vertical load factor ( N

z ) vs. pitch control force (F ELEVATOR ) 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 de monstrate the tufts have no effect on tail stall.

(4) Compliance by Analysis . For turbojet powered ai rplanes with irreversible, powered pitch control systems, the flight tests described in paragraph 13 (e) (2) (b) may not be necessary. However, a detailed analys is, 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, confi guration 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 cer tification basis.

(b) If sandpaper ice results in ICTS sus ceptibility 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

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f. Pneumatic Deicer Boots . Section 23.1419(d) cont ains 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 recogniti on of emergency and abnor mal operating conditions, the AFM procedures are effective, recommended airs peeds are safe and that the airplane can be landed safely. These demonstrations should be conducted with antic ipated 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 minimu m 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

V REF • 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

V REF • Approach and landing demonstration

If the autopilot is intended to be used with th e 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

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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 pa rt 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 de tails on the Appendix C icing envelopes. Appendix O was developed to provide a represen tative icing environment for s upercooled large drops (SLD), which are not included in Appendix C and which include freezing drizzl e and freezing rain
conditions. An FAA detailed re port on the development of Appe ndix O is available from the FAA Technical Center (reference repo rt DOT/FAA/AR-09/10, dated March 2009)

(1) Appendix O defines freezing drizzle and fr eezing rain environments by using four spectra of drop sizes with asso ciated 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 sm aller drops with diameters less than 100 μm.

(b) Freezing drizzle with a MVD greater th an 40 microns. In addition to freezing drizzle drops, this environment also contains smaller drops, with di ameters 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 usi ng Appendix C are that for Appendix O, the applicant must now——

(a) Consider four icing conditions rather th an 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 Appe ndix O icing conditions. Following detection, the airplane must be capable of operating safely while exiting all icing conditions.AC 23.1419-2E

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Certification for 23.1420(a)(1)) re quires a means of alerting flightcrews when Appendix O conditions are encountered (§ 23.1420(a)(1)).

(2) § 23.1420(a)(2). If the applicant seek s 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, fo llowing 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 por tion 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 upo n 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 wh ich the aircraft is not approved. A 2009 review of engineering tool capabilitie s found that current technology does not support distinguishing between freezing drizzle and freezing rain in fl ight. Therefore certific ation for a portion of Appendix O will be challenging and will require clos e coordination with certifying authorities. Certification for a portion of Appendix O allows latitude for certifi cation with a range of techniques and technology that ma y be available in the future.

(b) However, initial certificat ions could be restricted to operation in Appendix O conditions by phase of flight. However, if certif ication is sought for ta keoff/landing in freezing drizzle based solely on weather re porting provided by the airport, ce rtification 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 th e applicant seek s certification for all of the icing conditions described in A ppendix 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 fli ght in icing without any specific ai rplane 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 superc ooled large droplet conditions:

(a) Ice shapes aft of protect ed areas of lifting surfaces. Appendix O icing conditions may result in a ridge of ice or ice roughness af t 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 aircra ft upset. Aircraft may also incur reduced maximum lift and stall at lower angles of att ack, independent of the flight control system. Appendix O ice buildups can result in increases in stall speeds and pot entially a lter stall
characteristics.AC 23.1419-2E

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(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 unprotect ed airframe regions. Areas of the airframe which do not accrete ice under Appendix C conditi ons 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 ai r 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 conditio ns, 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 lowe r wing surface, for example). Ice accretions may be rough and cause larg e local drag increases.

(e) Engine considerations. I ce accumulation on the airframe and on air induction system components resulting from Appe ndix O icing conditions s hould be analyzed for potential ingestion of ice by the engine (rela tive 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 th ey are in Appendix O icing condi tions and have taken action to begin exiting from all icing conditions. The time th at 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 l onger for a detection means rely ing on the flightcrew seeing and recognizing a visual icing cue than it is for an ice detection sy stem 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 demonstr ated 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 fo r freezing rain would be equal or smaller.,AC 23.1419-2E

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(b) Aircraft Certified to Detect a nd 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 ap proved, 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 accretion 1

En Route No accretion

Holding Exposure sequence:

(1) Either Appendix C holding ice or Appendix O holding ice for which the airplane is approve d, whichever is applicable,

(2) Pre-detection ice,

(3) Accretion from one standard cl oud horizontal extent (17.4 nautical miles) in Appendix O conditions for which the airplane is not approved, followed by

(4) Accretion from one standard cl oud horizontal extent (17.4 nautical miles) in Appendix C conti nuous 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

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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 de tect-and-exit ice and the combination
of:

(1) Ice accreted during a descent in the cruise configuration from the
maximum vertical extent of th e 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 accretion 1

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 thos e in which the airplane is certified to operate (min imum of two minutes).

Failures of the Ice Protection System No accretionAC 23.1419-2E

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(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 requ irements 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 fe et above the takeoff surface assuming ice accretion starts at lift-off. No ice accretion prior to lift-off if Type II, III or T ype 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 configurat ion 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 cl imb through 3,500 feet in freezing
rain.

En Route Ice accreted during the en-route phas e of flight.

Holding Ice accreted during a hold with no reduction for horizontal cloud extent (i.e., the hold is conducted enti rely 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 maneuv ering 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

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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 holdi ng 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 protec tion system, plus the time for the ice protection system to pe rform its intended function.

Pre-detection Ice
Accretion Ice accreted during the time for th e 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 com putations or both. Current CFD programs do not provide roughness information. Roughness levels a nd 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, su ch 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

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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 ici ng. Smooth and spherical elements should not be used because they may result in non-conservative aerodynamic results.

2. For computed ice shapes, the roughness si mulation should be extended aft to the limits of predicted accretion (where the ice accretion th ickness 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 configur ation changes), angles of attack, power or thrust settings, etc. for the flight phases and icing conditi ons 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

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3. In determination of cri tical 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 accre tions (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 identifie d 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 a dverse effect on sta ll angle of attack and handling characteristics may be used fo r compliance with the airplane performance requirements if any difference in performa nce 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 ici ng 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 intercyc le ice, unless data substantiate s another amount. The applicant can assume there is zero efficiency loss at an ai rplane total temperature of 0 °C, and interpolate between this temperature and the static temperatures in Figure 2.AC 23.1419-2E

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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 NumberPropeller Thrust Loss, %

-5 C OAT

-10 C OAT and colder

Figure 2 - SLD Prope ller Thurst Loss

(b) Testing, analyses or simila rity should be conducted to verify the deice system minimizes intercycle and runback ice accretions.

d. Engineering Tools. Appendix 7 of this AC provides gu idance 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 complia nt with critical SLD ice shapes.

(1) Detect and Exit SLD Conditions. Appendix 8 contains an example flight test program to show comp liance 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 certif ied. 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

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(a) Takeoff. Appendix 9 contains an exam ple 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 th e airplane operate safely in the SLD icing conditions defined in Part 25, Appendix O.

(1) Flight testing in measured, natura l 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 enc ounters with Appendix O
conditions.

(c) For certification to 23.1420( a)(3), flight test encounter s should include at least one freezing drizzle and one freezing rain encounter.

(2) For airplanes certificated to detect Appendix O icing cond itions and safely exit all icing conditions, flight testing in measure d, natural Appendix O conditions should not be required to show complia nce to § 23.1420(a)(1) if:

(a) Design analyses show that the critic al 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 wh ere the capability exists, icing tunnel tests or icing tanker tests, and analytical code s are used to determine critical ice shapes on lifting surfaces.

1. The simulated, critical ice shapes ar e flight tested to show compliance with applicable Subpart B regulations.

(c) Appendix O detection method(s) are cer tified as describe d 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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15. Ice and Exceedance Icing Conditions Detection. Sections 23.1419(e) specifies requirements regarding activation of the IPS. Th ese 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 a pplicable. 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 a nd an advisory ice detection system, or AFM procedures to activate the IPS ba sed on visible moisture and temp erature. 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 procedur es or automatically activate the IPS before an unsafe accumulation of ice on the airframe, engine co mponents, 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 wi thin all of the required icing conditions and airplane operating en velope. If the ice detector ca nnot detect ice at low freezing
fractions and ice accretes on the ai rplane in such icing conditions , the applicant should show that the airplane can be operated safely with the ice accretions. If sa fe operation cannot be substantiated, installatio n of an icing conditions detector may be required. Approval of the primary ice detector should incl ude flight tests in measured na tural 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 de tection 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 re ferenced or monitored surfaces, should advise the flightcrew to initiate operation of the IPS us ing AFM procedures. An advisory system is not the prime means used to determine if the IPS shou ld be activated. The AFM must state the flight crew has primary responsibility for detecting ic ing 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, limita tions, and installation.

(3) Certification of an ice detection system

(a) Certification plan. The applicant should present an icing certification plan to the cognizant aircraft certifi cation office. This plan should include the method selected for demonstrating the ice detector sy stem’s compliance with §§ 23.1301, 23.1309, 23.1419, 23.1420, and all other applicable sections. Advisory Ci rcular 20-73 A, Appendix K, provides guidance on certification of ice detector systems. That a ppendix provides guidance regarding ice detection response times as the freezing frac tion drops below 1. That guidan ce is equally applicable to advisory and primary ice detection systems.AC 23.1419-2E

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(b) Performance of the ice det ector system when installed. In addition to the guidance in Advisory Circular 20-73 A, Appendix K, the follo wing 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 applicab le portion of Append ix 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 airp lane. This could includ e icing tunnel and icing
tanker tests to evaluate ice dete ctor performance. The appli cant may use droplet impingement analysis to determine that the ice detector f unctions properly over the dr oplet range of Appendix C and the applicable portions of Appendix O when validated through natura l 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 wher e 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 lim itations 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 detec tion system to detect these conditions.

5. The detector and its installati on should minimize nuisance warnings.

6. SAE AS5498 "Minimum Operationa l Performance Specification for Inflight Icing Detection System s" provides a standard and qua lification considerations for inflight ice detection systems.

(c) Ice detector system safety considerations

. The unannunciated failure of a primary ice detection system is assume d 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 se vere hazard category. Ic e detector reliability, hardware and software criticality requirements, for both primary and advisory systems, shall be
consistent with the hazard classification for i ce detectors resulting from a 1309 hazard analysis. If visual cues are the primary m eans of ice detection, the pilots retain responsibility to monitor and detect ice accretions when an advisory ice detection system is in stalled. However, the natural tendency of flightcrews to become accustom ed to using the advisory ice detection system elevates the importance of the detector and increa ses the need to make flightcrews aware of an advisory ice detection system fa ilure. Therefore, an undetected failure of the advisory iceAC 23.1419-2E

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detector should be considered a major hazard.

(4) Visual cues. Visual cues can either be dire ct observation of ice accretions on the airplane’s protected surfaces or observation of ice accretions on re ference surfaces.

(a) The first indications of any of the fo llowing are examples of what could be
used as visual cues.

1. Accretions forming on the windshiel d 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 protect ed surfaces cannot be obs erved, 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 th at can be periodically de-iced to allow the flightcrew to determine if the ai rframe 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 with in the flightcrew’s vision scan area while seated and performing their normal duties at various airplane attitudes.

2. Visual cues should be visible duri ng 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 ai rplane, 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 accretio ns to assess visibility in and out of cloud. Methods used to
substantiate visual cues shoul d be agreed to with appropria te certification authorities..AC 23.1419-2E

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(e) Airplane Fli ght Manual (AFM). The limitations section of the AFM must specify that the IPS must be operated when ice accretion is detected a nywhere on the airplane
and also must describe the visual cues verified in certification.

