0 

U.S. Department 

of Transportation 

Federal Aviation 

Administration 

Advisory

Circular 

Subject: Performance and Handling 

Characteristics in Icing Conditions 

Date: 10/27114 AC No: 25-25A 

Initiated By: ANM-110 

This advisory circular describes an acceptable means of showing compliance with the airplane 

performance and handling characteristics certification requirements for flight in the icing 

conditions defined in Appendices C and 0 of Title 14, Code of Federal Regulations part 25. 

If you have suggestions for improving this AC, you may use the feedback form at the end of this 

AC. 

Michael Kaszycki 

Acting Manager, Transport Airplane Directorate 

Aircraft Certification Service 
10/27/14 AC 25-25A

CONTENTS

Paragraph Page

ii

Chapter 1. Introduction ................................................................................................................ 1-1

1.1 Purpose.......................................................................................................................... 1-1

1.2 Applicability. ................................................................................................................ 1-1

1.3 Cancellation. ................................................................................................................. 1-2

Chapter 2. Requirements and Guidance....................................................................................... 2-3

2.1 Overview....................................................................................................................... 2-3

2.2 Proof of Compliance, § 25.21(g). ................................................................................. 2-6

2.3 Propeller Speed and Pitch Limits, § 25.33.................................................................... 2-7

2.4 Performance—General, § 25.101. ................................................................................ 2-7

2.5 Stall Speed, § 25.103. ................................................................................................... 2-8

2.6 Failure Conditions, § 25.1309....................................................................................... 2-8

2.7 Flight-Related Systems. ................................................................................................ 2-9

2.8 Airplane Flight Manual, § 25.1581 through § 25.1587. ............................................. 2-10

Chapter 3. Acceptable Means of Compliance—General........................................................... 3-13

3.1 Overview..................................................................................................................... 3-13

3.2 Flight Testing.............................................................................................................. 3-14

3.3 Wind Tunnel Testing and Analysis............................................................................. 3-16

3.4 Engineering Simulator Testing and Analysis. ............................................................ 3-16

3.5 Engineering Analysis.................................................................................................. 3-16

3.6 Ancestor Airplane Analysis. ....................................................................................... 3-16

Chapter 4. Acceptable Means of Compliance—Flight Test Program ....................................... 4-17

4.1 Overview..................................................................................................................... 4-17

4.2 Stall Speed, § 25.103. ................................................................................................. 4-17

4.3 Accelerate–Stop Distance, § 25.109. .......................................................................... 4-18

4.4 Takeoff Path, § 25.111................................................................................................ 4-18

4.5 Landing Climb: All–Engines–Operating, § 25.119. ................................................... 4-19

4.6 Climb: One-Engine-Inoperative, § 25.121.................................................................. 4-19

4.7 En Route Flight Paths, § 25.123. ................................................................................ 4-20

4.8 Landing, § 25.125. ...................................................................................................... 4-20

4.9 Controllability and Maneuverability—General, § 25.143. ......................................... 4-20
10/27/14 AC 25-25A

CONTENTS (CONTINUED)

Paragraph Page

iii

4.10 Longitudinal Control, § 25.145................................................................................... 4-26

4.11 Directional and Lateral Control, § 25.147. ................................................................. 4-26

4.12 Trim, § 25.161............................................................................................................. 4-27

4.13 Stability—General, § 25.171. ..................................................................................... 4-27

4.14 Demonstration of Static Longitudinal Stability, § 25.175. ......................................... 4-27

4.15 Static Lateral–Directional Stability, § 25.177............................................................. 4-28

4.16 Dynamic Stability, § 25.181. ...................................................................................... 4-29

4.17 Stall Demonstration, § 25.201/Stall Characteristics, § 25.203. .................................. 4-29

4.18 Stall Warning, § 25.207. ............................................................................................. 4-31

4.19 Wind Velocities, § 25.237. To show compliance with this requirement:................... 4-32

4.20 Vibration and Buffeting, § 25.251. ............................................................................. 4-33

4.21 Natural Icing Conditions, § 25.1419(b). ..................................................................... 4-33

4.22 Failure Conditions, § 25.1309..................................................................................... 4-37

Appendix A. Airframe Ice Accretions........................................................................................ A-1

Appendix B. Simulated Ice Accretions........................................................................................B-1

Appendix C. Design Features......................................................................................................C-1

Appendix D. Examples of Airplane Flight Manual Limitations and Operating Procedures 

for Operations in Supercooled Large Drop Icing Conditions..................................................... D-1

Appendix E. Related Regulations and Advisory Circulars..........................................................E-1

Appendix F. Acronyms................................................................................................................F-1
10/27/14 AC 25-25A

CONTENTS (CONTINUED)

iv

TABLES

Number Page

Table 3-1. Means for Showing Compliance .............................................................................. 3-13

Table 4-1. Controllability and Maneuverability—Trim Speeds................................................ 4-21

Table 4-2. Test Conditions—Lateral Control Characteristics ................................................... 4-23

Table 4-3. Test Maneuver—§ 25.143(i)(2)................................................................................ 4-25

Table 4-4. Holding Scenario—Maneuvers................................................................................ 4-35

Table 4-5. Approach/Landing Scenario—Maneuvers............................................................... 4-36

Table A-1. Appendix O Detect-and-Exit Ice Accretions per Flight Phase................................. A-8

Table A-2. Appendix O Ice Accretion per Flight Phase........................................................... A-12

Table E-1. Related Regulations ...................................................................................................E-1

Table E-2. Related Advisory Circulars........................................................................................E-3

Table F-1. Acronyms, Terms, and Definitions............................................................................F-1
10/27/14 AC 25-25A

1-1

CHAPTER 1. INTRODUCTION

1.1 Purpose.

1.1.1 This advisory circular (AC) describes an acceptable means of showing compliance with 

the airplane performance and handling characteristics certification requirements for 

flight in the icing conditions defined in Appendices C and O of Title 14, Code of 

Federal Regulations (14 CFR) part 25. Part 25 contains the airworthiness standards for 

transport category airplanes.

1.1.2 The following appendices appear at the end of this AC:

• Appendix A, Airframe Ice Accretions.

• Appendix B, Simulated Ice Accretions.

• Appendix C, Design Features.

• Appendix D, Examples of Airplane Flight Manual Limitations and Operating 

Procedures for Operations in Supercooled Large Drop Icing Conditions.

• Appendix E, Related Regulations and Advisory Circulars.

• Appendix F, Acronyms and Definitions.

