U.S. Department 

of Transportation 

Federal Aviation

Administration

Advisory 

Circular

 

Subject: CERTIFICATION OF PART 

23 AIRPLANES FOR FLIGHT IN 

ICING CONDITIONS

Date: April 19, 2007 

Initiated by: ACE-100

AC No: 23.1419-2D

FOREWORD 

This advisory circular (AC) sets forth an acceptable means of showing compliance with Title 14 

Code of Federal Regulations (14 CFR), part 23, for the approval of airplane ice protection 

systems for operating in the icing environment defined by part 25, Appendix C. 

S/Charles L. Smalley 

Charles L. Smalley 

Acting Manager, Small Airplane Directorate 

Aircraft Certification Service. 

4/19/07 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 ............................................................................................ 5 

 8. Planning.................................................................................................. 5 

 9. Design Objectives................................................................................... 6 

10. Analyses and Ground Testing ................................................................ 6 

 11. Flight Test Planning ............................................................................... 18 

 12. Flight Tests............................................................................................. 19 

13. Performance and Flying Qualities.......................................................... 29 

 14. Ice Shedding ........................................................................................... 48 

15. Placarding and AFM .............................................................................. 49 

16. Instructions for Continued Airworthiness.............................................. 54 

17. Ground Deicing Fluids........................................................................... 62 

Appendix 1 Definitions.............................................................................................. A1-1 

Appendix 2 Guidelines for Determining Certification Basis on Flight in Icing 

Approval STCs and Amended TCs.................................................... A2-1 

Appendix 3 Guidelines for Supplemental Type Certificates (STC) and 

Amended Type Certificates on Airplanes.......................................... A3-1 

Appendix 4 Guidelines for Certifying Ice Protection Systems on Airplanes 

Not for Flight in Icing Approval (“Non-Hazard” Basis) ................... A4-1 

Appendix 5 Guidelines for Approval of Replacement Parts for Airframe

 Deicing Systems................................................................................. A5-1 

Appendix 6 Part 23 Subpart B Tests for Section 23.1419 at Amendment 23-43 ...... A6-1 

Appendix 7 Ice Contaminated Tailplane Stall ........................................................... A7-1 

Appendix 8 AFM Limitations and Normal Procedures Sections............................... A8-1 

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 

5-1 Summary of Test Requirements for Replacement of 

Airframe Deicing Components....................................................... A5-1

6-1 Part 23 Subpart B Tests for Section 23.1419 at Amendment 23-43 ... A6-1

iii (and iv) 

4/19/07 AC 23.1419-2D 

1. What is the purpose of this AC? This Advisory Circular (AC) sets forth an acceptable 

means, but not the only means, of demonstrating compliance with the ice protection requirements 

in Title 14 of the Code of Federal Regulations (14 CFR) part 23. The Federal Aviation 

Administration (FAA) will consider other methods of demonstrating compliance that an applicant 

may elect to present. This material is neither mandatory nor regulatory in nature and does not 

constitute a regulation. 

2. Who does this AC apply to? The guidance provided in this document is directed to airplane 

manufacturers, modifiers, foreign regulatory authorities, and FAA small airplane type 

certification engineers, and their designees. This AC applies to airplane ice protection systems in 

any normal, utility, acrobatic or commuter category part 23 airplane. 

3. Cancellation. AC 23.1419-2C, Certification of Part 23 Airplanes for Flight in Icing 

Conditions, dated July 21, 2004, and AC 23.143-1, Ice Contaminated Tailplane Stall (ICTS), 

dated December 20, 2001, are canceled. In addition, all policy related to the certification of ice 

protection systems on part 23 airplanes, issued prior to this AC, and is superseded by this AC. 

4. Applicability. The guidance provided here applies to the approval of airplane ice protection 

systems for operating in the icing environment defined by part 25, Appendix C. The guidance 

should be applied to new Type Certificates (TCs), Supplemental Type Certificates (STCs), and 

amendments to existing TCs for airplanes under part 3 of the Civil Aviation Regulations (CAR) 

or its predecessor regulations, and part 23, for which approval under the provisions of § 23.1419 

is desired. 

5. Related Regulations and Documents. 

a. Regulations. By their adoption in amendment 23-14, which shows their requirements are 

directly related, §§ 23.929, 23.1309, and 23.1419 are applicable to a part 23 airplane icing 

certification program regardless of the certification basis for the basic airplane; however, for those 

airplanes certificated in accordance with part 3 of the CAR or earlier, and through part 23 at 

amendment 23-13, the application of these sections may be limited to the equipment being used 

for ice protection. Some systems that were previously approved on the airplane may need to be 

modified to improve their reliability when those systems are utilized as part of that airplane's icing 

approval. 

(1) With the adoption of amendment 23-43, § 23.1419 was revised to do the following: 

to specify that the performance, controllability, maneuverability, and stability must not be less 

than that required by subpart B of part 23; add the requirement for flight testing in measured, 

natural icing conditions; provide specific test requirements; clarify the requirements for 

information that must be provided to the pilot, and allow approval of equivalent components that 

have been previously tested and approved, and that have demonstrated satisfactory service if the 

installations are similar. 

1
AC 23.1419-2D 4/19/07 

(2) Prior to the adoption of amendment 23-43, some part 23 airplanes were certificated 

for flight in icing using § 25.1419. 

(3) In addition to the previously mentioned requirements (§§ 23.929, 23.1309, and 

23.1419), other sections should be applied depending upon the ice protection system design and 

the original certification basis of the airplane. Refer to AC 20-73A, Appendix C, Table C-2. 

Many of the requirements in Table C-2 of AC 20-73A are also applicable, even without approval 

for flight in icing conditions. Further guidance on establishing a certification basis for flight in 

icing approval can be found in Appendix 2 of this AC. 

b. ACs. Copies of current editions of the following publications may be downloaded from

the FAA's Regulatory and Guidance Library (RGL) www.rgl.faa.gov or obtained from the U.S. 

Department of Transportation, Subsequent Distribution Office, Ardmore East Business Center, 

3341 Q 75th Avenue, Landover, MD 20785: 

AC 20-73A “Aircraft Ice Protection,” August 16, 2006. 

AC 20-115B “Radio Technical Commission for Aeronautic, Inc. Document 

RTCA/DO-178B,” January 11, 1993. 

AC 20-117 “Hazards Following Ground Deicing and Ground Operations in 

Conditions Conducive to Aircraft Icing,” December 3, 1982.

AC 20-147 “Turbojet, Turboprop, and Turbofan Engine Induction System Icing 

and Ice Ingestion,” February 2, 2004. 

AC 21-16E “RTCA Document DO-160E, Environmental conditions and Test 

Procedures for Airborne Equipment,” December 20, 2005. 

AC 21-40 “Application Guide for Obtaining a Supplemental Type Certification,” 

May 6, 1998. 

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

 Aeronautical Products,” April 28, 2003. 

 

AC 23-16A “Powerplant Guide for Certification of Part 23 Airplanes and 

Airships,” February 23, 2004. 

AC 23-17B “Systems and Equipment Guide for Certification of Part 23 

Airplanes,” February 23, 2004. 

AC 23.629-1B “Means of Compliance with Title 14 CFR, Part 23, § 23.629, Flutter,” 

September 28, 2004. 

2 
4/19/07 AC 23.1419-2D 

AC 23.1309-1C “Equipment, Systems, and Installations in Part 23 Airplanes,” March 

23, March 12, 1999. 

AC 91-74 “Pilot Guide Flight in Icing Conditions,” December 12, 2002. 

AC 120-58 “Pilot Guide Large Aircraft Ground Deicing,” September 30, 1992. 

AC 120-60B “Ground Deicing and Anti-icing Program,” December 20, 2004. 

AC 135-16 Ground Deicing & Anti-icing Training & Checking,” December 12, 

 1994. 

AC 135-17 Pilot Guide-Small Aircraft Ground Deicing (pocket),” December 14, 

 1994. 

Copies of the current AC may be purchased from the Superintendent of Documents, P.O. Box 

371954, Pittsburgh, PA 15250-7954. Make check or money order payable to the Superintendent 

of Documents: 

AC 23-8B “Flight Test Guide for Certification of Part 23 Airplanes,” August 14, 

 2003. 

6. Related Reading Material.

a. FAA Orders. 

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

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

National Technical Information Service in Springfield, Virginia 22161: 

(1) FAA Technical Report DOT/FAA/CT-88/8, "Aircraft Icing Handbook" (March 

1991), includes reference material on ground and airborne icing facilities, simulation procedures, 

and analytical techniques. This document represents all types and classes of aircraft and is 

intended as a working tool for the designer and analyst of ice protection systems. Updates can be 

found on the FAA Technical Center web site: 

http://aar400.tc.faa.gov/Programs/FlightSafety/icing/eaihbk.htm 

(2) FAA Technical Report ADS-4, "Engineering Summary of Airframe Icing Technical 

Data," and Report No., FAA-RD-77-76, "Engineering Summary of Powerplant Icing Technical 

Data," provide technical information on airframe and engine icing conditions, and methods of 

detecting, preventing, and removing ice accretion on airframes and engines in flight. Although 

most of the information contained in ADS-4 and FAA-RD-77-76 reports is still valid, some is 

3 
AC 23.1419-2D 4/19/07 

outdated, and more usable information is now available through recent research and experience, 

and is included in the Aircraft Icing Handbook. 

(3) FAA Technical Report DOT/FAA/AR-01/91, "A History and Interpretation of 

Aircraft Icing Intensity Definitions and FAA Rules for Operating in Icing Conditions" (November 

2001), provides a good reference for understanding icing operational rules. 

(4) FAA Technical Report DOT/FAA/AR-02/68, "Effect of Residual and Intercycle Ice 

Accretions on Airfoil Performance" (May 2002), details icing tunnel testing to determine 

intercycle and residual ice on a 23012 airfoil, and wind tunnel testing of uniform sandpaper and 

intercycle ice shapes. 

(5) FAA Technical Report DOT/FAA/CT-TN86/11, “Fluid Ice Protection Systems,” 

July 1986. 

(6) National Aeronautics and Space Administration (NASA)/TP—2000-209908, 

“NASA/FAA Tailplane Icing Program: Flight Test Report” (March 2000), provides reference 

information on Ice Contaminated Tailplane Stall (ICTS). Assumptions, ice shapes, and certain 

other data are not necessarily representative or appropriate for use with other projects. The above 

report and other reference material on ICTS are also available at the NASA Glenn Research 

Center Icing Branch website: icebox.grc.nasa.gov. 

c. Technical Standard Order (TSO): A copy of the current edition of the following 

publication may be obtained from the Federal Aviation Administration, Aircraft Certification 

Service, Aircraft Engineering Division, Technical Programs and Continued Airworthiness 

Branch—AIR-120, 800 Independence Avenue, SW, Washington, DC 20591 or from the FAA 

website at www.faa.gov: 

TSO-C16 “Air-Speed Tubes (Electrically Heated),” September 1, 1948. 

TSO-C16a “Electrically Heated Pitot and Pitot-Static Tubes,” October 6, 2006. 

TSO-C54 “Stall Warning Instruments,” October 15, 1961. 

d. SAE Documents. The Society of Automotive Engineers (SAE), Inc. Aerospace 

Recommended Practice (ARP) and Aerospace Information Report (AIR) documents are available 

from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001 or from their website at 

www.sae.org: 

ARP4761 “Guidelines and Methods for Conducting the Safety Assessment Process on 

Civil Airborne Systems and Equipment,” December 1, 1996.

AIR4367 “Aircraft Ice Detectors and Icing Rate Measuring Instruments, “April 1, 

 1995. 

4 
4/19/07 AC 23.1419-2D 

AIR5504 “Aircraft Inflight Icing Terminology,” September 17, 2002. 

AIR1168/V1 “Ice, Rain, Fog, and Frost Protection,” July 1, 1989, part of “Applied 

Thermodynamics Manual,” September 1, 1992. 

 . 

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. 

The SAE and a working group for Task 11A of the FAA Inflight Aircraft Icing Plan have 

developed the following documents: 

ARP5903 “Droplet Impingement and Ice Accretion Computer Codes, October 16, 

 2003. 

ARP5904 “Airborne Icing Tankers,” October 21, 2002. 

ARP5905 “Calibration and Acceptance of Icing Wind Tunnels,” September 18, 2003. 

e. Miscellaneous Documents. 

(1) British Specification (BS) 2G-135, “Specification for Electrically-Heated Pitot and 

Pitotstatic Pressure Heads,” 1967. 

(2) American Society for Testing and Materials (ASTM) G76-95, “Standard Test 

Method for Conducting Erosion Tests by Solid Particle Impingement Using Gas Jets”

7. Background. 

AC 20-73A contains a detailed history of ice protection regulations for part 23 airplanes. 

8. Planning.

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

with FAA Order 8110.4C and AC 20-73A. The certification plan should describe all of the 

applicant's efforts intended to lead to certification. This plan should identify, by item to be 

certificated, the certification methods that the applicant intends to use. It should provide for a 

certification checklist. Regarding § 23.1419, it should clearly identify analyses and tests, or 

references to similarity of designs that the applicant intends for certification of the ice protection 

system. These methods of showing compliance should be agreed upon between the applicant and 

the FAA early in the type certification program. Detailed guidance for STCs or amended TCs on 

5 
AC 23.1419-2D 4/19/07 

part 23 airplanes approved for flight in icing can be found in Appendix 3 of this AC. It is 

imperative that the applicant obtains FAA concurrence prior to conducting certification tests. 

b. Installations without Flight in Icing Approval. There may be times when applicants 

may want to certificate an ice protection system installation but do not want to obtain flight in 

icing approval. In the past these systems have been called “non-hazard” installations. This means 

that the aircraft is prohibited from flight in icing conditions but there is some ice 

protection to facilitate an exit from an inadvertent icing encounter. Guidance for the approval of 

these types of ice protection systems can be found in Appendix 4 of this AC. 

c. Replacement Parts for Airframe Ice Protection Systems. The requirements leading to 

approval of replacement airframe deicing systems or airframe thermal deicing or anti-icing 

systems are detailed in Appendix 5 of this AC. 

9. Design Objectives. The applicant must demonstrate by analyses and tests that the 

airplane is capable of safely operating throughout the icing envelope of part 25, Appendix 

C. The envelope can be reduced for airplanes certificated for operation where systems or 

performance limitations (e.g., altitude), not related to ice protection, exist. 

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

substantiate decisions involving application of selected ice protection equipment and to 

substantiate decisions to leave normally protected areas and components unprotected. Such 

analyses should clearly state the basic protection required, the assumptions made, and 

delineate the methods of analysis used. All analyses should be validated either by tests or by 

methods agreed to by the FAA. This substantiation should include a discussion of the 

assumptions made in the analyses and the design provisions included to compensate for 

these assumptions. Analyses are normally used for the following: 

a. Areas and Components to be Protected. The applicant should examine the areas listed 

in AC 20-73A to determine the degree of protection required. 

An applicant may find that protection is not required for one or more of these areas and 

components. If so, the applicant should include supporting data and rationale in the analysis for 

allowing them to go unprotected. The applicant should demonstrate that allowing them to go 

unprotected does not adversely affect the handling or performance of the airplane. 

b. Ice Accretion Analyses. 

(1) Impingement Limit Analyses. The applicant should prepare a drop impingement 

and water catch analysis of the wing, horizontal and vertical stabilizers, propellers, and any other 

leading edges or protuberances such as antennas that may require protection. This analysis should 

consider the various airplane operational configurations and associated angles of attack. This 

analysis is needed to establish the upper and lower aft droplet impingement limits that can then be 

used to establish the aft ice formation limit and the extent of the protection surface coverage 

6 
4/19/07 AC 23.1419-2D 

needed. The applicant should consult AC 20-73A, “Aircraft Ice Protection” for more detailed 

information. 

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

characteristics are to be evaluated should be determined for each flight phase as discussed in 

paragraph 13.b. of this AC. The parameters to be considered are the flight conditions (e.g., 

airplane configuration, airspeed, angle of attack, altitude) and the icing conditions of part 25, 

Appendix C (temperature, liquid water content, mean effective drop diameter). The applicant 

should substantiate the critical mean effective drop diameter, Liquid Water Content (LWC), and 

temperature that result in the formation of an ice accretion that is critical to the airplane's

operational characteristics. For deicing systems, intercycle, residual, and runback ice accretions 

should be considered. 

(3) The 45-Minute Hold Condition. The 45-minute hold criterion should be evaluated 

when determining critical ice shapes for which the operational characteristics of the overall 

airplane are to be analyzed. See AC 20-73A for more information. 

(a) A mean effective droplet diameter of 22 microns and a liquid water content of 

0.5 gm/m3

 with no horizontal extent correction are normally used for this analysis; however, the 

applicant should substantiate the specific values used, including temperature, which represent the 

critical conditions for the airplane's performance and handling qualities. Critical flight conditions 

should be considered such as weight and speed for critical angle of attack, and airspeed and 

altitude for maximum water catch. For example, minimum holding speed should be evaluated, 

but a higher airspeed that the airplane may operate at may be more critical because of the lower 

angle of attack and higher water catch. 

(b) The critical ice shapes derived from this analysis should be compared to critical 

shapes derived from other analyses (climb, cruise, and descent, approach) to establish the most 

critical simulated ice shapes to be used during dry air flight tests. 

c. Airframe. 

(1) Structural Analyses. 

(a) The structural analyses should include analyses which establish that critical ice 

build-ups on antennas, masts, and other components attached externally to the airplane do not 

result in hazards. Flight tests in simulated or natural icing conditions or with simulated ice shapes 

may be used to substantiate the structural analyses; however similarity to previous approved 

designs is a common method of compliance. 

(b) Determine that the temperature gradient produced on heated windshields does 

not adversely affect windshield structural integrity. 

(2) Flutter Analyses. AC 23.629-1B, “Means of Compliance with Title 14 CFR, Part 

23, § 23.629, Flutter,” provides guidance for showing compliance with § 23.629. The flutter 

7 
AC 23.1419-2D 4/19/07 

analyses should reflect any mass accumulations on unprotected and protected surfaces from

exposure to part 25, Appendix C icing conditions, including any accretions that could develop on 

control surfaces. The 45-minute hold should also be considered. Ice accretions due to failure of 

the ice protection system should also be addressed. 

d. Power Sources. 

(1) Power Source Analysis. The applicants should evaluate the power sources in their 

ice protection system design. Electrical, bleed air, and pneumatic sources are normally used. A 

load analysis or test should be conducted on each power source to determine that the power 

source is adequate to supply the ice protection system, plus all other essential loads throughout 

the airplane flight envelope under conditions requiring operation of the ice protection system. 

(2) Effect on Essential Systems. The effect of an ice protection system component 

failure on power availability to other essential loads should be evaluated, and any resultant hazard 

should be prevented on multi-engine designs and minimized on single-engine designs. The 

applicant should show that there is no hazard to the airplane in the event of any power source 

failure during flight in icing conditions. Two separate power sources (installed so that the failure 

of one source does not affect the ability of the remaining source to provide system power) are 

adequate if the single source can carry all the essential loads. 

(a) Two-Engine Airplanes require two sources in accordance with § 23.1309(c). 

All power sources that affect engine or engine ice protection systems for multi-engine airplanes 

must comply with the engine isolation requirements of § 23.903(c). 

(b) Single-Engine Airplanes. Section 23.1309(a) requires that the ice protection 

system be designed to minimize hazards to the airplane in the event of a probable malfunction or 

failure. Failure condition classifications of “major”, “hazardous” or “catastrophic” are considered 

hazards. Complete loss of the airframe ice protection system has been considered at least “major” 

on past single engine certification programs. Since experience has shown that the failure of 

generators currently in service is probable, for example, systems that utilize a generator, such as 

an alternator, would require two sources of electrical power. This is also consistent with past 

project specific guidance on interpretation of § 23.1309, which stated that the level of safety in a 

single engine airplane is established by engine reliability and the ice protection system should not 

compromise it. For other types of power sources, additional reliability evaluation of the power 

source under system loads and environmental conditions may be required if a single source 

system is planned. 

(c) Load Shedding. Determine if load shedding can be accomplished after a 

partial failure condition. If applicable, a load shedding sequence should be provided so the pilot 

may assure that adequate power is available to the ice protection equipment and other necessary 

equipment for flight in icing conditions. 

(3) Electromagnetic Compatibility. The effect, if any, of ice protection system

operation on other airplane systems must be determined to show compliance to § 23.1309(a). 

8 
4/19/07 AC 23.1419-2D 

(a) Designs should minimize Magnetic Direction Indicator (MDI) deviations. If 

the ice protection system causes greater than an l0-degree deviation, then the placard requirement 

of § 23.1327 (amendment 23-20) should be applied in lieu of previous requirements. Refer to 

AC 23-17B for guidance on using a magnetic compass as a mitigating factor in a system safety 

assessment for cockpit heading display. 

e. Failure Analysis. AC 23.1309-1C provides guidance and information for an acceptable 

means, but not the only means, for showing compliance with the requirements of § 23.1309(a) 

and (b) (amendment 23-49) for equipment, systems, and installations in 14 CFR, part 23 

airplanes. The regulatory requirements are in § 23.1309. Substantiation of the hazard 

classification of ice protection system failure conditions is typically accomplished through 

analyses and/or testing. It has been standard industry practice to assign a probability of 

encountering icing conditions of “one” for an airplane certificated for flight in icing.

(1) During the analyses, each identifiable failure within the system should be examined 

for its effect on the airplane and its occupants. Examples of failures that need to be examined 

include: 

(a) Those that allow an ice shape to accrete in size greater than design levels , to 

accrete asymmetrically, or accrete in areas that were normally protected; or 

(b) System failures such as loss of pneumatic boot vacuum, overheat of a thermal 

system, or leak in a hot air bleed air line. 

(2) A probable malfunction or failure is any single malfunction or failure that is 

expected to occur during the life of any single airplane of a specific type. This may be

determined on the basis of past service experience with similar components in comparable 

airplane applications. This definition should be extended to multiple malfunctions or failure 

when: 

(a) The first malfunction or failure would not be detected during normal operation 

of the system, including periodic checks established at intervals that are consistent with the degree 

of hazard involved; or

(b) The first malfunction would inevitably lead to other malfunctions or failures. 

A procedure requiring a pilot to exit icing conditions would not be acceptable after any failure 

condition that would become catastrophic within the average exposure time it takes to exit icing 

conditions. 

(3) Power Source Failure. Assure that no probable failure or malfunction of any power 

source (electrical, fluid, bleed air, pneumatic, and so forth) will impair the ability of the remaining 

source(s) to supply adequate power to systems essential to safe operation during icing flight. 

9 
AC 23.1419-2D 4/19/07 

(4) Failure Annunciations. Warning information must be provided to alert the crew to 

unsafe system operating conditions and to enable them to take appropriate corrective action in 

accordance with § 23.1309(b)(3). 

(a) The requirement for warning information in § 23.1309(b)(3) is dependent on 

the severity of the failure, not dependent on the probability of the failure. 

(b) A means to indicate to the crew that the ice protection system is receiving 

adequate electrical power, bleed air pressure, vacuum, or fluid pump output, and so forth, as 

appropriate, and it is functioning normally. Annunciation would not be required for obvious, 

inherent failures, such as failure of a fluid windshield system. 

(c) Means to indicate that the pneumatic deicing boot system is receiving adequate 

pressure is required in accordance with § 23.1416. 

1. The boots should be shown to operate at the pressure threshold of the 

annunciation. 

2. Annunciation when the boots are receiving adequate pressure has been 

used in previous certifications. For boots that cycle automatically, annunciation lights may be 

provided when the boots are not receiving adequate pressure when commanded, in lieu of lights 

that illuminate during each inflation cycle. This promotes the dark cockpit concept, and it’s easier

to detect the presence of a light rather than the absence of a light. 

3. Annunciations of failures should be consistent with § 23.1309(b)(3) and 

§ 23.1322. 

(5) Circuit and Protective Devices. 

(a) Determine that the design incorporates electrical overload protection that opens 

regardless of operating control position. 

(b) Verify that the design is such that no protective device is protecting more than 

one circuit essential to continued safe flight (for example, pitot heat and stall warning transducer 

heat are considered separate essential circuits and should be provided separate protection). 

(c) Ice protection monitor and warning circuits should be considered separate from

control circuits and each should provide individual circuit protection. 

(d) On airplanes equipped with dual power sources, a power distribution system 

having a single bus and a single circuit breaker protecting the ice protection system is not 

acceptable.

(6) Windshield Heat Systems. There are requirements in § 23.775(g). A probable 

single failure of a transparency heating system should not adversely affect the integrity of the 

airplane cabin or create a potential danger of fire.

10 
4/19/07 AC 23.1419-2D 

f. Similarity Analyses. 

(1) In the case of certification based on similarities to other type certificated airplanes 

previously approved for flight in icing conditions, the applicant should specify the reference 

airplane model and the component to which the reference applies. Specific similarities should be 

shown for physical, functional, thermodynamic, pneumatic, aerodynamic, and environmental 

areas. Analyses should be conducted to show that the component installation and operation is 

equivalent to the previously approved installation. 

(2) Similarity requires an evaluation of both the system and installation differences that 

may adversely affect the system performance. An assessment of a new installation should 

consider differences affecting the aircraft and the system. Similarity may be used as the basis for 

certification without the need for additional tests provided:

(a) Only minimal differences exist between the previously certificated system and 

installation, and the system and installation to be certificated; and 

(b) The previously certificated system and installation have no unresolved icing 

related service history problems. 

(3) FAA Order 8110.4C should be consulted regarding the use of previously approved 

FAA data. 

(4) If there is uncertainty about the effects of the differences, additional tests or 

analyses, or both, should be conducted as necessary and appropriate to resolve the open issues. 

g. Induction Air System Protection. The induction air system for airplanes is certificated 

for ice protection in accordance with § 23.1093. These requirements are for all airplanes even 

those not certificated for flight in icing conditions. Thus ice protection systems installed on 

previously type certificated airplanes to protect the engine induction air system should be 

adequate and need not be re-examined, unless the inlet is being modified, the original certification 

basis is inadequate, or an in-flight AFM limitation was used to comply with the falling and 

blowing snow regulation. When natural icing flight tests are conducted to show compliance to 

§ 23.1419, engine operation, engine ice protection system procedures, and engine inlet ice 

accretion should be evaluated if flight tests in measured, natural icing conditions were not 

previously accomplished on the engine/inlet configuration. See AC 23-16A and AC 20-147 for 

more information. 

(1) Engine Ice Protection – Flight Idle. Turbojet engine ice protection should be 

automatic once the engine ice protection system is activated. The engine must be protected from

ice with the throttle against the idle stop, which may require an automatic increase in thrust when 

the engine ice protection system is activated. 