(5) Temperature cue. The temperature cue used in comb ination 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 shoul d 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 temperatur e. This would ease the flight crew 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 displa y of static air temperature or a placard can be provided showing corrections for temperature vs. air speed to the ne arest degree Centigrade in the region of interest (that is, around 0oC).

(b) Airplane Fli ght Manual (AFM). The limitations section of the AFM should identify the specific static or total air temperat ure 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 operate d during certain phases of flight, the applicant should consider ice accretions that form during thes e phases and establish that the airplane is able to safely operate in the c ontinuous maximum and intermittent maximum icing conditions of Appendix C and the ap plicable portions of Appendix O.

c. Compliance With § 23.1419(f).

(1) This paragraph of § 23.1419 requires that after the initial activ ation 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 provid ed 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

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(a) A system that senses ice accretion on a detector and correlates it to ice accretion on a protected surface. This system th en 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 accreti ons 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 discusse d 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 worklo ad and human factors considerations, a timed system without an ice sens ing capability should not be used to meet this requirement. The ice shedding effectiveness of th e selected means for cycling the ice protection system should be evaluated during te sting in natural icing conditions.

d. Compliance With § 23.1403. Compliance with §23.1403 applies to aircraft certified for flight into icing conditions. The requireme nt is intended to address any visual ice accumulation requirements such as activating ic e protection systems (§23.1419) or determining whether an exit from severe icing conditions (§23.1420( a)(1) or (a)(2)) is requi red. If the aircraft operating procedures do not depe nd on crew observation of ice acc retions, 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 necessa ry, 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 Appe ndix 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 dem onstrated 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 aircra ft operational conditions and in Appendix O icing conditions. The applicant may us e analysis to determine that the ice detector is located properly for functioning throughout the droplet range of Appendix O conditions whenAC 23.1419-2E

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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 c onditions conducive to Appendix O ice accumulation may make natural icin g flight tests a difficult mean s of demonstrating that the system functions in conditions exceeding Appendix C. The applicant may use flight tests of the airplane under simulated icing c onditions (icing tanker). The a pplicant may also use icing wind tunnel tests of a representative airfoil section and i ce 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 pr essure fluctuations in the flow field from contamination over the wing surface. This technology does exist, but full development is necessary before incorporat ing 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 observat ion of ice accretions on reference surfaces. Responding to a cue should not require the flightcr ew 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 spin ners aft of a re ference point,

 Accretions forming on radomes aft of a reference point, and/or

 Accretions forming aft of protected surfaces.

(a) Verification. See guidance fo r Appendix C conditions in paragraph 15.a.(4).

(b) Time to detect condi tions 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 su rface feature that it is ad hered to), the distance from the pilots (for example, windshield vs. en gine vs. wingtip), and th e 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 accumulati on of enough ice to be reliably identified by either pilot in all atmosp heric 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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2. For a visual reference located on a wing, wing mounted engine, or wing tip
– 5 minutes.

(c) Validation. Visual cues should be validat ed 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 vi sual cues on the window s of the cockpit, a combination of appendix C natural icing encount ers validating 3D ice accretion or impingement analysis will satisfy the two method approach de scribed 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 re ference 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 characterist ics of the leading edge of the airfoil. Models designed for testing over a wide range of AOAs may have limi ted 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 im pingement for visual cues, and the CFD codes
can then be used to further validate ov er 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 cu es of 14 CRF Part 25 Appendix O conditions, an acceptable method would be to compare the anal ytical 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 te sting 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 instrume ntation should be approp riate for the conditions (e.g. if validating for large drops, the instrument ation should be capable of measuring large drops).

16. Ice Shedding. Ice shed from forward airplane st ructure and components could result in damage or erode engine or pow erplant 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 subj ect 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 fuse lage and from the wings may cause significant propeller damage. Control surfac es such as elevators, ailerons, flaps, and spoilers are also subject to damage.AC 23.1419-2E

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Current trajectory and impingement analysis may not adequately predict such damage. Unpredicted ice shedding paths from forwar d 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 trajectorie s and damage to the airplane. The airplane should be exposed to an icing c ondition of magnitude a nd duration sufficient to create the expected worst-case ice accretion, including the 45-m inute hold, and then flown into warmer temperatures to facilitate shedding. Flig ht test evaluation should also account for the critical, predicted trajectories in terms of nor mal operational angle of attack and sideslip. Trajectory and impingement analysis may be us ed 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 pict ures are excellent for documenting ice shedding trajectories and impingements, while still photog raphy may be used to document the extent of damage. Any damage should be evaluated for acceptability.

If flight tests are not conducte d, an impact damage analysis s hould consider the worst-case ice shed event. The impact damage analysis may ta ke 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 i ce sheds to break up to 1⁄2 of the original slab length. Ice that is not slab-shaped (e.g. doubl e-horn shapes or radome “caps”) should not be assumed to break up during the shed event, howev er 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 wi ngs and airframe can have an effect on airplane characteristics and autopilot perfor mance. Autopilot operations may mask the onset of an icing condition/configuration that would pr esent 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 as ymmetry), altitudes, and deceleration device configurations. However, if the autopilot pe rformance 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 autopilo t 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 ai rcraft handling qualities. Critical ice shapes must be chosen with the particular test purpose in mind. Tests might have to be performed withAC 23.1419-2E

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multiple configurations of ice shapes which address possible handling qualities/performance and/or control surface hinge moment issues. The applicant will need to di scuss this topic with the administrator prior to final approval. If ne cessary, 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 e dge ice accretions could affect control power and control hinge moments resulting in incorrect autopilot gains. These evaluations s hould 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 ici ng conditions to check for unusual trimming and potential for ice to accrete in cont rol surface gaps and jam controls.

(2) In case flight in any portion of A ppendix 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 te sts should be accomplished.

(3) De-icing. If the airplane is conf igured with a de-icing system, the autopilot should demonstrate satisfactory performanc e 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 accepta ble test program for qualification of the autopilot in Appendix C and applicable Ap pendix O in addition to th e tests in natural icing
conditions: Note: The autopilot should be evaluated duri ng the course of the cer tification program with ice shapes. Appendix O ice shapes may degr ade 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 append ix O (detect and exit and approved portions), conduct the following maneuver: autopilot maximu m angle of bank turn in one direction andAC 23.1419-2E

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then rapid reversal of angle of bank in the ot her direction. Autopilot should smoothly roll into and out of turns without larg e overshoots in bank angle or during roll out on headings.

(2) Approach - If the auto pilot has the ability to fly a coupled instrument approach and/or go-around, conduct the following maneuver s 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 thes e 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 Ta ble 10, trim at the specified speeds and conduct the following maneuvers:

1. S et 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

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(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 on e direction. If the auto pilot were to disengage while holding this lateral trim, the result would be that the airplane could undergo a rolling moment that could possibly take th e pilot by surprise. Therefore, an indication will be required to permit the crew to manually disengage the autopi lot and take control prior to any automatic autopilot disengagement. Unusual control posit ion or bank angle may be shown to be an acceptable indication.

18. Placarding and AFM. This AC provides guidance on airp lanes 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 fo r 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 w ith § 23.1541. Examples of such placards are:

(1) Kinds of opera tion not approved

(a) If compliance to § 23.1419 not shown, “F light 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 Seve re Icing Conditions Prohibited. ”

(2) Fluid filler

 inlets for fluid freezing point de pressants 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 protec tion system while in icing conditions or prior to encountering icing conditions. The Limitations section of th e 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 opera ting procedures section of this manual. Where specific operational speeds and performance in formation have been established for such conditions, this information must be use d.” 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 contai n a statement similar to “This airplane is approved for flight in icing condi tions as defined in part 25, Appe ndix C.” For these airplanes,AC 23.1419-2E

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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 stat ement “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 ex tended 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-ic ing flight for compliance to § 23.1523, it will be required for flight in icing conditions based on operational requirements. Sim ilarly, if an autopilot equipped airplane is approved for any por tion or phase of flight in A ppendix O conditions, the autopilot will be required to operate in those Appendix O conditions.

(a) Autopilot operation should be prohib ited if any of the following are experienced in icing conditions:

1. Mistrim indication or autop ilot alert prior to disconnect

2. Unusual control force or control deflection, or unusua lly large control forces to move flight controls when th e autopilot is disconn ected 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 prohibit ed if any of the following conditions in icing f light are experienced:

1. Severe icing;

2. Freezing drizzle or freezing rain

(4) Performance. Performance limitations should be pres ented for flight in icing that reflect any effects on lift, dr ag, 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 refe rence in the Limitations section of the AFM.AC 23.1419-2E

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(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 pr e-takeoff visual and t actile inspection of the wing leading edge and upper surf ace in ground icing conditions. In the case of the inability to ascertain if the fuel temperature is above freezi ng, the requirement to perform a visual/tactile
check can be deleted if it can be shown that undetected ice accumula tion does not occur on the wing upper surface due to cold soaked fuel. Gr ound icing conditions should be defined by the airplane manufacturer, but one example is define d as the Outside Air Temperature (OAT) below 5 degrees C (41 degrees F), and one of the following conditions:

(aa) Visible moisture (rain, drizzle, sl eet, snow, fog, etc.) is present;

or

(bb) The airplane was exposed to visibl e 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 (whi ch 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; orAC 23.1419-2E

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(cc) Add an AFM Limitation that re quires a visual and tactile pretakeoff check if it cannot be ascertained that the wing fuel temperatur e 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 (A ppendix O and C) icing conditions immediately upon recogn ition that the Appendix O ic ing conditions exceed the certification boundary. Example language is provided below:

“Severe icing may result from environmental cond itions outside of those for which the airplane is certified. Intentional flight into severe ici ng 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 a nd controllability of the airplane.

Operations in icing conditions were evaluated as part of the certific ation 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, fr eezing rain or other severe icing conditions is prohibi ted. A flight delay or diversio n to an alternate airport is required if these conditions exist at the depart ure or destination air ports. {Applicant should insert visual cue description he re} 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 i mmediate approach and landing as required to exit all icing conditions . Stay clear of all icing cond itions for the remainder of the flight, including landing, unless it can be determ ined 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 secti on should contain appr opriate limits that consider the certification assumptions with respec t to portion (phase of flight, freezing drizzle, freezing rain, etc.) Example language for an airp lane approved to takeoff and land in Appendix

O is below:

“ “Severe icing may result from environmental cond itions outside of those for which the airplane is certified. Intentional flight into severe ici ng 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 a nd controllability of the airplane.AC 23.1419-2E

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Operations in icing conditions were evaluated as part of the certifi cation 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 in to freezing drizzle or freezing rain conditions is prohibited. If freezing drizzle or freezing ra in conditions are encountered during a hold (in any airplane configuration) or in the en route phase of flight (c limb, cruise, or descent with high lift devices and gear retracted), or if {Applican t should insert cue descri ption here}, immediately request priority handling or declare an emergency from air traffi c control to facilitate a route or altitude change to exit all ici ng conditions. Stay clear of all ic ing conditions for the remainder of the flight, including landing, unle ss it can be determined that ice accretions no longer remain on

the airframe.”

(c) The Limitations section must contain speci fic detection criteria – visual cues, specific to the aircraft that indi cate flight is in appendix O ici ng conditions for which it is not approved.

(7) Equipment Limitations.