1.2 Applicability.

1.2.1 The guidance provided in this AC is directed towards airplane manufacturers, 

modifiers, foreign regulatory authorities, and Federal Aviation Administration (FAA) 

transport airplane type certification engineers, flight test pilots, and their designees.

1.2.2 The material in this AC is neither mandatory nor regulatory in nature and does not 

constitute a regulation. It describes acceptable means, but not the only means, for 

showing compliance with the applicable regulations. The FAA will consider other 

methods of showing compliance that an applicant may elect to present. While these 

guidelines are not mandatory, they are derived from extensive FAA and industry 

experience in determining compliance with the relevant regulations. If, however, we 

become aware of circumstances that convince us that following this AC would not 

result in compliance with the applicable regulations, we will not be bound by the terms 

of this AC, and we may require additional substantiation or design changes as a basis 

for finding compliance.

1.2.3 The material in this AC does not change or create any additional, regulatory 

requirements, nor does it authorize changes in, or permit deviations from, regulatory 

requirements.
10/27/14 AC 25-25A

1-2

1.3 Cancellation.

This AC cancels AC 25-25, Performance and Handling Characteristics in the Icing 

Conditions Specified in Part 25, Appendix C, dated September 10, 2007.
10/27/14 AC 25-25A

2-3

CHAPTER 2. REQUIREMENTS AND GUIDANCE

2.1 Overview.

2.1.1 For certification for flight in icing conditions, § 25.21(g)(2) requires that an airplane 

meet certain performance and handling qualities requirements while operating in the 

icing environment defined in part 25, Appendix C. In addition, § 25.1420 requires 

applicants to consider icing conditions beyond those covered by Appendix C for 

airplanes with a maximum takeoff weight less than 60,000 pounds or with reversible 

flight controls. The additional icing conditions that must be considered for these 

airplanes are the supercooled large drop (SLD) icing conditions defined in part 25, 

Appendix O. Appendix A of this AC provides detailed guidance for determining ice 

accretions in both Appendix C and Appendix O icing conditions that can be used for 

showing compliance.

2.1.2 For airplanes with a maximum takeoff weight less of than 60,000 pounds or with 

reversible flight controls to be certified for flight in icing conditions, § 25.1420 requires 

applicants to do one of the following:

2.1.2.1 Not seek approval for flight in the SLD atmospheric icing conditions 

defined in Appendix O.

2.1.2.2 Seek approval for flight in only a portion of Appendix O icing conditions.

2.1.2.3 Seek approval for flight throughout the entire Appendix O atmospheric 

icing envelope.

2.1.3 For airplanes with a maximum takeoff weight equal to or greater than 60,000 pounds 

that do not have reversible flight controls, applicants are not required to consider the 

icing conditions of Appendix O. The guidance provided in this AC related to Appendix 

O icing conditions does not apply to those airplanes.

2.1.4 Because an airplane may encounter SLD icing conditions at any time while flying in 

icing conditions, certain safety requirements must be met for the SLD icing conditions 

of Appendix O for airplanes with a maximum takeoff weight less than 60,000 pounds or 

with reversible flight controls, even if the airplane will not be certified for flight in the 

complete range of Appendix O atmospheric icing conditions. For those airplanes that 

will not be certified for flight in all icing conditions defined in Appendix O,

§ 25.21(g)(3) requires certain part 25, subpart B, requirements to be met in SLD

atmospheric icing conditions beyond those for which the airplane will be certified. 

Compliance with these requirements in addition to the requirements for flight in 

Appendix C icing conditions are intended to provide adequate airplane performance and 

handling qualities for a safe exit from all icing conditions after an encounter with SLD

atmospheric icing conditions beyond those for which the airplane will be certified.

2.1.5 If an airplane with a maximum takeoff weight less than 60,000 pounds or with 

reversible flight controls is not to be certified for flight in all of the SLD icing 
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2-4

conditions of Appendix O, then § 25.1420 requires a means of indicating when the 

airplane has encountered icing conditions beyond those for which it is certified. See 

AC 25-28, Compliance of Transport Category Airplanes for Flight in Icing Conditions, 

dated October 27, 2014, for guidance on acceptable means of detecting and indicating 

when the airplane has encountered icing conditions beyond those for which it is 

certified. The applicant should provide procedures in the airplane flight manual (AFM)

that will enable the flightcrew to make a safe exit from all icing conditions after an

encounter with icing conditions beyond those for which the airplane is certified.

2.1.6 To certify an airplane with a maximum takeoff weight less than 60,000 pounds or with 

reversible flight controls for operations in Appendix O icing conditions only for certain

flight phase(s), the applicant should define the flight phase(s) for which approval is 

sought in a way that will allow a flightcrew to easily determine whether the airplane is 

operating inside or outside its certified icing envelope. The critical ice accretion or 

accretions used to show compliance with the applicable requirements should cover the 

range of airplane configurations, operating speeds, angles-of-attack, and engine thrust 

or power settings that may be encountered during that phase of flight (not just at the 

conditions specified in the part 25, subpart B, requirements). For the ice accretion 

scenarios defined in paragraph A.4.3.3 of Appendix A of this AC, the applicable flight 

phases are takeoff (including the ground roll, takeoff, and final takeoff segments), 

en route, holding, and approach/landing (including both the approach and landing 

segments).

2.1.7 Ice accretions used to show compliance with the applicable subpart B regulations 

should be consistent with the extent of the desired certification for flight in icing 

conditions. Appendices C and O define the ice accretions, as a function of flight phase, 

that must be considered for certification approval for flight in those icing conditions. 

Any of the applicable ice accretions (or a composite accretion representing a 

combination of accretions) may be used to show compliance with a particular subpart B 

requirement if it is either the ice accretion identified in the requirement or one shown to 

be more conservative than that. In addition, the ice accretion with the most adverse 

effect on handling characteristics may be used for compliance with the airplane 

performance requirements if each difference in performance is conservatively taken into 

account. Ice accretion(s) used to show compliance should take into account the speeds, 

configurations (including configuration changes), angles-of-attack, power or thrust 

settings, etc. for the flight phases and icing conditions they are intended to cover. For 

example, if the applicant desires certification for flight in the SLD icing conditions of 

Appendix O in addition to those of Appendix C, compliance with the applicable subpart 

B requirements may be shown using the most critical of the Appendix C and Appendix 

O ice accretions.