11 
AC 23.1419-2D 4/19/07 

(2) Delay of Icing Approval. Manufacturers have chosen to delay showing compliance 

to § 23.1419, and therefore receive flight in icing approval, until after type certification. The 

main reason is usually not to delay obtaining type certification of the basic airplane for marketing 

or contractual reasons. The airplane is prohibited from flight in known or forecast icing 

conditions until a finding of compliance to § 23.1419 is made. However, the airplane may 

inadvertently encounter icing conditions, and the engines should operate without a sustained loss 

of power and there should not be a need to shutdown an engine in flight. Compliance to 

§ 23.1093 is required for basic type certification, and the engine as a result will have ice 

protection capability. An example would be an ice protection system for the engine inlet. 

Airframe ice protection systems can be considered part of the engine ice protection system if the 

possibility exists of ice accreting on the airframe in an inadvertent encounter and shedding into 

the engines. An example is ice accreting on the inboard wing of airplanes with aft fuselage 

mounted engines. Applicants who delay icing certification until after type certification must 

show compliance to § 23.901(d) by one of the following methods: 

(a) A trajectory analysis, supplemented by flight testing in measured natural icing 

or flight testing behind an airborne icing tanker, as described in paragraph 14 of this AC, to show 

the amount of ice that accretes in five minutes at critical part 25, Appendix C continuous 

maximum conditions does not shed into any engine; or 

(b) Analysis which shows the mass of ice that accretes in five minutes in critical 

part 25, Appendix C continuous maximum conditions is less than the mass of ice shown to be 

ingested by the engine for compliance to § 33.77. This analysis should assume: 

1. The spanwise length of the ice shape is the maximum length that can be 

ingested without striking the inlet lip or engine spinner. 

2. The ice shape on the wing leading edge does not break chordwise, i.e., 

the ice above and below the stagnation line should be considered. 

3. In lieu of five minutes of ice accretion, credit can be used for operational 

ice protection systems, with the exception in paragraph (4). The most critical of the following 

should be used: 

(aa) Two minutes representing delayed system activation; 

(bb) Intercycle/residual ice for deicing systems for operating speeds 

above 160 Knots Calibrated Airspeed (KCAS). Below 160 KCAS, empirical data should 

substantiate that deicing systems shed ice at each cycle. 

(cc) Runback ice in 5 minutes for thermal systems. 

4. Flight testing in measured natural icing or flight testing behind an 

airborne icing tanker would be required for novel ice protection systems, such as the graphite 

thermal deicing system. 

12 
4/19/07 AC 23.1419-2D 

h. Propeller Ice Protection. 

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

(a) Substantiates the chordwise and spanwise ice protection coverage 

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

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

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

i. Pitot Probe Ice Protection. 

(1) Conditions Within the Part 25, Appendix C Icing Envelope. 

(a) Airplanes Incorporating Airspeed Systems With TSO C16 Authorizations. 

Compliance to the TSO-C16 qualification standard for electrically heated pitot probes is not 

sufficient by itself in demonstrating compliance to the installation requirements of 

§ 23.1309(b)(1) and § 23.1419. Section 23.1309(b)(1) requires that the system must perform its 

intended function under any foreseeable operating condition. Section 23.1419 requires that an 

airplane certificated for flight in icing must be able to safely operate in part 25, Appendix C icing 

conditions. It is unlikely that the conditions of part 25, Appendix C that are critical to the air data 

system equipment will be encountered during flight tests. Although functioning of pitot probes 

are evaluated in natural icing conditions during certification test programs, there is no 

requirement to flight test at the part 25, Appendix C icing limits because the low probability of 

finding those conditions imposes a burden. TSO C16, Air-speed tubes (electrically heated) 

require compliance to the performance specifications of SAE Aeronautical Standard AS393. This 

standard and AS393A (out-of-date), are non-current. SAE AS393A includes a test to demonstrate 

deicing and anti-icing capability, but only temperature and airspeed are specified. Liquid water 

content is not specified but it influences heat requirements. Consequently certification programs 

should supplement the icing flight tests with an icing tunnel test and/or airborne icing tanker test 

data, as necessary, or reference testing that has been accomplished by the pitot probe 

manufacturer, or show similarity to a similar, icing approved airplane with no negative service 

history. In-service experience during severe atmospheric conditions has shown that pitot tubes 

qualified to the older standards have resulted in airspeed fluctuations and even loss of indicated 

airspeed. As these components should perform as intended in all expected atmospheric 

environments, it is reasonable to require that they be qualified to the Continuous and intermittent 

maximum icing conditions defined in part 25, Appendix C. 

(b) Airplanes Incorporating Airspeed Systems With TSO C16a 

Authorizations. TSO C16a, Electrically heated pitot and pitot-static tubes, references 

SAE Aeronautical Standard AS8006 and supplements the icing requirements with specific part 

25, Appendix C icing conditions and specific liquid water content tests from British Specification 

(BS) 2G.135 “Specification for Electrically-Heated Pitot and Pitot-Static Pressure Heads”. 

13 
AC 23.1419-2D 4/19/07 

Analysis, icing tunnel tests, or flight tests dedicated to probe heat evaluation, are not required. 

See paragraph 12.c.(3) for air data system evaluations that are accomplished during a natural icing 

flight test program. 

(2) Conditions Outside of the Part 25, Appendix C Icing Envelope. Although part 

25, Appendix C only considers the liquid water content of icing conditions, recent cloud 

characterization research has indicated that approximately 40 percent of icing condition events 

consist of liquid water drops and ice crystals (mixed phase icing conditions). The operating rules 

do not prohibit operations in mixed phase and ice crystal icing conditions. The incident history 

indicates that flightcrews have experienced temporary loss of or misleading airspeed indications 

in icing. It is likely that some of these incidents were due to ice crystals. Pitot tubes are mounted 

such that they typically are high efficiency collectors of ice crystals. Encountering high 

concentrations of ice crystals can lead to blocked pitot probes as the energy required to melt the 

ice crystals can exceed Appendix C design requirements.. More recent standards indicate that 

these components should be qualified for operation in atmospheric conditions beyond the 

environment described by part 25, Appendix C, specifically during ice crystal and mixed phase 

icing conditions. Recently, some aircraft manufacturers and foreign certification authorities have

required pitot and pitot-static probes to be tested in ice crystal and mixed phase icing conditions 

along with supercooled liquid water conditions. As a result, some pitot tube manufacturers now 

use the icing environment of British Specification (BS) 2G.135 “Specification for ElectricallyHeated Pitot and Pitot-Static Pressure Heads,” as modified by the maximum rate that the icing 

tunnel facility can produce ice crystal, in addition to the requirements of the TSO. Even though 

the part 23 and part 25 regulations only address liquid water and testing in the mixed phase or ice 

crystal conditions are not required for FAA approval, it is good design practice to assure the pitot 

heat is sufficient for the ice crystal and mixed phase conditions of BS 2G.135. 

j. Stall Warning Ice Protection. Compliance to the TSO qualification standard for stall 

warning instruments (TSO-C54) is not sufficient by itself in demonstrating compliance to the 

installation requirements of § 23.1309(b)(1) and § 23.1419. 

(1) Conditions Within the Part 25, Appendix C Icing Envelope. TSO-C54, “Stall 

Warning Instruments”, requires compliance to the performance specifications of 

SAE Aeronautical Standard AS403A with some exceptions and additions. This standard is noncurrent. As in AS393A, the requirements include a test to demonstrate deicing and anti-icing 

capability, but only temperature and airspeed are specified. The precipitation test conditions of 

AS403A include moderate icing conditions for Type II instruments. However, "moderate" is not 

defined. The same comments from 9i (1) apply. The applicant is responsible for showing that 

stall warning heat is adequate throughout the part 25, Appendix C icing envelope. 

(2) Conditions Outside of the Part 25, Appendix C Icing Envelope. The same

comments from paragraph 10i(2) above apply to stall warning ice protection systems. 

k. Static Pressure Systems. Each static port design or location should be such that 

correlation between air pressure in the static system and true ambient pressure is not altered when 

flying in icing conditions. Means of showing compliance include the following: anti-icing 

14 
4/19/07 AC 23.1419-2D 

devices, alternate source for static pressure, or demonstration by test that port icing does not occur 

under any condition. Where the port is thermally protected, a thermal evaluation should be 

conducted to demonstrate that the protection is adequate. 

l. Ice Detection 

(1) Regulation. Requirements for ice detection are in § 23.1419(d). 

(a) A means must be identified or provided, and described in the AFM, for 

identifying ice accretion.

(b) Adequate lighting must be provided for ice detection at night. 

1. An ice inspection light that illuminates a reference surface or a wing 

leading edge is normally provided. 

2. A hand-held flashlight is not acceptable as ice detection light.

(2) Ice Detection System. Besides the pilot's appraisal of icing conditions (i.e., defined 

by temperature and visible moisture or visual detection of ice accretions on wiper blades, window 

frames or propeller spinner, etc.), some airplanes use Flight Ice Detection Systems (FIDS). FIDS 

may either directly detect the presence of ice on an airplane reference surface or detect that the 

airplane is in icing conditions. There are basically two classes of FIDS: 

(a) Advisory Flight Ice Detection System. An advisory FIDS provides 

information to advise the flightcrew of the presence of ice accretion or icing conditions. The 

flight crew has primary responsibility for detecting icing conditions or ice accretions, using the 

means defined in the AFM, and activating the Ice Protection Systems (IPSs). Advisory FIDS can 

automatically activate the IPS. However, the AFM must state the flight crew has primary 

responsibility for detecting icing conditions or ice accretions.

(b) Primary Flight Ice Detection System. A Primary FIDS (PFIDS) is 

considered the sole means used to determine when the IPS must be activated. The IPS may be 

automatically activated by the PFIDS or the PFIDS may provide a flight deck signal that will 

direct the crew to manually activate the IPS. 

(c) Certification of FIDS. Installation of an ice detection system is considered a 

safety enhancement since the icing conditions may be identified or confirmed at an early stage 

and appropriate actions can be initiated in a timely manner. However, recent investigations have 

shown that previously certificated ice detection systems may not detect airframe and engine icing 

in some part 25, Appendix C conditions. It has been demonstrated in an icing wind tunnel that 

atmospheric moisture may fail to freeze on ice detector probes even though ice may be accreting 

on other airplane surfaces in low freezing fraction conditions. With the continuing development 

of ice detection systems and due to recent in-service incidents, the FAA has determined there is a 

need to define specific criteria to certify ice detection systems that are used as the sole means of 

determining when the ice protection systems are activated. See AC 20-73A. 

15 
AC 23.1419-2D 4/19/07 

(d) Icing Conditions Outside of Part 25, Appendix C. Ice detectors typically have 

limitations with certain atmospheric phenomena, e.g. ice crystal conditions, outside of part 25, 

Appendix C, which the applicant must understand and not rely on the PFIDS to detect these 

conditions. There have been cases (an anomaly that has affected some engine models) where 

atmospheric ice crystals ingested in the initial fan stages of jet engines have melted, and re-accreted 

on subsequent low pressure compressor stages or initial stages to the high pressure compressor 

resulting in engine core ice. Subsequent shedding of this type of ice accretion has resulted in at least 

one unrecoverable engine surge. Therefore, applicants must be aware of the potential limitations of

engines during ice crystal conditions without reliance on the ice detection system. Current policy 

considers this potential condition in § 23.1093(b)(1)(ii) which requires 

demonstration of adequate engine performance in ice crystal conditions during falling or blowing 

snow. 14 CFR part 23 and part 33 regulations and compliance methods intend to provide 

unrestricted engine operation throughout the atmospheric environmental envelope. 

m. Fluid (Freezing Point Depressant) Systems. Freezing point depressant fluid systems 

have been successfully certificated on part 23 airplanes. However, this type of system is not as 

common as other ice protection systems and that prompted the FAA in 1986 to publish 

information on certification of these systems in DOT/FAA/CT-TN86/11. Certification highlights 

from this publication are repeated below. 

(1) Analyses. The two critical analyses required are the fluid flow rate required and an 

evaluation of the operational angles of attack, which will dictate chordwise coverage. 

(2) Fluid Capacity. The fluid capacity does not have to exceed the maximum 

endurance of the airplane but the minimum should be as follows in Table 1. 

TABLE 1. FLUID CAPACITY 

Airplane Type Minimum Fluid Capacity is the greater of: 

Turbojet powered airplanes 

90 minutes or 15 percent of the maximum

endurance based on the flow rate required in 

continuous maximum icing conditions 

Turbopropeller airplanes with maximum

operating altitude above 30,000 feet 

Turbopropeller airplanes with maximum

operating altitude 30,000 feet and below 

150 minutes or 20 percent of the maximum 

endurance based on the flow rate required in 

continuous maximum icing conditions 

Reciprocating engine powered airplanes 

16 
4/19/07 AC 23.1419-2D 

(3) Fluid Quantity. 

(a) There should be a fluid quantity indicator to allow the crew to determine how 

much longer the fluid will last. The fluid quantity indicator should be evaluated to determine that 

it is plainly visible to the pilot and that the indicator provided can be effectively read. 

(b) If it is desired that the airplane be dispatched with less than full fluid in the 

reservoir, the AFM should contain a chart or table to allow the crew to determine the minimum 

fluid level. The AFM limitations should state a minimum dispatch fluid level of 90 minutes based 

on the flow rate required in continuous maximum icing conditions.

(4) Fluid Characteristics. 

(a) The freezing point depressant fluids used become a gel at very cold 

temperatures and the temperature extremes to which the airplane will be operated should be 

considered when evaluating the reservoir, pump and plumbing installations. 

(b) Certain fluids used in ice protection systems, such as the alcohol used in older 

propeller systems, are flammable. Components of these systems must meet the flammable fluid 

protection requirements of § 23.863. No components of these systems may be installed in 

passenger or crew compartments without the protection required by § 23.853(d) (prior to 

amendment 23-34) or § 23.853(e) (after amendment 23-34). An accessible shutoff should be 

provided in systems using flammable fluids. 

(c) The effect of fluid ingestion into engines, Auxiliary Power Units (APUs), and 

accessories should be evaluated. The compatibility of the fluid with engine components should 

be examined to verify that adverse reactions such as corrosion or contamination do not occur, or 

are prevented through inspection or other measures 

(d) The effect of fluid compatibility with electrical contacts and with airframe 

components, particularly composite materials, should be evaluated. The applicant should verify 

that adverse reactions such as corrosion or contamination do not occur, or are prevented through 

inspection or other measures (for example, if ethylene glycol is a component fluid, then silver and 

silver-plated electrical switch contacts and terminals should be protected from contamination by 

the ethylene glycol to avoid a fire hazard). 

(e) There should be sufficient AFM and maintenance manual warnings on 

handling fluids. AL5 is 85 percent mono-ethylene glycol, which is considered extremely toxic. 

(f) Another freezing point depressant fluid, TKS80, is available. Icing tunnel tests 

of TKS80 and AL5 fluids have shown that they perform differently. The fluid reservoir should be 

placarded to permit only the fluid(s) that have been tested during certification. 

(g) To avoid confusion, the fluid filler tank cap should be distinguishable from 

other caps such as fuel and a placard stating approved fluid should be located near the filler cap. 

17 
AC 23.1419-2D 4/19/07 

(h) There should be adequate drainage in the areas that hold or can receive spillage 

from leaks. 

(5) Windshield Visibility. The effect of the fluid on windshield visibility should be 

evaluated to show compliance to § 23.775(f) if either the windshield or propellers are protected 

with a freezing point depressant system. On many of the approved installations the windshield 

system is turned off just prior to landing. 

11. Flight Test Planning. When operating any airplane in an icing environment, degradation in 

performance and flying qualities may be expected. The primary purposes for flight testing an 

airplane equipped for flight in icing conditions is to evaluate such degradation, determining that 

the flying qualities remain adequate, and that performance levels are acceptable for this flight 

environment. For airplanes with a certification basis of 23-43 or higher, § 23.1419(a) requires 

that an airplane comply with the performance, stability, controllability and maneuverability 

regulations of part 23, Subpart B. Flight testing in measured, natural icing conditions is required 

by § 23.1419(b) unless similarity is used as the method of compliance. In addition, unless 

similarity can be used, § 23.1419(b) requires at least tunnel testing, dry air testing, or airborne 

tanker testing. 

a. The flight tests and analyses of flight tests should: 

(1) Evaluate normal operation of the airplane with the ice protection system installed in 

non-icing flight. 

(2) Evaluate operation of the airplane with anticipated in-flight accumulations of ice. 

(3) Verify the analyses conducted to show adequacy of the ice protection systems 

throughout the icing envelope of part 25, Appendix C. 

(4) Develop procedures and limitations for the use of the ice protection system in 

normal, abnormal, and emergency conditions.

b. Flight tests for a typical part 23 airplane icing certification are generally conducted in 

three stages: 

(1) Initial Dry Air Tests With Ice Protection Equipment Installed And Operating. 

Initial dry air tests are usually the first steps conducted to extend the basic airplane certification to 

evaluate the airplane with the ice protection system installed and operating. The initial dry air 

tests are conducted to verify that the ice protection system does not affect the flying qualities of 

the basic airplane in clear air. Dry air tests are used to: 1) verify proper ice protection system

operation, 2) collect protected surface temperature data to validate thermal analysis, and 3) 

evaluate the effect of increased electrical and/or bleed demands on the engines and other installed 

systems. 

18 
4/19/07 AC 23.1419-2D 

(2) Dry Air Tests With Predicted Simulated Ice Shapes Installed. Dry air tests with 

predicted, simulated critical ice shapes installed are usually the second step for certification for 

flight in icing. Airplane performance and handling characteristics are evaluated with these 

simulated ice shapes. 

(a) Simulated ice on unprotected areas are typically determined by analysis codes. 

(b) Simulated ice on protected areas is typically determined by a combination of 

analysis and empirical data. Analyses are usually validated by ground tests such as icing tunnel 

tests where the design variables can be controlled to some extent, and the testing is more 

economical, versus icing flight tests. 

c. Flight Test Safety. FAA Order 4040.26A “Aircraft Certification Service Flight Safety 

Program” should be consulted for flight test risk assessments and risk mitigations. Many ice 

shape test flights, and stall testing with ice accretions, are considered high risk. Many applicants 

have equipped their ice shape flight test airplane with a stall/spin chute.

Flight Tests in Icing Conditions. Flight tests in icing conditions, including artificial 

icing tests such as flight behind an airborne icing tanker aircraft, are normally employed to 

demonstrate that the ice protection system performs under flight conditions as the analysis or 

ground test indicated. These demonstrations should be made at various points (targeting critical 

points) in the icing envelope of part 25, Appendix C, to verify the airplane's ability to safely 

operate throughout that icing envelope. 

12. Flight Tests. The following sections cover the major flight tests and/or analyses normally 

performed to substantiate the flight aspects of an ice protection system: 

a. Initial Dry Air Tests with Ice Protection Equipment Installed. Depending upon the 

detailed design of the ice protection system, some preliminary ground tests of the equipment may be 

warranted to verify the basic function of each item. Quantitative data on such items as temperatures 

of thermal devices, fluid flow rates and flow patterns on liquid devices, or operating pressures of 

pneumatic components may be obtained as necessary to verify the system designs. The airplane 

should be shown to comply with the certification requirements when all ice protection system

components are installed and functioning. This can normally be accomplished by performing tests 

at those conditions found to be most critical to basic airplane aerodynamics, ice protection system

design, and powerplant functions. .Several commonly used ice protection system components are 

discussed below to illustrate typical flight test practices. Other types of equipment should be 

evaluated as their specific design dictates. 

(1) Pneumatic Leading Edge Boots.

(a) Operation. Boot inflation rate and inflated boot shape are important parameters 

in ice accretion removal. Tests should demonstrate a rapid rise and decrease in operating pressures 

for effective ice removal. This pressure rise time, as well as the maximum operating pressure for 

each boot, should be evaluated throughout the altitude band of part 25, Appendix C—Mean Sea 

19 
AC 23.1419-2D 4/19/07 

Level (MSL) to 22,000 feet above MSL—unless performance constraints or aircraft limitations 

unrelated to the ice protection system in the AFM restrict the airplane to a lesser altitude range.

(b) Minimum Operating Temperature. Boots should be operated in flight at the 

minimum envelope temperature (-22 degrees Fahrenheit (F) of part 25, Appendix C, to demonstrate 

adequate inflation/deflation and throughout the entire flight envelope. Boots should be operated 

near the proposed AFM operating temperature limit, if below -22 degrees F, to demonstrate that no 

damage occurs. The appropriate speed and temperature (if any) limitation on activation of boots 

should be included in the AFM. 

(c) Effect of Inflated Boots. The operation of the boots (inflation) should have no 

hazardous effect on airplane performance and handling qualities. An example of an unacceptable 

hazardous effect is that some boot inflation sequencing schemes result in abnormal pitch attitude 

changes. If there are anomalous pitch changes in any configuration, appropriate information or 

limitation should be in the AFM. This can be shown by inflating the boots at several speeds in the 

flight envelope from stall speed to (VNE + VD)/2 or (VMO + VD)/2 and observing the reaction of the 

airplane. This test can be hazardous and should be approached in a build-up manner by inflating the 

boots at incremental airspeeds starting from the middle of the flight envelope. 

(d) Water Contamination. Consideration should be given to the potential for 

accumulation of liquid water inside the pneumatic deicing boots, which could freeze within the 

system and prevent proper operation. The pneumatic and boot arrangement should be examined 

for low points, which may collect water, and consideration should be given to the installation of 

water drainage points. Periodic inspection and drainage procedure instructions should be 

provided in the appropriate manual. Similarly, placement of the pressure sensor(s) should be 

evaluated to prevent misleading boot inflation indications. An evaluation of the effectiveness of 

water/air separators and/or drainage holes should be accomplished by flying through precipitation 

followed by a verification of proper boot inflation at freezing altitudes.

(2) Electric Propeller Boots.

(a) Dry Air Function Flight Test. 

1. System Function. When flying in dry air, the systems should be 

monitored to confirm proper function. It is suggested that system current, brush block voltage 

(between each input brush and the ground brush), and system duty-cycles be monitored to assure 

that proper power is applied to the deicers. 

2. Temperature Measurements. If not furnished by the manufacturer, 

surface temperature measurements may be made during dry air tests. These surface temperature 

measurements are useful for correlating analytically predicted dry air temperatures with measured 

temperatures or as a general indicator that the system is functioning and that each deicer is 

heating. 

20 
4/19/07 AC 23.1419-2D 

3. Vibration. The system operation should be checked throughout the full 

certificated Revolutions Per Minute (RPM) and propeller cyclic pitch range expected during icing 

flights. Any significant vibrations should be investigated. 

(b) Maximum Temperature. Consideration should be given to the maximum

temperatures that a composite propeller blade may be subjected to when the deicers are energized. 

It may be useful to monitor deicer bond-side temperatures. When performing this evaluation, the 

most critical conditions should be investigated. For example, this may occur on the ground 

(propellers non-rotating) on a hot day with the system inadvertently energized. Service difficulty 

reports have indicated propeller damage during de-ice/anti-ice system activation during 

maintenance without the engines running. 

(c) Precipitation. The system should be monitored to confirm proper function in 

precipitation. There have been designs that allowed water to reach the electrical brush blocks and 

prevent their operation. 

(3) Electric Windshield Anti-Ice. 

(a) Thermal Analysis Validation. Dry air flight tests should be conducted in 

support of the systems design, as required. Inner and outer windshield surface temperature 

evaluations of the protected area may be needed to support thermal analyses. Thermal analysis 

should substantiate that the surface temperature is sufficient to maintain anti-icing capability 

without causing structural damage to the windshield. In the case of add-on plates, temperatures of 

the basic airplane windshield, inside and out, may also be needed, particularly with pressurized 

airplanes. 

(b) Cockpit Visibility. An evaluation of the visibility, including distortion effects 

through the protected area at maximum heat, should be made in both day and night operations to 

show compliance to § 23.775(f).

(c) Size of Protected Area. The size and location of the protected area should be 

reviewed for adequate visibility, especially for a circling approach and landing conditions. 

Crosswinds and runway light visibility during instrument landings need to be considered. 

(4) Pitot and Static Pressure Sources. If the air data system configuration of either the 

pitot or the static source(s) differs from that of the basic airplane, then airspeed and altimeter 

system calibrations should be evaluated for compliance with the certification requirements. A 

component surface temperature evaluation may be necessary to verify thermal analyses. Section 

23.1325(b) requires that static pressure port design or location should be such that the correlation 

between air pressure in the static pressure system and true ambient atmospheric static pressure is 

not altered when the airplane encounters icing conditions. Section 23.1325(b)(3) allows antiicing means or an alternate source of static pressure may be used in showing compliance with the 

requirement. 

21 
AC 23.1419-2D 4/19/07 

(5) Stall Warning and Angle-of-Attack Sensors. Ice could form on these sensors if 

these devices are not protected. When the icing approval requires installation of new or modified 

sensors, that sensor's function should be evaluated for compliance with the certification 

requirements. These sensors may not require heat for ice protection if substantiated by analyses. 

A surface temperature evaluation may be necessary to verify thermal analyses. Consideration 

should be given to ice formations on the airframe in the vicinity of the sensor mounting location 

that may affect the sensor's operation. 

(6) Pitot Tube. Section 23.1323 requires a heated pitot tube or an equivalent means of 

preventing malfunction due to icing for airplanes certificated for instrument flight rules or flight 

in icing conditions. Section 23.1326 requires a pitot tube heat indicating system if a flight 

instrument pitot heating system is installed to comply with § 23.1323. 

(7) Fluid (Freezing Point Depressant) Systems. 

(a) Fluid Coverage. Dry air testing should include evaluation of fluid flow paths 

to determine that adequate and uniform fluid distribution over the protected surfaces is achieved. 

Colored fluid or colored water with camera documentation may be used. A range of angles of 

attack should be evaluated with both high and low volume rates. Inlets or openings where fluid 

ingestion will have a detrimental effect should be evaluated. 

(b) Aircraft Performance. Dry air testing should also include performance 

testing with the system operating since drag increases have been documented on previous 

certification programs. 

(c) Temperature. The system should be functionally tested at the minimum part 

25, Appendix C ambient temperatures. 

(d) Windshield. The fluid anti-ice/deice systems may be used to protect 

propellers and windshields, as well as leading edges of airfoils. The fluid for windshield fluid 

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

demonstrate that it does not become opaque at low temperature.

(e) Cockpit Annunciations. Means of indicating fluid flow rates, quantity 

remaining, and so forth, should be evaluated to determine that the indicators are plainly visible to 

the pilot and that the indications provided can be effectively read. 

(8) Compressor Bleed Air Systems. The effect of any bleed air extraction on engine 

and airplane performance should be examined and shown in the AFM performance data. The 

surface heat distribution analysis should be verified for varying flight conditions including climb, 

cruise, hold, and descent. A temperature evaluation may be necessary to verify the thermal 

analyses. If a minimum engine speed is required for ice protection system operation, the ability to 

perform normal and emergency descents should be evaluated. If compressor bleed air is used for 

anti-icing an engine cowl that is made of composite material, a thermal analysis/survey should be 

conducted to assure there is no engine cowl delamination or other structural failure. 