(a) The Limitations section must contai n 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 th e IPS be activated at the first sign of ice accretion anywhere on the airplane. The procedur es 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 accr etion, however AFM may st ate that ice protection must be activated “at first sign of ice accreti on or ice detection annunciation, whichever occurs

first.” (b) A list of all equipment required for f light 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 op erative 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 equipmen t operations as applicable (for example, minimum temperature for boot opera tion, maximum altitude for boot operation, and maximum outside air temperature for opera tion of thermal ice protection systems). (e) Limitations on operating time for ice pr otection 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 lis t of required placards.AC 23.1419-2E

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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 airm anship, the appropriate procedures should be included in the FAA-approved AFM, AFM revisi on, or AFM supplement. These procedures should include use of the system(s) in a safe manner.

(1) Preflight. Preflight action necessary to mi nimize the potential of enroute emergencies associated with th e 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. Mechani cal systems such as pneumatic boots should be visually observed for operation. Fluid systems s hould 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, partic ularly after a long pe riod of inactivity.

(b) The quantity of fluid in the reservoi r tank, if a fluid ice protection system, should be checked. The AFM should speci fy 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 condi tions, including all flight re gimes. The AFM should include procedures that advise upon which conditions th e ice protection equipment should be activated.

(a) For fluid anti-ice/deice systems, in formation and method(s) for determining the remaining flight operation time should be provided.

(b) Procedures for operation of the ice pr otection 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 completi on of an entire deicing cycle af ter leaving icing conditions. An anti-icing system should not be de-activ ated before leaving icing conditions.

(c) The following statement should be included, including those airplanes approved for Appendix O conditions: “Convective cl ouds, 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 vari ous flight phases in icing conditions should be considered (e.g., whether flaps or landing gear exte nded, airspeed). AFMAC 23.1419-2E

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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 warni ng system to the non-icing schedule if the design permits, after leaving ici ng conditions should be specifie d. 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 sh ould include proper pilot response to cockpit warnings and a means to diagnose system failures

(1) Procedures to be followed when ice pr otection systems fail and/or warning or monitor alerts occur, or suspected unannunc iated failures occur, should be provided. Examples include minimum airspeeds to precl ude wing stall and reduced flap deflection to preclude ice contaminated tailplane stall (ICTS).

(2) Include any changes to other AFM abnor mal 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 pr ocedures. An example for a vi sual cue on the aircraft is:

The following shall be used to identify freezing ra in/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 th e 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 be low plus five degrees C OAT. (2) Droplets that splash or splatter on im pact at temperatures below plus five degrees C OAT.AC 23.1419-2E

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(3) It is possible to experience severe i ce accretions not visible to the flight crew, such as lower wing surface ac cretion on a low wing airplane or propeller blade accretion. Performan ce losses greater than the performance section of the AFM may be an indicat ion of severe ic ing 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. Inform ation should include reco mmended use of flight controls, minimum airspeeds, conf iguration 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 detec tion of Appendix O if a pplicant demonstrates retraction can be safely accomplished, critic al ice shape determination accounted for ice accretion with flaps extended, testin g to Subpart B used the appropr iate flap, and applicant shows by analysis there will not be mechanical inte rference 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 informa tion 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 proced ures to assess its suitability in icing conditions and include in AFM. The procedure should consider basic ai rmanship techniques which establish the reattachment of the boundary layer (flow) of air ove r 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 Tailpl ane 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 li mitations 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 sp eeds for all icing approved configurations should be provided.AC 23.1419-2E

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(2) Takeoff performance.

(a) Effects of ice protection system operati on and/or ice accretions, if applicable, on takeoff distance and takeoff pat h, 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 perfor mance with critical ice accretions should be presented in the AFM in th e 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 appro aching 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 acc retions should be presented in the AFM in the same format as the basic non-icing data. (b) Approach climb data, if required to be de termined, should be presented in the AFM in the same format as the basic non-icing data. (c) Landing distance, if requir ed 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 A ppendix 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 te sted. 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 se rious degradation of performance or handling

characteristics.

(8) Maintenance Manual. The AFM should reference the maintenance manual for ice protection surface cleaning procedures, or applica tion of ice adhesion inhi bitors, if the flight crew can be expected to perform this functi on. The AFM should recommend application of ice

adhesion inhibitors in accordance wi th the manufacturers instructions.AC 23.1419-2E

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19. Instructions for Continued Airworthiness.

a. Requirements. Instructions for Continued Airwor thiness (ICA) are required in accordance with 14 CFR 21.50(b) and 23.1529. ICA shoul d be prepared in accordance with part 23, Appendix G. As a minimum th e following should be addressed:

(1) Basic description of the ice protectio n 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 appli cable component including cleaning, inspecting, adjusting, testing and lubrication

(5) Overhaul or replacement periods for components, if an y

(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 fr equency of use of ice adhesion inhibitors

(11) Special equipment or materials, such solven ts, cements, edge filler, conductive edge sealer, rollers for pneum atic 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 pr otection system. This inspection should concentrate on extraneous fluid bu ild-up on electrical c ontacts, flight control surface bearings, bellcranks, etc. The ice prot ection system fluid evaporates very slowly. Therefore, contaminates that colle ct in the fluid in areas of join ts, 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 t ears. The repair process for thes e types of damage is critical because proper operation of the boots could be affect ed. If leaks or pinholes are not periodicallyAC 23.1419-2E

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repaired, the entire system coul d become inoperable if water, dr awn in by the vacuum that holds the boots deflated, subsequently refreezes and bl ocks 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 proce dures (data may be provided by

the deicer manufacturer’s to addre ss 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 sy stem operating pressure. Cycling should continue until the repair or boot fails. The normal deflation tim e may be shortened to speed up the test. For example, a 174-second deflation cycle can be re duced to 18 seconds while maintaining the six-second inflation time. Any ma terial applied to the whole su rface 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 co mbination of high temperature and fluid exposure may cause deterior ation and should be evalua ted, see paragraph (e).

(d) Proof and Burst Pressure Testing. This testing should be accomplished to show compliance to § 23.1438(b). When conduc ting the proof pressure test at 1.5 times maximum operating pressure, the repaired deici ng boot should hold that pressure for 60 seconds and the repair should not fail. After the proof pr essure test, the system should be inflated at maximum operating pressure, isolated, and the pre ssure 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 temper ature (160 degrees F) an d 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 reduc tion, 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 e xposure 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 erod e 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 armAC 23.1419-2E

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rig that exposes the boot to a rainfall rate of one inch pe r hour at 300 to 500 Miles Per Hour (MPH) (depending on the airplane maximum speed); using one to tw o 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 inte rmittent maximum icing conditions. It is particularly important to cover the range of temperatures and li quid 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 mate rial should be electri cally 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 considerati on is the effect of the repa ir 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 fa bric, be bonded together?

It is recommended that boot ma nufacturers 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 in ternal layers of the boot.

(e) Applicability of the repair procedure. Broken stitches re present 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 Propell er and Engine Inlet Deicing Boots. Boot manufacturers historically have not developed repair procedures for electrothermal deicing boots

because the thermal mass characteristics of th e repaired location will change and affect iceAC 23.1419-2E

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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 evalua ted include: fuels, oil, hydrauli c fluids, glycol/water mixture, deicing boot age, appearance and ice adhe sion 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 doe s not provide a “cold spot” on th e deicing boot, resulting from either a higher thermal mass or lower th ermal 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, shoul d 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 indire ctly (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 shoul d have similar thermal conductivity of the deicing boot material. The effect of the chem icals 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 considerati on is the effect of the repa ir 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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(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 informa tion 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 a nd anti-icing of aircraft before takeoff. (1) Why use ground deicing fluids? Aircraft are deiced be fore takeoff and, as required, anti-iced using thickened pseudo-plasti c fluids. This proce dure provides temporary protection from ice adhering to the ai rcraft’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 wh en certain ground deici ng fluids are applied

before takeoff.

(1) Performance. The presence of thickened fl uid may affect the airplane’s performance because the fluids may not complete ly 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 airp lanes with reversible control surfaces.

(3) Vibration and Controllability. The fluid may also collect in the balance bays of aerodynamically or weight balanced control surf aces, due to inadequate drainage. This may result in unbalanced control surfaces, unexpected changes in control forc es, and control surface vibrations. Additionally, there ha s 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 contro l surface hinge lines. When the re sidue of the evaporated anti-icing fluid is re-hydrated by humidity, rain or duri ng 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 de pressant, usually a glycol compound, which evaporates when the anti-icing fl uid dries. Rehydrated fluid has been found in and around gapsAC 23.1419-2E

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between stabilizers, elevators, ta bs, and hinge areas. This esp ecially 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 contro l movement. This phenomenon has not been experienced when a two-step deic ing/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 § 2 3.1419. Typically the effect of fluids on the airplane are evaluated by the airf rame manufacturer, after type certi fication, at the request of an operator that is seeking approva l of a ground deicing a nd 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 cert ification to prevent re-designs after type certification if it is anticipate d operators will use ground deici ng/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 ai rplane performance or co ntrollability after the application of deice/anti-ice fl uids. 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 airp lanes. 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 ma nufacturers in evalua ting fluids for their specific designs.

(1) Design.

(a) The airplane design should be anal yzed for possible collection sites.

(b) The design should incorporate drain hole s, particularly in control surface balance bays.

(2) Airplane Performance. There have been various methods to evaluate performance. Typically the lowest takeoff gr oss 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 wi thout fluids. Flow-off of fluids from the wing was simultaneously documented during takeoff roll and rotation. Stall speed s 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 coeffi cient between the clean airplane and airplane with fluid hasAC 23.1419-2E

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been considered acceptable for jet powered airpla nes, and an 8% decremen t has been considered acceptable for propeller powered airplanes.

(c) Takeoffs at fixed pitch angles are perfo rmed with and without fluid. Several pitch angles representing the rang e 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 approve d takeoff flap position, with all engines operating:

1. Control power and control force during rotation at the scheduled V R

.

2. Controllability during takeoff with rotation at 10 knots or 7%, whichever is less, below the scheduled V R

.

3. Controllability tests (± 40o bank an gle changes, ± 0.5g or stall warning) with takeoff flaps, as soon as practical after liftoff, either at V 2 +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 ta keoff flap position, with simulated one engine inoperative:

1. Control power and control force during rotation at V R

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 V 2 or the speed at 50 feet, depending on airplane category.

(4) Fluids.

(a) Number of Fluids. The airplane ma nufacturer should eval uate 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

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(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 appl icable surfaces (including the horizontal stabilizer) should be treated. Slats/flaps should be in the r ecommended 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 coldes t outside air temperatur e 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 pse udo-plastic fluids to be approved fo r the airplane. Post flight inspections should be conducted to determine if flui d 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 a pproved, 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 airpla nes are an increase in takeoff speeds and use of flaps.

(3) Procedures. Pre-flight or post-flight inspec tion and cleaning of areas in which

fluid residue is shown to occur.

(4) Performance. Any increases in takeoff distan ce due to takeoff speeds increased above the established threshold should be presen ted 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 whic h 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 incr eased on contaminated runways.

f. Instructions for Continued Airworthiness. The following, if app licable, should be

addressed in maintenance manual:AC 23.1419-2E

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(1) Inspection.

(a) Drain holes.

(b) Control balance bays.

(c) Identified aerodynamically quiet areas.