2.1.8 Certification experience has shown that it is usually unnecessary to consider ice 

accumulation on the propeller, induction system, or engine components of an 

inoperative engine when demonstrating airplane handling qualities. Similarly, for ice 

accreted anywhere on the airplane, the mass of any accreted ice need not normally be 

considered.
10/27/14 AC 25-25A

2-5

2.1.9 Requirements and guidance for flight in icing conditions also apply to operation of the 

airplane after leaving icing conditions until it is determined that no ice accretions 

remain on the airplane’s critical surfaces.

2.1.10 Ice-contaminated tailplane stall (ICTS) refers to a phenomenon identified as a causal 

factor in several airplane incidents and accidents. It results from airflow separation on 

the lower surface of the tailplane because ice is present. ICTS can occur if the angle-ofattack of the horizontal tailplane exceeds its stall angle-of-attack. Even very small 

quantities of ice on the tailplane leading edge can significantly reduce the 

angle-of-attack at which the tailplane stalls. An increase in tailplane angle-of-attack, 

which may lead to a tailplane stall, can result from changes in airplane configuration 

(for example, extending flaps, which increases the downwash angle at the tail or the 

pitch trim required) or flight conditions (a high approach speed, gusts, or maneuvering, 

for example). An ICTS is characterized by reduction or loss of pitch control or pitch 

stability while in, or soon after leaving, icing conditions. A flight test procedure for 

determining susceptibility to ICTS is presented in paragraph 4.9.4, Low g Maneuvers 

and Sideslips, of this AC.

2.1.10.1 For airplanes with unpowered longitudinal 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 cause the longitudinal control (for example, the control 

column) to suddenly move forward with a force beyond the capability of 

the flightcrew to overcome. On some airplanes, ICTS has been caused by 

a lateral flow component coming off the vertical stabilizer, as may occur 

in sideslip conditions or because of a wind gust with a lateral component.

2.1.10.2 Aerodynamic effects of reduced tailplane lift should be considered for all 

airplanes, including those with powered controls. Airplanes susceptible to 

this phenomenon are those having a near zero or negative tailplane stall 

margin with tailplane ice contamination.

2.1.11 There have been airplane controllability incidents in icing conditions as a result of ice 

on unprotected leading edges of extended trailing edge flaps or flap vanes. The primary 

safety concern illustrated by these incidents is the potential for controllability problems 

due to the accretion of ice on trailing edge flap or flap vane leading edges while 

extending flaps in icing conditions. The flight tests specified in table 4-5 of this AC, in 

which handling characteristics are tested at each flap position while ice is being 

accreted in natural icing conditions, are intended to investigate this safety concern. 

Unless controllability concerns arise from these tests, it is not necessary to conduct 

flight tests with simulated ice accretions on the extended trailing edge flap or flap vanes 

or to include extended trailing edge flap or flap vane ice accretions when evaluating 

airplane performance with flaps extended.

2.1.12 SLD icing conditions, or runback ice in any icing condition, can cause a ridge of ice to 

form aft of the protected area on the upper surface of the wing. This can lead to 
10/27/14 AC 25-25A

2-6

separated airflow over the aileron. Ice-induced airflow separation upstream of the 

aileron can have a significant effect on aileron hinge moment. Depending on the extent 

of the separated flow and the design of the flight control system, ice accretion upstream 

of the aileron may lead to aileron hinge moment reversal, reduced aileron effectiveness, 

and aileron control reversal. Although airplanes with deicing boots and unpowered 

aileron controls are most susceptible to this problem, all airplanes should be evaluated 

for roll control capability in icing conditions. Acceptable flight test procedures for 

checking roll control capability are presented in paragraphs 4.9.3, 4.15, and 4.17.2.5 of 

this AC and consist of bank-to-bank roll maneuvers, steady heading sideslips, and 

rolling maneuvers at stall warning speed.

2.2 Proof of Compliance, § 25.21(g).

2.2.1 You may show compliance with certification requirements for flight in icing conditions 

by any of the means discussed in chapter 3, Acceptable Means of Compliance–General, 

paragraph 3.1, Overview, of this AC.

2.2.2 Certification experience has shown that, for airplanes of conventional design applying 

for flight in icing conditions, it is usually not necessary to perform additional detailed 

substantiation of compliance with requirements of the following sections of part 25:

• § 25.23, Load distribution limits.

• § 25.25, Weight limits.

• § 25.27, Center of gravity limits.

• § 25.29, Empty weight and corresponding center of gravity.

• § 25.31, Removable ballast.

• § 25.231, Longitudinal stability and control.

• § 25.233, Directional stability and control.

• § 25.235, Taxiing condition.

• § 25.253(a) and (b), High-speed characteristics.

• § 25.255, Out-of-trim characteristics.

2.2.3 If different stall warning system or stall identification system activation settings are 

used for flight in icing conditions (for example, if the stall warning or stall identification 

system activation settings are changed when the ice protection system is activated), it is 

acceptable to return to the non-icing settings when the critical wing surfaces are free of 

ice. The applicant should validate that the means for determining when the critical wing 

surfaces are free of ice accretions is reliable under all expected operating conditions.
10/27/14 AC 25-25A

2-7

2.3 Propeller Speed and Pitch Limits, § 25.33.

Certification experience in meeting § 25.33 has shown that it may be necessary to 

impose additional propeller speed limits for operations in icing conditions.

2.4 Performance—General, § 25.101.

2.4.1 This regulation states that the propulsive power or thrust available for each flight 

condition must be appropriate to the airplane operating limitations and normal 

procedures for flight in icing conditions.

2.4.2 In general, propulsive power or thrust available may be determined by suitable analysis, 

substantiated when required by appropriate flight tests. An example would be when 

determining the power or thrust available for showing compliance with § 25.119. The 

following aspects should be considered:

2.4.2.1 Operation of induction system ice protection.

2.4.2.2 Operation of propeller ice protection.

2.4.2.3 Operation of engine ice protection.

2.4.2.4 Operation of airframe ice protection.

2.4.3 The applicant should consider the following when determining the change in 

performance due to flight in icing conditions: 

2.4.3.1 Thrust loss due to ice accretion on propulsion system components, 

including the engine induction system and other engine components, and 

the propeller spinner and blades, with normal operation of the ice 

protection system.

2.4.3.2 Incremental airframe drag due to ice accretion with normal operation of 

the ice protection system.

2.4.3.3 Changes in operating speeds provided in the AFM for flight in icing 

conditions.

2.4.4 Certification experience has shown that a suitable conservative analysis or flight test 

can determine any increase in drag (or decrease in thrust) resulting from ice 

accumulation on the landing gear, propeller, induction system, and engine components. 