22 
4/19/07 AC 23.1419-2D 

(9) Ice Inspection Light(s). Ice inspection lights may be necessary if operations are 

dependent upon observing ice accumulations at night (§ 23.1419(d)). Ice inspection lights should 

be evaluated both in and out of clouds during night flight to determine that adequate illumination 

of the component of interest is available without excessive glare, reflections or other distractions 

to the flight crew. These tests may be conveniently accomplished both in and out of clouds 

during dry air tests. Use of a hand-held flashlight for ice detection is not acceptable. As 

described in § 23.1419(d), “The Airplane Flight Manual or other approved manual material must 

describe the means of determining ice formation and must contain information for the safe 

operation of the airplane in icing conditions.” A primary ice detection system may be certificated 

(see AC 20-73A for guidance), but such a system would require an Equivalent Level of Safety 

(ELOS) for section 23.1419(d) if an ice inspection light is not installed. 

b. Dry Air Tests with Simulated Ice Shapes.

(1) Why Do Simulated Ice Shape Flight Testing? The installation of simulated ice 

shapes allows airplane performance and handling characteristics to be evaluated in stable dry air 

conditions with the critical ice shape being held constant (no change of ice accretion due to 

erosion, shedding, and so forth, that can occur with natural ice shapes). Dry air flight tests with 

simulated ice shapes installed also result in a considerable reduction in the amount of flight 

testing that would otherwise be required to accumulate the test ice shapes, and then evaluate their 

effects on airplane performance and handling characteristics in stable air. 

(2) Flight Test Safety. Dry air tests with simulated ice shapes can be hazardous if not 

approached safely; therefore, the dry air flight test evaluation should be performed using a buildup technique, considering increases in spanwise coverage and dimensions of simulated ice shapes 

prior to full span ice shape tests. 

(3) Simulated Ice Shapes. 

(a) Critical Ice Accretions. Consideration should be given to the type of ice 

protection systems (for example: mechanical, fluid, thermal, or hybrid), and the most adverse ice 

conditions (shape or shapes, texture, location, and thickness) for the relevant aerodynamic 

characteristics for the following, as appropriate: delayed system turn on, intercycle ice, failure 

conditions, runback ice, and residual ice. Consideration should also be given to unprotected 

areas. See paragraph 13b for more information. These predictive methods should be 

conservative and should address the conditions associated with the icing envelope of part 25, 

Appendix C, that are critical to the airplane's performance and handling qualities in critical phases 

of the airplane's operational envelope, including climb, cruise, descent, holding pattern, approach, 

and landing. Ice shapes critical for performance may not necessarily be critical for handling 

qualities. See AC 20-73A for more information on determining critical ice shapes and 

corroboration of these ice shapes with natural icing flight test ice accretions. See AIAA-2007-

1090, “Residual and Intercycle Ice on Lower Speed Aircraft with Pneumatic Boots” for more 

information on critical ice shapes for pneumatic deicing boots. 

23 
AC 23.1419-2D 4/19/07 

(b) Ice Detection Systems. For aircraft that have an ice detection system, 

consideration must be given to delays in ice detection and annunciation. These delays may 

include slow ice detector response at temperatures near freezing (low freezing fraction as 

discussed in AC 20-73A) and the number of probe heat cycles utilized for annunciation or 

automatic ice protection activation. 

(c) Engine and Cooling Inlets. If ice is expected to accumulate at the engine or 

cooling inlets during icing encounters, then tests should be performed with critical ice shapes, 

typically representing a 45 minute hold, installed on these inlets. Tests should consider the 

critical operating temperatures and altitudes within Appendix C icing conditions. Generator 

cooling tests should be performed with the maximum icing load on the electrical system. 

(4) Flight Test Objectives.

(a) Performance. The effect of the ice shapes on stall speeds and airplane climb 

performance should be determined. Stall warning margins and maneuvering capability should 

also be evaluated. Operating speeds, stall warning speeds, and AFM performance information 

should be adjusted, if necessary, to provide acceptable performance capability and stall warning 

margins. The computation of the effects of ice on AFM performance should include reductions in 

engine power or thrust resulting from the applicable operating mode of the ice protection system. 

(b) Handling Qualities. Handling characteristics are expected to degrade in icing 

conditions and should be investigated to determine that the “airplane is capable of operating 

safely.” For certification basis before amendment 23-43, subpart B requirements are used as 

guidelines. For certification basis at amendment 23-43 and higher, several subpart B 

requirements also apply in icing conditions. This is addressed in paragraph 13a. The results of 

these tests may be used in preparing specific AFM operating procedures and limitations for flight 

in icing conditions. 

(c) Air Data Calibrations. If ice accretion is predicted to alter the position error 

of the production air data system (e.g. radome ice accretion), the position error would need to be 

determined using air data calibration flight tests (i.e. tower fly-by, trailing cone, speed course) 

with the critical, simulated ice shapes determined by analysis.

c. Flight Tests in Icing Conditions. Flight tests in measured natural icing and the use of 

simulated icing tools such as airborne icing tankers and icing wind tunnels are normally employed 

to demonstrate that the ice protection system performs under flight conditions as the analysis or 

other tests indicate. They are also used to confirm the analyses used in developing the various 

components (for example, ice detectors) and ice shapes and, in the case of natural icing tests, to 

confirm the conclusions reached in flight tests conducted with simulated ice shapes. Testing 

should be accomplished at various points in the icing envelope of part 25, Appendix C, to verify 

the airplane's ability to safely operate throughout that icing envelope. 

24 
4/19/07 AC 23.1419-2D 

(1) Instrumentation. Sufficient instrumentation should be planned to allow 

documentation of important airplane, system and component parameters, and icing conditions 

encountered. The following parameters should be considered: 

(a) Altitude, airspeed, and engine power.

(b) Temperatures. Static air temperature, engine component temperatures (for 

example, oil, heat exchanger fluids, cylinder head), electrical generation equipment temperatures, 

surface temperatures, interlaminate temperatures, and any other key temperatures that could be

affected by ice protection equipment, by ice accumulation or other key temperatures that are 

necessary for validation of analyses. 

(c) Liquid water content can be measured using a hot-wire based instrument, 

calibrated drum, or other equivalent and acceptable means. 

(d) Median volumetric droplet diameter can be approximately determined by 

using a drop snatcher to expose gelatin oil or soot slide and then measuring the resultant impact 

craters, or by use of more sophisticated equipment such as a laser based droplet measuring and 

recording instrument. 

(e) Cameras and dimensional reference aids to assist in determining ice 

accretion thickness and ice accretion coverage. 

(2) Artificial Icing. 

(a) Why Do Artificial Icing Tests? Testing in artificial icing environments such 

as icing tunnels or behind airborne icing tankers represents one way to predict the ice protection 

capabilities of individual elements of the ice protection equipment. The high liquid water content 

and large drop size conditions of Appendix C are easily simulated and not frequently encountered 

in natural icing flight tests. Due to the usually small dimensions of the artificial icing 

environment, testing is usually limited to sections of lifting surfaces, to components having small 

exposed surfaces such as heated pitot tubes, antennas, air inlets including engine induction air 

inlets, empennage, and other surfaces having small leading edge radii and windshields. 

(b) Airborne Icing Tankers. An artificial icing exposure may be obtained by the 

use of onboard spray nozzles forward of the component under examination or by flying the test 

airplane in the cloud generated by an airborne icing tanker. Recommended procedures for airborne 

icing tanker testing, including instrumentation requirements, are in SAE ARP 5904, “Airborne 

Icing Tankers.” 

(c) Icing Tunnels. Icing tunnel tests have been accepted for definition of preactivation, intercycle, residual, and runback ice on protected surfaces with the following

considerations: 

25 
AC 23.1419-2D 4/19/07 

1. Scaling. A full-scale test article is preferable due to uncertainties in ice 

accretion scaling. Refer to AC 20-73A for more information on scaling test parameters. 

2. Conformity. The test article must be conformed. Although parts of the 

ice protection system may be simulated, critical system parameters must be conformed. An 

example would be deicing boot steady state pressure, and pressure rise time and decay time. 

3. Tolerances. Ice protection system tolerances on the production airplane, 

such as boot operating pressure, must be accounted for. 

4. Operational Consideration. Proposed ice protection system operation 

(activation procedures, ice detection system delay, and deicing boot cycle times) must be 

accounted for in the test matrix. 

5. Spray Times. If the facility cannot produce the required LWC, spray 

times can be adjusted to provide the equivalent water catch for part 25, Appendix C cloud lengths. 

If large ice shapes or runback ice is expected, test ambient temperature may have to be adjusted to 

provide an equivalent freezing fraction. Temperatures can change the ice adhesion/shed 

characteristics and this should be taken into account when adjusting test parameters. The test 

matrix should include sufficient time in continuous maximum conditions to evaluate the stability

and cyclic nature of intercycle and residual ice. Certain unique design features, such as stall strips

mounted on deicing boots, may not readily shed ice and spray times up to 45 minutes need to be 

evaluated. 

6. Test Section. An outboard wing section is usually tested since it is 

typically more critical for aerodynamic degradations due to the reduced scale relative to the wing 

root (on wings incorporating significant taper ratios). It will also have higher water collection 

efficiency and may operate at a lower angle of attack, thereby promoting greater aft impingement

of droplets on the suction surface. For thermal systems, the outboard sections also represent the 

extremities of the bleed air system where temperature and pressure losses are the greatest, which 

can be critical for runback accretions. The distribution of icing cloud parameters along the test 

span should be taken into account. 

(3) Natural Icing. 

(a) Why Do Flight Tests In Natural Icing Conditions? Section 23.1419(b) 

requires flight test in measured natural icing conditions. Flight tests in natural icing conditions 

are necessary to demonstrate the acceptability of the airplane and ice protection system for flight 

in icing conditions. AC 20-73A provides additional information that would be useful when 

establishing a natural icing flight test program. 

(b) What Icing Conditions Should Be Tested? 

1. Continuous Maximum Icing Conditions. At least one exposure to 

icing conditions within the part 25, Appendix C, continuous maximum envelope should be 

26 
4/19/07 AC 23.1419-2D 

obtained. The exposure should be sufficiently stabilized to obtain valid data. It is often difficult 

to obtain temperature stabilization in brief exposures. Additional exposures may be required to 

allow extrapolation to the envelope critical conditions by analysis. Test data obtained during 

these exposures may be used to validate the analytical methods used and the results of any 

preceding simulated icing tests.

2. Intermittent Maximum Icing Conditions. Past experience has shown 

that flight testing in natural intermittent maximum icing conditions may be hazardous due to 

accompanying severe turbulence and possible hail encounters that may heat loads, critical shapes, 

accumulation, and accumulation rates, and so forth) are adequate under these conditions, and 

sufficient ground or flight test data exists to verify the analysis, then hazardous flight testing 

should be avoided. 

3. 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. 

(c) How Much Ice Should Be Allowed to Accrete? extensively damage the test 

airplane. When design analyses show that the critical ice protection design points (that is, 

1. Normal Ice Protection System Operation. Sufficient data should be 

taken to allow correlation with dry air tests using simulated ice shapes. This should be 

accomplished with a target accretion thickness equivalent to the 45-minute dry air ice shapes on 

an unprotected part of the wing. Handling qualities and performance should be subjectively 

reviewed and determined to be in general correlation with those found in dry air testing. Refer to 

paragraph 13.a. for performance, stability, control and maneuverability requirements. 

2. Delayed Ice Protection System Activation. In addition, flying qualities 

and performance should be qualitatively evaluated with the ice accumulations existing just prior 

to operation of deice (as opposed to anti-ice) components. The ice protection systems are to be 

activated by the flight crew in accordance with approved AFM procedures when icing conditions 

exist; however, for anti-ice components, tests should be conducted that simulate inadvertent icing 

encounters in which the pilot may not recognize that the airplane is about to enter an icing 

condition and the anti-ice component may not be activated until actual ice build-up is noticed. A 

delayed ice accumulation event of 30 seconds to two minutes has been used in these tests to 

simulate the flight crew's failure to recognize an icing condition. For engine ice protection 

systems, which for aft fuselage mounted engines can include the inboard wing ice protection 

system, a delay of two minutes is utilized to validate the ice shedding analyses and § 33.77 ice 

slab test results. For the delayed ice accumulation time event, consideration should be given to 

the icing conditions; the icing recognition means available, recommended crew procedures, and 

ice protection system performance of the particular aircraft. The tests to be accomplished are 

summarized in Table 3 of paragraph 13c of this AC. 

27 
AC 23.1419-2D 4/19/07 

(d) 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. Some considerations are: 

1. Engine operation and equipment operation such as oil cooling and 

generator cooling under maximum load should be monitored during icing tests and be found 

acceptable for this operation If data is analyzed in accordance with § 23.1043, the temperatures 

need to be corrected only to 32 degrees F, not a hot day. Natural icing flight tests should include 

evaluation of ice protection systems with bleed air from engines when the throttle is at the flight 

idle stop. Refer to AC 20-147 for additional guidance for turbojet engines.

2. Engine alternate induction air sources should remain functional in an 

icing environment. 

3. Fuel system venting should not be affected by ice accumulation. 

4. Retractable landing gear should be available for landing following an 

icing encounter. Gear retraction should not result in an unsafe indication because of ice accretion. 

5. Ice shedding from components including antennas and propellers should 

cause no more than cosmetic damage to other parts of the airplane, including aft-mounted engines 

and propellers. If flight testing is used to validate shedding trajectories, there should be dedicated 

test points to evaluate shedding. Examples would be flying in warmer temperatures to facilitate 

ice shedding, and evaluating various operational angles of attack and sideslip. 

6. Stall Warning and Maneuver Margin. With ice accretions on the 

airplane, acceptable stall warning (aerodynamic or artificial) and stall protection, if a stall 

protection system is installed, should be provided to validate the results of the dry air ice shape 

testing. The stall warning should meet the requirements of § 23.207(a), (b), and (c). The type of 

stall warning in icing conditions should be the same as in no icing conditions. Biasing of the stall 

warning and stall protection system, i.e. resetting trigger points to lower angles of attack when ice 

protection is initiated, may be necessary to achieve required maneuver margins to stall. The 

maneuver margin requirements § 23.207(d) should be demonstrated in icing conditions. The stall 

warning margin should be evaluated with various ice accretions as summarized in Table 3. See 

paragraph 13.c. 

NOTE 1: This test and any stall or handling qualities tests should be 

accomplished in daytime visual meteorological conditions, after accreting ice, for 

safety. . 

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

8. Ice detection cues or ice detection system operation that the pilot relies

on for timely operation of ice protection equipment should be evaluated in all anticipated flight 

conditions, including night. 

28 
4/19/07 AC 23.1419-2D 

9. Ice inspection lights should be evaluated in natural icing and night 

conditions to verify that they illuminate ice build-up areas, are adequate under the conditions 

encountered, and do not introduce objectionable glare. Evaluate the cabin defogging system's

capability to clear side windows for observation of boot ice protection system operation and ice 

accumulation. If a defogging system is not provided, the windows should be easily cleared by the 

pilot without adversely increasing pilot workload. 

10. Flight Control Systems. Primary and secondary flight control surfaces 

should remain operational after exposure to icing conditions. Evaluations should confirm that 

aerodynamic balance surfaces are not subject to icing throughout the airplane's operating envelope 

(weight, Center Of Gravity (CG), and speed), or that any ice accumulation on these surfaces does

not interfere with or limit actuation of the control for these surfaces including retraction of flaps, 

slats and/or landing gear for a safe go around from the landing configuration. 

11. Air Data Systems. Ice accretions on pitot probes, static sources, 

temperature probes, angle of attack and stall warning sensors, and accretions forward of these 

sensors such as accretions on radomes or other probes should be evaluated to determine the effect, 

if any, on the position error of the aircraft’s production air data system and proper operation of stall 

warning or stall protection systems. 

12. Autopilot. All autopilot modes should be evaluated in natural icing 

conditions to validate the dry air ice shape test results. All autopilot modes should function 

properly in icing conditions. Airframe leading edge ice accretions could affect control power and 

control hinge moments resulting in incorrect autopilot gains. These evaluations should also show

that autopilot actuators function properly and do not freeze up. The autopilot should be engaged 

for an extended period of time in natural icing conditions to check for unusual trimming and 

potential for ice to accrete in control surface gaps and jam controls.”

13. Vibration and Buffet. Should be evaluated, including propeller vibration. 

14. Pilot Workload. The workload in icing conditions should be evaluated 

when showing compliance to § 23.1523. Ice detection, ice protection system operation and 

monitoring, and autopilot operation and monitoring (including periodic disconnects), as a 

minimum should be evaluated. 

15. Documentation of Ice Accretions. Ice accumulation on unprotected and 

protected areas, and behind protected areas, should be observed and documented. Remotely 

located cameras either on the test airplane or on a chase airplane have been used to document ice 

accumulations on areas that cannot be seen from the test airplane's flight deck or cabin. Visual 

devices such as rods and/or paint stripes may be used to aid in visual dimensional analysis of ice 

accretions. Care should be taken since some measuring devices may accrete ice and alter analysis 

of accretions on a surface of importance. Surfaces may be painted a dark color since rime and 

mixed ice accretions may be difficult to see on white surfaces. The edges of paint stripes can be 

efficient ice collectors if not smoothed and must be accounted for. The location of all external 

29 
AC 23.1419-2D 4/19/07 

instrumentation installed for icing flight tests, including cameras and visual devices, should be 

analyzed to verify that ice-shedding hazards are not introduced. 

13. Performance and Handling Qualities. Airplane performance and handling qualities are 

degraded by ice accumulations in various ways depending upon type, shape, size, and location of 

these accumulations. If numerous unprotected areas exist, the weight and center of gravity effects 

of the ice formations should also be evaluated.

a. Flight Tests 

(1) Section 23.1419 at Amendment 23-43 or Later. In accordance with § 23.1419(a), 

"capable of operating safely" means that airplane performance, controllability, maneuverability, 

and stability may be degraded from the non-iced airplane but must not be less than the 

requirements in part 23, subpart B. Guidance for each subpart B regulation, as related to icing, is 

in Appendix 6 of this AC. Unless noted otherwise, the guidance is applicable to all airplane 

categories for which compliance to § 23.1419 is being shown. 

(a) Configurations and Flight Conditions. The handling qualities test matrix for 

ice shapes can be reduced from the basic (no ice) matrix, with concurrence from the administrator, 

to configurations and flight conditions that were deemed critical based on the no ice testing (basic 

aircraft certification). It is not required to test flight conditions at altitudes above the part 25, 

Appendix C icing envelopes. 

(b) Harmonization. The FAA and the European Aviation Safety Agency (EASA) 

are harmonizing the performance and handling qualities requirements of part 25. This 

harmonization project will standardize the performance and handling qualities requirements, and 

provide additional guidance material for certification of part 25/large airplanes to safely operate in

the icing conditions of part 25/CS-25, Appendix C. Much of this performance and handling 

qualities guidance has been adopted for part 23 airplanes and is presented in Appendix 6 of this 

AC. There have been some modifications for part 23 applications. For example performance 

criteria had to reflect different categories of airplanes (commuter category, normal category below 

6,000 lb. maximum weight, and normal category above 6,000 lb. maximum weight). Also, stall 

speed tolerance criteria in some cases were modified to reflect lower stall speeds of part 23 

airplanes compared to transport airplanes. 

(c) Stall Speed. Section 23.1419, amendment 23-43, requires “...airplane 

performance...must not be less than that required in part 23, subpart B.” The stall speed 

requirements of § 23.49 are included in subpart B performance. For part 23 aircraft that do not 

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

must not exceed 61 knots. Recent flight testing of deicing boot-equipped aircraft with simulated 

intercycle/residual ice has shown stall lift coefficient losses of 17 percent to 23 percent with flaps 

extended. These lift losses were experienced on an airplane equipped with a stick pusher and on 

an airplane whose stall was defined by aerodynamic wing stall. This can represent a significant 

performance penalty for new aircraft if they had to be designed to meet the 61-knot stall speed 

requirement with ice on protected surfaces. Recently certificated single engine part 23 airplanes 

30 
4/19/07 AC 23.1419-2D 

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

is at or near 61 knots. Performance penalties would be large. As an example, calculations for one 

recently certificated single engine airplanes show that useful load in icing would have to be 

reduced by 40 percent in order to meet the 61-knot stall speed requirement with no major 

redesign. 

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

October 3, 1990 (55 FR 40598), for the proposed rule that was to become amendment 23-43, the 

FAA stated the background for imposing subpart B requirements on part 23 airplanes versus part 

25 transport airplanes: “The justification given was that normal and transport category airplanes 

must operate in about the same icing environment, but the normal category airplane is more likely 

to remain in icing conditions for longer periods of time because it may not have the performance 

capability to exit the icing environment as readily as transport category airplanes.” Normal 

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

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

airplanes. The requirement to meet subpart B performance was added to guarantee there would 

be a given level of excess power that could be used to exit icing conditions. An increase in stall 

speed in icing would not prevent an airplane from meeting the subpart B performance 

requirements if it was accounted for in analyses and testing. 

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

accretions, the applicant should consider the following compensating features to propose an 

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

the following compensating features would not adversely affect safety since it is safer to make a 

forced landing at higher speed than it is to inadvertently stall the airplane. There have been many 

fatal accidents in icing conditions attributed to the latter. 

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

requirement of § 23.49(c); 

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

AC complies with the stall warning requirements of § 23.207. 

(aa) For aircraft with artificial stall warning systems, paragraph 13a 

(1)2, may require a bias in the stall warning schedules (resetting trigger points to lower angles of 

attack when ice protection is initiated) to maintain adequate stall warning margins. 

(bb) For aircraft without artificial stall warning systems, 12a (1)(c)2, 

may require one to be installed to meet minimum stall warning margin requirements. Meeting 

§ 23.207(d) may require an increase in operational speeds in icing to preclude nuisance stall 

warnings. 

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

and operating speeds. 

31 
AC 23.1419-2D 4/19/07 

4. Most importantly, the airplane with critical ice accretions has acceptable 

stall characteristics and is safely controllable with normal piloting skill as required by §§ 23.201 

and 23.203. 

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

met with the higher stall and operating speeds. 

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

nose/tail wheel steering system of § 23.745, if applicable, are met with the higher landing speeds. 

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

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

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

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

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

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

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

operation in icing conditions. 

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

amendment 23-29. This regulation was promulgated as a result of a National Transportation 

Safety Board (NTSB) recommendation and a 1983 study, which indicated at least half of off field 

forced landings were a result of fuel mismanagement. 

The above approach represents only the minimum consideration, other issues may 

have to be considered depending on the aircraft design. In the petition for exemption, the 

applicant needs to state why it would be in the public interest and include the weight penalty in 

icing conditions as a result of complying with the 61-knot stall speed regulation. 

(2) Section 23.1419 at Amendment 23-14. The definition of “capable of operating 

safely” is not defined in the regulation. The tests and pass/fail criteria of paragraph 13a (1) 

should be used as a guide to develop a test program that demonstrates the airplane is capable of 

operating safely in the part 25, Appendix C, icing envelope. The regulations italicized in 

Appendix 6 of this AC are not typically addressed in showing compliance to § 23.1419 at 

amendment 23-14. 

b. Ice Accretions. 

(1) Airframe Ice Accretions. 

(a) Definition of Ice Accretions. The most critical ice accretions in terms of 

handling characteristics and/or performance for each flight phase should be determined. The 

32 
4/19/07 AC 23.1419-2D 

parameters to be considered are the flight conditions (e.g., airplane configuration, airspeed, angle 

of attack. altitude) and the icing conditions of part 25, Appendix C (temperature, liquid water 

content, mean effective drop diameter). Table 2, parts I and II summarize the ice accretions for 

each flight phase for normal ice protection system operation.

33 
AC 23.1419-2D 4/19/07 

TABLE 2. ICE ACCRETION DEFINITIONS, PART 1 of 2 

Ice 

Accretion 

Normal, Utility and Acrobatic 

Categories or Turbojet Airplane with a 

takeoff configuration that includes 

leading edge high lift devices 

Commuter Category or Turbojet 

Airplanes with a takeoff configuration 

that does not include leading edge high 

lift devices 

Takeoff None if the AFM prohibits takeoff with 

any ice, snow and frost on the wing and 

control surfaces. Otherwise, “polished” 

frost, as permitted by the parts 91 and 

135 operating rules should be defined 

by the applicant, show that procedures 

are practical (pilot can determine when 

it is acceptably polished), and simulated 

for flight test evaluation if not 

prohibited for takeoff in the AFM. 

Ice accretion occurring between liftoff 

and 400 feet above the takeoff surface, 

assuming accretion starts at liftoff in the 

“takeoff maximum icing’ conditions, on: 

• unprotected surfaces; and 

• the protected surfaces 

appropriate to normal IPS 

 operation; or 

• the protected surfaces if IPS 

operation is prohibited for takeoff. 

(It should be assumed no flight 

crew action to activate the ice 

protection will occur until at least 

400 feet above the ground level, 

or higher if specified in the 

 AFM.) 

“Takeoff maximum icing” conditions 

defined as: 

• cloud liquid water content of 

 0.35 g/m3

; 

• cloud droplets Mean Effective 

Diameter (MED) of 20 microns; 

and ambient air temperature at 

ground level of minus 

nine degrees Centigrade (C) 

This ice accretion may be simulated by 

100 grit sandpaper on the leading edge, 

unless another roughness is 

substantiated. 

34 
4/19/07 AC 23.1419-2D 

TABLE 2. ICE ACCRETION DEFINITIONS, PART 1 of 2 (Continued) 

Ice 

Accretion 

Normal, Utility and Acrobatic 

Categories or Turbojet Airplane with a 

takeoff configuration that includes 

leading edge high lift devices 

Commuter Category or Turbojet 

Airplanes with a takeoff configuration 

that does not include leading edge high 

lift devices 

Also the following ice accretions should 

be addressed: 

• Takeoff ice accretions defined 

under Normal, Utility and 

Acrobatic Categories, if required. 

• If a turbojet airplane without wing 

leading edge high lift devices, 

contamination simulated by 40-

grit sandpaper on wing leading 

edges and the entire upper wing 

surface should be flight tested 

unless the AFM requires a pretakeoff visual and tactile 

inspection of the wing leading 

edge and upper surface, and any 

other surface deemed critical, in 

ground icing conditions. 

35 
AC 23.1419-2D 4/19/07 

TABLE 2. ICE ACCRETION DEFINITIONS, PART 2 of 2 

Ice 

Accretion 

Normal, Utility and Acrobatic 

Categories or Turbojet Airplane with a 

takeoff configuration that includes 

leading edge high lift devices 

Commuter Category or Turbojet 

Airplanes with a takeoff configuration 

that does not include leading edge high 

lift devices 

Final 

Takeoff 

Not applicable. Same as “takeoff” ice except ice 

accretion occurs between liftoff and 

1,500 feet above the takeoff surface. 

Enroute Ice accretion on the unprotected surfaces, and any ice accretion on the protected 

surfaces appropriate to normal ice protection system operation, during the en route 

phase, in part 25, Appendix C, continuous or intermittent maximum icing 

conditions. 