(2) Cleaning. High-pressure washing with a hot T ype 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 re quire subsequent lubrication.

g. Runway Deicing Fluids. Airplane manufacturers shoul d 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 runway s. This resulted in the use of potassium formates and/or acetates. These chemicals (org anic 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 ot her 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 applie d to aircraft and also to promote the formation of anti-icing fluid re sidue gel in aerodynamically qui et areas of the aircraft.AC 23.1419-2E Appendix 1

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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, LW C, 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 Volu me Diameter (MVD),” determined using rotating multi-cylinders and assuming a Langmuir distribution.

c. Artificial Ice. A structure formed from material ot her than frozen water, but intended to represent an ice accretion. See “simulated ice shapes.”

d. Critical Ice. The aircraft surface ice shape form ed 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 f light 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 an d structural damage from shed ice, engine thrust, engine control, and aeroelastic stability.

e. Deice or Deicing. The periodic shedding or rem oval of ice accumulations from a surface. This occurs by destroying the bond be tween 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 gr ound 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 falli ng 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 airAC 23.1419-2E Appendix 1

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temperatures less than zero degrees C (superc ooled), remains in liquid form, and freezes upon contact with objects on the surface or airborne.

j. Ice Crystals. Any one of a number of macrosc opic, crystalline forms in which ice

appears.

k. Icing Conditions. The presence of atmospheric mo isture and temperature conducive to airplane icing.

l. Intercycle Ice. Ice that builds up on a deiced surf ace 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 gi ven 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 diamet er that divides the total liquid water content present in the drop size distri bution in half, i.e., half the water volume will be in larger drops and half th e 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 di vides 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 crys tals and supercooled liquid water drops.

q. Monitored Surface. The surface of concern regardi ng 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 prio r 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 protect ion system, for example, the surface of a deicing boot or ther mal ice protection system.AC 23.1419-2E Appendix 1

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u. Reference Surface. The observed (directly or indirec tly) 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 pr esence of ice on the monitored surface. Examples of reference surfaces include windshield wiper bl ades or bolts, windshield posts, ice evidence probes, propeller spinner ice, and the surface of ice detectors. Th e 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 th at are connected to the pitch, roll, or yaw control surfaces by direct mechanical linkages, cabl es, or push-pull rods such that pilot effort produces motion or force about the co ntrol 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 th e 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 cont rol 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 surf ace deflections to be obtained at high speeds.

x. Runback Ice. Ice formed from the freezing or refreez ing 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 deic ing 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 unfro zen 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 surfacesAC 23.1419-2E Appendix 1

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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

M FC Maximum Mach number for stability characteristics
MMEL Master Minimum Equipment ListAC 23.1419-2E Appendix 1

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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

V FE Flaps Extended Speed
VIT Variable Incidence Tailplane

V LE Landing Gear Extended Speed

V MC Minimum Control Airspeed

V MO Maximum Operating Airspeed

M MO Maximum Operating Mach Number

V NE Never Exceed Airspeed

V R Takeoff rotation speed

V S1 Stall speed in a specific configuration

V REF Reference Landing Approach Airspeed

V 2 Takeoff safety speedAC 23.1419-2E Appendix 2

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APPENDIX 2. GUIDELINES FOR DETERMI NING CERTIFICATION BASIS ON

FLIGHT IN ICING APPROVAL STCS AND AMENDED TCS

1. My CAR 3 (or earlier certific ation basis) aircraft has ice protection systems installed and is not placarded against flight into know n 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 t ype 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 equipm ent 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 pr otection 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 thos e from another manufacturer, the certification basis can remain unchanged; see Appendix 5 of this AC for more info rmation. If it is another type of system, for example replacing a pneumatic deicing system w ith 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 si nce a modification to an ice protection system is considered “not signifi cant” 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 aircra ft be approved for flight in icing?

Yes, as long as the systems are installed pe r type design data and the POH, AFM, or AFM supplement associated with the ice protection sy stems do not prohibit flight in icing conditions (or “flight into known icing”). Retroactive removal of flight into known ici ng 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 co ntain flight in icing approval. What is the certification basis if I add ice protection systems?

Under the Changed Product Rule, adding approval fo r flight in icing cond itions is considered a significant change (AC 21.101-1) and compliance should be shown to the latest amendment. InAC 23.1419-2E Appendix 2

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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 complianc e to § 23.1419(a), which requires that the airplane meet Subpart B performance in icing conditions, may be impracti cal for some CAR 3 airplanes. The Changed Product Rule allows the applicant to elect comp liance to amendment 23-14 for that particular paragraph of § 23.1419. In this case the performa nce 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 c ertified for flight in icing in accordance with § 23.1419. The later mo del does have a different engine installed with higher horsepower and a different ice prot ection system. Can I install the exact same ice protection systems as the la ter model, install a new engi ne with at least the same horsepower, and be certified for flight in icing?

Yes, and similarity may be used to show comp liance to the applicable regulations. However, there may be some testing required. The cu rrent method of compliance to § 23.1419 includes tests (susceptibility to ice contaminated tailplan e stall, for example) that may not have been accomplished during certificat ion of the later model.AC 23.1419-2E Appendix 3

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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 wh ich the applicant wants approval under the provisions of § 23.1419. Increase in gross wei ght, changes in engine power, and propeller changes could affect approval in icing and thes e areas would have to be evaluated using AC 23.1419-2D as the method of compliance. An app licant wishing to use an alternate Means of Compliance (MOC) needs to consul t the Standards Office. Whethe r 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 aftert hought or totally disregarded on many modification programs on ai rcraft certified for flight in icing conditions. In some cases, the rationale used was that since the i ce protection systems were not modified, icing regulations do not need to be addressed. Th is 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 acce ssory inlet changes

(5) Antennae installations or ot her external modifications

(6) Gross weight increases

(7) CG envelope increaseAC 23.1419-2E Appendix 3

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(8) Flight envelope increase

(9) Turboprop conversion

(10) Modifications to lifting surfaces

(11) Installation of vor tex 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, comm on 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 (origi nal airplane and modified airplane) should be accomplished back to back by the same test pilo t. Stall warning should also be evaluated. Although the margins are not a concern at high powe r, they need to evaluate if higher power masks any stall warning cues. The following tests should be accomplished:

(aa) Stall characteristics and st ability of minimum weight and maximum weight, aft CG limit

(bb) Controllability at forward CG limit and critical weight.AC 23.1419-2E Appendix 3

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2

. Susceptibility to ice contaminated tailplane st all 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 pow er is usually more critical than idle. This cannot be done with analysis on a propeller airpla ne 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 ve rtical 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 pr oposed 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 amoun t of ice mass that could be shed should be compared to a similar, approved engine instal lation 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 reduc tion, 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 modifi ed 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 (e xcept wooden propellers) and other engine installations must be protected against the accumulation of ice as necessary to enable satisfactory functioning without appr eciable 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 comp lies with propeller structural and vibration regulations, and deicing system failure modes, as discusse d in § 23.929 of AC 23-16, cannot cause an unairworthy condition.AC 23.1419-2E Appendix 3

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(c) The typical analysis report from the deicing boot manufacturer is not sufficient by itself to show compliance to § 23.929. The typical report calc ulates intercycle ice thickness for various flight and icing conditions, but doe s not calculate the effect on propeller efficiency, which must be done to show no appreci able loss of thrust. For STCs, it would be acceptable to show that intercycle ice is equal to or less than th e accretions obtained on the same propeller on an airplane that was flight tested in icing c onditions and shown to have no appreciable loss in thrust.

(d) The typical deicing boot manufacturer repo rt also contains a caveat that it does not address propeller runback ic e. Similarity to another propell er that was flight tested in icing conditions is usually done to address r unback. Similarity would include propeller and deicing boot aerodynamic and thermal similarity, de icing cycle time, prope ller RPM, and flight conditions. Note that metal and composite propellers have different thermal masses.

(e) As a final qualitative check for bot h intercycle and runback ice on new airplane programs, airplane perfor mance is checked during flight test s in icing conditions. A test point as close to minus 22 degrees F as possi ble 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 condition s. 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 paragr aph 1e (1) (a) of this appendix should be
followed.

(h) If the proposed propeller(s) and/or deici ng system are predicted to increase the size of intercycle ice, the effect s 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 characteristic s of the propeller boots should be
shown to be the same as original certified system.

(aa) If the temperature characteristic s and deice timing cycle are shown to be changed, flight testing in measured natu ral icing conditions are required to evaluate propeller deicing and airplane performance

(bb) If the temperature characteristic s 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 accomplis hed as close to –22 degrees F as possible.AC 23.1419-2E Appendix 3

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2

. A rational analysis of the heat generated by the system should be made and compared to the existing system if the syst em is located in area s 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 su ch installations, or other external
installations such as drain masts are installed on aircraft, the inst aller 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 performan ce reduction of lifting surfaces;

4

. There is no ice related effect on dow nstream 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 th e conservative analysis fails, the analysis can be refined to determine if the initial analysis was overly cons ervative. 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 cri tical 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

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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 a ccretion 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 detrim ental effects due to th e ice accretions if:

1

. The installation is upstream of air da ta 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 ma y 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 eval uate unprotected areas such as fuel

vents.

(c) If the following flight testing with no ice show no degradation from the unmodified aircraft, and no margin al 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 performa nce data in icing conditions need to reflect higher stall speeds.AC 23.1419-2E Appendix 3

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(e) C limb performance in icing conditions shoul d be evaluated to determine if the airplane is capable of operating safely.

(f) An analysis should show increased wei ght makes the airplane equal or less susceptible to tailplane stall. The analysis s hould evaluate tail trim requirements and tail ice accretion at the higher airp lane angle of attack.

(g) The service history of th e airplane should be review ed to determine if stall warning and low airspeed awar eness 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 ma kes an airplane more susceptible to ice contaminated tailplane stall. This should be addressed by flight tes ting 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 al titude is applied for, the applicant
should demonstrate:

1

. The ice protection system opera ting pressures (for pneumatic systems) or temperatures (for hot air systems) by dry air testing; and

2

. The stall speeds and stall characterist ics associated with ice accretions if these are shown to be influenced by Mach number.

(b) The effect of increased cruise airspe eds 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 pneuma tic lines, resulting in failure of some or all zones of the pneumatic system. The applicant ne eds to show that the pneumatic deicing system will continue to function in icing conditions.AC 23.1419-2E Appendix 3

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(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 estab lished and published in the AFM/POH.

(10) Modifications to Lifting Surfaces.

(a) Critical ice accretions (i ncluding pre-activation, in tercycle, 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 ar e changed or the modifications could affect control power or control surface hinge moments, flight test ing 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, fo rward 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 increas e 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 n ear the leading edge, the applicant should provide data on expected ice ac cretions. Flight conditions to consider are the 45-minute hold, descent, and approach. Substant iation of the effects on stall speed s, 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 coul d affect control power or contro l surface hinge moments, flight testing with simulated ice accre tions 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

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2

. Stall speeds; stall warning and contro llability at maximum weight, forward CG limit;

3

. ICTS susceptibility at light weight, fo rward CG limit if the aircraft has unpowered, reversible elevators or propellers.