Certification experience has also shown that runback ice may be critical for propellers, 

so runback ice on the propeller should be addressed. Research has shown that ice 

accretions on propellers, and resulting thrust loss, may be larger in Appendix O SLD

icing conditions than in Appendix C icing conditions for some designs. Applicants may 

conduct airplane performance checks in natural icing conditions, icing tanker tests, 

icing wind tunnel tests, or propose the use of an assumed (conservative) loss in 
10/27/14 AC 25-25A

2-8

propeller efficiency. Testing should include a range of outside air temperatures, 

including warmer (near freezing) temperatures that could result in runback icing.

2.4.5 Apart from using appropriate speed adjustments to account for operation in icing 

conditions, all changes in the procedures established for takeoff or go-around should be 

agreed to by the responsible aircraft certification office (ACO).

2.5 Stall Speed, § 25.103.

Certification experience in meeting this requirement has shown that, for airplanes of 

conventional design, the effects of Mach number on stall speeds is unaffected by the 

presence of ice accretions.

2.6 Failure Conditions, § 25.1309.

2.6.1 The applicant should analyze failure modes of the ice protection system and resulting 

effects on airplane handling and performance in accordance with § 25.1309. In 

determining the probability of a failure condition, the applicant should assume that the 

probability of entering the icing conditions defined in part 25, Appendix C, is “1.” As 

explained in AC 25-28 and AC 25.1419-2, Compliance with the Ice Protection 

Requirements of § 25.1419(e), (f), (g), and (h), dated October 27, 2009, on an annual 

basis, the average probability of encountering the icing conditions defined in Appendix 

O may be assumed to be 1 x 10-2 per flight hour. This probability should not be reduced 

on a phase-of-flight basis. The ice accretion to use for failures of the ice protection 

system is defined in paragraph A.3 of appendix A of this AC.

Note: This guidance is not intended to apply to failures of other systems (or the 

engines) that may indirectly affect airplane handling and performance in icing 

conditions due to any effects of those failures on an otherwise normally functioning ice 

protection system. In such situations, the ice protection system itself is considered to be 

operating normally, although performance of its anti-ice or deice function may be 

degraded.

2.6.2 The guidance in this AC for a normal (that is, non-failure) condition is applicable, with 

the failure ice accretion, for probable failure conditions of the ice protection system that 

are (1) not annunciated to the flightcrew, or (2) annunciated to the flightcrew, but the 

associated procedure does not require exiting icing conditions.

2.6.3 For probable ice protection failure conditions annunciated to the flightcrew, when the 

associated operating procedure requires the airplane to leave the icing conditions as 

soon as practicable, the following applies: The applicant should show that, with the ice 

accretion resulting from the failure, the airplane’s performance and handling 

characteristics are adequate as determined by a system safety analysis in accordance 

with § 25.1309. The operating procedures and related speeds may restrict the airplane’s 

operating envelope, but the size of the restricted envelope should be consistent with the 

safety analysis.
10/27/14 AC 25-25A

2-9

2.6.4 For failure conditions that are improbable but not extremely improbable, the analysis 

and substantiation of continued safe flight and landing required by § 25.1309 should 

take into consideration whether the failure is annunciated, and what associated 

operating procedures and speeds would be used following the failure condition.

2.7 Flight-Related Systems.

The applicant should consider flight-related systems aspects when determining 

compliance with the subpart B flight requirements for flight in icing conditions. For 

example, the following considerations may be relevant.

2.7.1 Ice protection systems may not adequately perform their anti-ice or deice functions at 

some engine power or thrust settings. This may result in a need to establish a minimum 

useable power or thrust setting for operation in icing conditions, and this can affect 

descent or approach capabilities. The applicant should also consider the effect of power 

or thrust settings in determining the applicable ice accretions. For example, at low 

engine power or thrust, a thermal bleed air system may not be able to evaporate the 

liquid water completely after melting the ice, resulting in the potential for runback ice.

2.7.2 Ice may block control surface gaps, or freeze seals, causing increased control forces, 

control restrictions, or blockage.

2.7.3 Ice may block unprotected inlets and vents. This may affect flight controls or the 

propulsive thrust available, as well as powerplant control and cooling and aerodynamic 

drag.

2.7.4 Airspeed, altitude, or angle-of-attack sensing errors may occur due to ice accretion 

forward of the sensors (for example, radome ice). Control feel systems that use dynamic 

pressure inputs may also be affected.

2.7.5 There may be an effect on operation of stall warning and stall identification reset 

features for flight in icing conditions, including effects of failure to operate.

2.7.6 Operation of icing condition sensors, ice accretion sensors, and automatic or manual 

activation of ice protection systems may be affected.

2.7.7 Flight guidance and automatic flight control systems operation may be affected. See 

AC 25.1329-1C, Approval of Flight Guidance Systems, dated October 27, 2014, for 

guidance on compliance with § 25.1329 for flight in icing conditions, including stall 

and maneuverability evaluations with the airplane under flight guidance system control.

2.7.8 There may be an effect on installed thrust. Consideration of installed thrust includes 

consideration of ice protection systems operation when establishing acceptable power or 

thrust setting procedures, and when evaluating control, stability, temperature lapse rates, 

rotor speed margins, temperature margins, automatic takeoff thrust control system 

(ATTCS) operation, and power or thrust lever angle functions.
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2-10

2.8 Airplane Flight Manual, § 25.1581 through § 25.1587.

2.8.1 Section 25.1581 states that an AFM must be furnished with each airplane and must 

contain information necessary for safe operation because of design, operating, or 

handling characteristics. To comply with this requirement, the AFM Limitations section 

should include the following:

2.8.1.1 The limitations required to ensure safe operation in icing conditions.

2.8.1.2 Performance limitations. These should be presented for flight in icing and 

reflect all effects on lift, drag, thrust, and operating speeds related to 

operating in icing conditions. These limitations may be presented in the 

AFM performance section and included as limitations by specific 

reference in the AFM Limitations section.

2.8.1.3 All airspeed limitations associated with flight in icing conditions, such as 

the minimum airspeed for each normal airplane configuration in icing 

conditions.

2.8.1.4 As applicable, a statement similar to the following:

“In icing conditions, this 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.”

2.8.1.5 For turbojet airplanes without leading edge high-lift devices, unless all ice 

contamination would otherwise be detected and removed from the wing 

leading edges and upper surfaces before takeoff, statements similar to the 

following:

“Takeoff may not be initiated unless the flightcrew verifies that a visual 

and tactile (hands on surface) check of the wing upper surfaces and 

leading edges has been accomplished, and the wing has been found to be 

free of frost, ice, or snow in conditions conducive to ice/frost/snow 

formation. Conditions conducive to ice/frost/snow formation exist 

whenever the outside air temperature is below 6 °C (42 °F) and any of the 

following exists:

• Visible moisture is present in the air or on the wing.