Holding Ice accretion on the unprotected surfaces, and any ice accretion on the protected 

surfaces appropriate to normal ice protection system operation, during a 45-minute 

hold in part 25, Appendix C, continuous maximum icing conditions. 

Approach 

And 

Landing 

Ice accretion on unprotected surfaces same as “Holding” ice, and ice accreted on 

protected surfaces appropriate to normal system operation during an approach and 

landing. Upper surface impingement due to reduced angle of attack with flap 

extension, ice on flap leading edge, and ice on leading devices when extended 

need to be addressed. Runback ice has been observed to develop on leading edge 

slats on some designs when extended, but not when retracted. Duration of 

approach phase is time to accrete 0.5 inches of ice on unprotected part of wing 

with highest collection efficiency. Duration of landing phase is time to accrete 

0.25 inches of ice on unprotected part of wing with highest collection efficiency. 

PreActivation The ice accretion prior to normal system operation is the ice accretion formed on 

the unprotected and normally protected surfaces prior to activation and effective 

operation of any ice protection system in continuous maximum atmospheric icing 

conditions. Ice detection procedures, ice detector system design and performance, 

and operating procedures (e.g., boot activation, fluid system flow rate) should be 

considered. 

Intercycle See Appendix 1 of this AC for definition. For airspeeds below 160 KCAS, 

empirical data should substantiate that deicing systems shed ice at each cycle. 

Residual See Appendix 1 of this AC for definition. 

Runback See Appendix 1 of this AC for definition. This ice type is frequently a byproduct 

of partially evaporative (running wet) ice protection systems and thermal deicing 

systems, but can also occur on deicing boots at a small temperature band near 

freezing. Empirical data should be obtained at the following conditions, as a 

minimum, at the LWC values within part 25, Appendix C: 

a. outside air temperatures of 24 degrees to 28 degrees F; 

36 
4/19/07 AC 23.1419-2D 

TABLE 2. ICE ACCRETION DEFINITIONS, PART 2 of 2 (Continued) 

Ice 

Accretion 

Normal, Utility and Acrobatic 

Categories or Turbojet Airplane with a 

takeoff configuration that includes 

leading edge high lift devices 

Commuter Category or Turbojet 

Airplanes with a takeoff configuration 

that does not include leading edge high 

lift devices 

Runback 

(Cont.) 

b. total air temperatures of 24 degrees to 35.5 degrees F; 

c. time required to transit a continuous maximum cloud of up to 55 nm, 

correcting liquid water content for horizontal extent. 

Critical The ice accretion, applicable to the phase of flight that has the most adverse effect 

on performance and flying qualities. For protected surfaces, intercycle ice, 

residual ice, and runback ice should be accounted for. Pre-activation ice should be 

accounted for if the AFM requires the flightcrew to wait for a specified amount of 

ice accretion prior to activation the ice protection systems, or for systems, such as 

fluid systems, in which system effectiveness may take several minutes. In order to 

reduce the number of ice accretions to be considered when demonstrating 

compliance: 

(1) The more critical of takeoff ice and final takeoff ice may be used throughout 

the takeoff phase. 

(2) Holding ice may be used for the en route, holding, approach, landing, and goaround flight phases if it can be substantiated to be more critical than the ice 

accretions in those phases. 

(3) Holding ice may also be used for the takeoff phase provided it can be 

substantiated to be more critical than takeoff ice and final takeoff ice.

(4) The ice accretion that has the most adverse effect on handling characteristics 

may be used for climb performance tests provided any difference in climb 

performance is conservatively taken into account.

(5) In some instances the shapes determined in the various flight phases and flight 

conditions may be “enveloped” into one critical shape. 

(b) Shape and Texture of Simulated Ice. The shape and texture of the simulated 

ice should be developed, and substantiated by agreed methods. The ice shapes should be agreed to 

by the FAA prior to ice shape flight testing. 

1. Common practices for developing ice shapes include: 

(aa) Use of computer codes; 

(bb) Flight in measured natural icing conditions; 

37 
AC 23.1419-2D 4/19/07 

(cc) Icing wind tunnel tests; and 

(dd) Flight in a controlled artificial icing cloud (e.g. airborne icing 

tanker). 

2. The ice accretion resulting from the largest drops possible in Appendix C 

icing conditions should be considered for critical ice shapes. A Langmuir D drop distribution, 40 

μm median drop diameter, continuous maximum icing conditions, should be considered. See AC

20-73A. 

3. Natural icing or airborne tanker testing may show ice shapes or accretion

locations more critical than those simulated. Ice shape testing of critical test points would then 

need to be re-flown with these more critical shapes. 

(c) Ice Adhesion Inhibitors. For the determination or validation of intercycle and 

residual ice shapes and roughness on deicing boots, the application of any ice adhesion inhibitor 

such as ICEX is not permitted for natural icing flight tests, artificial icing flight tests or icing tunnel 

tests. This is because the use of ICEX cannot be controlled in operations and the effectiveness in 

operations degrades over time. (Intercycle ice is the ice accretion that exists on a deicing system

surface just prior to an actuation of the deicing system; residual ice is the accretion remaining 

immediately after an actuation.) Other products that enhance appearance or life should also not be 

applied. Deicing boots can be cleaned at the start of a natural icing or artificial icing test program

per recommended maintenance procedures. 

(2) Propeller Icing. To date, climb performance analyses and climb flight testing with 

ice shapes have not taken into account propeller efficiency losses due to ice accretion on the 

propeller blades. Deicing boot manufacturer’s analyses show that intercycle ice does exist with 

propeller deicing systems and their analyses do not account for ice runback. The outer part of the 

blade, which normally is not protected, theoretically has sufficient centrifugal force to shed ice. 

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. Although this 

condition was outside of part 25, Appendix C icing conditions, there is a possibility that this may 

occur within some portions of part 25, Appendix C. 

 

(a) Airplane performance in icing conditions should include the propeller efficiency 

losses caused by propeller intercycle ice. This may be accomplished by 

analysis. 

(b) Propeller efficiency loss should be at least 10 percent to account for runback ice 

and intercycle ice, unless data substantiates another amount. 

(c) Airplane performance during natural icing flight testing should be quantitatively 

compared with performance during ice shape flight tests. On reciprocating and 

turboprop powered airplanes, if there is degradation in performance compared to 

38 
4/19/07 AC 23.1419-2D 

the ice shape results, propeller efficiency losses due to propeller ice accretions 

should be investigated.

(3) Failure Ice Accretions. Flight tests with failure ice shapes representing failures not 

shown to be extremely improbable should be conducted to validate hazard classifications and to 

develop procedures for safe operation following a failure. For example, this testing may show 

that landing flap settings may have to be reduced following failure of the empennage ice 

protection system. 

(a) Failure ice accretion is defined as: 

1. “Holding” ice as defined in Table 2 for unprotected surfaces; and 

2. For protected surfaces, one-half the accretion specified for unprotected 

surfaces (22.5 minutes) if the associated AFM operating procedure requires the airplane to leave 

the icing conditions as soon as possible, unless another value is agreed to by the responsible 

aircraft certification office. 

3. For failure conditions that are: (a) not annunciated to the flight crew, or (b) 

annunciated to the flight crew, but the associated AFM procedure does not require exiting the 

icing conditions, the guidance in this AC for a normal (i.e., non-failure) condition is applicable 

with the failure ice accretion 

(b) If the failure is annunciated, and the AFM procedure requires exiting icing 

conditions, the applicant may propose an ice accretion based on a realistic exit scenario in lieu of 

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

1. For the system to annunciate the failure (e.g., one deicing boot cycle); 

2. For the pilot to decide on a course of action and notify Air Traffic 

Control (ATC) (e.g., two minutes); and 

3. To exit the icing conditions. 

(c) The time to exit should include a 180-degree standard rate turn and transiting a 

17.4-nautical mile, part 25, Appendix C continuous maximum cloud. Besides the design standard 

17.4 nautical mile horizontal cloud extent, a cloud extent of 46-nautical miles (adjusted for liquid 

water content per part 25, Appendix C), which is expected for 10 percent of icing encounters, 

should also be considered in the safety analysis. The exit scenario shall include the possibility 

that the airplane may have to climb 4,000 feet out of icing if it results in a longer time than 

traversing the part 25, Appendix C cloud. 

c. Natural Icing Flight Tests. Whether the performance and handling qualities flight 

testing has been performed with simulated ice shapes or in natural icing conditions, additional 

limited flight testing described in this section should be conducted in natural icing conditions. 

39 
AC 23.1419-2D 4/19/07 

Where flight testing with simulated ice shapes is the primary means for showing compliance, the 

objective of the tests described in this section is to corroborate the handling characteristics and 

performance results obtained in flight testing with simulated ice shapes. It is acceptable for some

ice to be shed during the testing due to air loads or wing flexure, etc., or during transit to a higher 

altitude or test area for safety reasons. However, an attempt should be made to accomplish the 

test maneuvers as soon as possible after exiting the icing cloud to minimize the atmospheric 

influences on ice shedding. During any of the maneuvers specified in Table 3, the performance 

and behavior of the airplane should be consistent with that obtained with simulated ice shapes. 

There should be no unusual control responses or uncommanded airplane motions. Additionally, 

during the level turns and bank-to-bank rolls, there should be no buffeting or stall warning. 

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. 

Minimum 

Holding 

• Level, 40-degree banked turns; 

• Bank-to-bank rapid rolls, 30 degrees – 

30 degrees; 

• Climb or level performance evaluation; 

• Autopilot tests 

• Straight stall (1 knot/sec. deceleration 

rate, wings level, power off) 

Landing flaps, 

gear down 

Time to 

accrete 0.75 

inches on 

unprotected 

part of wing 

with highest 

collection 

efficiency 

VREF

• Level, 40-degree banked turns; 

• Bank-to-bank rapid rolls, 30 degrees – 

30 degrees; 

• Climb or level performance evaluation; 

• Straight stall (1 knot/sec. deceleration 

rate, wings level, power off). 

Flaps up, 

gear up 

Defined preactivation ice Optional 

• Level, 40-degree banked turns; 

• Bank-to-bank rapid rolls, 30 degrees – 

30 degrees; 

• Climb or level performance evaluation; 

• Autopilot tests 

• Straight stall (1 knot/sec. deceleration 

rate, wings level, power off). 

d. Control System and Stall Protection System Tolerances. The same airplane and 

system production tolerances used in the non-icing tests should be used when evaluating 

performance and handling qualities with ice accretions. Ice protection system production 

tolerances should be addressed during flight testing in natural icing conditions. Examples are 

provided in Table 4. Stall speed and warning system tolerance are critical when establishing 

tolerances for production acceptance flights. 

40 
4/19/07 AC 23.1419-2D 

TABLE 4. FLIGHT TEST TOLERANCES 

Test Tolerances

Stall speed 

• Elevator to minimum trailing edge up if stall defined by aft 

control stop 

• Stick pusher, if equipped, set for minimum angle of attack 

• Flap travels should be set to minimum allowable settings 

Stall warning • Set for maximum angle of attack (minimum margin). 

Stall characteristics • Elevator to maximum trailing edge up. 

• Stick pusher, if equipped, set for maximum angle of attack 

Maneuver margin • Stall warning set for minimum angle of attack. 

Natural icing flight tests • Pneumatic boots set for minimum pressure 

• Electrothermal systems set at minimum current 

e. ICTS. To remove the risk of contaminated tailplane stall from the operating envelope of 

the airplane, the applicant should demonstrate by tests or a combination of analyses and tests, that 

the airplane is safely controllable and maneuverable during all phases of flight. 

(1) Background. See Appendix 7 of this AC. 

(2) Evaluation of Susceptibility to ICTS by Flight Test 

(a) Longitudinal control and susceptibility to ICTS should be evaluated during the 

following flight tests with critical ice shapes installed:

1. Flap extensions 

2. Recovery from stalls 

3. Level flight accelerations

4. Longitudinal control tests required by 14 CFR 23.145. 

(b) Susceptibility to ICTS should also be evaluated by conducting the zero-g 

pushover maneuver and steady heading sideslip. 

1. Configuration. 

(aa) All combinations of wing flaps and landing gear should be tested 

beginning with zero flaps up to the maximum flap setting to be approved for landing following an 

icing encounter. Since increased flap extension will increase the potential for ICTS, flight testing 

should proceed cautiously as the flaps are further extended. 

41 
AC 23.1419-2D 4/19/07 

(bb) Critical weight and CG position (normally full forward at light 

weight). 

(cc) Speeds from 1.2 VS1 or Reference Landing Approach Airspeed 

(VREF)-5 knots, as appropriate to the wing flap position, up to the maximum speed to be

encountered operationally in a given flap or gear configuration that will not result in exceeding 

Flaps Extended Speed (VFE) or Landing Gear Extended Speed (VLE), as applicable, during the 

maneuver. The speeds VS1 and VREF may have to be redefined with critical ice shapes. 

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

2. Ice Shapes: The applicant specifies the critical ice case(s) for

investigation in terms of location, shape, thickness, and texture, and obtains FAA concurrence for 

the ice shape(s) to be investigated. 

(aa) The critical shape(s) should contribute to the largest adverse hinge 

moment, lowest stall angle, greatest tail lift loss, and lowest control surface effectiveness. 

(bb) More than one shape may require testing. If a clean wing (no ice 

accretion) can result in increased negative Angle-of-Attack (AOA) on the horizontal tail, ice 

shapes on the wing should be removed. The critical ice accretion case(s) should include an 

allowance for the ice shape accreted during any time delays in activation of the ice protection 

system associated with ice detection or observation systems, intercycle and residual ice, runback 

ice, or the accretion that may be reasonably expected in service. 

(cc) It should be noted that ice accreted with the flaps retracted might 

result in a more critical condition than ice accreted with the flaps extended. Ice accretion shape 

and thickness need not be greater than that resulting from exposure to the icing conditions defined 

in Appendix C to Part 25 or the 45-minute hold condition of this AC, whichever is more critical. 

(dd) Ice on the vertical stabilizer should also be considered for the 

sideslip case. 

(ee) ICTS susceptibility should be evaluated with pre-activation ice. 

In many cases the pre-activation ice may be simulated by sandpaper ice. A thin ice layer 

simulated by sandpaper has been found to be critical on some aircraft and should be evaluated 

along with critical ice accretions on airplanes with a reversible longitudinal control system. 

(ff) Failure conditions of the ice protection system should also be 

addressed. Maximum landing flap extension with a failed ice protection system may be defined at 

an intermediate position. This should become an airplane limitation for a failure. 

3. Zero-g pushover maneuver. This is a maneuver to generate a nose 

down pitch rate so as to increase the angle-of-attack of the air flow over the horizontal stabilizer. 

Before the maneuver, the test pilot determines initial entry speeds and pitch attitudes to achieve 

the target load factor and target airspeed as the airplane pitches through approximately level 

flight.

42 
4/19/07 AC 23.1419-2D 

(aa) The objective of the pushover maneuver is to push the pitch 

control in the nose-down direction to obtain the test load factor (g level) and be at the test 

airspeed as the nose passes through the horizon. Note any lightening of the pitch control push 

force during the build-up to the test end. Begin the maneuver with the airplane trimmed or 

trimmed as nearly as possible at the test power, configuration, and test (target) speed. The 

airplane is dived to gain sufficient airspeed above the test airspeed to allow a pull-up (nose above 

the horizon), followed up by a rapid pitch over as the test airspeed is approached to achieve the 

test load factor and airspeed as the nose passes through the horizon. 

(bb) The pushover series begins by moving the control column

forward while evaluating for any reduction of required control force or force reversal. Continue 

the test points incrementally by increasing the amplitude of forward control inputs to obtain lower 

target load factors until a zero-g flight condition is obtained or, if limited by elevator power, to the 

lowest load factor attainable. The target load factors need to be maintained long enough to allow 

an evaluation of the longitudinal force required. During the pitch down maneuver, the test pilot 

should not change the rate of longitudinal control or reverse control movement as this may alter 

pitch rate and tail surface geometry to disqualify that test point. 

(cc) For pre-activation ice, when the activation of the ice protection 

system does not require the flight crew to wait for a specified ice accumulation, the pushover 

maneuver can be accomplished to 0.5g rather than 0g.

(dd) For failure ice accretions, when the failure is annunciated to the 

flight crew and the procedures are to exit icing conditions, the pushover maneuver can be 

accomplished to 0.5g rather than 0g.

(ee) A push longitudinal control force should be required throughout 

the test maneuver. Stop the test if a control force lightening to less than zero, or a pull pitch 

control force is required to achieve the test load factor (g level). 

(ff) The airplane should demonstrate suitable controllability and 

maneuverability throughout the maneuver, including recovery, with no tendency to diverge in 

pitch or other indications of a stalled tailplane. 

(gg) During the pitch-down maneuver, any pilot produced change in 

elevator deflection toward the nose-up direction disqualifies that test point. 

4. Steady state sideslip maneuver. Establish the airplane incrementally in

a straight, steady heading sideslip, up to the sideslip angle appropriate to normal operation of the 

airplane used to demonstrate compliance with § 23.177, Static directional and lateral stability. 

The airplane should demonstrate suitable controllability and maneuverability throughout the 

maneuver with no tendency to diverge in pitch. 

(c) Other Parameters that May Indicate a Stalled Tailplane. If the test aircraft

is instrumented, the following parameters may indicate a stalled tailplane: 

 

43 
AC 23.1419-2D 4/19/07 

1. The relationship of pitch rate (q) versus elevator deflection (δE) after the 

elevator is returned Trailing Edge-Up (TEU). If stalled, the elevator could deflect substantially 

before the airplane pitch rate starts to return to zero. This also appears as reduced elevator 

effectiveness, CmδE. 

 

2. If the elevator stalls, the aircraft will continue toward zero-g regardless of 

the force applied by the pilot to return to one-g flight. This may be determined by examining the 

slope of the plot of vertical load factor (Nz) vs. pitch control force (FELEVATOR) after the elevator is 

returned TEU.

 

3. Flow visualization methods (tufts) will usually indicate the onset of 

destabilization by flow reversal over a substantial portion of the suction (lower) surface of the 

horizontal tail. This indication often appears slightly before pilot tactile force cues. Critical tests 

would have to be repeated without the tufts to demonstrate the tufts have no effect on tail stall. 

(4) Compliance by Analysis. For turbojet powered airplanes with irreversible, powered 

pitch control systems, the flight tests described in paragraph 13 (e) (2) (b) may not be necessary. 

However, a detailed analysis, as a minimum, should show that: 

(a) The airplane has adequate (consult Small Airplane Directorate) margin to tail 

stall angle of attack; and

(b) Airplanes of similar size, configuration and operating envelope have 

demonstrated an acceptable service history with respect to ICTS. 

(5) AFM Limitations and Procedures.

(a) Maximum landing flaps may be limited to the “takeoff/approach” configuration 

due to ICTS characteristics, either with normal operation of the ice protection systems or with a 

failed horizontal tail system. This is true regardless of the certification basis. Literal interpretation 

of § 23.1419, amendment 23-43 means that the aircraft would have to comply with the 61-knot 

stall speed in icing at the takeoff/approach flap setting if the flap setting was limited to preclude 

ICTS with normal ice protection system operation. The FAA would also consider the exemption 

approach described above for the 61-knot rule to address higher stall speeds for those aircraft that 

limit flaps to takeoff/approach setting with ice accretions to preclude ICTS. 

(b) If sandpaper ice results in ICTS susceptibility and limited flap deflection for 

landing, the AFM procedure for limiting flap should be based on visible moisture and temperature 

rather than airframe ice accretions if the flight crew cannot see the tail. 

f. Pneumatic Deicer Boots. Many AFMs specify a minimum ice accumulation thickness

prior to activation of the deicer boot system. This practice has been in existence due to the belief 

that a bridge of ice could form if the boots are operated prematurely. Flight testing and icing 

tunnel testing of several “modern” boot designs have not shown evidence of “ice bridging”, and 

no degradation in ice shedding performance, when the boots were activated at the first sign of ice 

44 
4/19/07 AC 23.1419-2D 

accretion. Although the ice may not shed completely with one cycle of the boots, this residual ice 

will be removed during subsequent boot cycles. Tunnel testing is documented in FAA Technical 

Report DOT/FAA/AR-02/68, "Effect of Residual and Intercycle Ice Accretions on Airfoil 

Performance" (May 2002), and recommends that activating the deicing boots “early and 

often” are given more consideration as a means of limiting the size of intercycle and residual ice 

accretions. “Modern” boots are defined as high operating pressure (nominal greater than 

15 Pounds Per Square Inch Gauge (PSIG)) and fast inflation and deflation times. Both one-inch 

diameter tube designs operating at a nominal 18 PSIG, and 1.75-inch diameter tube designs 

operating at a nominal 15 PSIG, have been evaluated. The tests documented in FAA Technical 

Report DOT/FAA/AR-02/68 were conducted at approximately 175 KCAS. Additional tunnel 

tests at airspeeds typical of many part 23 airplanes are documented in AIAA-2007-1090, 

“Residual and Intercycle Ice for Lower Speed Aircraft with Pneumatic Boots.” These tests 

conducted at 145 KCAS and below, showed that it may take many boot cycles to effectively shed 

the ice. It may appear that the boots are not having any effect at all until shedding occurs. 

Waiting for a specified amount of ice did not improve ice shedding. The recommended AFM 

procedure for boot operation should be to operate the boots in an appropriate continuous mode at 

the first sign of ice and not to wait for a specific amount of ice to accumulate. The boots should 

be operated until icing conditions are exited and ice no longer adheres to the airframe. 

(1) For applicants that choose to recommend a measurable ice accumulation prior to 

activation of the boots, flight tests in simulated or natural icing conditions should be 

accomplished to verify that the crew could detect and recognize the specified ice accumulation 

thickness. The following test criteria have been accepted for previous flight test programs: 

(a) The pilot or a crewmember should be provided a means to detect from his crew 

position, under both day and night operation, the accumulation level the applicant has specified 

for activation of the boot system for proper ice removal. 

(b) The applicant should show that an ice accumulation margin exists that allows 

for errors in crew recognition of the ice accumulation level. 

(2) In addition, for applicants that choose to recommend a measurable ice accumulation 

prior to boot activation, this pre-activation ice accretion must be considered when determining 

critical ice accretions for performance, stability, control, and stall testing. 

NOTE 2: Usually, selection of the deicing boots to operate causes one cycle of 

inflation and deflation of all boots, but not necessarily at the same time. Some

systems are designed such that all the boots do not complete the cycle if the deicing 

boots are selected off during the middle of one cycle. For these systems, there 

should be an AFM warning to the flight crew to select the ice protection on for at 

least one complete cycle of the deicing boots. This note is equally applicable to any 

deicing system. 

(3) Deicing systems should have a mode that will automatically cycle the system after 

activation to reduce pilot workload. For deicing systems that do not have a timer to cycle the 

45 
AC 23.1419-2D 4/19/07 

system automatically once activated, the additional task of manually cycling deicing systems on 

pilot workload should be evaluated. A recent part 23 applicant found that definition of airframe

deicing boot intercycle and residual ice steered them toward one-minute boot cycles and the 

workload evaluation dictated an automatic timer for the boots. 

g. Emergency and Abnormal Operating Conditions. Flight investigations should be 

conducted to verify that, after pilot recognition of emergency and abnormal operating conditions, 

the airplane handling qualities have not deteriorated to the extent that the AFM procedures for the

condition are ineffective, that AFM procedures and recommended airspeeds are safe, and that the 

airplane can be landed safely. These demonstrations should be conducted with anticipated 

residual ice accumulation on normally protected surfaces. The tests in Table 5 represent a sample 

matrix for a part 23 airplane with failure ice shapes defined in paragraph 13b(3). 

TABLE 5. FAILURE ICE ACCRETION FLIGHT TESTS 

Ice Shape 

Configuration 

Configuration 

and Trim Speed Maneuver 

One wing zone 

failure 

Flaps up and minimum 

holding 

• Level, 40-degree banked turns; 

• Bank-to-bank rapid rolls, 

30 degrees – 30 degrees; 

• Determine minimum safe airspeed. 

• Approach and landing 

demonstration 

Empennage zone 

failure 

Full landing flaps and VREF • ICTS evaluation; 

• Sideslips 

Total wing and 

empennage zone 

failure 

• ICTS evaluation 

• Level, 40-degree banked turns; 

• Bank-to-bank rapid rolls, 

30 degrees – 30 degrees; 

• Deceleration to stall warning 

(natural acceptable), recover after 

one second. 

• Approach and go-around 

demonstration 

Pilot's windshield ice 

protection failure 

Full landing flaps and VREF • Approach and landing 

demonstration 

46 
4/19/07 AC 23.1419-2D 

h. Super Cooled Large Drop (SLD) Conditions. Accidents and incidents related to loss of 

airplane control have raised the concern that airplanes operating in certain meteorological 

conditions can accrete ice, not only aft of the protected areas but also on the wing lower surface. 

This may result in lateral control difficulties due to disturbed flow over the control surfaces, stall 

at a reduced angle of attack, and/or drag penalties. The meteorological conditions involved are 

called SLD because they consist of drop sizes larger than those defined in part 25, Appendix C. 

An inadvertent encounter of such conditions may result in an unsafe condition that must be 

addressed. The FAA and EASA are currently harmonizing rulemaking and guidance for flight in 

icing conditions that exceed part 25, Appendix C icing conditions. This policy in this paragraph 

is in the interim and will be replaced when the harmonized regulations and guidance are issued 

for part 23 airplanes. 

(1) Roll Control in SLD Conditions. The following guidance, with some

modifications, is contained in a July 23, 1997 Policy Memorandum issued by the Transport 

Directorate and coordinated with the Standards Office. This policy memorandum was applicable 

to certain part 25 and part 23 airplanes. In October 1994, a fatal accident involving a transport 

category airplane occurred in which severe icing conditions were reported in the area. During 

extensive testing, the accident profile was replicated by ice shapes developed from testing in an 

icing cloud having droplets in the size range of freezing drizzle at a temperature near freezing. 

This condition created a ridge of ice aft of the deicing boots and forward of the ailerons, which 

resulted in uncommanded motion of the ailerons and rapid roll of the aircraft. The NTSB 

recommended that the FAA develop a test procedure to identify the unsafe aileron hinge moment 

characteristics. The FAA has identified the susceptibility to loss of control following exposure to 

supercooled large droplets as an unsafe condition that may exist on other aircraft. The FAA is 

particularly concerned with airplanes that are equipped with non-powered roll control systems, 

since non-powered roll flight controls do not have the physical advantage of hydraulic or 

electrical power to assist the pilot in overcoming the large control forces that may exist from

differential pressure resulting from flow separation over the roll control surfaces. Therefore, 

airplanes certified for flight in icing equipped with non-powered roll control systems should be 

evaluated for susceptibility to roll upset in the event the airplane is exposed to certain freezing 

drizzle conditions. 