(13) Addition of or Re location 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 autopilo ts 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 accid ents and are factual. Based on our service experience, even though there ar e no regulatory requirements addr essing autopilots in airplanes approved for known icing, applicants are strongly en couraged to include features that mitigate these autopilot induced accident scenarios. Wher e it would be impractical to add such a feature, the design should include adequate trim in moti on 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 repl acement deicing boots is applicable.AC 23.1419-2E Appendix 4

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APPENDIX 4. GUIDELINES FOR CERTIF YING 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 ai rcraft is prohibited from flight in icing conditions but there is some ice protection to facilitate an exit from an inadvertent icing encounter. The following guidan ce 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, maneuve rability, stability, trim , ground/water handling, vibration and buffet, and, if appli cable, high speed characteristics. If any of these are affected, it should be shown that applicable regulations ar e still complied with a nd place the appropriate information in the AFM. Compliance should be acco mplished with dry air f light tests. If the system is being evaluated as an amended TC or ST C, it is not necessary to investigate all weight and CG combinations and flight conditions when results from the airpla ne certification testing clearly indicate the most critical combination to be tested.

b. In some cases the effect of system operati on may need to be evaluated. For pneumatic deicing boots, the operation of the boots (inflatio n) 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 appropria te 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 subpa rt D. The load conditions determined from Subpart C should be used in this evaluation. The individual ice prot ection system components
should also be evaluated to determine that th ey would withstand the load conditions from Subpart C if their failure can cause a hazard. Thermal effect s on structure of thermal ice protection systems and fluid/structure compatibil ity of freezing point depressant systems should
be evaluated.

b. An evaluation of flutter characteristics to ac count for the added mass of the ice protection systems should be made per § 23.629.

c. If a thermal windshield ice prot ection system is installed, an evaluation of the visibility due to distortion effects through the protecte d area should be made. In accordance with § 23.775(g), a probable single failur e of a transparency heating system should not adversely affect the integrity of the airplane cab in or create a potential danger of fire.AC 23.1419-2E Appendix 4

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d. For wing and empennage electrical deicing sy stems, 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 minimu m the effect of the ice protection system
installation should be addre ssed by analysis and design.

4. SUBPART E – POWERPLANT. For an airplane not certif icated 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 provi ding 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, opera ting envelope, and airplane ice accretion sites
should be included in th e 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 accreti on 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 subs equent lockup of controls

(c) Evaluation of autopilot operation and recommended operation in icing

(d) Qualitatively evaluate climb performance

(e) Evaluate degradation inwindshield visibility

(4) Dry air ice shape flight tests

(a) Ice shapes

1. Five minute accretions on unprotected areas

2. Protected area ice accretionsAC 23.1419-2E Appendix 4

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(b) Objectives

1. Evaluate stability and controllability

2. Evaluate increase in stall speed.

b. Compliance to the latest applicable am endment 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 singl e 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 regulati on, the system would not be an essential load.

(4) Show that the system when operating norma lly does not create a greater hazard than operating with no ice protection system. For ex ample, on systems where there is runback the applicant should show that the r unback ice does not cause a great er hazard than the ice accretion with no ice protection. Hazards to address would be st alls, 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

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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 prot ection system controls and annunciations should be in the

AFM.

c. The AFM should contain a WARNING that sta ll 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 in stalled 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 accreti on, if applicable.

f. Autopilot operation procedures.

(1) For aircraft equipped with an autopilot, the autopilot shou ld 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 cont rol surface gaps or frozen actuators.

(2) There should be a WARNING that the autopi lot will NOT maintain airspeed if ice accretes on the airplane. MONITOR airspeed closely.

g. Instructions for continue d airworthiness in accordance with § 23.1529 should be provided.AC 23 1419-2E Appendix 5

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APPENDIX 5. GUIDELINES FOR A PPROVAL 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 cert ification basis and similarity w ith the original part(s), as
summarized in Table 5-1 and discus sed in the following paragraphs:

TABLE 5-1. SUMMARY OF TEST REQUI REMENTS 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 certifi cation basis does not include CAR § 3.712 or § 23.1419, the deicing system is optional equipment and not requir ed. 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 functi on 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 charac teristics, 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 rem oves or prevents ice accretion.

b. For aircraft whose certificat ion basis is CAR § 3.712 or an original issue under § 23.1419, an STC is required. Original certific ation of these aircra ft only required that pneumatic deicers be installed per approved data and that they have a positive means of deflation. No icing flight test s 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 dete rmine factors such as variance with the original design, the original certif ication requirements, and the service history of the original product.AC 23.1419-2E Appendix 5

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The replacement parts must be shown to f unction properly, remove ice or prevent ice accretion as well as the previous ly installed equipment, and not introduce additional failure modes that could prevent continue d safe flight and la nding. Comparative test s of the original versus the replacement parts may be acceptable. If the original certification basis is to be utilized, it is highly r ecommended that an entry in the AFM supplement limitations section, or a placard, with the following wording be require d: “This airplane has not demonstrated compliance with the icing environment requ irements 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 m easured, natural icing conditions should be accomplished if the replaceme nt parts are of differe nt materials or have different design characteristics. Supplemental te sting in artificial icing conditions (icing tunnel, tanker) should also be accomplished to cover th e complete part 25, Appendix C envelope. The replacement parts must be shown to function pr operly, 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 perf ormance and flying qualities as discussed in paragraph 13a (2) of this AC s hould be accomplished. The Standards Office should be contacted since the requireme nt 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 accr etions, the service history of th e airplane, and flight testing accomplished during the original certification wi th protected surface ice accretions. Follow-on applications of the new parts in aircraft other than the initial ce rtification may then be approved through similarity provided the conditions in § 23.1419(c) are me t. There may be cases where
minor modifications would not require additional measured, na tural flight tests.

d. For replacement parts on an aircraft whose certification basis is § 23.1419, amendment 23-43 or higher or those aircraft wher e the applicant wants to add “flight in icing conditions” operational approval, an STC is required. Flight test ing in measured, natural icing conditions is required if the replacement parts are of different materials or have different design characteristics. Supplemental testing in simu lated icing conditions (i cing 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 mode s that could prevent continued safe flight and landing. A matrix of performance and flying qualitie s as discussed in para graph 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 wh ere minor modifications would not require additional measured, natural flight tests.

3. Engineering judgment must be used to determ ine that the modifications would not affect the effectiveness of the ice pr otection in natural ic ing conditions. If there is any question as to the need for a particular design to be subject to natural ici ng 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. Ag ain, seemingly benign differences can have significant negative eff ects on an aircraft's ice protection capability.AC 23.1419-2E Appendix 6

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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 al l 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) wi th 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 lo adings, as determined during the noncontaminated airplane tests, are re quired. Natural icing flight tests may be accomplished at a nominal CG.

Load
distribution
limits 23.23 Only critical weight and CG lo adings, 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 loa d, weight, and CG limits for flight in icing. Operation in icing conditions should be essentially transparent to the flightcrew in th at no icing-specific methods of operation (other than activating i ce 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 fi ve degrees C instead of plus 30 degrees C. It can be assume d 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. Si milarity to previously flighttested configurations or qualita tive 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 determin ed and published in the AFM.AC 23.1419-2E Appendix 6

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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 wit hout a wing leading edge high lift device and commuter category airpla nes, if the applicant seeks certification for flight in icing c onditions, if the stall speed with
takeoff ice accretion exceed th e threshold defined in § 23.51(d).

If applicable, when determining the takeoff speeds V 1 , V R , and V 2 for flight in icing cond itions, the values of V MCG and V MC 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 accr etion 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

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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 w ith engine power losses associated with operating ice protection equipment that are not prohibited for
takeoff.

The effect of ice accretion on clim b performance (lift, drag and climb speed) must be accounted for if not excepted per § 23.65(c). For example, accounting for take off 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 perf ormance 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 airpla nes 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 tu rboprop powered airplanes. The effect of Appendix C takeoff ice accretion must be accounted for (except for § 23.67(c)(1) on commu ter category airplanes and turbojets without a wing leading edge high lift device, such as slats, if the stall speed increase or cl imb performance degradation are above the thresholds defined in § 23.67(e). Flight testing of the
takeoff ice accretion should be acc omplished to evaluate stall speed and climb performance.

Enroute
climb/descent 23.69 Must be determined with “Enrout e” ice if the enroute climb speed selected in icing is more than th e non-icing speed by the greatest of three KCAS or three percent V S1 , 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

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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 protect ion 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 i ce 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

V S0 . The V MC 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 V REF , 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 V REF in icing conditions is greater than V REF 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 fl ap 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 concurre ntly with other tests, and during the flight, when conducting ice shap e and natural Appendix C flight testing. In lieu of the evaluati on of sudden engine failures for multiengine airplanes, the following is accomplished:

If the non-icing V MC is used for takeoff speeds, it must be shown that the airplane is safely cont rollable and maneuv erable at the
minimum V 2 for takeoff with the criti cal engine inoperative and

with “takeoff” ice accretion.

If the non-icing V MC is used for V REF , it must be shown that the airplane is safely controllable and maneuverable during a go-around starting at the minimum V REF with the critical engine inoperative

and with critical ice accretion.

23.143 (c) Maximum control forces are applicable.AC 23.1419-2E Appendix 6

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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 concurre ntly with other tests, and during the flight, when conducting ice shap e 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-ac tivation 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, V

REF (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 Tabl e 2. A 0.5g pushover and 1.5g pull-up are required for pre-activation i ce in lieu of the 0g pushover.AC 23.1419-2E Appendix 6

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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 V MO /M MO are not conducted for icing certification.

23.145 (d) Not required.

23.145 (e) Evaluation of failure of primary l ongitudinal flight control system not required for ic ing certification.

Directional and
lateral control 23.147 (a)(b) Critical configuration(s) determ ined from the non-contaminated airplane tests must be evaluated.

23.147 (c) Evaluation of failure of primary la teral flight control system not required for icing certification.

Minimum control speed 23.149

(a) Definition of V MC , applicable to landing pha se 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, V MC speeds with
critical ice must be evaluated to determine if the proposed V REF speed in icing complies with § 23.73. Static V MC tests may be used.

23.149 (d) Not required.

23.149 (e) Applicable to landing ph ase 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) determ ined from the non-contaminated airplane tests must be evaluated.

Rate of roll 23.157 Airplane must comply w ith “takeoff” ice accretions for paragraph (a) and critical ic e accretions for paragraph (b). Controllability may be degraded from the non-iced airpla ne but must still be compliant.AC 23.1419-2E Appendix 6

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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-cont aminated airplane tests should be
reviewed to determine whether th ere are any cases where there was marginal compliance. If so, or if qualitative evaluations with ice accretions show any control anom alies, 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 th e non-iced airplane but must still be compliant.

Demonstration
of static longitudinal stability 23.175 Critical configuration(s) determ ined 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-contamin ated 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) determ ined from the non-contaminated airplane tests must be evaluate d with critical ice accretions.AC 23.1419-2E Appendix 6

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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 exc eed 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 desi gns the controllability at stall warning should be evaluated. Recove ry 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/t hrust to establish a 1 kt/sec deceleration rate, and at stall warn ing apply power/thrust. Evaluate the aircraft response, need for dire ctional/lateral c ontrol, airspeed increase, and altitude loss (assu ming 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 att ack activation of the stick pusher.

Turning flight
stalls 23.203 Turning stalls should be evalua ted 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 de signs the autopilot operation up to stall warning and controllabil ity at stall warning should be
evaluated.

Accelerated turning stalls 23.203 (a)(2) Accelerated turning stalls not requ ired unless tests with no ice show marginal compliance`````AC 23.1419-2E Appendix 6

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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 inco rporates anticipation, deceleration
rates slower than 1 kt/s ec may need to be conducted to evaluate the highest angle of attack activati on of the stall warning system.