• The difference between the dew point temperature and the outside air 

temperature is less than 3 °C (5 °F).

• Standing water, slush, ice, or snow is present on taxiways or runways.”

Note: An acceptable means for showing that residual ice contamination 

could be detected and removed without needing a visual and tactile check 

would be to show that, on an airplane operated in accordance with 

§ 121.629(c), a wing ice protection system or primary wing ice detection 

system can be used while the airplane is on the ground. In this case, the 
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2-11

AFM Limitations section should include a statement similar to the 

following:

“The [wing ice protection system or ice detection system–applicant to 

identify which one] must be operating after deicing until immediately 

before starting the takeoff roll whenever conditions conducive to 

ice/frost/snow formation exist.”

2.8.2 To comply with § 25.1583(e), Kinds of operation, the AFM Limitations section should 

clearly identify the extent of each approval to operate in icing conditions, including the 

extent of any approval to operate in the SLD atmospheric icing conditions defined in 

part 25, Appendix O.

2.8.3 For airplanes not certified to operate throughout the atmospheric icing envelope of part 

25, Appendix O, for every flight phase, the Limitations section of the AFM should also 

identify the means for detecting when the certified icing conditions have been exceeded 

and state that intentional flight, including takeoff and landing, into these conditions is 

prohibited. A requirement to exit all icing conditions must be included if icing 

conditions for which the airplane is not certified are encountered. 

2.8.4 To comply with § 25.1585, the AFM operating procedures should include the following 

information:

2.8.4.1 Flight in icing conditions operating procedures should include both (1) 

normal operation of the ice protection system, and (2) operation of the 

airplane following ice protection system failures. All changes in 

procedures for other airplane system failures that affect the capability of 

the airplane to operate in icing conditions should be included.

2.8.4.2 Normal operating procedures should reflect the procedures used to certify 

the airplane for flight in icing conditions. These include configurations, 

speeds, ice protection system operation, and powerplant and systems 

operation for takeoff, climb, cruise, descent, holding, go-around, and 

landing. For airplanes not certified for flight in all of the SLD atmospheric 

icing conditions defined in part 25, Appendix O, procedures should be 

provided for safely exiting all icing conditions if the airplane encounters 

Appendix O icing conditions that exceed the icing conditions for which

the airplane is certified.

2.8.4.3 For turbojet airplanes without leading edge high-lift devices, the AFM 

normal operating procedures section should contain a statement similar to 

the following, along with procedures to ensure that such contamination is 

detected and removed before takeoff:

“WARNING

Minute amounts of ice or other contamination on the leading edges or 

wing upper surfaces can result in a stall without warning, leading to loss of 

control on takeoff.”
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2.8.4.4 Non-normal operating procedures should include procedures to be 

followed in the event of annunciated ice protection system failures and 

suspected unannunciated ice protection system failures. If flight in icing 

conditions results in any changes to other non-normal procedures 

contained in the AFM, these changes should also be included.

2.8.5 Performance information, derived in accordance with part 25, subpart B, should be 

provided in the AFM for all relevant phases of flight in accordance with § 25.1587.

2.8.6 Examples of AFM limitations and operating procedures for operations in SLD icing 

conditions (i.e., Appendix O) are contained in appendix D of this AC.
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CHAPTER 3. ACCEPTABLE MEANS OF COMPLIANCE—GENERAL

3.1 Overview.

3.1.1 This chapter describes acceptable methods and procedures that an applicant may use to 

show that an airplane meets the airplane performance and handling characteristics 

requirements of subpart B in the atmospheric icing conditions of part 25, Appendices C 

and O.

3.1.2 The applicant should show compliance by one or more of the methods listed in this 

chapter as agreed to by the responsible ACO.

3.1.3 The compliance process should address all phases of flight, including takeoff, climb, 

cruise, holding, descent, approach, landing, and go-around, as appropriate to the 

airplane type, considering its typical operating regime and the extent of its certification 

approval for operation in the atmospheric icing conditions of part 25, Appendix O.

3.1.4 The design features described in appendix C of this AC should be considered when 

determining the extent of the substantiation program.

3.1.5 Appropriate means for showing compliance include the items listed in table 3-1 below. 

These compliance means are explained in more detail in following chapters of this AC.

Table 3-1. Means for Showing Compliance

Item Description

Flight Testing Flight testing in dry air using simulated ice 

accretions or with ice accretions created in 

natural icing conditions.

Wind Tunnel Testing and Analysis An analysis of results from wind tunnel tests 

with simulated or actual ice accretions.

Engineering Simulator Testing and 

Analysis

An analysis of results from engineering 

simulator tests.

Engineering Analysis An analysis that may include the results from 

any of the other means of compliance as well 

as the use of engineering judgment.

Ancestor Airplane Analysis An analysis of results from a closely related 

ancestor airplane (an airplane model from 

which this airplane model is a derivative).
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3.1.6 Means of compliance guidance for determining the applicable ice accretion on the 

airframe is provided in appendix A of this AC.

3.1.7 Guidance for developing simulated ice accretions is given in appendix B of this AC.

3.2 Flight Testing.

3.2.1 Overview.

3.2.1.1 Section 21.35 requires applicants to perform all flight tests that the 

Administrator finds necessary to show compliance with the applicable 

requirements of part 25.

3.2.1.2 The extent of the flight test program should consider results of 

certification flight tests conducted with the uncontaminated airplane. This 

is the airplane without ice accretions, or the “clean” airplane. Design 

features of the airplane as discussed in appendix C of this AC should also 

be considered.

3.2.1.3 It is not necessary to repeat, this time with ice accretions, the extensive 

airplane performance and handling characteristics test program that is 

conducted with the uncontaminated airplane. A suitable program sufficient 

to demonstrate compliance with the requirements can be established from 

experience with airplanes of similar size, and from review of design 

features of the ice protection system, control system, wing, horizontal and 

vertical stabilizer, and the performance and handling characteristics of the 

uncontaminated airplane. In particular, it is not necessary to investigate all 

weight and center-of-gravity combinations when results from the 

uncontaminated airplane clearly indicate the most critical combination to 

be tested. It is also not usually necessary to investigate the flight 

characteristics of the airplane with ice accretions at high altitude (that is, 

above the highest altitude for the atmospheric icing envelope specified in 

part 25, Appendices C and O) if the ice protection system continues to 

provide the same level of protection as at lower altitudes.