(2) Stall. In March 2001, a transport category, regional turboprop airplane reported 

encountering icing conditions and within several minutes experiencing a loss of control in stall, 

losing approximately 8,000 feet before recovering at 10,000 feet. The NTSB determined that the 

lift curve (slope and maximum lift coefficient) derived from the flight data recorder was 

significantly lower than the lift curve determined by flight testing simulated intercycle ice which 

was developed by icing tunnel tests of part 25, Appendix C conditions. The FAA has identified 

the reduction in lift due to supercooled large droplets, and subsequently possible stall prior to 

warning, as an unsafe condition that may exist on other aircraft. 

(3) Icing Conditions. Ice accretions to be addressed are: 

(a) Supercooled droplets having maximum diameters of approximately 

400 microns; 

47 
AC 23.1419-2D 4/19/07 

(b) An LWC of approximately 0.33 grams per cubic meter. 

NOTE 3: For this condition, the LWC strongly affects the rate at which the ice 

feature develops. A higher LWC results in more rapid formation of the ice feature, 

while a lower LWC results in a slower formation of the ice feature. The 

LWC should be adequate to produce an ice feature during the exposure interval 

that will start to shed on its own accord and then reform. 

(c) A median volumetric diameter of approximately 170 microns. 

NOTE 4: The cloud physics instrumentation, calibration, and data processing 

methodologies should be presented for acceptance by the FAA. 

(d) Temperatures near freezing such that runback conditions exist at the stagnation 

line (as a minimum total air temperatures of 24 degrees to 35.5 degrees F should be investigated); 

and 

NOTE 5: For this test, temperature is a critical factor. Not only is the 

temperature critical to the development of the ice shape and dimension, static air 

temperature excursions above freezing, although short in duration, can reverse the 

ice accretion process. 

(e) Operation at holding speeds and holding configurations. Light weight and 

maximum possible holding airspeed should be evaluated to obtain lowest possible angle of attack. 

(f) An encounter of 20 minutes. 

(4) Flight Tests.

(a) Tests. The tests in Table 3 should be evaluated at minimum holding airspeed, 

maximum weight, all possible holding configurations and at VREF, maximum weight, all possible 

approach and landing configurations, except deceleration to stall may be stopped at a low speed 

alarm, or natural stall warning. 

(b) Simulated Ice Shapes. Simulated ice shapes representing the ice accretions 

determined in paragraph 13.h (3) should be conducted. Alternatively, a quarter round, forward 

facing step shape may be flown, with the height calculated analytically based on water catch in 

the icing conditions in paragraph 13.h.(3). The shapes should be installed symmetrically along 

the full span of the wings, behind the protected area on the upper and lower surface. 

(c) Pass/Fail Criteria 

1. When manually flying the airplane: 

(aa) There shall be no hazardous degradation of the handling qualities 

of the airplane. 

48 
4/19/07 AC 23.1419-2D 

(bb) It should be possible to readily arrest and reverse roll rate using 

only lateral control input, and the lateral control force should not reverse with increasing control 

deflection. 

2. Any autopilot disconnect in altitude hold, attitude hold and heading hold 

mode must not result in the following: 

(aa) bank angle of more 60 degrees, 

(bb) a load on any part of the structure exceeding the lesser of either 

the structure’s load limit or 2g, 

(cc) a normal acceleration less than 0 g, 

(dd) a roll force greater than 50 lbs. during the recovery action, 

(ee) an excessive altitude loss, 

(ff) hazardous degradation of the handling qualities of the airplane, 

(gg) engagement or disengagement of a mode leading to hazardous 

consequences. 

(5) There should be a means for the flightcrew to determine when the airplane has 

entered into a supercooled large droplet environment, to enable the crew to take appropriate 

action. 

(6) There should be appropriate crew information provided in the AFM that describes 

the limitations and procedures to be observed while exiting the supercooled large droplet 

environment. The FAA has found that the limitations and procedures specified in Appendix 8 of 

this AC are an acceptable means of providing this information, unless tanker testing has shown 

other cues or ice shape flight testing has shown other procedures are more appropriate. 

14. Ice Shedding. Ice shed from forward airplane structure could result in damage or erode 

engine or powerplant components, as well as lifting, stabilizing, and flight control surface leading 

edges. Fan and compressor blades, impeller vanes, inlet screens and ducts, as well as propellers, 

are examples of powerplant components subject to damage from shedding ice. For pusher 

propellers that are very close to the fuselage and well back from the airplane's nose, ice shed from 

the forward fuselage and from the wings may cause significant propeller damage. Control 

surfaces such as elevators, ailerons, flaps, and spoilers are also subject to damage, especially 

those that are thin metallic, non-metallic, or composite constructed surfaces. Trajectory and 

impingement analysis may not adequately predict such damage. Unpredicted ice shedding paths 

from forward areas such as radomes and forward wings (canards) have been found to negate the 

results of this analysis. For this reason, flight tests should be conducted to supplement trajectory 

and impingement analysis. If flight tests are not conducted, a damage analysis should consider 

the worst-case ice shed event. Video or motion pictures are excellent for documenting ice 

49 
AC 23.1419-2D 4/19/07 

shedding trajectories and impingements, while still photography may be used to document the 

extent of damage. Any damage should be evaluated for acceptability. In flight testing the 

airplane should be exposed to an icing condition of magnitude and duration sufficient to create the 

expected worst-case ice accretion, including the 45-minute hold. Flight 

test evaluation should also account for critical, predicted trajectories in terms of normal 

operational angle of attack and sideslip. 

15. Placarding and AFM. This AC provides guidance on airplanes for which the certification 

basis requires an AFM. Guidance for AFMs in this AC also applies to AFM supplements. 

a. Placarding. Any placarding necessary for the safe operation of the airplane in an icing 

environment must be provided in accordance with § 23.1541. Examples of such placards are: 

(1) Kinds of operation approved (for example, "Flight in Icing Conditions Approved if 

Ice Protection Equipment is Installed and Operational”). 

(2) Equipment limits (for example, "Operation of Windshield Anti-Ice May Cause 

Compass Deviation in Excess of 10 degrees)”. 

(3) Speed restrictions (for example, "Maximum Speed for Boot Operation—175 Knots 

Indicated Airspeed (KIAS))”. 

(4) Fluid filler⎯inlets for fluid freezing point depressants should bear a placard 

showing approved fluid type and quantity. 

b. AFM. The AFM should provide the pilot with the information needed to operate the ice 

protection system and operate in icing conditions. Information should include: 

(1) Operating Limitations Section. Suggested areas to be addressed are as follows: 

(a) Limitations on operating time for ice protection equipment if these limitations 

are based on fluid anti-ice/deice systems capacities and flow rates. 

(b) Minimum airspeed limitations for each configuration approved for icing 

conditions. 

(c) Maximum airspeed limitation (if any)

(d) Environmental limitations for equipment operations as applicable (for example, 

minimum temperature for boot operation, maximum altitude for boot operation, and maximum 

outside air temperature for operation of thermal ice protection systems). 

50 
4/19/07 AC 23.1419-2D 

(e) A list of all equipment required for flight in icing conditions. Section 

23.1583(h) (CAR § 3.778) requires that this list be included in the Kind of Equipment List 

(KOEL). 

(f) Minimum engine speed if the airframe ice protection system does not function 

properly below this speed. 

(g) A list of required placards. 

(h) Performance limitations should be presented for flight in icing that reflect any 

effects on lift, drag, thrust, and operating speeds related to operating in icing conditions. These 

limitations may be presented in the Performance Information section of the AFM and included as 

limitations by specific reference in the Limitations section of the AFM 

(i) The Limitations section of the AFM should include, as applicable, a statement 

similar to the following: “In icing conditions the airplane must be operated, and its ice protection 

systems used as described in the operating procedures section of this manual. Where specific 

operational speeds and performance information have been established for such conditions, this 

information must be used.” 

(j) 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.” Modify as applicable or add any other surface deemed 

critical. 

(k) Visual/Tactile 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 visual and tactile inspection of the wing leading edge 

and upper surface in ground icing conditions. The Limitations section should specify a time limit 

for the tactile check. Nominally the tactile check must be accomplished within 5 minutes of 

takeoff, except it may be accomplished any time between final application of deicing fluid and 

takeoff if the airplane is deiced in accordance with an approved deicing program that complies 

with Section 121.629(c), and takeoff is accomplished within the maximum holdover time in a 

certificate holder's holdover timetable. In the case of the inability to ascertain if the fuel 

temperature is above freezing, the requirement to perform a visual/tactile check can be deleted if 

it can be shown that undetected ice accumulation does not occur on the wing upper surface due to 

cold soaked fuel. Ground icing conditions should be defined by the airplane manufacturer, but 

one example is defined as the Outside Air Temperature (OAT) below 5 degrees C (41 degrees F), 

or if it cannot be ascertained that the wing fuel temperature is above 32 degrees F (0 degrees C), 

and one of the following conditions: 

(aa) Visible moisture (rain, drizzle, sleet, snow, fog, etc.) is present; or 

51 
AC 23.1419-2D 4/19/07 

(bb) The airplane was exposed to visible moisture (rain, drizzle, sleet, 

snow, fog, etc.) since the previous landing; or 

(cc) The airplane experienced in-flight ice accretion since the previous 

takeoff; or 

(dd) The difference between the dew point temperature and the OAT is 

3°C (5°F) or less; or 

(ee) Water is present on the wing 

2. Turbojet airplanes without leading edge high lift devices and engines 

mounted behind wing. The manufacturer should either: 

(aa) Show that undetected ice accumulation does not occur on the 

wing upper surface due to cold soaked fuel; or 

(bb) Show that undetected ice accumulation on the wing upper surface 

caused by cold soaked fuel does not result in a hazard to the airplane due to engine ice ingestion; 

or 

(cc) Add an AFM Limitation that requires a visual/tactile pre-takeoff 

check if it cannot be ascertained that the wing fuel temperature is above 32 degrees F 

(0 degrees C), and the ground icing conditions listed above exist. 

(l) Configuration limitations, if any (for example, a reduced flap setting for 

approach and landing, and flaps up for holding or extended operations in icing conditions). 

(m) Exceedance icing conditions may be primarily water content related for 

thermal ice protection systems, primarily droplet diameter related for mechanical ice protection 

systems or some combination thereof. For exceedance icing conditions that may result from

environmental conditions outside the icing envelope established as the basis of the approval 

defined in part 25, Appendix C, information should be provided as follows (see Appendix 8 of 

this AC for an example): 

1. A means to identify an icing condition that exceeds the limits of the ice 

protection system for which the airplane is certificated. 

2. Recommended procedures and configurations when exiting the 

exceedance icing conditions. 

3. Procedures to follow during and after flight in these conditions in the 

event of degraded performance or handling characteristics. Information should include 

recommended use of flight controls, minimum airspeeds, configuration of high lift devices, drag 

52 
4/19/07 AC 23.1419-2D 

devices, automatic flight guidance system, engine power/propeller settings (as appropriate), and 

ice protection system operation. 

(n) Autopilot operation should be prohibited if any of the following conditions in 

icing flight are experienced: 

1. Severe icing; 

2. Unusual control force or control deflection, or unusually large control 

forces to move flight controls when the autopilot is disconnected periodically; or 

3. Indications of frequent autopilot retrimming during straight and level 

flight. 

(2) Operating Procedures Section. Section 23.1585(a) requires the pilot be provided 

with the necessary procedures for safe operation. The system components should be described 

with sufficient clarity and depth that the pilot can understand their function. Unless flight crew 

actions are accepted as normal airmanship, the appropriate procedures should be included in the 

FAA-approved AFM, AFM revision, or AFM supplement. These procedures should include 

proper pilot response to cockpit warnings, a means to diagnose system failures, and the use of the 

system(s) in a safe manner. 

(a) Preflight action necessary to minimize the potential of enroute emergencies 

associated with the ice protection system should be included when a flight is planned in IMC at 

temperatures below freezing. 

1. Ice protection systems should be checked by operating the systems and 

verifying proper cockpit annunciations. Mechanical systems such as pneumatic boots should be 

visually observed for operation. Fluid systems should be visually observed for evidence of fluid 

along the entire protected span. It may take several minutes for the entire panels to receive fluid, 

or the system may have air in it, particularly after a long period of inactivity. 

2. The quantity of fluid in the reservoir tank, if a fluid ice protection system, 

should be checked. The AFM should specify the fluid types that are approved. 

3. If two sources of electrical power or two pumps for fluid systems are 

provided, both should be checked during pre-flight. 

(b) Procedures should be provided to optimize operation of the airplane during 

penetration of icing conditions, including all flight regimes. The AFM should include procedures 

that advise upon which conditions the ice protection equipment should be activated. 

(c) Emergency or abnormal procedures, including procedures to be followed when 

ice protection systems fail and/or warning or monitor alerts occur, should be provided.

53 
AC 23.1419-2D 4/19/07 

 (d) For fluid anti-ice/deice systems, information and method(s) for determining the 

remaining flight operation time should be provided.

(e) For airplanes that cannot supply adequate electrical power for all systems at 

low engine speeds, load-shedding instructions should be provided to the pilot for approach and 

landing in icing conditions. 

(f) For aircraft equipped with an autopilot, the autopilot should be disconnected 

periodically to check for unusual control force or deflection, and to move the flight controls to 

check for evidence of ice accreting in control surface gaps or frozen actuators. For airplanes not 

equipped with an autothrottle, there should be a WARNING that the autopilot will NOT maintain 

airspeed if ice accretes on the airplane. MONITOR airspeed closely. 

(3) Performance Information Section. A brief statement that supercooled cloud test 

environment and freezing rain, freezing drizzle, or mixed conditions (as appropriate) have not 

been tested. These icing environmental conditions outside the icing envelope of part 25, 

Appendix C, may exceed the capabilities of the ice protection system, and it may result in a 

serious degradation of performance or handling characteristics. 

(a) Normal, Utility, and Acrobatic Category Airplanes. For these airplanes, 

general performance information should be provided to give the pilot knowledge of allowances 

necessary while operating in ice or with residual ice on the airframe. The following items are 

only examples that provide some guidelines and are not requirements. These guidelines may be 

revised for specific airplanes as appropriate:

1. An accumulation of inch of ice on the leading edges can cause a loss 

in rate of climb up to Feet Per Minute (FPM), a cruise speed reduction of up to KIAS as 

well as a significant buffet and stall speed increase (up to knots). Even after cycling the 

deicing boots, the ice accumulation remaining on the boots and unprotected areas of the airplane 

can cause large performance losses. With residual ice from the initial inch accumulation, 

losses up to FPM in climb, KIAS in cruise, and a stall speed increase of knots can 

result. With inch of residual accumulation, these losses can double. 

Exceptions:

● Balked landing climb data with critical ice accretions should be presented 

in the AFM in the same format as the basic non-icing data. 

● Approach climb data, if required to be determined, should be presented in 

the AFM in the same format as the basic non-icing data. 

● Effects of ice protection system operation and/or ice accretions, if 

applicable, on takeoff distance should be presented. 

54 
4/19/07 AC 23.1419-2D 

● For airplanes in which the service ceiling with critical ice accretions is 

less than 22,000 feet, enroute climb performance with critical ice accretions should be presented 

in the AFM in the same format as the basic non-icing data. 

2. Airspeed—MAINTAIN BETWEEN KIAS AND KIAS with 

____ inch or more of ice accumulation for appropriate configuration. 

3. Prior to a landing approach cycle the wing and stabilizer deice boots to 

shed any accumulated ice. Maintain extra airspeed on approach to compensate for the increased 

stall speed associated with ice on unprotected areas. Use caution when cycling the boots during 

an approach, since boot inflation with no ice accumulation may cause mild pitching and increase 

stall speeds by knots. It may also decrease stall warning margin by the same amount; and it 

may cause or increase rolling tendency during stall. 

4. Holding in icing conditions for longer than 45 minutes may reduce 

margins and could result in inadequate handling and control characteristics. 

5. Maintain engine speeds of RPM higher to assure proper operation of 

the airframe ice protection system.

(b) Commuter Category Airplanes. Data should be provided so that the balked 

landing climb limited weight and approach climb limited landing weight could be determined. 

These data should include the effect of drag due to residual ice on protected and unprotected 

surfaces, power extraction associated with ice protection system operation, and any changes in 

operating speeds due to icing. Also, the effect on landing distance due to revised approach 

speeds, and/or landing configurations, should be shown. 

(4) For airplanes with a certification basis at amendment 23-14 or higher, the AFM 

should contain a statement similar to “This airplane is approved for flight in icing conditions as 

defined in part 25, Appendix C.” For these airplanes, there should not be references to 

operational terms such as “light” or “moderate” ice or “known icing.” 

(5) The AFM should reference the maintenance manual for ice protection surface 

cleaning procedures if the flight crew can be expected to perform this function. 

c. Prior to AFM Requirement. If the airplane was certificated prior to the effective date of

the requirement for an AFM, then the combination of manuals, markings, and placards should 

adequately address the placard and AFM subjects previously discussed in this AC. 

16. Instructions for Continued Airworthiness. 

a. Requirements. Instructions for Continued Airworthiness (ICA) are required in 

accordance with 14 CFR 21.50(b) and 23.1529. ICA should be prepared in accordance with part 

23, Appendix G. As a minimum the following should be addressed: 

55 
AC 23.1419-2D 4/19/07 

 (1) Basic description of the ice protection system operation, components, and 

installation 

(2) Servicing information, such as fluid type and quantities

(3) Location of panels used for inspection, and/or instructions to access components 

(4) Scheduling information for each applicable component including cleaning, 

inspecting, adjusting, testing and lubrication

(5) Overhaul or replacement periods for components, if any 

(6) Instructions for removing and replacing components 

(7) Precautions, such as toxicity of freezing point depressant fluid or flammability of 

some cements

(8) Cleaning instructions, such as only soap and warm water for pneumatic deicing 

boots 

(9) Limitations on the materials that can be applied, such as ice adhesion inhibitors, 

rubber preservatives, cosmetic coatings 

(10) Recommendations on the frequency of use of ice adhesion inhibitors 

(11) Special equipment or materials, such solvents, cements, edge filler, conductive edge 

sealer, rollers for pneumatic boot installation. 

b. Fluid Ice Protection Systems. The tailcone, empennage and other areas aft of the TKS 

de-icing fluid flow should be inspected after each use of the ice protection system. This inspection 

should concentrate on extraneous fluid build-up on electrical contacts, flight control surface 

bearings, bellcranks, etc. The ice protection system fluid evaporates very slowly. Therefore, 

contaminates that collect in the fluid in areas of joints, skin laps, etc. may cause the acceleration 

of corrosive action. 

c. Repairs for Pneumatic Deicing Boots. Boot manufacturers have developed repair 

procedures for pinholes, cuts and tears. The repair process for these types of damage is critical 

because proper operation of the boots could be affected. If leaks or pinholes are not periodically 

repaired, the entire system could become inoperable if water, drawn in by the vacuum that holds 

the boots deflated, subsequently refreezes and blocks a pneumatic line. The performance of 

deicing boots is dependent on the height and speed of deicing boot inflation and of the 

composition of the surface ply and its ice adhesion characteristics. Repairs should not pinch off 

tubes and thereby reduce inflation height. With these concerns in mind, the following guidance 

represents a minimum that should be addressed for repair procedures: 

56 
4/19/07 AC 23.1419-2D 

(1) Testing. The following tests should be accomplished:

(a) Boot Cycle Testing. The integrity of the repair should be evaluated via boot 

cycling at the maximum normal system operating pressure. Cycling should continue until the 

repair or boot fails. The normal deflation time may be shortened to speed up the test. For 

example, a 174-second deflation cycle can be reduced to 18 seconds while maintaining the 

six-second inflation time. Any material applied to the whole surface of the boot should also be 

evaluated in this test. 

(b) Cold Temperature Cycling. The testing in (1) (a) should be repeated at a 

temperature of 0 degrees F or colder.

(c) Hot Temperature. The boots may be exposed to hot temperatures, especially 

after on the ground on a hot, sunny day. The combination of high temperature and fluid exposure 

may cause deterioration and should be evaluated, see paragraph (e). 

(d) Proof and Burst Pressure Testing. This testing should be accomplished to 

show compliance to § 23.1438(b). When conducting the proof pressure test at 1.5 times 

maximum operating pressure, the repaired deicing boot should hold that pressure for 60 seconds 

and the repair should not fail. After the proof pressure test, the system should be inflated at 

maximum operating pressure, isolated, and the pressure drop verified not to exceed three Pounds 

Per Square Inch (PSI) in one minute. 

(e) Fluids Susceptibility. The repair should be exposed to various fluids for at 

least 24 hours in combination with a high temperature (160 degrees F) and the boots cycled at 

nominal pressure for at least 24 hours. Fluids to be evaluated include: fuels, oil, hydraulic fluids, 

glycol/water mixture, deicing boot age reduction, surface treatments and ice adhesion products, 

and ground deicing fluids. One method of accomplishing this test is to soak a rag with the fluid, 

place on the deicing boot over the repair, seal to prevent evaporation, and place in an oven at 

160 degrees F for 24 hours. Following this exposure the boot is removed, and cycled for 

24 hours. The deicing boot should inflate and hold air, and the repairs should remain in place and 

not leak air.

(f) Sand and Rain Erosion. Sand and rain erosion testing should be 

accomplished to show that the repair does not erode at a greater rate than the boot. A typical sand 

erosion test is ASTM G-76-95. A typical rain erosion test is conducted on a whirling arm rig that 

exposes the boot to a rainfall rate of one inch per hour at 300 to 500 Miles Per Hour (MPH) 

(depending on the airplane maximum speed); using one to two Millimeter (mm) diameter drops. 

(g) The inflation height over the repaired area should be measured and compared 

against other unrepaired portions of the boot at temperatures covering the part 25, Appendix C 

envelope. 

(h) Ice Shedding. Ice shedding performance in the area of the repair, and of the 

whole boot if any material is applied to the whole boot, should be evaluated throughout the 

57 
AC 23.1419-2D 4/19/07 

part 25, Appendix C continuous maximum and intermittent maximum icing conditions. It is 

particularly important to cover the range of temperatures and liquid water contents of part 25, 

Appendix C and the expected operational airspeeds. Simulated icing tests, such as an icing 

tunnel, may be used. 

(2) Materials Properties. Any material applied to the boots should be compatible with 

the deicing boot material. Use of brittle repair materials is not recommended. If the boot is 

completely resurfaced with a material, that material should be electrically conductive to allow 

bleeding of static charge from the deicing boot. 

(3) Repair Process Limitations. The repair process should contain limitations and 

quality control procedures such as: 

(a) Size of repairs. The maximum allowed repair size should be established and 

tested. Another consideration is the effect of the repair failure on the airplane. 

(b) Location and depth of repairs. Can structural elements such as tube fabric or 

stitches be damaged or can the wrong internal layers, such as tube fabric, be bonded together? It 

is recommended that boot manufacturers limits be used. 

(c) Density of repairs. The maximum density of repairs (number per area) should 

be tested. It is recommended that boot manufacturers limits be used. 

(d) Application of solvents and other chemicals. The application of solvents and 

other chemicals used in the repair process that can disbond the boot should be controlled so that 

they cannot penetrate internal layers of the boot. 

(e) Applicability of the repair procedure. Broken stitches represent a structural 

failure of the boot and should not be repaired. There should also be guidelines as to when 

severely worn boots should be replaced. 

d. Repairs for Electrothermal Propeller and Engine Inlet Deicing Boots. Boot 

manufacturers historically have not developed repair procedures for electrothermal deicing boots 

because the thermal mass characteristics of the repaired location will change and affect ice 

shedding. The following guidance is a minimum that should be addressed for electrothermal boot 

repairs: 

(1) Testing. The following tests should be accomplished:

(a) Fluids Susceptibility. The repair should be exposed to various fluids and the 

boots operated. Fluids to be evaluated include: fuels, oil, hydraulic fluids, glycol/water mixture, 

deicing boot age, appearance and ice adhesion products, and ground deicing fluids. 

(b) Sand and Rain Erosion. Sand and rain erosion testing should be 

accomplished to show that the repair does not erode at a greater rate than the boot. 

58 
4/19/07 AC 23.1419-2D 

(c) Thermal Characteristics. The thermal conductivity of the repair should be 

evaluated to insure that it does not provide a “cold spot” on the deicing boot, resulting from either 

a higher thermal mass or lower thermal conductivity of the repair material. 

(d) Ice Shedding. Ice shedding performance in the area of the repair, and of the 

whole boot if any material is applied to the whole boot, should be evaluated throughout the 

part 25, Appendix C, continuous maximum and intermittent maximum icing conditions. 

Simulated icing tests, such as an icing tanker, may be used. 

(e) Vibration. The airplane should be tested in icing conditions to verify the repair 

on one blade does not directly or indirectly (due to ice shedding) cause unacceptable propeller 

vibration. 

(2) Materials Properties. Any material applied to the boots should be compatible with 

the deicing boot material. Use of brittle repair materials is not recommended. The material 

should be electrically non-conductive and should have similar thermal conductivity of the deicing 

boot material. The effect of the chemicals on the electrical wires or foil should be evaluated. 

(3) Repair Process Limitations. The repair process should contain limitations and 

quality control procedures such as: 

(a) Size of repairs. The maximum allowed repair size should be established and 

tested. Another consideration is the effect of the repair failure on the airplane. 

(b) Location and depth of repairs. Can heating elements such as wires or etched 

foil be damaged or can the resistance of the wire or foil be altered by the repair procedure?

(c) Density of repairs. The maximum density of repairs (number per area) should 

be tested. 

(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? 

17. 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 anti-icing 

fluid holdover time guidelines and the most recent information available on operating in ground 

icing conditions. Airplane operators use this information to develop aircraft ground deicing and 

anti-icing programs required by 14 CFR §§ 121.629(c) and 135.227(b) (3). Operators who 

operate under § 135.227(b) (1) or (2) may still utilize the Notice information as guidance in their 

ground deicing plan. AC 20-117, AC 135-16, AC 135-17, AC 120-58, and AC 120-60B provide 

additional information on deicing and anti-icing of aircraft before takeoff. 

59 
AC 23.1419-2D 4/19/07 

(1) Why use ground deicing fluids? Aircraft are deiced before takeoff and, as 

required, anti-iced using thickened pseudo-plastic fluids. This procedure provides temporary 

protection from ice adhering to the aircraft’s surfaces before takeoff. The thicker fluids (Type II, 

IV) provide considerably higher holdover times than the Type I fluids.

b. Potential Issues. The following have occurred in service resulting in re-designs and 

modified takeoff procedures and limitations when certain ground deicing fluids are applied before 

takeoff. 

(1) Performance. The presence of thickened fluid may affect the airplane’s 

performance because the fluids may not completely flow off the aircraft wing and lift devices 

before liftoff. 

(2) Longitudinal Control. Fluid residue may cause increased pilot control forces 

during takeoff rotation and climb for airplanes with reversible control surfaces.