In addition to the standard stall tests conducted in natural icing and with artificial ice shapes requi red to show compliance to § 23.1419(b), recovery at stall warni ng should also be evaluated by applying the manufacturer recommende d stall recovery procedures. The following three aircraft confi gurations 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 V REF 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

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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 sta ll warning + 1 second using appropriate aircra ft procedures.

Note: Evaluate the aircraft response, need for directional/lateral control, ai rspeed 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, th en 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 aircra ft procedures.

Maneuver margin 23.207 (d) 40-degree bank level altitude tu rns and 30 degree/30 degrees bankto-bank rolls at the flight condi tions 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-de gree turn is necessary, and the appropriate thrust may be simulate d with all engine s 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

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TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419

AT AMENDMENT 23-XX

Regulation 14 CFR
Section Guidance

Stall warningwith preactivation ice 23.207(g) Must be shown with pre-activation ic e 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 dece leration after waiting at least one second after stall warning. The pre- activation ice is defined in Table 2 of this Advisory Circular. Rec overy at stall warning should also be evaluated by applying the manufacturer recommended stall recovery procedures. The followi ng 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 V REF 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 re quired 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 accre tions 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 lo wer angles of attack when ice protection is initiated) may be required to achie ve 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 applican t should validate that the means
used to determine when the critic al wing surfaces are free of ice
accretions is reliable under al l 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

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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 w ith critical ice accretions. The results of the steady heading sides lip tests with critical ice may be
used to establish the safe cross wi nd component. If the flight test
data show that the maximum sidesl ip angle demonstrated is similar to that demonstrated with the non-contaminated airplane, and the flight characteristics (e.g., cont rol 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:

V CW = V REF * sin (sideslip angle) /1.5 where:

V CW is the crosswind component,

V REF is the landing reference speed appropriate to a minimum landing weight, and sideslip angle is that demonstrated at V REF Operation on unpaved
surfaces 23.235 Not required.

Operation on

water 23.237 Required only for seaplanes and am phibians certified for flight in icing conditions.. Spray
characteristics 23.239 Not required.

Vibration and
buffet 23.251 The non-icing tests should be acco mplished 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
V MO /M MO /V NE A speed at which it is demonstrated that the airframe will be free of
ice accretion.

Vibration due to prope ller icing/de-icing shoul d be evaluated during the natural icing testing. High speed
characteristics 23.253 If applicable, compliance shoul d be shown with airframe ice protection systems installed. No t required with ice accretions.AC 23.1419-2E Appendix 7

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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 asse ssment is described in detail in AC 25-XX. As described in the legend to that table, the capability of each tool fo r the various applications is classified as green, yellow, or orange, Reliance upon available si mulation methods combined with engineering judgment will be required for finding complian ce 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 cons ideration of cri tical-case icing conditions. General and specific con cerns that should be considered are discussed in this section

of the AC. While Table 7-1 illustrates the current state of simu lation capabilities, we expect that capabilities will improve in the future. We enc ourage applicants and research agencies to develop and validate the engineeri ng 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 mean s of compliance. Radomes, for example, have no engineering tools classified as green. In other cases, such as ar eas aft of protected areas, there is only one simulation tool that is classified as green.AC 23.1419-2E Appendix 7

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(1) Capabilities & Limitations of Engineering Tools and Measurement Instrumentation for Appendix O Icing Conditions

(a) Icing Tunnel

. A tunnel that uses a single pr essure source for spray bars cannot simultaneously produce the large and sma ll drop distributions (bi-model distributions) defined in Appendix O. However, NASA has deve loped a technique called “sequencing” that alternates large and small drop sprays to simu late Appendix O conditions. When icing tunnels are used as an element of the means of compliance:

1. Scale effects must be consider ed for tunnel blockage effects.

2. For FZDZ with a median-volume diameter (MVD)<40 μ m, 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 ar eas may be required to represent the local water
catch in these locations.

4. If there are concerns about the bi-m odal distribution affecting performance of ice protection systems, sequencin g should be considered. Sequencing 2 of freezing drizzle
conditions has been demonstrated in the IRT for unprotected surfaces. The sequencing technique approximates drop distributions found in natura l conditions, however, it results in rougher textures than Appendix C ice shapes.

5. Ice shapes in unprotected areas are ge nerally considered critical from the perspective of producing the larges t disruption to the airflow. With a large ice shape, details on the impingement limit characteristics, which ma y 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 th e drop distribution appropriate fo r simulation of the conditions desired. (The phrase “standard spray” method re fers to using the IRT nozzles in off-design conditions to generate larger drops for SLD cond itions.) In cases where the impingement limit characteristics are important, sequencing may be necessary.

6. In general, sequencing produces roughe r 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. 2005AC 23.1419-2E Appendix 7

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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 inappropr iately affect the ice shape.

9. The tunnel model should be a full scal e 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 subscal e hybrid airfoils with full-sc ale leading edges to determine leading edge ice shapes for large-chord airfoi l 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 anal ysis 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, veloci ty distribution and impingement characteristics. Although we anticipate that the hybrid airfoil design techniqu e 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 fusela ges 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, validat e location of detection devices, and determine total accretion
areas that could be used in drag estimates (if required).

11. The tunnel model should incorporate ge ometry 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 Appendi x O conditions. Some va lidation of collection efficiency and ice shapes has been accomplis hed 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 accretion s. 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 lim its, as well as for possible water runback. No current CFD method, however, can identify the breakup of wa ter into rivulets, roughness formation, ice sliding that may occur under thes e 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

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empirical data and test results (i f available), and engineering judg ment. This usually consists of determining the extent of possible ice formati on using some criteria from the computational analysis, such as ice extent, impingement lim its, or some minimum ice thickness level. The resulting ice shape would include intercycle or residual ice on the pr otected region and ice formed aft of the protected region. This resu lt is then combined with guidance on ice roughness levels, such as described elsewhere in this doc ument, to produce a rough ice region that can be
evaluated in wind tunnel test ing or flight tests.

1. Information can be calculated for dr op 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 effect s, 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, th e capabilities of performing anal yses with 3-D SLD CFD tools have not yet been evaluated. There are codes th at may have this poten tial, but no guidance can
be offered at this time for their use.

3. Some codes have limited capabilitie s 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 addre ssed 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 fo r the temperature (glaze, rime, etc.).

(c) Icing Tankers

1. Icing tankers have been used ex tensively 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 li mited 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. Additio nally, drop sorting effects are likely, because of higher fall rates of large drops w ithin an Appendix O distribution.

(d) Instrumentation. When making in-situ measurements of Appendix O conditions, it is important to note that tec hnology to make such measurements is rapidly changing. It is essential to cons ult experts in all phases of the measurement program, including those aware of the latest probl ems and strengths of each probe. You should use instrumentation
suited to the task.AC 23.1419-2E Appendix 7

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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 instru mentation must be calibrated. An often-overlooked aspect of a meas urement program is the need to calibrate the instruments.

3. Appropriate software and analysis te chniques are also essential, because complicated algorithms are often needed in the analysis.

4. Instruments are required to measure pa rticle concentrations as a function of size over the complete size range—2 μ m to at least 1,500 μ m—including cloud drops and precipitation drops. This may re quire more than one probe.

5. Liquid water content and ice water content (IWC) meas urements obtained by integrating 2-D images from spectral measuremen ts generally have larger errors than those obtained from probes specifically designed to ma ke such measurements. Consequently, it is recommended that probes designed to measure LW C and, if necessary, IWC, directly be used, recognizing that some hot-wire de vices detect larger drops (>50 μ m) with reduced efficiency. Mixed-phase clouds can occur frequently, so it is necessary to be able to discriminate between ice and liquid particles, especi ally for sizes larger than 50 μ m, so that ice particles are not incorrectly identified as SLDs.

6. For detect-and-exit airplanes (tho se certifying to §23.1420(a)(1)), it may not be necessary to measure IWC; but for airplane s using natural icing SLD flight tests to certify for a portion of Appendix O (§23.1420(a)(2)) or for unrestricted opera tions (§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 system s both on and aft of protected areas. For detect-and-exit airplanes (§ 23.1420(a )(1)) in freezing dri zzle conditions, icing tunnels alone may be used to develop ice sh apes, provided that the model appropriately represents the airfoil beyond the FZDZ icing limit. Roughness may be evaluated in icing tunnel testing and replicated on th e ice shapes for flight te sting. The standard spray 2 method should be used for anti-icing systems because of the vary ing 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 beenAC 23.1419-2E Appendix 7

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developed in the past for Appe ndix C icing conditions using anal ysis and observed ice shapes from Appendix C flight tests (t ypically holding ice shapes). For detect-and-exit airplanes (§ 23.1420(a )(1)) in freezing dri zzle conditions, one method of compliance would be to modify Appe ndix C ice shapes to account for the larger impingement regions produced in FZDZ as pred icted by the 3-D codes. You may use CFD codes to predict ice thickness. Ice roughness shoul d be in accordance with the section headed Standard Roughness Levels for Appendix O Ice Shapes later in this appendi x. The radome ice tested
should reflect the total mass associated with th e 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 inge stion or airframe damage pers pective, 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 detect ion require assessment of thei r capabilities in large drop conditions, based upon their sensi ng technology. Vibrating probe type ice detectors which detect ice accretion on a probe through a decrease in th e probe’s vibration frequency, may experience increased response time in large drop exposures because splashing and aerodynamic forces, particularly in near freezing te mperatures, can cause water to sh ed 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 freez ing. Therefore, use of CFD alone is not acceptable for showing that ice detectors functi on 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 adequa tely predict the shadow ing and concentration effects may be used to verify that the equipment is properly located. Because of the lack of engineering t ools 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 repr esentative of Appendi x O distributions and temperatures can be substantiated. However, if vi sual cues are certificated as the primary means of compliance with § 23.1420( a)(1)(i) and the airplane is equi pped with an ice detector system that is not required for complia nce with § 23.1420(a)(1)(i) or § 23.1420(c), then the ice detector need not be tested in natural Appendix O conditi ons. Certification of visu al cues for detect-and-AC 23.1419-2E Appendix 7

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exit airplanes is discussed later in this appendi x 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 posi tion 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 shadowi ng and concentration effects are acceptable as the only method for compliance wi th 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 coll ection efficiencies approaching "1," if performance has been shown in FZDZ cond itions, then a qualitative analysis based upon water-catch ratios may be used for extrapolat ion 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 ca ses, 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)<40 μ m. FZDZ conditions with an MVD less
than 40 μ m are similar to existing Appendix C dist ributions with the exception of a small percentage of the mass in drops larger than ty pical 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 a nd increase the wa ter catch. If visual cues are used for compliance with § 23.1420( a)(1)(i), it may be po ssible to use codes in combination with icing tunnels to verify the visu al cues. Visual cues should not be based on only one engineering method; a second, co rrelating method should be used.

2. Freezing Drizzle FZDZ>40 μ m. Where the capabilities of the tools
available for FZDZ>40 μ m are the same as for FZDZ<40 μ m, the applicant may use similar means of compliance that are adjusted for the FZDZ>40 μ m icing conditions. The tool capabilities are different for m echanical deicing system protect ed areas and areas aft of the protected areas.

Note: Icing tunnels are classified as yello w when used for testing for FZDZ

>40 μ m 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 areasAC 23.1419-2E Appendix 7

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and areas aft of the mechanically protected ar eas. Sequencing or standa rd distributions are acceptable, but the ratio of sequencing tim e to shed cycles should be examined.