3.2.1.4 Certification experience has shown that flight tests are usually necessary 

to evaluate the consequences of ice protection system failures on airplane 

performance and handling characteristics, and to demonstrate that the 

airplane is capable of continued safe flight and landing.

3.2.1.5 An example of an acceptable flight test program is provided in chapter 4, 

Acceptable Means of Compliance—Flight Test Program, of this AC.
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3.2.2 Flight Testing Using Approved Simulated Ice Accretions.

3.2.2.1 Tests for airplane performance and handling characteristics in icing 

conditions may be based on flight testing performed in dry air using 

simulated ice accretions that have been agreed to by the responsible ACO.

3.2.2.2 Additional limited flight tests should be conducted in natural icing 

conditions, as discussed in paragraph 3.2.3.2 below.

3.2.3 Flight Testing in Natural Icing Conditions.

3.2.3.1 If the applicant uses flight testing with ice accretions obtained in natural 

atmospheric icing conditions as the primary means of showing 

compliance, all relevant meteorological conditions (including liquid water 

content (LWC) and median volume diameter (MVD) of the cloud drops) 

should be measured and recorded. (The Appendix C icing envelopes use 

the term mean effective diameter (MED) rather than MVD, but this 

equates to MVD for the instrumentation used and the drop size 

distribution assumed at the time those envelopes were established.) The 

tests should ensure good coverage of the atmospheric icing conditions of 

part 25, Appendices C and O (consistent with the extent of the 

certification approval sought for operation in Appendix O icing 

conditions) and, in particular, the critical conditions for the airplane. The 

conditions for accumulating ice (including the icing atmosphere, airplane 

configuration, speed, and duration of exposure) should be agreed to by the 

responsible ACO.

3.2.3.2 If the applicant uses flight testing with simulated ice accretions as the 

primary means of showing compliance, additional limited flight tests 

should be conducted with ice accretions obtained in natural icing 

conditions. The objective of these tests is to corroborate the simulated ice 

accretions, and the handling characteristics and performance results 

obtained in flight testing with the simulated ice accretions. It is not 

necessary to measure the atmospheric icing characteristics (for example, 

LWC and MVD) of these flight test icing conditions. For derivative 

airplanes with aerodynamic characteristics and ice protection systems 

similar to the ancestor airplane, it may not be necessary to carry out 

additional flight tests in natural icing conditions if such tests have already 

been performed with the ancestor airplane. Depending on the extent of the 

Appendix O icing conditions for which certification is being sought, and 

the means used for showing compliance with the performance and 

handling characteristics requirements, it may also not be necessary to 

conduct flight tests in the natural icing conditions of Appendix O. See 

AC 25-28 for guidance on when it is necessary to conduct flight tests in 

the natural atmospheric icing conditions of Appendix O.
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3.3 Wind Tunnel Testing and Analysis.

To help substantiate acceptable performance and handling characteristics, the applicant 

may use analysis of results of dry air wind tunnel testing of models with the simulated 

ice accretions defined in Appendices C and O.

3.4 Engineering Simulator Testing and Analysis.

Results of an engineering simulator airplane analysis that includes effects of ice 

accretions defined in Appendices C and O may be used to help substantiate acceptable 

handling characteristics. Data used to model the effects of ice accretions for the 

engineering simulator may be based on results of dry air wind tunnel tests, flight tests, 

computational analysis, or on engineering judgment.

3.5 Engineering Analysis.

To help substantiate acceptable performance and handling characteristics, the applicant 

may use an engineering analysis that includes effects of the ice accretions defined in 

Appendices C and O. Effects of the ice accretions used in this analysis may be 

determined by analyzing results of dry air wind tunnel tests, flight tests, computational 

analyses, engineering simulator analyses, or by engineering judgment.

3.6 Ancestor Airplane Analysis.

3.6.1 To help substantiate acceptable performance and handling characteristics, the applicant 

may use an analysis of an ancestor airplane that includes effects of ice accretions as 

defined in Appendices C and O. This analysis should consider the similarity of the 

airplane configuration, operating envelope, performance and handling characteristics, 

and ice protection system of the ancestor airplane to the one being certified.

3.6.2 The analysis may include flight test data, dry air wind tunnel test data, icing tunnel test 

data, engineering simulator analysis, service history, or engineering judgment.
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CHAPTER 4. ACCEPTABLE MEANS OF COMPLIANCE—FLIGHT TEST PROGRAM

4.1 Overview.

4.1.1 This chapter provides guidance for developing an acceptable flight test program. Such a 

test program may be used if the applicant selects flight testing as the primary means for 

showing compliance with the requirements for airplane performance and handling 

qualities for flight in icing conditions and if that method of showing compliance is 

agreed to by the responsible ACO.

4.1.2 Section 25.21(a)(1) states that compliance with each requirement of subpart B must be 

shown by tests upon an airplane of the type for which certification is requested, or by 

calculations based on, and equal in accuracy to, the results of testing. In accordance 

with § 25.21(a)(1), calculations, if used, must provide at least the same degree of 

confidence of compliance as testing would provide.

4.1.3 Ice accretions for each flight phase are defined in part 25, part II of Appendices C and 

O. Additional guidance for determining the applicable ice accretions is provided in 

appendix A of this AC.

4.1.4 This example test program uses the holding ice accretion for the majority of the testing, 

assuming that it is the most conservative ice accretion. However, in accordance with 

part 25, Appendix C, part II(b), and part 25, Appendix O, part II(e), if the holding ice 

accretion is not as conservative as the ice accretion appropriate to the flight phase, then 

the ice accretion appropriate to the flight phase and icing conditions of Appendix C or 

O, as applicable, or a more conservative ice accretion, must be used. In general, the 

applicant may choose to use either a conservative ice accretion or the specific ice 

accretion appropriate to the particular phase of flight and icing conditions.

4.1.5 For the approach and landing configurations, in accordance with the guidance provided 

in paragraph 2.1.11 of this AC, the flight tests in natural icing conditions specified in 

table 4-5 of this AC are usually sufficient to evaluate whether ice accretions on trailing 

edge flaps adversely affect airplane performance or handling qualities. If these tests 

show that airplane performance or handling qualities are adversely affected, additional 

tests may be necessary to show compliance with the airplane performance and handling 

qualities requirements.

4.1.6 Unless otherwise specified, the speeds (for example, VSR, VREF, V2, etc.) referenced in 

the flight tests described in this AC refer to the speeds used with the appropriate ice 

accretion on the airplane.