(3) Vibration and Controllability. The fluid may also collect in the balance bays of 

aerodynamically or weight balanced control surfaces, due to inadequate drainage. This may result 

in unbalanced control surfaces, unexpected changes in control forces, and control surface 

vibrations. Additionally, there has been one turbojet airplane in which the elevator tab was found 

to be aerodynamically sensitive to accumulation of foreign materials on its surface, in this case 

ground anti-icing fluid, causing severe vibration and limit cycle oscillations.

(4) Freezing of Controls. Anti-icing fluid may collect and evaporate in quiet cove 

areas, like those along control surface hinge lines. When the residue of the evaporated anti-icing 

fluid is re-hydrated by humidity, rain or during washing of the airplane, it may freeze and lock the 

control surface when the airplane climbs to altitudes with subfreezing temperatures. The residue 

does not contain a freezing point depressant, usually a glycol compound, which evaporates when 

the anti-icing fluid dries. Rehydrated fluid has been found in and around gaps between 

stabilizers, elevators, tabs, and hinge areas. This especially can be a problem with non-powered 

controls. Some pilots reported that they have had to reduce altitude until the frozen residue 

melted, which restored flight control movement. This phenomenon has not been experienced 

when a two-step deicing/anti-icing procedure is used. The first step is generally a hot Type I fluid 

mixture which flushes out residue. 

c. When Should These Issues Be Addressed? The evaluations of the above issues are not 

required for showing compliance to 14 CFR § 23.1419. Typically the effect of fluids on the 

airplane are evaluated by the airframe manufacturer, after type certification, at the request of an 

operator that is seeking approval of a ground deicing and anti-icing program incorporating Type 

II or Type IV fluid. However, there are design features, analyses and tests that an airplane 

manufacturer may want to consider during certification to prevent re-designs after type

certification if it is anticipated operators will use ground deicing/anti-icing fluids. This

information is provided in this AC at the request of several airplane manufacturers. 

60 
4/19/07 AC 23.1419-2D 

d. How Should These Issues Be Addressed? Some issues can be addressed by design. 

There is currently no requirement to test for airplane performance or controllability after the 

application of deice/anti-ice fluids. The aerodynamics working group of the SAE G-12 Aircraft 

Ground Deicing Committee has been tasked to develop a SAE recommended practice for 

approving the use of fluids on airplanes. This recommended practice will be considered for part 

23 guidance in a subsequent revision to this AC. The following paragraphs summarize methods 

that have been used by manufacturers in previous projects to address these issues. They are 

provided to assist airplane manufacturers in evaluating fluids for their specific designs. 

(1) Design.

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

(b) The design should incorporate drain holes, particularly in control surface 

balance bays. 

(2) Airplane Performance. There have been various methods to evaluate performance. 

Typically the lowest takeoff gross weight and maximum flap position approved for takeoff is 

considered critical because of the lower scheduled takeoff rotation speed. Three methods that 

have been used by airplane manufacturers: 

 (a) Takeoff parameters such as time to rotate/lift-off and rotate/lift-off airspeeds 

have been compared during takeoffs with and without fluids. Flow-off of fluids from the wing 

was simultaneously documented during takeoff roll and rotation. Stall speeds have been checked 

at altitude with 1 knot/sec decelerations. 

 (b) Takeoffs with and without fluids have been performed back to back and the lift 

loss decrement at liftoff determined. The flight test measured lift loss was then corrected by 

computational fluid dynamics (CFD) to determine the lift loss decrement at stall. A 5.24% 

decrement in maximum lift coefficient due to fluid has been considered acceptable for jet 

powered airplanes, and an 8% decrement has been considered acceptable for propeller powered 

airplanes. 

 (c) Takeoffs at fixed pitch angles are performed with and without fluid. Several 

pitch angles representing the range of pitch angles at liftoff are tested. A 6% decrement in lift 

coefficient at liftoff has been considered significant.

(3) Controllability. 

(a) The following has been evaluated at minimum practical gross weight, with 

minimum approved and maximum approved takeoff flap position, with all engines operating: 

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

2. Control power and control force during rotation at 10 knots or 7%, 

whichever is less, below the scheduled VR. 

61 
AC 23.1419-2D 4/19/07 

3. Controllability tests (± 40o bank angle changes, ± 0.5g or stall warning) 

with takeoff flaps, as soon as practical after liftoff, either at V2 +10 or the speed at 50 feet + 10 

KIAS, depending on airplane category. 

4. Vibration/buffet at Vne or Vmo. 

(b) The following has been evaluated for multi-engine airplanes at minimum

practical gross weight, with maximum approved takeoff flap position, with simulated one engine 

inoperative: 

1. Control power and control force during rotation at VR

2. Controllability tests (± 30o bank angle changes, +1.3/-0.8g or stall 

warning) with takeoff flaps, as soon as practical after liftoff, either at V2 or the speed at 50 feet, 

depending on airplane category. 

(4) Fluids. 

(a) Number of Fluids. The airplane manufacturer should evaluate the type and 

brand of fluids to be approved for the airplane. A representative Type II fluid, and a Type IV 

fluid if approved in the AFM, should be tested. The viscosity of the fluid should be considered 

when determining the brand of fluid to test. Type III fluid need not be tested if Type II or IV 

fluid is tested and showed acceptable lift loss. If the Type II and IV testing showed takeoff 

procedures needed to be modified, than Type III fluid may not need to be tested if the takeoff 

procedures for Type III are similarly modified. 

(b) Fluid Application. 

1. Type II, III, and IV fluids should be applied undiluted. 

2. Procedures for de-icing and anti-icing should follow the proposed 

recommended procedures. All applicable surfaces (including the horizontal stabilizer) should be 

treated. Slats/flaps should be in the recommended position for fluid application. 

3. Takeoff tests should be conducted as soon as possible following antiicing fluid application. 

(c) It is preferable to test at the coldest outside air temperature at which the fluid 

can be used undiluted. 

(5) Airplane Systems. Any adverse effect on aircraft systems should be noted (e.g. 

ECS, APU inlet, vent blocking)

(6) Post Flight Inspections. Several flights should be conducted after one step 

applications of the thickened pseudo-plastic fluids to be approved for the airplane. Post flight 

62 
4/19/07 AC 23.1419-2D 

inspections should be conducted to determine if fluid residue is present on the airplane in areas 

that may cause one of the problems discussed in paragraph 17.b. 

e. Airplane Flight Manual 

(1) Fluids. The type and brands of fluid approved, along with any minimum outside air 

temperature limitation, should be in the Limitations section. 

(2) Limitations. Procedures modified as a result of ground fluids should be in the 

Limitations section. Examples for part 23 airplanes are an increase in takeoff speeds and use of 

flaps. 

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

residue is shown to occur. 

(4) Performance. Any increases in takeoff distance due to takeoff speeds increased 

above the established threshold should be presented in the Performance section. It should be 

noted that the takeoff testing is not required to be conducted on contaminated runways. Since 

runways may be contaminated in conditions in which these fluids will be used in operation, there 

should be a CAUTION that states the takeoff distance data is based on a dry runway, and that 

takeoff distances will be increased on contaminated runways.

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

addressed in maintenance manual: 

(1) Inspection.

 (a) Drain holes. 

(b) Control balance bays. 

(c) Identified aerodynamically quiet areas. 

(2) Cleaning. High-pressure washing with a hot Type I fluid/water mix in areas where 

fluid could accumulate. For those locations equipped with Type III fluids, in lieu of Type I fluids, 

it is suggested that a high pressure washing with a heated Type III/water mix be employed. Such 

a procedure may require subsequent lubrication. 

g. Runway Deicing Fluids. Airplane manufacturers should be aware that since 1997 a 

problem of catalytic oxidation has been occurring on aircraft using carbon brakes. In 1997, 

airports started using more environmentally friendly fluids to deice runways. This resulted in the 

use of potassium formates and/or acetates. These chemicals (organic salts) attack the carbon in 

the brake and create a catalytic oxidation which softens the carbon, causing it to flake and 

crumble undetected and unpredictably over time thus reducing the life and long-term efficiency of 

the brakes themselves. SAE G-12F, among other industry working groups, has been working for 

63 
AC 23.1419-2D 4/19/07 

some time to try and reduce these effects from runway de-icers. These runway fluids are now 

being found to adversely affect anti-icing fluid applied to aircraft and also to promote the 

formation of anti-icing fluid residue gel in aerodynamically quiet areas of the aircraft. 

64 
4/19/07 AC 23.1419-2D 

Appendix 1 

APPENDIX 1. DEFINITIONS 

1. DEFINITION OF TERMS. For the purposes of this AC, the following definitions should 

be used. 

a. Anti-Ice. The prevention of ice formation or accumulation on a protection surface, either 

by evaporating the impinging water or by allowing it to run back and off the surface or freeze on 

non-critical areas. 

b. Part 25, Appendix C Icing Conditions. The part 25, Appendix C certification icing 

condition standard for approving ice protection provisions on aircraft. The conditions are 

specified in terms of altitude, temperature, LWC, representative droplet size (MED), and cloud 

horizontal extent. 

NOTE 6: In part 25, Appendix C, the term “mean effective diameter” refers 

to what is now called the “Median Volume Diameter (MVD),” determined using 

rotating multi-cylinders and assuming a Langmuir distribution.

c. Artificial Ice. A structure formed from material other than frozen water, but intended to 

represent an ice accretion. See “simulated ice shapes.” 

d. Critical Ice. The aircraft surface ice shape formed within required icing conditions 

results in the most adverse effects for specific flight safety requirements. For an aircraft surface, 

the critical ice shape may differ for different flight safety requirements, e.g., stall speed, climb, 

aircraft controllability, control surface movement, control forces, air data system performance, 

dynamic pressure probes for control force “feel” adjustment, ingestion and structural damage 

from shed ice, engine thrust, engine control, and aeroelastic stability. 

e. Deice or Deicing. The periodic shedding or removal of ice accumulations from a 

surface. This occurs by destroying the bond between the ice and the protection surface. 

f. Freezing Drizzle. Drizzle is precipitation on the ground or aloft in the form of liquid 

water drops that have diameters less than 0.5 mm and greater than 0.05 mm (100 μm to 500 μm). 

Freezing drizzle exists at air temperatures less than zero degrees C (supercooled), remains in 

liquid form, and freezes upon contact with objects on the surface or airborne. 

g. Freezing Precipitation. Freezing rain or drizzle falling through or outside a visible 

cloud. 

h. Freezing Rain. Rain is precipitation on the ground or aloft in the form of liquid water 

drops which have diameters greater than 0.5 mm. Freezing rain is rain that exists at air 

temperatures less than zero degrees C (supercooled), remains in liquid form, and freezes upon 

contact with objects on the surface or airborne. 

A1-1 
AC 23.1419-2D 4/19/07 

Appendix 1 

i. Ice Crystals. Any one of a number of macroscopic, crystalline forms in which ice 

appears. 

j. Icing Conditions. The presence of atmospheric moisture and temperature conducive to 

airplane icing. 

k. Intercycle Ice. Ice that builds up on a deiced surface and exists immediately before 

actuation of the deice system. 

l. Liquid Water Content (LWC). The total mass of water contained in liquid drops 

within a unit volume or mass of air, usually given in units of grams of water per cubic meter 

(g/m3) or kilogram of dry air (g/kg). 

m. Mean Effective Diameter (MED). The calculated drop diameter that divides the total 

liquid water content present in the drop size distribution in half, i.e., half the water volume will 

be in larger drops and half the volume in smaller drops. The value is calculated, based on an 

assumed droplet size distribution, (e.g. Langmuir distribution) which is how it differs from

median volume diameter. 

n. Median Volume Diameter (MVD). The drop diameter that divides the total liquid water 

content present in the drop distribution in half, i.e., half the water volume will be in larger drops 

and half the volume in smaller drops. The value is obtained by actual drop size measurements. 

o. Mixed Phase Icing Conditions. Partially glaciated clouds at an ambient temperature 

below 0°C. The clouds contain ice crystals and supercooled liquid water drops. 

p. Monitored Surface. The surface of concern regarding the ice hazard, (e.g., the leading 

edge of a wing). Ice accretion on the monitored surface may be measured directly or correlated 

to ice accretion on a reference surface. 

q. Pre-Activation Ice. Protected surface ice accretion prior to the full effectiveness of the 

ice protection system.

r. Protected Surface. A surface containing ice protection, typically located at the surface’s 

leading edge. 

s. Protection Surface. Active surface of an ice protection system, for example, the surface 

of a deicing boot or thermal ice protection system.

t. Reference Surface. The observed (directly or indirectly) surface used as a reference for 

the presence of ice on the monitored surface. The presence of ice on the reference surface must 

occur prior to – or coincidentally with – the presence of ice on the monitored surface. Examples 

of reference surfaces include windshield wiper blades or bolts, windshield posts, ice evidence 

probes, propeller spinner ice, and the surface of ice detectors. The reference surface may also be 

the monitored surface. 

A1-2 
4/19/07 AC 23.1419-2D 

Appendix 1 

u. Residual Ice. Ice that remains on a protected surface immediately following the 

actuation of a deicing system.

v. Reversible Flight Controls. The flight deck controls that are connected to the pitch, 

roll, or yaw control surfaces by direct mechanical linkages, cables, or push-pull rods such that 

pilot effort produces motion or force about the control surface hinge line. Conversely, force or 

motion originating at the control surface (through aerodynamic loads, static imbalance, or trim

tab inputs, for example) is transmitted back to flight deck controls. 

(1) Aerodynamically Boosted Flight Controls: Reversible flight control systems that 

employ a movable tab on the trailing edge of the main control surface linked to the pilot's 

controls or to the structure in such a way as to produce aerodynamic forces that move, or help to 

move, the surface. Among the various forms are flying tabs, geared or servo tabs, and spring 

tabs. 

(2) Power-Assisted Flight Controls: Reversible flight control systems in which some

means is provided, usually a hydraulic actuator, to apply force to a control surface in addition to 

that supplied by the pilot to enable large surface deflections to be obtained at high speeds. 

w. Runback Ice. Ice formed from the freezing or refreezing of water leaving an area on an

aircraft surface that is above freezing and flowing downwind to an area that is sufficiently cooled

for freezing to take place. This ice type is frequently a byproduct of partially evaporative 

(running wet) ice protection systems, thermal deicing systems, and can occur on airfoils near 

freezing temperature. 

x. Simulated Ice. Ice shapes that are fabricated from wood, epoxy, or other materials by 

any construction technique. 

y. Supercooled Large Drops (SLD). Supercooled liquid water that includes freezing rain 

or freezing drizzle. 

z. Supercooled Drops. Water drops that remain unfrozen at temperatures below 0°C. 

Supercooled drops exist in clouds, freezing drizzle, and freezing rain in the atmosphere. These 

drops may impinge and freeze after contact on aircraft surfaces 

2. DEFINITION OF ACRONYMS. 

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 

A1-3 
AC 23.1419-2D 4/19/07 

Appendix 1 

ATC Air Traffic Control 

C Centigrade 

CAR Civil Air Regulations 

CFR Code of Federal Regulations 

CG Center of Gravity 

CS Certification Specification (EASA) 

ELOS Equivalent Level of Safety 

F Fahrenheit 

FAA Federal Aviation Administration 

FPM Feet Per Minute 

FSAT Flight Standards Information Bulletins for Air Transportation

EASA European Aviation Safety Agency 

EFIS Electronic Flight Information Systems 

FIDS Flight Ice Detection Systems 

ICA Instructions for Continued Airworthiness 

ICTS Ice Contaminated Tailplane Stall 

IMC Instrument Meteorological Conditions 

IPS Ice Protection System 

KCAS Knots Calibrated Airspeed 

KIAS Knots Indicated Airspeed 

KOEL Kind of Equipment List 

LOUT Lowest Operational Use Temperature 

LWC Liquid Water Content 

MDI Magnetic Direction Indicator 

MED Mean Effective Diameter 

MFC Maximum Mach number for stability characteristics 

MMEL Master Minimum Equipment List 

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 

A1-4 
4/19/07 AC 23.1419-2D 

Appendix 1 

TEU Trailing Edge Up 

TSO Technical Standard Order 

VFE Flaps Extended Speed 

VIT Variable Incidence Tailplane 

VLE Landing Gear Extended Speed 

VMC Minimum Control Airspeed 

VMO Maximum Operating Airspeed 

MMO Maximum Operating Mach Number 

VNE Never Exceed Airspeed

VR Takeoff rotation speed 

VREF Reference Landing Approach Airspeed 

V2 Takeoff safety speed 

A1-5 (and A1-6) 

4/19/07 AC 23.1419-2D 

Appendix 2 

APPENDIX 2. GUIDELINES FOR DETERMINING CERTIFICATION BASIS ON 

FLIGHT IN ICING APPROVAL STCS AND AMENDED TCS 

1. My CAR 3 (or earlier certification basis) aircraft has ice protection systems installed 

and is not placarded against flight into known icing. Am I approved for flight in icing 

conditions? 

These CAR 3 airplanes are permitted to fly in icing conditions if: 

• the ice protection systems are installed per type design data of the same model in the 

Type Certificate Data Sheet (TCDS); 

• the Pilot’s Operating Handbook (POH), AFM, or AFM supplement associated with the 

ice protection systems do not prohibit it; 

• the equipment listed in the KOEL is installed and functioning; and 

• the airplane complies with the equipment requirements of § 91.527 or § 135.227, if 

applicable. 

2. What if I have a CAR 3 (or earlier certification basis) airplane that is permitted to fly in 

icing conditions but I replace the ice protection system with another system? 

It depends on what is meant by another system. If it is replacement parts, such as replacing 

pneumatic deicing boots with those from another manufacturer, the certification basis can remain 

unchanged; see Appendix 5 of this AC for more information. If it is another type of system, for 

example replacing a pneumatic deicing system with a freezing point depressant system or 

electrothermal system, compliance to § 23.1419, amendment 23-14 must be shown. Section 

23.1419, amendment 23-43 would not be required since a modification to an ice protection 

system is considered “not significant” under the Changed Product Rule. 

3. As a follow-up to the last question, suppose I change my mind and want to re-install my 

ice protection systems. Will my aircraft be approved for flight in icing? 

Yes, as long as the systems are installed per type design data and the POH, AFM, or AFM 

supplement associated with the ice protection systems do not prohibit flight in icing conditions 

(or “flight into known icing”). Retroactive removal of flight into known icing approval can only 

be accomplished by the airworthiness directive process. 

4. I have a CAR 3 (or earlier certification basis) airplane that has no ice protection system 

installed and the type design data does not contain flight in icing approval. What is the 

certification basis if I add ice protection systems? 

Under the Changed Product Rule, adding approval for flight in icing conditions is considered a 

significant change (AC 21.101-1) and compliance should be shown to the latest amendment. In 

A2-1 
AC 23.1419-2C 4/19/07 

Appendix 2 

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 23.1416 23.1547 

23.929 23.1101 23.1326 23.1419 23.1559 

It is recognized that compliance to § 23.1419(a), which requires that the airplane meet Subpart B 

performance in icing conditions, may be impractical for some CAR 3 airplanes. The Changed 

Product Rule allows the applicant to elect compliance to amendment 23-14 for that particular 

paragraph of § 23.1419. In this case the performance regulations are used as guidelines as 

discussed in paragraph 13a (2) of this AC. 

5. My airplane has some ice protection systems installed but is not certified for flight in 

icing. A later model of my airplane, which is on the same TCDS, is certified for flight in 

icing in accordance with § 23.1419. The later model does have a different engine installed 

with higher horsepower and a different ice protection system. Can I install the exact same 

ice protection systems as the later model, install a new engine with at least the same 

horsepower, and be certified for flight in icing?

Yes, and similarity may be used to show compliance to the applicable regulations. However, 

there may be some testing required. The current method of compliance to § 23.1419 includes 

tests (susceptibility to ice contaminated tailplane stall, for example) that may not have been 

accomplished during certification of the later model. 

A2-2
4/19/07 AC 23.1419-2D 

Appendix 3 

APPENDIX 3. GUIDELINES FOR SUPPLEMENTAL TYPE CERTIFICATES (STC) 

AND AMENDED TYPE CERTIFICATES ON AIRPLANES 

1. APPLICATION. 

a. As stated in the “APPLICABILITY” section, the guidance in this AC applies to any 

STC or amended TC on an airplane for which the applicant wants approval under the 

provisions of § 23.1419. Increase in gross weight, changes in engine power, and propeller 

changes could affect approval in icing and these areas would have to be evaluated using AC 

23.1419-2D as the method of compliance. An applicant wishing to use an alternate Means of 

Compliance (MOC) needs to consult the Standards Office. Whether the certification basis for 

the STC or amended TC includes 14 CFR, § 23.1419 at amendment 23-14 or 23-43 is 

irrelevant as far as the tests that should be accomplished. The difference in the certification 

basis does not change the tests that must be accomplished, only their pass/fail criteria. 

b. Compliance to icing regulations has been either an afterthought or totally disregarded 

on many modification programs on aircraft certified for flight in icing conditions. In some

cases, the rationale used was that since the ice protection systems were not modified, icing 

regulations do not need to be addressed. This may be an incorrect assumption. Icing 

regulations may need to be addressed for any modification that could affect the following in 

icing conditions: 

(1) Aircraft performance 

(2) Flying qualities, 

(3) Engine operation 

(4) Essential system operation. 

c. If it is desired to retain flight in icing approval of the modified airplane, the following 

examples are modifications in which compliance to icing regulations need to be revisited: 

(1) Engine changes 

(2) APU 

(3) Propeller changes 

(4) Engine inlet or accessory inlet changes 

(5) Antennae installations or other external modifications 

(6) Gross weight increases 

(7) CG envelope increase 

A3-1 
AC 23.1419-2D 4/19/07 

Appendix 3 

(8) Flight envelope increase

(9) Turboprop conversion 

(10) Modifications to lifting surfaces 

(11) Installation of vortex generators 

(12) Modifications to ice protection systems 

(13) Addition of/or re-location of fuel vents 

(14) Addition of/or autopilot replacement. 

d. The icing regulations that are addressed in this appendix are: 

(1) § 23.929 

(2) § 23.1093 

(3) § 23.1301 

(4) § 23.1309 

(5) § 23.1416 

(6) § 23.1419 

e. The following guidance address some specific, common modifications: 

(1) Engine Changes. 

(a) Effects of increased engine power or thrust: 

1. On airplanes with a certification basis at amendment 23-14 or higher, 

any degradation in stall characteristics, stability or control, or marginal characteristics, due to 

increased engine power or thrust, will require re-evaluation with ice accretions. Since the 

pass/fail criteria are qualitative, testing (original airplane and modified airplane) should be 

accomplished back to back by the same test pilot. Stall warning should also be evaluated. 

Although the margins are not a concern at high power, they need to evaluate if higher power 

masks any stall warning cues. The following tests should be accomplished: 

(aa) Stall characteristics and stability of minimum weight and 

maximum weight, aft CG limit 

A3-2 
4/19/07 AC 23.1419-2D 

Appendix 3 

(bb) Controllability at forward CG limit and critical weight. 

2. Susceptibility to ice contaminated tailplane stall should be addressed for 

airplanes in which the engine thrust increase is greater than 10 percent or the airplane has a 

service history of ICTS susceptibility. Maximum power is usually more critical than idle. This 

cannot be done with analysis on a propeller airplane with reversible controls due to second order 

effects. Flight testing should be accomplished with 40-grit sandpaper and intercycle/residual ice 

on horizontal tailplane, intercycle/residual ice on vertical stabilizer, and 45-minute ice accretions 

on unprotected leading edge tail surfaces. 

• Engine Induction Icing. Refer to AC 23-16A for guidance. 

(c) Ice Shedding. Engine compliance data to § 33.77 should be compared 

between the currently installed engine and the proposed engine. If the ice slab used to show 

compliance is smaller for the proposed engine, ice shedding from the airframe should be readdressed. Data on ice shedding may be available from the airplane TC holder. Engine inlet 

lip ice shedding should be addressed. The amount of ice mass that could be shed should be 

compared to a similar, approved engine installation or to part 33 engine compliance data. 

(d) Effects of Decreased Engine Power, Thrust or Bleed Air. 

1. Ice Protection System Operation. Bleed air mass flows, pressures 

and temperatures of the proposed engine and of the existing, certified engine should be 

compared. If there is a reduction, the effectiveness of the ice protection systems must be 

substantiated. 

2. Airplane Performance. Airplane performance in icing conditions 

should be re-evaluated. 

(2) Essential APU. When an essential APU is modified or added, operation in icing 

conditions should be addressed similarly to engines since essential APUs are covered by 

§ 23.1093. 

(3) Propeller Changes. 

(a) Section 23.929 states that propellers (except wooden propellers) and other 

engine installations must be protected against the accumulation of ice as necessary to enable 

satisfactory functioning without appreciable loss of thrust when operated in the icing conditions 

for which certification is requested. 

(b) If the deicing system is listed on the propeller TCDS, it does not indicate that 

compliance to § 23.929 was shown. It means that the deicing system was shown to function 

properly, the deicing system complies with propeller structural and vibration regulations, and 

deicing system failure modes, as discussed in § 23.929 of AC 23-16, cannot cause an unairworthy condition. 

A3-3 
AC 23.1419-2D 4/19/07 

Appendix 3 

(c) The typical analysis report from the deicing boot manufacturer is not 

sufficient by itself to show compliance to § 23.929. The typical report calculates intercycle ice 

thickness for various flight and icing conditions, but does not calculate the effect on propeller 

efficiency, which must be done to show no appreciable loss of thrust. For STCs, it would be 

acceptable to show that intercycle ice is equal to or less than the accretions obtained on the same

propeller on an airplane that was flight tested in icing conditions and shown to have no 

appreciable loss in thrust. 

(d) The typical deicing boot manufacturer report also contains a caveat that it 

does not address propeller runback ice. Similarity to another propeller that was flight tested in 

icing conditions is usually done to address runback. Similarity would include propeller and 

deicing boot aerodynamic and thermal similarity, deicing cycle time, propeller RPM, and flight 

conditions. Note that metal and composite propellers have different thermal masses. 

(e) As a final qualitative check for both intercycle and runback ice on new 

airplane programs, airplane performance is checked during flight tests in icing conditions. A test 

point as close to minus 22 degrees F as possible should be included in the flight tests. 

(f) The propeller installation, including spinner and cowl geometry, must be 

compared to previously tested installations in icing conditions. Changes that could allow 

moisture to reach the brush blocks must be avoided. 

(g) If the proposed propeller is calculated to have higher efficiency than the 

existing, approved propeller, the guidance in paragraph 1e (1) (a) of this appendix should be 

followed. 

(h) If the proposed propeller(s) and/or deicing system are predicted to increase the 

size of intercycle ice, the effects of propeller ice shed onto other parts of the airplane should be 

addressed. 

(i) For New Propeller Deice Electrical Power Systems: 

1. The surface temperature characteristics of the propeller boots should be 

shown to be the same as original certified system. 