3. Freezing Rain (FZRA) (MVD<40 μ m & MVD>40 μ m). The capabilities
of the tools for FZRA are limited. To simulate accretions on unprotecte d surfaces and aft of protected areas, CFD codes may be used to de termine the difference in impingement region between FZRA and FZDZ. The increase in impi ngement area can then be simulated using a standard roughness in that region. For areas wher e a ridge of ice may form, a simulated ridge may be developed using a height developed an alytically based upon lo cal water catch. Ridge location could be developed from FZDZ tunnel te sts, and the height would be modified based upon the ratio of local water cat ch (determined with CFD) be tween FZDZ and FZRA. Other

concerns: Thermal Ice Protection Systems

— Analyses to assess water catch and melting/evaporation rates are acceptable for determining the cap abilities of thermal systems in FZRA, provided that the analyses are based upon the validated resu lts of the system capabilities performed for Appendix C and FZDZ. Any additiona l ice that may form on runback ice shapes in freezing rain should be accounted for by analys is of the runback volume. Potential roughness
effects ahead of the runback should be addressed.

Mechanical Ice Protection Systems — Fo r assessing mechanical ice protection system performance in FZRA, it is acceptable to us e the same pre-activation and intercycle and residual ice shapes as for FZDZ. The limits of accr etion should be determined using CFD tools.

Validation of Visual Cues — Use of qua litative analysis is acceptable for assessing whether visual cues used for FZDZ will function in FZRA conditions.

(b) Certification for a Portio n of Appendix O - § 23.1420(a)(2)
Current technology does not support disti nguishing between FZDZ and FZRA in flight. Because of this, airplanes should not be certificated for comp liance with § 23.1420(a)(2) based upon the boundaries between FZDZ and FZ RA. 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 dis tinguish between the appr oved portions and the unapproved portions of Appendix O w ith the current simulation tools. As a result, certification for a portion of Appendix O will be challengi ng and will require close coordination with certifying authorities. Certification for a portion of Appendix O that considers ph ase 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 porti on 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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(c) Certification fo r 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 cer tificated in accordance with § 23.1420(a)(3). However, the means of compliance should includ e flight tests in measured Appendix O icing
conditions.AC 23.1419-2E Appendix 8

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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 maximu m 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 a nd exit shapes must be increased if required for compliance to the maneuver margin requirements.

3. Landing distance (§ 23.75). The landing distances determ ined 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-engi nes-operating (§ 23.77).

When showing compliance with 23.1 420(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 co nfiguration, landing climb sp eed 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 airp lanes, the torque or pow er 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 maneuve rability. In the case of marginal compliance, or the force limits of § 23.143(c) being approached, additiona l substantiation may be necessary to establish compliance.AC 23.1419-2E Appendix 8

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Acceptable Test Program . The following represents an acce ptable test program for general controllability and maneuverability, subj ect 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 dedicat ed test points required, accomplished concurrently during other tests). d. Deploy and retract deceleration de vices 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 w ith all engines operating using the recommended procedure. f. Conduct an approach and landing using the reco mmended 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 w ithout longitudinal cont rol force reversal.

Changes in longitudinal control force to mainta in speed with increasing sideslip should be progressive, with no reversals or unacceptable discontinuities. Additionally, lateral control
movements and forces must not reverse and ther e should be no lateral co ntrol snatching (i.e. sudden, sharp oscillations or reversals in control force) with increasing an gle of sideslip .

Acceptable Test Program

.

a. The most critical weight, the most critical of aft or forward cente r 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 long itudinal control force reversal.AC 23.1419-2E Appendix 8

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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 sidesl ips to the sideslip appropria te for crosswind approach and landing with thrust or pow er 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 ai lerons. It is applicable to reversible and irreversible lateral control configurations since the effects of the following are being evaluated: Hinge moment reversal a nd other lateral anomalies Stall or partially stall of the outer wing

It should be possible to readily ar rest and reverse the roll rate us ing only lateral control input and
the lateral control force should not reverse wi th increasing control deflection. There is no quantitative requirement for roll rate but roll ra te capability should be qualitatively evaluated and shown to be adequate.

Acceptable Test Program . The following represents an acce ptable test program for general controllability and maneuverability, subj ect 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 la teral control deflection, ro ll 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 ai rplane passes a wings level attitude. v. Repeat the test procedure with 2/3 and then fu ll lateral control deflection unless the roll rate is judged to be excessive.AC 23.1419-2E Appendix 8

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Configuration Trim Speed

Holding configuration: minimum holdingspeed (highest expected holding angle-ofattack) Approach configuration VREF Highest lift landing c onfiguration: 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 positio ns (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. Ro ll excursions should not exceed the values in § 23.201(d) and 23.203(b)(4) by a large amount, and ro ll characteristics shoul d 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 w ith ice accretion show a signi ficant 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 accept able 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 substant iate 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 dura tion that only results in roughness, and the critical freezing rain ice shape should be flight tested. The number of these sh apes 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 ai rplane at the same initial stall speed factor used for stall speed determination. For power-on st alls, 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 id entification and recover using the same test technique as for the non-c ontaminated airplane. i. High lift devices retracted configuratio n: Straight/Power Off, Straight/Power On, Turning/Power Off, Turning/Power On. ii. Approach configuration: Strai ght/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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e. For at least one straight/power off stall in each configuration, during the deceleration and at speeds down to stall warn ing, roll aircraft left and right up to 10 degrees bank using lateral control. It must be possible to produce and correct roll by unreve rsed use of lateral control. There should be no snatching (i.e. sudden, sharp oscill ations or reversals in control force) of the pilot’s lateral control.

7. Stall Warning (§ 23.207). As stated in paragraph (i) of th e 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 Sy stem Operation (§ 23.207(h)). The detect and exit ice shape represents ice accretion after th e 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 sche dule designed for Appendix C ice accretions can comply with § 23.207(j). The intent is to avoid de signs that require pilot action to implement an Appendix O stall warning schedule. It is assumed that Appendi x 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 be low, trim the airplane at 1.5 VS1. i. High lift devices retracted configuratio n: Straight/Power Off, Straight/Power On, Turning/Power Off, Turning/Power On ii. Approach configuration: Stra ight/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 stal ling can be prevented using the same test technique as for the non-contaminated ai rplane, without enc ountering 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 A ppendix O icing conditions (for airplanes not certified for flight throughout the icin g conditions of Appendix O) (§ 23.207(h)). For assessing compliance with the i ce 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 ac tivation of the ice pr otection system are assumed to have taken place. The stall warning requirements for pre-de tection Appendix O (visual cues) are the same
as detect and exit. Therefore if one stall warning schedule is u tilized 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 complia nce with (§ 23.207(i).AC 23.1419-2E Appendix 8

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If the AFM will prohibit autopilot use followi ng detection of Appendi x O conditions, safe operation with autopilot engaged should be show n prior to detection of Appendix O conditions. Approaches to stall warning with pre-detection ice should be acco mplished to evaluate airplane response and verify acceptabl e 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 al l approach flap configur ations. 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 eval uated on an opportunity basis. The results of the steady heading sideslip tests w ith detect and exit ice ma y be used to establish the safe cross wind component. If the flight test data show th at the maximum sideslip angle
demonstrated is similar to that demonstrated with the noncontaminated airplane, and the flight characteristics (e.g. control forces and deflectio ns) are similar, then the non-contaminated airplane crosswind compone nt 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 rationa l analysis, a conservative analys is based on the results of the steady heading sideslip tests may be used to es tablish the safe crosswi nd 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 i ce accretion, or a reduced speed limit published in the AFM for SLD exit procedures.

14. Definition of Sideslip Angle Approp riate to the Type of the Airplane.

For the purpose of showing compliance the requireme nts 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 conservati vely crosswind operation, engine failure scenarios, and other conditions where sides lip may be experienced within the approved normal flight envelope.AC 23.1419-2E Appendix 8

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 In the absence of appropriate data, a c onservative approach is the adoption of:

o A value of 15 deg as a conservative appr oach provided that this value can be considered appropriate for the type of ai rcraft 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 theoreti cal sideslip value
for a 30 knots crosswind derived for tran sport category airplanes. This equation has been shown to conservatively repres ent (i.e., exceed) the sideslip angles
achieved in maximum crosswind takeoffs and landings and minimum static and dynamic control speed testing for a variet y of transport category airplanes.



##   kcas Airspeed V angle sideslip Where 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 valu e greater than the airpla ne capacity to generate sideslip at operational speeds repr esentative of takeoff and landing.

Note : The equation above maybe modified based on the experi ence of applicant by changing the constant value by th e demonstrated crosswind component obtained during the no-icing tests.

 Any other value agreed with the certification authority.AC 23.1419-2D Appendix 9

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APPENDIX 9. EXAMPLE FLIGHT TEST PROGRAM FOR COMPLIANCE TO § 23.21(C)(3) FOR APPROVAL TO TAKE OFF 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 si mulating 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 “tak eoff 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 i ce due to high flap deflection may have to be addressed).

3. The ice accretion(s) that has the mo st adverse effect on stall and handling qualities may be used for airplane performance te sts provided any difference in performance is conservatively taken into account.

4. The applicant should evaluate th e 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 surf aces may be analytically calculated.

5. Either the critical freezing drizzl e or freezing rain may be tested, if
substantiated to be more critical. Note that th e vertical extent of FZDZ is larger than FZRA.

c. Assumptions . For both unprotected and protecte d 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 a pplicable, propellers are free from frost, snow, or ice at the start of takeoff;

2. The test program assumes Type II, I II or IV fluids are approved for the airplane and these fluids keep th e lifting surfaces clean until lift-off;AC 23.1419-2E Appendix 9

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3. The ice accretion begins at liftoff;

4. The critical ratio of thrust/power-to-weight;

5. Failure of the critical engine occurs at V EF ; and

6. Crew activation of the ice protection system is in accordance with a normal operating procedure provided in the Airplane Fl ight Manual, except that after beginning the takeoff roll, it must be assumed that the crew ta kes 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 conf iguration, "Take-off Ice." 23.51 Takeoff speeds The values of V MCG and V MC determined for non-icing conditions may be used. The value of V S1 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 V 1 due to take-off in icing conditions may be determined by a suitable analysis. 23.57 Takeoff path The effect of the ta ke-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 th e 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 V S1 determined with applicable ice accretion.AC 23.1419-2D Appendix 9

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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-o ff 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 Hi ghest lift take-off conf iguration, 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 V S1 determined with “Enroute Ice.” Not applicable if climb speed and serv ice ceiling icing/non-icing comply with regulation.

23.69(b) Enroute flight path OEI Evaluated w ith “Enroute Ice.” Climb speeds are based

on V S1 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 appropr iate flight phasesAC 23.1419-2E Appendix 9

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23.45 General (performance) Applicable.

23.143(b) Smooth transitions in
conditions It must be possible to ma ke a smooth transition from one flight condition to an other (including turns and slips) without danger of exceeding the limit load factor, under any probable operating condition. AEO only. May be evaluated concur rently 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, V 50 or V 2 , "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, V 50 V 2 , "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 configur ation, "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

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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 configur ation, "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 a pproved takeoff high lift configurations with “Takeoff Ice.”

23.151 Acrobatic maneuvers Required for acroba tic and utility ai rplanes 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 Ic e. 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, 1.2V S or 1.1V MC , whichever is higher, "Final Takeoff Ice."

23.161 Trim Evaluated concurre ntly with ot her 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 RE VISION TO AC 23.1419-2D

23.45 General (performance) Applicable.

23.175 Demonstration of Static Long. Stab. Only paragraph (a) is ap plicable, evaluated with

“Enroute Ice”.