4.2 Stall Speed, § 25.103.

4.2.1 The stall speed for intermediate high lift configurations (for takeoff configurations, for 

example) can normally be obtained by interpolation. However, additional tests may be 

necessary if—
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4.2.1.1 A stall identification system (for example, a stick pusher) activation point 

is set as a function of the high lift configuration,

4.2.1.2 The activation point is reset for icing conditions, or

4.2.1.3 Significant configuration changes occur with extension of trailing edge 

flaps (such as extension of wing leading edge high lift devices).

4.2.2 Acceptable Test Program.

The following specifications represent an example of an acceptable test program subject 

to the provisions outlined paragraph 4.2.1 of this AC.

Maneuvers

4.2.2.1 Load the airplane to a forward center-of-gravity position appropriate to the 

airplane configuration.

4.2.2.2 Conduct the test at the stall test altitude used in non-icing tests.

4.2.2.3 Trim at an initial speed of 1.13 to 1.30 VSR. Decrease speed at a rate not to 

exceed 1 knot per second until an acceptable stall identification is 

obtained. Perform this maneuver with the following ice accretions:

4.2.2.3.1 In high lift devices retracted configuration—final takeoff ice.

4.2.2.3.2 In high lift devices retracted configuration—en route ice.

4.2.2.3.3 In holding configuration—holding ice.

4.2.2.3.4 In lowest lift takeoff configuration—holding ice.

4.2.2.3.5 In highest lift takeoff configuration—takeoff ice.

4.2.2.3.6 In highest lift landing configuration—holding ice.

4.3 Accelerate–Stop Distance, § 25.109.

To comply with this requirement, the effect of any increase in V1 for taking off in icing 

conditions may be determined by a suitable analysis.

4.4 Takeoff Path, § 25.111.

In accordance with § 25.105(a), the applicant should conduct takeoff evaluations to 

substantiate the speed schedule and distances for takeoff in icing conditions if the 

following applies:
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4.4.1 VSR in the configuration defined by § 25.121(b) with the takeoff ice accretion exceeding

VSR for the same configuration without ice accretions by more than the greater of 3 

knots or 3 percent.

4.4.2 Any need for a takeoff speed increase, and any effects of thrust loss or drag increase on 

the takeoff path, may be determined by a suitable analysis.

4.5 Landing Climb: All–Engines–Operating, § 25.119.

The following specifications represent an example of an acceptable test program for 

showing compliance with § 25.119.

Maneuvers

4.5.1 The holding ice accretion should be used.

4.5.2 The airplane should be loaded to a forward center-of-gravity position appropriate to the 

airplane configuration.

4.5.3 The airplane should be in the highest lift landing configuration, at a landing climb speed 

no greater than VREF.

4.5.4 Stabilize the airplane at the specified speed and conduct two climbs or drag polar 

checks as agreed to by the responsible ACO.

4.6 Climb: One-Engine-Inoperative, § 25.121.

The following specifications represent an example of an acceptable test program for 

showing compliance with § 25.121.

Maneuvers

4.6.1 The airplane should be loaded to a forward center-of-gravity position appropriate to the 

configuration.

4.6.2 Stabilize the airplane at the specified speed with one engine inoperative (or simulated 

inoperative if all relevant effects of an inoperative engine can be taken into account) and 

conduct two climbs or drag polar checks in each of the following airplane 

configurations, with the specified ice accretions, to substantiate the asymmetric drag 

increment as agreed to by the responsible ACO. 

4.6.2.1 High lift devices retracted configuration, final takeoff climb speed—final 

takeoff ice.
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4.6.2.2 Lowest lift takeoff configuration, landing gear retracted, V2 climb speed—

takeoff ice.

4.6.2.3 Approach configuration appropriate to the highest lift landing 

configuration, landing gear retracted, approach climb speed—holding ice.

4.7 En Route Flight Paths, § 25.123.

The following specifications represent an example of an acceptable test program to 

show compliance with § 25.123.

Maneuvers

4.7.1 The en route ice accretion should be used.

4.7.2 The airplane should be loaded to a forward center-of-gravity position appropriate to the 

airplane configuration.

4.7.3 The airplane should be in the en route configuration at the en route climb speed.

4.7.4 Stabilize the airplane at the specified speed with one engine inoperative (or simulated 

inoperative if all relevant effects of an inoperative engine can be taken into account) and 

conduct two climbs or drag polar checks to substantiate the asymmetric drag increment 

as agreed to by the responsible ACO.

4.8 Landing, § 25.125.

The effect of any landing speed increase on the landing distance may be determined by 

a suitable analysis.

4.9 Controllability and Maneuverability—General, § 25.143.

4.9.1 A qualitative and quantitative evaluation is usually necessary to show compliance with 

the controllability and maneuverability requirements of § 25.143. Depending on how 

clearly compliance is demonstrated, or whether the force limits or stick force per g 

limits of § 25.143 are being approached, additional substantiation may be necessary to 

ensure that the airplane complies.

4.9.2 Acceptable Test Program.

The following specifications represent an example of an acceptable test program to

evaluate general controllability and maneuverability, subject to the provisions outlined 

above.
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Maneuvers

4.9.2.1 The holding ice accretion should be used.

4.9.2.2 The airplane should be loaded to a medium to light weight, with an aft

center-of-gravity position, and symmetric fuel loading.

4.9.2.3 In the configurations listed in table 4-1 below, trim the airplane at the 

specified speeds and conduct the following maneuvers:

4.9.2.3.1 Thirty-degree banked turns left and right with rapid reversals.

4.9.2.3.2 A pull-up to 1.5 g (except that this may be limited to 1.3 g at VREF) and a 

pushover to 0.5 g (except that the pushover is not required at VMO and 

VFE).

4.9.2.3.3 Include deployment and retraction of deceleration devices.

Table 4-1. Controllability and Maneuverability—Trim Speeds

Configuration Trim Speed

High lift devices retracted configuration 1.3 VSR and

VMO or 250 KIAS, whichever is less

Lowest lift takeoff configuration 1.3 VSR and

VFE or 250 KIAS, whichever is less 

Highest lift landing configuration VREF and

VFE or 250 KIAS, whichever is less

VSR – Reference Stall Speed

VMO – Maximum operating limit speed

KIAS – Knots indicated airspeed

VFE – Maximum flap extended speed

VREF – Reference landing speed

4.9.2.4 In the lowest lift takeoff configuration, at the greater of 1.13 VSR or V2MIN, 

with one engine inoperative (simulated), conduct 30° banked turns left and 

right with normal turn reversals and, in wings-level flight, a 5-knot speed 

decrease and increase.