(aa) If the temperature characteristics and deice timing cycle are shown 

to be changed, flight testing in measured natural icing conditions are required to evaluate 

propeller deicing and airplane performance 

(bb) If the temperature characteristics and deice timing cycle are shown 

to be unchanged, a demonstration of propeller deicing and airplane performance in natural icing 

conditions should be performed. 

(cc) Flight testing should be accomplished as close to –22 degrees F as 

possible. 

A3-4 
4/19/07 AC 23.1419-2D 

Appendix 3 

2. A rational analysis of the heat generated by the system should be made 

and compared to the existing system if the system is located in areas where ice accretion and 

runback could be affected, such as the spinner. 

(4) Engine Inlet or Accessory Inlet Changes. Guidance is provided in the “engine 

changes” section above. It should be noted that § 23.1093 applies to engine oil and accessory 

cooling inlets as well as induction inlets. 

(5) Antennas, Installations or Other External Modifications.

(a) When antennas, cameras, fairings for such installations, or other external 

installations such as drain masts are installed on aircraft, the installer should show the following: 

1. The predicted ice accretion does not contribute significantly to drag; 

2. There is no ice-shedding hazard due to impact or ingestion on 

downstream structure, engines or propellers. See paragraph 14 of the AC for guidance on ice 

shedding. 

3. There is no ice related performance reduction of lifting surfaces; 

4. There is no ice related effect on downstream air data sensors or ice 

detectors. 

(b) A very conservative, simple analysis may be accomplished first to show the 

objectives (a) 1 and (a) 2. If the conservative analysis fails, the analysis can be refined to 

determine if the initial analysis was overly conservative. The conservative analysis can assume

the following: 

1. The water catch area is the full frontal area of the installation; 

2. Collection efficiency is one. 

3. No runback or evaporation of impinging water.

4. Assume the shape on blade antenna will be similar to airfoils and the 

shape on low profile antennae will be single horn shapes. 

(c) The installer should determine the critical icing condition, and the 45-minute 

hold in continuous maximum conditions needs to be included. If the analysis shows a problem, 

then one or more of the following can be accomplished:

1. Determine realistic collection efficiency either with an ice accretion code 

or with the “FAA Icing Handbook”; 

A3-5 
AC 23.1419-2D 4/19/07 

Appendix 3 

2. Determine the real impingement limits by using an icing code, which may 

reduce the collection area; 

3. Run the full configuration in an icing code to determine if the installation 

is in a shadow zone. 

4. If drag is a problem, run an ice accretion code to determine a more 

realistic ice shape. 

(d) Flight tests in measured natural icing or with simulated ice shapes should be 

accomplished to determine if there are any detrimental effects due to the ice accretions if: 

1. The installation is upstream of air data sensors or an ice detector; or 

2. The installation is on a lifting surface or 

3. The installation could create a wake on a lifting surface. As an example, 

if an external modification is large enough (e.g. dish antenna), it may interfere with the flow field 

around the tail and the susceptibility to ICTS may need to be addressed. 

(e) The one exception to (d) 2 is fairings. An analysis to show the impact on 

maximum lift coefficient, in combination with flight tests with no ice accretions, may be 

acceptable. 

(6) Gross Weight Increases. 

(a) At the increased angle of attack for a given airspeed, the impingement limits 

will change. An impingement analysis needs to be accomplished to show the ice protection 

coverage remains adequate. 

(b) The impingement analysis should also evaluate unprotected areas such as fuel 

vents. 

(c) If the following flight testing with no ice show no degradation from the 

unmodified aircraft, and no marginal characteristics, flight testing with ice (or simulated ice 

accretions) are not required: 

1. Stall warning, stall characteristics, and stability at maximum weight, aft 

CG limit

2. Stall speeds and controllability at maximum weight, forward CG limit. 

(d) Operational speeds and AFM/POH performance data in icing conditions need 

to reflect higher stall speeds. 

A3-6 
4/19/07 AC 23.1419-2D 

Appendix 3 

(e) Climb performance in icing conditions should be evaluated to determine if the 

airplane is capable of operating safely. 

(f) An analysis should show increased weight makes the airplane equal or less 

susceptible to tailplane stall. The analysis should evaluate tail trim requirements and tail ice 

accretion at the higher airplane angle of attack. 

(7) CG Envelope Increase. Generally, the same guidance used for gross weight 

increases can be used for CG envelope increases. The one exception is when an increase of 

forward center of gravity limit on airplanes makes an airplane more susceptible to ice 

contaminated tailplane stall. This should be addressed by flight testing for airplanes with 

unpowered, reversible elevators or with propellers. An analysis may be acceptable for other 

configurations. 

(8) Flight Envelope or Operating Procedure Changes. 

(a) If an increase in maximum operating altitude is applied for, the applicant 

should demonstrate: 

1. The ice protection system operating pressures (for pneumatic 

systems) or temperatures (for hot air systems) by dry air testing; and 

2. The stall speeds and stall characteristics associated with ice accretions 

if these are shown to be influenced by Mach number. 

(b) The effect of increased cruise airspeeds and increased altitudes that could 

affect windshield ice accretion, and adequacy of the windshield heat, should be addressed. 

 

(c) The effect of different operating airspeeds and altitudes that could affect 

critical ice accretions. 

(9) Turboprop Conversion. 

(a) If the ice protection systems utilize engine bleed air for operation, the 

pneumatic lines may accumulate more water than the current unmodified type design. This 

water can subsequently refreeze and block the pneumatic lines, resulting in failure of some or all 

zones of the pneumatic system. The applicant needs to show that the pneumatic deicing system

will continue to function in icing conditions. 

(b) The pneumatic deicer operating pressure may also decrease at lower engine

RPMs. A minimum engine RPM for acceptable pneumatic operating pressure, which should 

allow for descent, should be established and published in the AFM/POH. 

A3-7 
AC 23.1419-2D 4/19/07 

Appendix 3 

(10) Modifications to Lifting Surfaces.

(a) Critical ice accretions (including pre-activation, intercycle, residual, and 

runback) may have to be re-defined, especially if the changes affect wing angle of attack. Stall 

strips are good collectors of ice and are an example where leading edge ice accretions should be 

re-defined. If ice accretions are changed or the modifications could affect control power or 

control surface hinge moments, flight testing with simulated ice accretions should be 

accomplished to evaluate one or more of the following: 

1. Stall warning, stall characteristics, and stability at maximum weight, aft 

CG limit; 

2. Stall speeds, stall warning, controllability and performance at maximum 

weight, forward CG limit; 

3. ICTS susceptibility at light weight, forward CG limit if the aircraft has 

unpowered, reversible elevators or propellers. 

4. For unprotected winglets, flutter margins needs to be addressed. 

(b) Susceptibility to ICTS should be addressed for either horizontal or vertical tail 

modifications or wing modifications that are predicted to increase ICTS susceptibility. ICTS 

susceptibility may be addressed by analysis on jet-powered aircraft with irreversible elevator 

controls. 

(11) Installation of Vortex Generators. 

For vortex generators that are installed near the leading edge, the applicant should 

provide data on expected ice accretions. Flight conditions to consider are the 45-minute hold, 

descent, and approach. Substantiation of the effects on stall speeds, stall characteristics, and 

stability and control should be provided. 

(12) Modifications to Ice Protection Systems. 

(a) Critical ice accretions may have to be re-defined. If ice accretions are 

changed or the modifications could affect control power or control surface hinge moments, flight 

testing with simulated ice accretions should be accomplished to evaluate one or more of the 

following: 

1. Stall warning, stall characteristics, and stability at maximum weight, aft 

CG limit; 

2. Stall speeds; stall warning and controllability at maximum weight, forward 

CG limit; 

A3-8 
4/19/07 AC 23 1419-2D 

Appendix 3 

3. ICTS susceptibility at light weight, forward CG limit if the aircraft has 

unpowered, reversible elevators or propellers. 

(13) Addition of or Relocation of Fuel Vent. 

As a minimum an impingement analysis and/or similarity should be used to show that 

ice does not obstruct the fuel vents. 

(14) Addition or Replacement of Autopilot 

Guidance in this AC, paragraphs 12 and 13 for autopilots should be consulted. There are 

specific scenarios in which autopilots can get the pilot into trouble in an airplane approved for 

flight into known icing. Those scenarios resulted in accidents and are factual. Based on our 

service experience, even though there are no regulatory requirements addressing autopilots in 

airplanes approved for known icing, applicants are strongly encouraged to include features that 

mitigate these autopilot induced accident scenarios. Where it would be impractical to add such a 

feature, the design should include adequate trim in motion cues. For replacement autopilots, the 

design of the original and replacement autopilots should be compared. 

A3-9 (and A3-10) 

4/19/07 AC 23 1419-2D 

Appendix 4 

APPENDIX 4. GUIDELINES FOR CERTIFYING ICE PROTECTION SYSTEMS 

ON AIRPLANES NOT CERTIFICATED FOR FLIGHT IN ICING 

1. APPLICABILITY. There may be times when applicants may want to certificate an ice 

protection system installation on an airplane that is to remain not certificated for flight in icing. 

This used to be called a “non-hazard” basis. This means that the aircraft is prohibited from flight 

in icing conditions but there is some ice protection to facilitate an exit from an inadvertent icing 

encounter. The following guidance provides a reference; novel systems may require additional 

considerations. 

2. SUBPART B – FLIGHT.

a. The applicant must show that installation of the system (not operating) does not affect 

performance, stalls, controllability, maneuverability, stability, trim, ground/water handling, 

vibration and buffet, and, if applicable, high speed characteristics. If any of these are affected, it 

should be shown that applicable regulations are still complied with and place the appropriate 

information in the AFM. Compliance should be accomplished with dry air flight tests. If the 

system is being evaluated as an amended TC or STC, it is not necessary to investigate all weight

and CG combinations and flight conditions when results from the airplane certification testing 

clearly indicate the most critical combination to be tested. 

b. In some cases the effect of system operation may need to be evaluated. For pneumatic 

deicing boots, the operation of the boots (inflation) should have no hazardous affect on airplane 

performance and handling qualities. The effect of pneumatic boot operation on stall speed and 

stall warning should be evaluated and appropriate information placed in the AFM. Freezing 

point depressant systems when operating have been shown to increase drag. 

3. SUBPART D – DESIGN AND CONSTRUCTION. 

a. The ice protection systems should be evaluated to determine the impact to the airframe

structure per the applicable regulations in subpart D. The load conditions determined from

Subpart C should be used in this evaluation. The individual ice protection system components 

should also be evaluated to determine that they would withstand the load conditions from

Subpart C if their failure can cause a hazard. Thermal effects on structure of thermal ice 

protection systems and fluid/structure compatibility of freezing point depressant systems should 

be evaluated. 

b. An evaluation of flutter characteristics to account for the added mass of the ice protection 

systems should be made per § 23.629. 

c. If a thermal windshield ice protection system is installed, an evaluation of the visibility 

due to distortion effects through the protected area should be made. In accordance with 

§ 23.775(g), a probable single failure of a transparency heating system should not adversely 

affect the integrity of the airplane cabin or create a potential danger of fire. 

A4-1
AC 23.1419-2D 4/19/07 

Appendix 4 

d. For wing and empennage electrical deicing systems, the indirect effects of lightning 

maybe an issue. The airplane must be shown to be protected against catastrophic effects from

lightning in accordance with § 23.867. As a minimum the effect of the ice protection system

installation should be addressed by analysis and design. 

4. SUBPART E – POWERPLANT. For an airplane not certificated for flight in icing, 

compliance to § 23.929 is not required but compliance to § 23.1093 is required. 

5. SUBPART F – EQUIPMENT.

a. On airplanes with a certification basis of amendments 23-20 and higher, compliance to 

§ 23.1301 must be shown. Compliance to § 23.1301 would entail showing the airplane can 

safely exit inadvertent icing encounters by providing the data in paragraphs (1) through (5). 

Subsequent installations on other aircraft models can be based upon similarity to the natural icing 

tests that were conducted provided that the installations can be shown to be sufficiently similar 

(ref. paragraph 10.f.). Airfoil size, shape, operating envelope, and airplane ice accretion sites 

should be included in the similarity analysis: 

(1) A functional flight test in dry air 

(2) Icing tunnel tests in part 25, Appendix C icing conditions 

(a) Evaluate the ice protection system operation 

(b) Determine protected area ice accretion such as runback, intercycle ice 

(3) Empirical flight test data (natural icing or tanker) 

(a) Validate ice accretions for ice shape flight testing

(b) Evaluate and document susceptibility of movable control surfaces to fixed 

surface bridging/freezing and subsequent lockup of controls

(c) Evaluation of autopilot operation and recommended operation in icing 

(d) Qualitatively evaluate climb performance 

(e) Evaluate degradation in windshield visibility 

(4) Dry air ice shape flight tests 

(a) Ice shapes 

1. Five minute accretions on unprotected areas 

A4-2 
4/19/07 AC 23.1419-2D 

Appendix 4 

2. Protected area ice accretions 

(b) Objectives 

1. Evaluate stability and controllability 

2. Evaluate increase in stall speed. 

b. Compliance to the latest applicable amendment of § 23.1309 should be shown. See 

AC 23.1309-1C for additional guidance. To show compliance to § 23.1309 the following would 

apply: 

(1) Show that installation of the system, and normal operation of the system, does not 

affect operation of essential equipment. Examples are: 

 

(a) Electromagnetic interference testing 

(b) Operation of the stall warning system. 

(2) Show that hazards are minimized on single engine airplanes and prevented for 

multi-engine airplanes in the event of a probable failure. Examples of failures that should be 

addressed: 

(a) Auto inflation of deicing boots 

(b) Failures that could cause an asymmetric wing condition 

(c) Bleed air leaks of thermal systems 

(d) Electrical shorts in electrothermal systems. 

(3) Compliance can be by analysis or test or a combination. The loss of the ice 

protection system would not have to be considered since the airplane is not approved for flight in 

icing. For the purposes of the current regulation, the system would not be an essential load. 

(4) Show that the system when operating normally does not create a greater hazard than 

operating with no ice protection system. For example, on systems where there is runback the 

applicant should show that the runback ice does not cause a greater hazard than the ice accretion 

with no ice protection. Hazards to address would be stalls, tailplane stalls, and engine operation 

if applicable. 

c. To show compliance to § 23.1351 an electrical load analysis should be done if the ice 

protection system utilizes the airplane’s primary electrical power system. If the ice protection 

system utilizes its own alternator/generator, other regulations in § 23.1351 may be applicable. 

d. Compliance to § 23.1416 and § 23.1419 are not required. 

A4-3 
AC 23 1419-2D 4/19/07 

Appendix 4 

6. SUBPART G – OPERATING LIMITATIONS AND INFORMATION. 

a. A cockpit placard in view of the pilot and the AFM should state that the airplane is 

prohibited from flight in icing conditions. 

b. A description of all ice protection system controls and annunciations should be in the 

AFM. 

c. The AFM should caution that stall warning in icing conditions might not be reliable and 

must not be relied upon in icing conditions, even with a heated stall warning sensor. 

d. Stall speeds with the system installed or system operating, if increased from the baseline 

airplane, should be published in the AFM. An incremental delta increase may be used for all 

configurations, if appropriate. 

e. Procedures to mitigate locked controls due to ice accretion, if applicable. 

f. Autopilot operation procedures. 

(1) For aircraft equipped with an autopilot, the autopilot should be disconnected 

periodically to check for unusual control force or deflection, and to move the flight controls to 

check for evidence of ice accreting in control surface gaps or frozen actuators. 

(2) There should be a WARNING that the autopilot will NOT maintain airspeed if ice 

accretes on the airplane. MONITOR airspeed closely. 

g. Instructions for continued airworthiness in accordance with § 23.1529 should be 

provided. 

 A4-4 
4/19/07 AC 23 1419-2D 

Appendix 5 

APPENDIX 5. GUIDELINES FOR APPROVAL OF REPLACEMENT 

PARTS FOR AIRFRAME DEICING SYSTEMS 

1. The requirements leading to approval of replacement airframe deicing systems (propellerdeicing systems will be addressed in a revision) or airframe thermal deicing or anti-icing systems 

are functions of the project certification basis and similarity with the original part(s), as 

summarized in Table 5-1 and discussed in the following paragraphs: 

TABLE 5-1. SUMMARY OF TEST REQUIREMENTS FOR REPLACEMENT AIRFRAME 

DEICING COMPONENTS 

Aircraft 

Approved for 

Flight in Icing 

Conditions? 

Certification

Basis 

Approval 

Process 

Required 

Tests to Show

Safe Operation 

throughout Part 

25, Appendix C 

Icing Conditions 

Natural Icing Flight 

Tests 

No PMA Not required Not required 

Yes CAR § 3.712 STC See paragraph b. See paragraph b. 

Yes 23-0 to 23-13 STC See paragraph b. See paragraph b. 

Yes 23-14 to 23-42 STC Required See paragraph c. 

Yes 23-43 or higher STC Required Required 

a. For aircraft whose certification basis does not include CAR § 3.712 or § 23.1419, the 

deicing system is optional equipment and not required. In this case, the replacement parts can be 

approved via the Parts Manufacturer Approval (PMA) process in 14 CFR, part 21, subpart K. 

The replacement parts must be shown to function properly, remove ice or prevent ice accretion 

as well as the previously installed equipment, not introduce additional failure modes that could 

prevent continued safe flight and landing, and not affect stall characteristics, stability or control 

of the airplane in dry air. Comparative tests of the original versus the replacement parts are 

acceptable to show how the part removes or prevents ice accretion. 

b. For aircraft whose certification basis is CAR § 3.712 or an original issue under 

§ 23.1419, an STC is required. Original certification of these aircraft only required that 

pneumatic deicers be installed per approved data and that they have a positive means of

deflation. No icing flight tests were required, and airplanes were considered “approved for flight 

into known icing” when the airplane was equipped with a complement of certificated deicing or 

anti-icing equipment spelled out in operational requirements. For replacement parts in these 

aircraft it is advisable for the Aircraft Certification Office (ACO) to contact the ACO 

maintaining the original type design data to determine factors such as variance with the original 

design, the original certification requirements, and the service history of the original product. 

A5-1 
AC 23 1419-2D 4/19/07 

Appendix 5 

The replacement parts must be shown to function properly, remove ice or prevent ice 

accretion as well as the previously installed equipment, and not introduce additional failure 

modes that could prevent continued safe flight and landing. Comparative tests of the original 

versus the replacement parts may be acceptable. If the original certification basis is to be 

utilized, it is highly recommended that an entry in the AFM supplement limitations section, or a 

placard, with the following wording be required: “This airplane has not demonstrated 

compliance with the icing environment requirements of 14 CFR, part 25, Appendix C. 

c. For replacement parts on an aircraft whose certification basis is § 23.1419, 

amendments 23-14 through 23-42, an STC is required. Flight testing in measured, natural icing 

conditions should be accomplished if the replacement parts are of different materials or have 

different design characteristics. Supplemental testing in artificial icing conditions (icing tunnel, 

tanker) should also be accomplished to cover the complete part 25, Appendix C envelope. The 

replacement parts must be shown to function properly, remove ice or prevent ice accretion as 

well as the previously installed equipment, and not introduce additional failure modes that could 

prevent continued safe flight and landing. A matrix of performance and flying qualities as 

discussed in paragraph 13a (2) of this AC should be accomplished. The Standards Office should 

be contacted since the requirement to flight test in measured, natural icing conditions is 

dependent on a number factors such as whether AFM performance in icing conditions is based 

on protected surface ice accretions, the service history of the airplane, and flight testing 

accomplished during the original certification with protected surface ice accretions. Follow-on 

applications of the new parts in aircraft other than the initial certification may then be approved 

through similarity provided the conditions in § 23.1419(c) are met. There may be cases where 

minor modifications would not require additional measured, natural flight tests. 

d. For replacement parts on an aircraft whose certification basis is § 23.1419, 

amendment 23-43 or higher or those aircraft where the applicant wants to add “flight in icing 

conditions” operational approval, an STC is required. Flight testing in measured, natural icing 

conditions is required if the replacement parts are of different materials or have different design 

characteristics. Supplemental testing in simulated icing conditions (icing tunnel, tanker) may 

also be required to cover the complete part 25, Appendix C envelope. The replacement parts 

must be shown to function properly, remove ice or prevent ice accretion as well as the previously 

installed equipment, and not introduce failure modes that could prevent continued safe flight and 

landing. A matrix of performance and flying qualities as discussed in paragraph 13a (1) of this 

AC should be accomplished. Follow-on applications of the new parts in aircraft other than the 

initial certification may then be approved through similarity provided the conditions in 

§ 23.1419(c) are met. There may be cases where minor modifications would not require 

additional measured, natural flight tests. 

2. Engineering judgment must be used to determine that the modifications would not affect the 

effectiveness of the ice protection in natural icing conditions. If there is any question as to the 

need for a particular design to be subject to natural icing tests, the ACO should contact the 

Standards Office as well as the ACO that performed the original certification and the national 

resource specialist for aircraft icing. Again, seemingly benign differences can have significant 

negative effects on an aircraft's ice protection capability. 

A5-2 
4/19/07 AC 23.1419-2D 

Appendix 6 

APPENDIX 6. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT 

AMENDMENT 23-43 

1. In accordance with § 23.1419(a), Amendment 23-43, "capable of operating safely" means 

that airplane performance, controllability, maneuverability, and stability may be degraded from

the non-iced airplane but must not be less than the requirements in part 23, subpart B. Guidance 

for each subpart B regulation, as related to icing, is in the following Table 6-1. 

2. The definition of “capable of operating safely” is not defined in the regulation at Amendment 

23-14. For airplanes with a certification basis before 23-43, the tests and pass/fail criteria in the 

Table 6-1 should be used as a guide to develop a test program. The regulations italicized in the 

table are not typically addressed in showing compliance to § 23.1419 at amendment 23-14. 

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDMENT 23-43 

Regulation 

14 CFR 

Section Guidance 

Proof of 

compliance 

23.21 Only critical weight and CG loadings, as determined during the noncontaminated airplane tests, are required. Natural icing flight tests 

may be accomplished at a nominal CG. 

Load 

distribution 

limits 

23.23 Only critical weight and CG loadings, as determined during the noncontaminated airplane tests, are required. Tests in which lateral load is 

critical, such as stall characteristics, should include tests with 

maximum allowable fuel asymmetry. 

There should not be different load, weight, and CG limits for flight in 

icing. Operation in icing conditions should be essentially transparent 

to the flightcrew in that no icing-specific methods of operation (other 

than activating ice protection systems) should be required. This 

philosophy is also based on human factors issues to reduce operational 

complexity and flightcrew workload. 

General 

(Performance) 

23.45 Must comply, except performance should be determined up to a 

temperature of standard plus five degrees C instead of plus 

30 degrees C. It can be assumed that ice accretion will not be present 

on the airframe at temperatures warmer than plus five degrees C. For 

deicing systems, the average drag increment and propeller efficiency 

determined over the deicing cycle may be used for performance 

calculations. Propeller deicing codes do not address propeller runback 

icing. Similarity to previously flight-tested configurations or 

qualitative performance evaluations in natural icing should be 

accomplished. 

A6-1 
AC 23.1419-2D 4/19/07 

Appendix 6 

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDMENT 23-43 

(Continued) 

Regulation 

14 CFR 

Section Guidance 

Stall speed 23.49 Must comply with critical ice accretions. See paragraph 13a (1) (c) for 

exemption considerations to the 61-knot stall speed requirement. Stall 

speeds with critical ice accretions should be determined and published 

in the AFM. 

Takeoff 

speeds 

23.51 When determining the takeoff speeds V1, VR, and V2 for flight in icing 

conditions, the values of VMCG and VMC determined for non-icing 

conditions may be used. If 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 KCAS or 

three percent VS1, the speed at 50 feet or V2 must be increased to 

remain compliant. 

Takeoff 

performance 

23.53 The effect of operating ice protection systems on engine performance 

should be accounted for. 

Takeoff performance in icing conditions must be calculated with 

“takeoff” ice if: 

a. 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 KCAS or three percent VS1; and 

b. If commuter category, the degradation of the gradient of climb 

determined in accordance with § 23.67(c)(2) is greater than onehalf of the applicable actual-to-net takeoff path gradient reduction 

defined in § 25.61(b); and 

c. If multi-engine normal, utility or acrobatic category, the 

degradation of the gradient of climb determined in accordance with

§ 23.67(a) or (b) is greater than one-half of the applicable actual-tonet takeoff path gradient reduction defined in § 25.61(b). 

Acceleratestop distance 23.55 Applicable for commuter category only. The effect of any increase 

due to takeoff in icing conditions may be determined by analysis. 

A6-2 
4/19/07 AC 23.1419-2D 

Appendix 6 

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDMENT 23-43 

(Continued) 

Regulation 

14 CFR 

Section Guidance 

Takeoff path 23.57 

Takeoff 

distance and

takeoff run 

23.59 Applicable for icing for commuter category only if the conditions 

described above in 23.53 are met. May be calculated by a suitable 

analysis. 

Takeoff 

flight path 

23.61

Climb: 

general 

23.63 Must be compliant with critical ice accretions, except ambient 

temperatures above 41-degrees F do not need to be addressed. 

Climb: all 

engine 

operating 

23.65 Must be shown to be compliant with engine power losses associated 

with operating ice protection equipment that are not prohibited for 

takeoff. Climb performance losses due to ice accretion are normally 

not appropriate below 400 feet since the airplane should not depart 

with ice on the airplane. However, if ice protection system operation 

is prohibited for takeoff or the AFM does not specifically prohibit 

takeoff with frost on the wing and control surfaces, effect of ice 

accretions must be considered if: 

a. 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 KCAS or three percent VS1, and 

b. for airplanes in which 23.65(a) is applicable, the degradation of the 

gradient of climb determined in accordance with § 23.65(a)) with 

“takeoff” ice is greater than 1.6 percent, and 

c. for airplanes in which 23.65(b) is applicable, the degradation of the 

gradient of climb determined in accordance with § 23.65(b) with 

“takeoff” ice is greater than 0.8 percent. 

*Takeoff 

climb: one 

engine 

inoperative 

23.66 If applicable must be compliant. 

* Italicized regulations indicate tests not typically accomplished for 23.1419 at 

 amendment 23-14. 

A6-3 
AC 23.1419-2D 4/19/07 

Appendix 6 

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDMENT 23-43 

(Continued) 

Regulation 

14 CFR 

Section Guidance 

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: 

a. 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 KCAS or three percent VS1; and 

b. If commuter category, the degradation of the gradient of climb 

determined in accordance with § 23.67(c)(2) is greater than onehalf of the applicable actual-to-net takeoff path gradient reduction 

defined in § 25.61(b), and 

c. If multi-engine normal, utility or acrobatic category, the 

degradation of the gradient of climb determined in accordance 

with § 23.67(a) or (b) is greater than 0.3 percent. 

For paragraphs (b) (1), (c) (1), and (c) (2), “takeoff” ice applies, and 

for paragraph (c) (3) “Final Takeoff” ice applies, rather than critical ice 

accretions. 