23.177 Static lateraldirectional stability Approved take-off lift configurations, V 50 or V 2 , "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 th at there are no marginal compliance aspects with the non-contaminated airplane, it is not necessary to demonstrate dynamic stability in specific tests. Qualitative evaluations shoul d 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 a nd turning stalls only. No accelerated turning stall. Configurations
evaluated:

All approved take-off lift configurations, "Takeoff

Ice."

Lowest lift take-off configur ation, “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 a ssessed in conjunction with stall speed testing and sta ll characteristics testing.AC 23.1419-2D Appendix 9

A9-7 

### Part 23 SLD ARC REPORT
APPENDIX D – RECOMMENDED RE VISION 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 tu rns at specified bank:

Approved take-off lift configurations, V 50 or V 2 , 40° bank, "Takeoff Ice."

Approved take-off lift configurations, V 50 or V 2 , 30° bank, simulated thrust for OEI, "Takeoff Ice."

Lowest lift take-off configuration, all-enginesoperating initial climb spee d, 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 te sts. Crosswind capability can be determined similar to Appendix C.

23.235 Operation on unpaved
surfaces Not required.

23.237 Operation on water Appli cable – no dedicated testsAC 23.1419-2E Appendix 9

A9-8 

### Part 23 SLD ARC REPORT
APPENDIX D – RECOMMENDED RE VISION 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, V
ne , 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 freezi ng rain conditions, several scenarios that result in additional ice accretions are possible:

1. The airplane has to immedi ately 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 condi tions in a subsequent flight phase
and must exit.

b. In the last two scenarios, ice may or ma y not sublimate off, depending on the flight and ambient conditions. It is possible that freezi ng 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 accr ete. 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 subs tantiate 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 A ppendix O detect and exit ice shapes that are empirically determined by combining the critic al Appendix O takeoff i ce 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 hol ding need not be considered).AC 23.1419-2D Appendix 9

A9-9 

### Part 23 SLD ARC REPORT
APPENDIX D – RECOMMENDED RE VISION 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 observa tions 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 chan ges 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 receiv ed 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 airp lanes 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 wi th 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 fr eezing 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 wint er seasons did you have to divert your Part 23 aircraft because of freezi ng 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 wi nter 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 3Part 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-1Part23IcingAccidentSurveyFAA-SADP-231cingARCPart 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-2DifferencesBetweenP23&P25•Part23hasmanytimesmoreaccidentseachyearwhencomparedtopart25+Training groundsfor newpilots+Lessregulationonprivateuse+Fewerprofessionalflightcrews+Fewer typeratingrequiredaircraft+Etc.•Numberofaccidentsallowsforstatisticallyrelevantanalysisnotpossibleinpart25FMSPDP-23lcingPRCPart 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-3U.S.ActiveAircraft•PistonTurboprop•TurbojetRotorcraft_Gliders_lighterThanAirActiveAircraftExperimentalLightSport•320,000Worldwide•228,000US•163,103U.S.Piston•145,497USSinglePiston•17.515USTwinPistonSoure",tAAFAA-SADP-231cingARCPart 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-4PistonAirplanesManufacturedAnnuallyu.s.ActivePistonFleet163,103AirplanesL{)0L{)0L{)0L.()0L{)0L{)coL()<.D <.DI'--- I'---OJ OJa:>0)0 0 00) 0) 0) 0) 0) 0) 0) 0) 0)000...--- ...--- ...--- ...--- ...--- ...--- ...--- ...--- ...---C"J C"J C"JGil"""Stati..;...Dat.Part 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-52008U.S.ActivePistonFleetHours•SingleEngine§91TwinEngine§91•SingleEngine§135TwinEngine§135292,000404,0002,328,000r--......-.12,746,000FAA-SADP-231cingARCPart 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-6PopulationofData•NTSBIcingAccidents1990-2009+DatasetprovidedtoGAOduring2010independentreview of icingaccidents+NTSBdatafrom1988+ is standardizedoCommonaccidentthemesoFrequencyofevents•457"IcingAccidents"from1990-2009+Fatal-212+SeriousInjury-51+MinorInjury- 48+NoInjury-146FMSPDP-23lcingPRCPart 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-71:DJ1[(()TotalGAAccidentstoP-23IcingAccidentsGAAccidentsto P-23lcingAccidents (1990-2009NTSBData)r---------"""-0GAAccidents_P-23lcingAccidentsP.231dngaccktllfltsal1l124%ofGAacddentIov..last:20yeaT1(1990-2009HTSSData)P·23tctngaCddentlhawdedlNdbyabou:3tlm...lnceth.earty1990,(1m·2009NTSBData)__-r__--______-'--________--,-419991991199219931994199519951997 19951999=2001200220032004==2007= =FMSPDP-23lcingPRCPart 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-8400100FatalGAAccidentstoFatalP-23IcinAccidentsGAFatalAccidentstoP-23FatalIcingAccidents(1990-2009NTSBData)\----.,•GAFatalAccidents_P-23IcingFatalAccidentsFmlP-23IcingIcddenbllre2.94%offabilGAIcddenblOVIfInt20YUfW(1990-2009NTS8Data)FltalP·23Icing..cddMtlhavededlnedbyIbcti:hatfsincethearty1990. (1990-2009NTSBData)199919911992 1993 19941995 19951997 19951999=2001=20032004= =2007= =FMSPDP-23lcingPRCPart 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-9CommonThemes•MajorThemes:+Non-FIK Iaircraftintoforecasticingconditions+Attemptedflightwithgroundice&frost+Lossofforwardvisibility+StallonLandingtoSomeAccumulations+InductionSystemIcing+SLDoverwhelmsde/anti-IcesystemsFMSPDP-23lcingPRCPart 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-10"Other"IcingAccidents•StallonApproachDuetoSomeIce•FrozenPitot/Static•Anti/De-IceSystemFailures•Didn'tUseAnti-IceSystem•LossofTractiononLanding•Didn'tMaintainMinimumIcingAirspeed•UnknownFMSPDP-23lcingPRCPart 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-111990·2001§23IcingAccidentCausesTnT"•IcingwiNoEqpt.Gnd.Ice/Frost•SLD(w/FIKI)Induction Ice(FIKI).WindshieldIcingOther15%20%FAA-SADP-231cingARCPart 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-121990·2001§23FatalIcingAccidentCauses109Total•IcingwiNoEqpt.Gnd.Ice/Frost•SLD(w/FIKI)InductionIce(FIKI).WindshieldIcingOther1%19%3%5%13%FAA-SADP-231cingARCPart 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-13"Other"IcingAccidents•StallonApproachDuetoSomeIce•FrozenPitot/Static•Anti/De-IceSystemFailures•Didn'tUseAnti-IceSystem•LossofTractiononLanding•Didn'tMaintainMinimumIcingAirspeed•UnknownFMSPDP-23lcingPRCPart 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-141990·2001§23FIKIlcingAccidentCauses51Total_WindshieldIcingStallonFlare_SLD(w/FIKI)GroundIce_FailedSystemSkidonRunway_Other4%12%12%FAA-SADP-231cingARCPart 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-151990·2001§23FatalFIKIApprovedlciAccidentCausesTotal•WindshieldIcingDidn'tUseGroundIce•FailedSystem17%13%22%FAA-SADP-231cingARC.SLDOther18%Part 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-16OperationalRuleEffectiveness•OperationalIssues•LargeSafetyBenefit(ExistingFleetsoLarge)•MoreDifficulttoControlthan DesignoAssume30%EffectivePeak(RampUp/RampDown)•MajorityofAccidentsareOperationalIssues.53%FlightintoicingwinoequipmentoEducationCampaign(30%Effective)=15%ReductioninIcingAccidentsImmediately.20%GroundicingtakeoffsoEducationCampaign(30%Effective)=6%ReductioninIcingAccidentsImmediatelyFMSPDP-23lcingPRCPart 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-17DesignRuleEffectiveness•DesignRuleEffectiveness+SmallerSafetyBenefit+MoreDefiniteResults+SlowerBenefit(NewModelstoExistingModels)oExistingFleet228,000Airplanes01%retiremenUyearoNewNon-FI K1-1333/yearoNewFIKI(SLDProof)-1616peryearoNewDesignsAdopted@ 1O%/yeartoyear10FMSPDP-23IcingPRCPart 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-18DesignRuleEffectiveness•SLDRepresents6%ofAccidentsToday+"Bulletproof'Design(100%effective,TypicalProductionRates,10%NewDesignAdoptionfYear)5101520FMSPDP-23lcingPRCTotalIcingAccidentReduction0%0%0.2%0.4%0.6%FatalIcingAccidentReduction0%0%0.1%0.3%0.5%FIKllcingAccidentReduction0%0.1%0.4%0.9%1.3%FatalFIKIAccidentReduction0%0.1%0.7%1.6%2.5%Part 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-19SuggestedDirection•AutoIceDetectionRepresents18%ofFatalFIK IAccidentsToday+"Bulletproof'Design(100%effective,TypicalProductionRates,10%NewDesignAdoptionfYear)FMSPDP-23lcingPRCFatalFIKIAccidentReduction0%50.1%10.5%151.1%201.7%Part 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-20DesignRuleEffectiveness•FailureDetectionRepresents12%ofFIK IEquippedAccidentsToday+"Bulletproof'Design(100%effective,TypicalProductionRates,10%NewDesignAdoptionfYear)5101520FMSPDP-23lcingPRCFIKllcingAccidentReduction0%0.1%0.3%0.7%1.1%FatalFIKIAccidentReduction0%0.1%0.3%0.7%1.1%Part 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-21SummaryChart•ReductionsinTotallcingAccidents(23peryear)5101520Total20yrFlightintoIcingwloEquip.5%10%15%10%5%47TakeoffwlGroundFrost2%4%6%4%2%19SLDIcing0%0%0.2%0.4%0.6%-=OperationalChanges-=DesignChangesFMSPDP-23lcingPRCWISIcing0%0.1%0.7%1.6%2.5%4Part 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-22SummaryChart•ReductionsinFatallcingAccidents(10peryear)5101520Total20yrFlightintoIcingwloEquip.6%12%18%12%6%24TakeoffwlGroundFrost1%2%4%2%1%4SLDIcing0%0%0.1%0.3%0.5%0-=OperationalChanges-=DesignChangesFMSPDP-23lcingPRCW/SIcing0%0.0%0.0%0.1%0.1%0Part 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-23SummaryChart•ReductionsinFIK IApprovedIcingAccidents(5per0% 0% 0%1%0%50.1% 0.1% 0.1%2%0.1%100.5%0.5%0.4%4% 0.3%151.2%1.1% 0.9%2%0.7%201.8%1.7%1.3%1%1.1%Total20yr 10 2 0-=OperationalChanges-=DesignChangesFMSPDP-23lcingPRCPart 23 SLD ARC REPORTAPPENDIX F – GAMA PART23 ICING ACCIDENT SURVEYFEB 2012 - Revision BPage F-24SummaryChart•ReductionsinFatalFIKIApprovedIcingAccidents(2peryear)0% 0% 0%2%0%50.1% 0.1% 0.1%4%0%10.5%0.3%0.7% 7%0.1%151.1%0.7%1.6%4%0.2%201.7%1.1%2.5%0.41.1%Total20yr0 0 0 2 0-=OperationalChanges-=DesignChangesFMSPDP-23lcingPRC