Enroute 

climb/descent 

23.69 Must be determined with “Enroute” ice if the enroute climb speed 

selected in icing is more than the non-icing speed by the greatest of 

three KCAS or three percent VS1, or if the service ceiling with 

“Enroute” ice is less than 22,000 ft. MSL. The enroute climb speed 

must be at least the minimum airspeed specified in the AFM 

limitations section. 

Glide: single 

engines 

airplanes 

23.71 If applicable and if ice protection systems become inoperative with 

engine out, the best glide speed in icing must be determined if different 

from the non-icing speed by more than three KCAS. May be 

determined analytically.

Reference 

landing 

approach 

speed 

23.73 Must be based on stall speed with critical ice accretion if VREF in icing 

exceeds VREF in non-icing conditions by more than 4 knots at 

maximum landing weight. The VMC determined for non-icing 

conditions may be used if the vertical tail does not have ice accretion 

in normal system operation. If based on the non-ice VREF , the airplane 

with critical ice accretions should still comply with the stall warning 

and maneuver margin requirements of § 23.207.

A6-4 
4/19/07 AC 23.1419-2D 

Appendix 6 

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDMENT 23-43 

(Continued) 

Regulation 

14 CFR 

Section Guidance 

Landing 

distance 

23.75 Must be determined with critical ice accretion if VREF in icing 

conditions is greater than VREF in non-icing conditions by more than 

four knots. The effect of landing speed increase on the landing 

distance may be determined by analysis. 

Balked 

landing 

23.77 Must be compliant with critical ice accretions, all ice protection 

systems operational, all landing flap settings, at an ambient 

temperature of 41 degrees F. 

23.143 If the non-icing VMC is used for takeoff speeds, it must be shown 

that the airplane is safely controllable and maneuverable at the 

minimum V2 for takeoff with the critical engine inoperative and with 

“takeoff” ice accretion. 

If the non-icing VMC is used for VREF, it must be shown that the 

airplane is safely controllable and maneuverable during a go-around 

starting at the minimum VREF with the critical engine inoperative and 

with critical ice accretion.

Susceptibility to ICTS should be evaluated with critical ice accretions, 

sandpaper ice and pre-activation ice as discussed in paragraph 13.e. of 

this AC. 

Susceptibility to control anomalies in SLD conditions as discussed in 

paragraph 13.h. of this AC should be addressed. 

Longitudinal 

control 

23.145 The tests in paragraphs (a) and (b) (1) and (b) (2) must be 

accomplished. For the other tests, the results from the noncontaminated airplane tests should be reviewed to determine whether 

there are any cases where there was marginal compliance. If so, or if 

qualitative evaluations with ice accretions show control anomalies, 

these cases should be repeated with ice. Controllability may be 

degraded from the non-iced airplane but must still be compliant. 

Analysis, the results of the non-icing tests to show compliance to 

§ 23.145(e), and the results of controllability tests with ice accretions 

may be used to show compliance to § 23.145(e). 

A6-5 
AC 23.1419-2D 4/19/07 

Appendix 6 

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDMENT 23-43 

(Continued) 

Regulation 

14 CFR 

Section Guidance 

General 

(control) 

23.141 Must be shown to be compliant with critical ice accretions. 

Directional 

and lateral 

control 

23.147 Critical configuration(s) determined from the non-contaminated 

airplane tests must be evaluated. Analysis, the results of the non-icing 

tests to show compliance to § 23.147(c), and the results of 

controllability tests with ice accretions may be used to show 

compliance to § 23.147(c). 

Minimum 

control speed 

23.149 If the vertical tail is unprotected or has intercycle/residual/runback ice 

during ice protection system normal operation, VMC speeds with 

critical ice must be evaluated to determine if the proposed VREF speed 

in icing complies with § 23.73. Static VMC tests may be used. 

Acrobatic 

maneuvers 

23.151 Not applicable for icing certification. 

Control during 

landings 

23.153 Must be shown to be compliant with critical ice accretions. 

Elevator

control force 

in maneuvers 

23.155 Critical configuration(s) determined from the non-contaminated 

airplane tests must be evaluated. 

Rate of roll 23.157 Airplane must comply with “takeoff” ice accretions for paragraph (a) 

and critical ice accretions for paragraph (b). Controllability may be 

degraded from the non-iced airplane but must still be compliant. 

Tests should be conducted with 1/3, 2/3, and full roll control 

authority. In addition, to check for hinge moment reversals other roll 

control anomalies, perform this test with holding ice accretions, 

minimum holding speed, at maximum weight, at all approved holding 

configurations. Recovery roll control should not be initiated until the 

airplane has rolled through 50 degree bank. 

Trim 23.161 The results from the non-contaminated airplane tests should be 

reviewed to determine whether there are any cases where there was 

marginal compliance. If so, or if qualitative evaluations with ice 

accretions how any control anomalies, these cases should be repeated 

A6-6 
4/19/07 AC 23.1419-2D 

Appendix 6 

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDMENT 23-43 

(Continued) 

Regulation 

14 CFR 

Section Guidance 

Trim 

(Cont.) 

23.161 

(Cont) 

with ice. Otherwise, no dedicated tests with ice accretions required, 

qualitative evaluations can be accomplished concurrently with other 

tests. 

General 

(stability) 

23.171 Must be shown to be compliant with critical ice accretions. 

Static 

longitudinal 

stability 

23.173 Stability may be degraded from the non-iced airplane but must still be 

compliant. 

Demonstration of static 

longitudinal 

stability 

23.175 Critical configuration(s) determined from the non-contaminated 

airplane tests must be evaluated. 

Static 

directional 

and lateral 

stability 

23.177 Must evaluate steady heading sideslips in accordance with paragraph 

(d). These tests should check for hinge moment reversals about the 

lateral and directional axis up to full rudder deflection. The results 

from the non-contaminated airplane tests to show compliance with 

paragraphs (a) and (b) should be reviewed to determine whether there 

are any cases where there was marginal compliance. If so, these cases 

should be repeated with ice. Stability may be degraded from the noniced airplane but must still be compliant. 

Dynamic 

stability 

23.181 Critical configuration(s) determined from the non-contaminated 

airplane tests must be evaluated with critical ice accretions. 

Wings level 

stall 

23.201 As a minimum wings level stalls with cruise, approach and landing 

flaps, power off and on, should be evaluated with critical ice 

accretions. Roll may slightly exceed 15 degrees if characteristics 

qualitatively determined to be safe. Stall characteristics should also be

evaluated when the airplane is stalled with the autopilot engaged, 

unless the design of the autopilot precludes its ability to operate 

beyond stall warning. For these designs the controllability at stall 

warning should be evaluated. Recovery at stall warning should also be 

A6-7 
AC 23.1419-2D 4/19/07 

Appendix 6 

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDMENT 23-43 

(Continued) 

Regulation 

14 CFR 

Section Guidance 

Wings level 

stall 

(Cont.) 

23.201 

(Cont.) 

evaluated by only applying engine power or thrust. Evaluations 

should be accomplished by trimming at minimum AFM icing 

airspeed, setting the autopilot in altitude hold (for turns commanding 

a heading change), reducing power/thrust to establish a 1 kt/sec 

deceleration rate, and at stall warning apply power/thrust. Evaluate 

the aircraft response, need for directional/lateral control, airspeed 

increase, and altitude loss (assuming autopilot will disconnect as 

designed at stall warning). 

Turning 

flight and 

accelerated 

turning stalls 

23.203 Turning stalls should be evaluated with critical ice accretions 

similarly to wings level stalls. Accelerated turning stalls not required 

unless tests with no ice show marginal compliance. Stall 

characteristics should also be evaluated when the airplane is stalled 

with the autopilot engaged, unless the design of the autopilot 

precludes its ability to operate beyond stall warning. For these 

designs the autopilot operation up to stall warning and controllability 

at stall warning should be evaluated. 

Stall warning 23.207 

(a)-(c) 

Should be evaluated concurrently with stall speed and stall 

characteristics tests. The type of stall warning with critical and preactivation ice accretions should be the same as with the noncontaminated airplane. The stall warning margin with critical ice 

accretions should be compliant. For pre-activation ice, the margin 

can be less than the Subpart B requirement but it should be positive 

and shown to be adequate. Biasing of the stall warning (resetting 

trigger points to lower angles of attack when ice protection is 

initiated) may be required to achieve acceptable margins to stall. The 

method of biasing should be evaluated. Adequacy of stall warning 

when airplane is decelerated with autopilot engaged, and recovery at 

stall warning with power only, should be evaluated. 

Maneuver 

margin

23.207 (d) 40-degree bank level altitude turns and 30 degree/30 degrees bank-tobank rolls at the flight conditions specified in the regulation should 

be accomplished to demonstrate the airplane is free of buffet and stall 

warning with critical ice accretions. All takeoff and approach flap 

settings should be evaluated. For one-engine inoperative evaluations, 

only a 30-degree turn is necessary, and the appropriate thrust may be 

simulated with all engines operating at a reduced power/thrust. 

A6-8 
4/19/07 AC 23.1419-2D 

Appendix 6 

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDMENT 23-43 

(Continued) 

Regulation 

14 CFR 

Section Guidance 

Accelerated 

stall 

warning 

margin

23.207 (e) Not required unless tests with no ice show marginal compliance. 

Spinning 23.221 Not required.

Longitudinal 

stability and 

control 

23.231 Must be shown to be compliant. 

Directional 

stability and 

control 

23.233 Must be shown to be compliant with critical ice accretions. The 

results of the steady heading sideslip tests with critical ice may be 

used to establish the safe cross wind component. If the flight test data 

show that the maximum sideslip angle demonstrated is similar to that 

demonstrated with the non-contaminated airplane, and the flight 

characteristics (e.g., control forces and deflections, bank angle) are 

similar, then the non-contaminated airplane crosswind component is 

considered valid. 

If the results of the comparison discussed above are not clearly 

similar, and in the absence of a more rational analysis, a conservative 

analysis based on the results of the steady heading sideslip tests may 

be used to establish the safe crosswind component. The crosswind 

value may be estimated from:

VCW = VREF * sin (sideslip angle) /1.5 where: 

VCW is the crosswind component, 

VREF is the landing reference speed appropriate to a minimum landing 

weight, and sideslip angle is that demonstrated at VREF

Operation 

on unpaved 

surfaces 

23.235 Not applicable for icing certification.

A6-9 
AC 23.1419-2D 4/19/07 

Appendix 6 

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDMENT 23-43 

(Continued) 

Regulation 

14 CFR 

Section Guidance 

Operation 

on water 

23.237 Not applicable for icing certification. 

Spray 

characteristi

cs 

23.239 Not applicable for icing certification. 

Vibration 

and buffet 

23.251 The non-icing tests should be accomplished with the ice protection 

systems installed. 

Should be qualitatively evaluated in conjunction with other dry air ice 

shape flight tests up to the lower of: 

250 KCAS

VMO/MMO/VNE

A speed at which it is demonstrated that the airframe will be free of ice 

accretion. 

Vibration due to propeller icing/de-icing should be evaluated during 

the natural icing testing.

High speed 

characteristics 

23.253 If applicable, compliance should be shown with airframe ice protection 

systems installed. Not required with ice accretions. 

A6-10 
4/19/07 AC 23.1419-2D 

Appendix 7 

APPENDIX 7. ICE CONTAMINATED TAILPLANE STALL (ICTS) BACKGROUND 

1. BACKGROUND. When the leading edge of a horizontal tailplane becomes contaminated 

with ice accretions, control of the aircraft may be severely affected. The ICTS phenomenon in 

its extreme form may result in an uncontrollable nose-down pitching event. 

a. What is ICTS? ICTS occurs due to airflow separation on the lower surface of the 

tailplane that is caused by the angle-of-attack of the horizontal tailplane being increased above 

the reduced stall angle-of-attack that can result when even small quantities of ice have formed on 

the tailplane leading edge. The increase in tailplane angle-of-attack can result from airplane 

configuration (for example, increased flap extension increasing the downwash angle or trim

required for the CG position) and/or flight conditions (for example, high approach speed 

resulting in reduced tail angle-of-attack, gusts, maneuvering or engine power changes). ICTS is 

characterized by a reduction or loss, sometimes sudden, of pitch control or stability while 

operating in, or recently departing from, icing conditions. For airplanes with longitudinal control 

systems that are not powered (reversible control systems), the pressure differential between the 

upper and lower surfaces of the stalled tailplane may result in a high elevator hinge moment, 

forcing the elevator trailing edge down. This elevator hinge moment reversal can be of sufficient 

magnitude to draw the control column forward with a level of force that is beyond the combined 

efforts of the flightcrew to overcome. ICTS reduces tail lift or diminishes the effectiveness of

the primary and secondary control surfaces. Diminished control effectiveness ranges from

reduced elevator authority to sudden, large and unexpected changes in required control forces. 

Tab driven reversible pitch control designs may have insufficient authority to overcome the 

elevator hinge moments resulting from ICTS. On some airplanes, ICTS has been caused by a 

lateral flow component coming from the vertical stabilizer, as may occur in sideslip conditions or 

due to a gust with a lateral component. 

b. Has ICTS occurred on airplanes? Following a number of accidents and incidents 

involving airplanes certificated under 14 CFR parts 23 and 25 for flight in icing conditions, and 

specifically an accident involving a British Aerospace BA-3101 airplane on December 26, 1989, 

the NTSB issued Safety Recommendation A-90-087. 

c. What has been done to evaluate susceptibility of airplanes to ICTS?

(1) In 1991, the FAA reviewed the pitch control and stability factors of various 

airplanes to determine the susceptibility of those airplanes to ice contaminated tailplane stall. 

The review included discussions with manufacturers of airplanes certificated for flight in known 

icing, analysis of stall margin design parameters, and methods used to show compliance with 14 

CFR 23.143, Controllability and Maneuverability. Findings included: 

(a) Lack of clear understanding and uniformity in applying the regulations due to 

complexity of the issue.

(b) Need for uniform and detailed guidance. 

A7-1 
AC 23.1419-2D 4/19/07 

Appendix 7 

(c) Shortage of basic data on the subject. 

(2) Before 1994, no uniform quantitative criteria or standardized acceptance procedures 

were available to show compliance with Title 14 CFR part 23, § 23.143 or its predecessor, CAR 

Part 3, § 3.106. In 1994, after examining available engineering data and its own guidance on this 

subject, the FAA decided to give more detailed and uniform guidance on demonstrating 

compliance. The FAA issued policy letters applicable to all airplanes and sponsored research 

with NASA to understand better ice contaminated tailplane stall. Based on the results of the data 

and guidance review, and with input from the joint FAA/NASA research project, the FAA 

determined that guidance would be helpful for two steps in the process leading to certification. 

The first step is the design phase when the preliminary design parameters of the airplane are 

determined. The second step is the method of evaluation of compliance with the regulations. 

(a) During the design process, the manufacturer can evaluate airplane response 

characteristics and efficiently resolve serious problems using various modeling tools such as 

wind tunnel testing and computational fluid dynamics analysis. This AC does not address this 

process. 

(b) Susceptibility of an airplane design to ICTS should be considered when 

demonstrating compliance to the pitch control requirements of CFR 23.143. The demonstration 

should include: 

1. flight at the critical airspeed; 

2. artificial ice accretions on the horizontal tailplane; and 

3. flight testing in the critical trailing edge flap and power configuration. 

(3) In 2001, the FAA incorporated the 1994 policy letters into AC 23.143-1, “Ice 

Contaminated Tailplane Stall.” 

(4) The guidance in AC 23.143-1 has been incorporated into this AC and AC 23.143-1 

has been cancelled.

d. When can ICTS occur? 

(1) Tailplane stall can occur with ice accretions on the tailplane when: 

(a) wing flaps are extended; 

(b) engine power is increased; 

(c) the pilot makes a nose-down control input; 

(d) the airplane increases speed or encounters gust conditions; or 

A7-2 
4/19/07 AC 23.1419-2D 

Appendix 7 

(e) a combination of these factors with flaps extended. 

(2) Tailplane stall has been reported on several airplane type designs with small 

quantities of ice observed on the airplane. In some cases, the critical ice accretion for 

susceptibility to ICTS has been a thin rough layer of ice on the protected and unprotected 

portions of the leading edge that accretes during the time that: 

(a) The airplane enters icing conditions. 

(b) The flightcrew recognizes the icing conditions and activates the ice protection 

system. 

(c) The ice protection system performs its intended function. 

(3) Since flaps are normally only extended to the landing position during final approach 

to landing, an ICTS event under these conditions has a high probability of being catastrophic due 

to the associated low ground clearance 

e. What are some pilot cues to ICTS? Pilots may sense ICTS or impending ICTS as one or a 

combination of: 

(1) difficulty to trim in the pitch axis; 

(2) a pulsing or buffeting of the longitudinal control; or 

(3) a lightening of longitudinal control push force (or an increase in pull force)

necessary to command a new pitch attitude. 

f. How does a pilot recover from ICTS? These may not be recognized as cues of ICTS. 

The pilot may incorrectly interpret these cues as aerodynamic warning of an impending wing 

stall and perform the wrong, possibly catastrophic, corrective action since recovery techniques 

for a wing stall are opposite those of an ICTS. It is critical for the pilot to promptly and correctly 

diagnose the abnormal condition and apply the right corrective measures, which typically are a 

pull up, flap retraction, and power reduction. 

2. FACTORS AFFECTING SUSCEPTIBILITY OF AN AIRPLANE TO ICTS.

a. Airplane Design Variables. The aft location of the tailplane relative to the wing, the lift 

generated by the wing, and the spanwise lift distribution of the wing will affect the wing 

downwash induced tailplane AOA. Lift generated by wings with airfoils capable of high lift and 

equipped with efficient trailing edge flaps may induce a significant increase in the tailplane 

AOA. The airplane AOA, the wing downwash induced AOA, the tailplane fixed incidence 

angle, the tailplane design stall AOA, and the adverse effects of surface roughness on the 

tailplane stall AOA all influence the tailplane AOA margin and susceptibility to stall. 

A7-3 
AC 23.1419-2D 4/19/07 

Appendix 7 

b. Tail Design Variables. 

(1) Vertical position of the horizontal tail and the aerodynamic effects of the surfaces 

forward of the horizontal tail. (“T”, cruciform, conventional). 

(2) Fixed incidence tailplane with elevator and trim tab. 

(3) Variable Incidence Tailplane (VIT) with elevator. 

(4) All-moving tailplane (stabilator) with and without a trim-servo tab. 

(5) Characteristics of vertical stabilizer interaction with T and cruciform tails. 

(6) CLMax, Coefficient of Maximum Lift of wing and tailplane. 

c. Center of Gravity (CG). Most forward CG loading conditions are usually most adverse 

to 1-g tailplane stall because of the greater balancing down load required by the tail. A greater 

download on the tail is developed by either increased incidence on a VIT, or greater trailing edge

up deflection of the elevator. 

d. Flap Extension. Extension of flaps increases the downwash at the tail and moves the

wing center of lift aft, increasing nose-down pitching moment and requiring more tail download. 

In addition, the AOA of the airplane is reduced for the same lift. The tail is subjected to a 

negative increase in local AOA. The extension of wing flaps, therefore, brings the horizontal tail 

closer to its stall AOA. Extending flaps from the retracted position may involve an increase in 

effective wing chord as well as an increase in camber. These changes in wing geometry:

(1) shift the center of pressure aft; 

(2) increase the nose-down pitching moment; 

(3) increase the wing lift coefficient at the same AOA; and 

(4) likely increase the local airflow downwash angle aft of the flaps (even for T-tail 

configurations). 

Because of these tests, maximum landing flap extension may be defined at an intermediate 

position which then must become an airplane limitation for flights into icing conditions. In this 

instance, landing gear position warnings as a function of flap position and degraded landing 

performance data should be considered. 

e. Speed/Load Factor. In 1-g flight, higher airspeeds result in reduced aircraft AOA and a 

more negative tailplane AOA. For the same reasons as described in paragraph 4 above, higher 

speed is more adverse to ICTS in 1-g flight. Also, during dynamic maneuvers (such as 

A7-4 
4/19/07 AC 23.1419-2D 

Appendix 7 

pushovers), lower speeds put the tailplane at a more critical state (more negative AOA) due to 

the ability to generate higher pitch rates. 

f. Engine Power. The effects of power or thrust on ICTS susceptibility are airplane 

specific. Increasing engine power on high thrust line aircraft (thrust line above the CG) requires 

more nose-up trim. This raises the risk of ICTS. In addition, increasing engine power on 

propeller driven airplanes tends to be adverse to ICTS due to increases in strength and angle of 

wing downwash, especially with flaps extended. 

g. Maneuvering. There are two elements of maneuvering that increase vulnerability to 

ICTS: nose-down pitch control input, and for some configurations, sideslip. 

(1) Nose-down pitch control input. When the elevator is deflected to the nose-down 

position, horizontal tail camber is changed and tail lift is reduced. Since a nose-down pitching 

moment exists that is not completely balanced by the tail, the airplane will pitch nose-down and 

there will be angular rotation rate about the CG. The resultant aerodynamic effect on the 

horizontal tailplane due to this rotation rate in the nose-down direction is an increased negative 

AOA which may increase susceptibility to tailplane stall. 

(2) Side slip. On “T” and cruciform tail configurations, local flow separation on the 

tailplane can start with sideslip due to initiation of separation at the junction of the horizontal and 

vertical stabilizer. This condition is worsened by ice accretions on the vertical stabilizer or 

structure forward of the horizontal stabilizer even if, in some cases, the horizontal tail leading 

edge is uncontaminated. The effects of a contaminated vertical stabilizer should also be 

considered when evaluating the susceptibility of a contaminated horizontal tailplane to ICTS 

in a sideslip. On low tail configurations, impingement of flap tip vortices on the empennage may 

result in elevator self deflection and lead to similar control problems in the pitch axis. Sideslip 

can also result in asymmetric conditions on the horizontal stabilizer due to prop wash effects. 

Airplanes without counter-rotating propellers produce asymmetric local flow conditions. The 

steady heading sideslip should evaluate the effects of both left and right sideslip conditions. 

h. Gusts and Turbulence. Gust or airplane gust response may contribute to ICTS. Gusts 

may occur parallel to any airplane axis. The direct effect of a gust on the resultant airflow 

may be adverse. The flight tests should be robust enough to evaluate the characteristics of the 

tail for various combinations of conditions.

A7-5 (and A7-6) 

4/19/07 AC 23.1419-2D 

Appendix 8 

APPENDIX 8. AFM LIMITATIONS AND NORMAL PROCEDURES SECTIONS 

1. LIMITATIONS SECTION. The following text and warning information should be 

inserted in the limitations section of the AFM:

a. Flight in meteorological conditions described as freezing rain or freezing drizzle, as 

determined by the following visual cues, is prohibited: 

(1) Unusually extensive ice accreted on the airframe in areas not normally 

observed to collect ice. 

(2) Accumulation of ice on the upper surface or lower surface of the wing aft of the 

protected area. 

(3) Accumulation of ice on the propeller spinner farther back than normally observed. 

If the airplane encounters conditions that are determined to contain freezing rain or 

freezing drizzle, the pilot must immediately exit the freezing rain or freezing drizzle 

conditions by changing altitude or course. 

NOTE 7: The prohibition on flight in freezing rain or freezing drizzle is not 

intended to prohibit purely inadvertent encounters with the specified 

meteorological conditions; however, pilots should make all reasonable efforts to 

avoid such encounters and must immediately exit the conditions if they are 

encountered. 

b. 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 8: The autopilot may mask tactile cues that indicate adverse changes 

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

autopilot when any ice is visible on the airplane. 

c. All wing ice inspection lights must be operable prior to flight into known or forecast 

icing at night. 

NOTE 9: This supersedes any relief provided by the Master Minimum

Equipment List (MMEL).” 

2. NORMAL PROCEDURES SECTION. The following text and warning information 

should be inserted in the normal procedures section of the AFM: 

A8-1 
AC 23.1419-2D 4/19/07 

Appendix 8 

WARNING 

• If ice is observed forming aft of the protected surfaces of the 

wing or if unusual lateral trim requirements or autopilot trim

warnings are encountered, accomplish the following: 

• If the flaps are extended, do not retract them until the airframe

is clear of ice. 

• The flight crew should reduce the angle-of-attack by increasing 

speed as much as the airplane configuration and weather allow, 

without exceeding design maneuvering speed. 

• 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. 

• Exit the icing area immediately by changing altitude or course; and 

• Report these weather conditions to air traffic control. 

CAUTION 

Flight in freezing rain or freezing drizzle, may result in hazardous 

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 using the ice 

protection systems, and it may seriously degrade the performance 

and controllability of the airplane. 

a. The following shall be used to identify freezing rain/freezing drizzle icing conditions: 

(1) Unusually extensive ice accreted on the airframe in areas not normally observed to 

collect ice. 

(2) Accumulation of ice on the upper surface or lower surface of the wing aft of the 

protected area. 

(3) Accumulation of ice on the propeller spinner farther back than normally observed. 

b. The following may be used to identify possible freezing rain/freezing drizzle conditions: 

(1) Visible rain at temperatures below plus five degrees C OAT. 

(2) Droplets that splash or splatter on impact at temperatures below plus five degrees C 

OAT. 

A8-2 
4/19/07 AC 23.1419-2D 

Appendix 8 

(3) Performance losses larger than normally encountered in icing conditions. It is 

possible to experience severe ice accretions not visible to the flight crew, such as wing lower 

surface accretion on a low wing airplane or propeller blade accretion. 

c. Procedures for Exiting the Freezing Rain/Freezing Drizzle Environment. These 

procedures are applicable to all flight phases from takeoff to landing. Monitor the outside air 

temperature. While ice may form in freezing drizzle or freezing rain at temperatures as cold as 

minus 18 degrees C, increased vigilance is warranted at temperatures around freezing with 

visible moisture present. If the visual cues specified in the AFM for identifying possible freezing 

rain or freezing drizzle conditions are observed, accomplish the following: 

(1) Exit the freezing rain or freezing drizzle icing conditions immediately to avoid 

extended exposure to flight conditions outside of those for which the airplane has been 

certificated for operation. Asking for priority to leave the area is fully justified under these 

conditions. 

(2) Avoid abrupt and excessive maneuvering that may exacerbate control difficulties. 

(3) Do not engage the autopilot. The autopilot may mask unusual control system forces 

(4) If the autopilot is engaged, hold the control wheel firmly and disengage the 

autopilot. 

(5) If an unusual roll response or uncommanded control movement is observed, reduce 

the angle-of-attack by increasing airspeed or rolling wings level (if in a turn), and apply 

additional power, if needed. 

(6) Avoid extending flaps during extended operation in icing conditions. Operation 

with flaps extended can result in a reduced wing angle-of-attack, with ice forming on the upper 

surface further aft on the wing than normal, possibly aft of the protected area. 

(7) If the flaps are extended, do not retract them until the airframe is clear of ice. 

(8) Report these weather conditions to ATC. 

NOTE 10: An alternate means of providing this information in the AFM may 

be approved by the certifying agency.

A8-3 (and A8-4)