4.9.2.5 Conduct an approach and go-around with all engines operating using the 

AFM approach and go-around procedure.
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4.9.2.6 Conduct an approach and go-around with one engine inoperative 

(simulated) using the AFM one-engine-inoperative approach and 

go-around procedure.

4.9.2.7 Conduct an approach and landing using the AFM approach and landing 

procedure. In addition, you should demonstrate satisfactory controllability 

during a landing at VREF minus 5 knots. These tests should be done at 

heavy weight and forward center-of-gravity.

4.9.2.8 Conduct an approach and landing with one engine inoperative (or with one 

engine simulated to be inoperative if all effects associated with an engine 

failure can be taken into account) using the procedure provided in the 

AFM.

4.9.3 Evaluation of Lateral Control Characteristics.

Aileron hinge moment reversal and other lateral control anomalies have been identified 

as causal factors in icing accidents and incidents. The following maneuvers, along with 

the following two evaluations, are intended to determine susceptibility of the airplane to 

aileron hinge moment reversals or other adverse effects on lateral control characteristics 

due to ice accretion.

Evaluations

4.9.3.1 Evaluate lateral controllability during deceleration to the stall warning 

speed (covered in paragraph 4.17.2.5 of this AC), and

4.9.3.2 Evaluate static lateral-directional stability (covered in paragraph 4.15 of 

this AC).

Maneuvers

4.9.3.3 For each of the test conditions specified in table 4-2 below, Perform the 

following maneuvers:

4.9.3.3.1 Establish a 30° banked level turn in one direction.

4.9.3.3.2 Using a step input of approximately 1/3-full lateral control deflection, roll 

the airplane in the other direction.

4.9.3.3.3 Maintain the control input as the airplane passes through a wings level 

attitude.

4.9.3.3.4 At approximately 20° of bank, apply a step input in the opposite direction 

to approximately 1/3-full lateral control deflection.
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4.9.3.3.5 Release the control input as the airplane passes through a wings level 

attitude.

4.9.3.3.6 Repeat this test procedure with 2/3- and up-to-full lateral control 

deflection unless the roll rate or structural loading is judged excessive. It 

should be possible to readily arrest and reverse the roll rate using only 

lateral control input, and the lateral control force should not reverse with 

increasing control deflection.

Table 4-2. Test Conditions—Lateral Control Characteristics

Test Condition

1 Holding configuration, holding ice accretion, maximum landing weight, 

forward center-of-gravity position, at minimum holding speed (highest 

expected holding angle-of-attack)

2 Landing configuration, holding ice accretion, medium to light weight, 

forward center-of-gravity position, at VREF (highest expected landing 

approach angle-of-attack)

4.9.4 Low g Maneuvers and Sideslips.

The maneuvers in paragraph 4.9.4.3 of this AC represent an example of an acceptable 

test program for showing compliance with controllability requirements in low g 

maneuvers and in sideslips to evaluate susceptibility to ice-contaminated tailplane stall.

4.9.4.1 Section 25.143(i)(2).

4.9.4.1.1 The regulation states: “It must be shown that a push force is required 

throughout a pushover maneuver down to a zero g load factor, or to the 

lowest load factor obtainable if limited by elevator power or other design 

characteristic of the flight control system. It must be possible to promptly 

recover from the maneuver without exceeding a pull control force of 

50 pounds....”

4.9.4.1.2 An example of another design characteristic of the flight control system 

that would limit the lowest obtainable load factor would be a g-limiting 

envelope protection system.

4.9.4.2 Section 25.143(i)(3).

4.9.4.2.1 For sideslips, the regulation requires that: “Any changes in force that the 

pilot must apply to the pitch control to maintain speed with increasing
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sideslip angle must be steadily increasing with no force reversals, unless 

the change in control force is gradual and easily controllable by the pilot 

without using exceptional piloting skill, alertness, or strength.” (See 

paragraph 4.15.1 of this AC for lateral-directional aspects).

4.9.4.2.2 Abrupt changes in the control force characteristic, unless so small as to be 

unnoticeable, would not be considered compliant with the requirement that 

the force be steadily increasing. A gradual change in control force is a 

change that is not abrupt and does not have a steep gradient. It can be 

easily managed by a pilot of average skill, alertness, and strength. Control 

forces in excess of those permitted by § 25.143(d) would be considered 

excessive.

4.9.4.3 Test maneuvers used to show compliance with the regulatory requirements 

quoted in paragraphs 4.9.4.1.1 and 4.9.4.2.1 above should be conducted 

using the following ice accretions, configurations, and procedures:

Maneuvers

4.9.4.3.1 The holding ice accretion should be used. For airplanes with unpowered 

elevators, these tests should also be performed with sandpaper ice.

4.9.4.3.2 The airplane should be loaded to a medium to light weight, at the most 

critical center-of-gravity position, with symmetric fuel loading, and should 

be in the highest lift landing configuration.

4.9.4.3.3 Test maneuver for showing compliance with § 25.143(i)(2) is provided in 

table 4-3 below.
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Table 4-3. Test Maneuver—§ 25.143(i)(2)

Step Maneuver

1 Start with the airplane in trim, 

or as near as possible to being in 

trim, at the most critical of the 

following trim speeds:

(1) Trim speed 1.23 VSR, target speed not 

more than 1.23 VSR.

(2) Trim speed VFE, target speed not less 

than VFE - 20 knots.

2 Pull up to a suitable pitch 

attitude, then—

(1) Push over in a continuous maneuver 

(without changing trim) to reach zero g 

normal load factor or, if limited by 

elevator control authority (or other design 

characteristic), the lowest load factor 

obtainable at the target speed, as the 

airplane’s pitch attitude passes through

approximately level flight (that is, through 

the horizon), and

(2) Perform this maneuver with idle power 

or thrust and with go-around power or 

thrust.

4.9.4.3.4 Test maneuver for showing compliance with § 25.143(i)(3): Conduct 

steady heading sideslips to full rudder input, 180 pounds rudder force, or 

full lateral control authority (whichever comes first) at a trim speed of 

1.23 VSR and with the power or thrust needed for a -3° flight path angle.

4.9.5 Controllability Prior to Activation and Operation of the Ice Protection System.

The following is an example of an acceptable test program for showing compliance 

with § 25.25.143(j).

Maneuvers

4.9.5.1 For the configurations, speeds, and power settings listed below, with the 

ice accretion specified in the requirement, trim the airplane at the specified 

speed, conduct a pull-up maneuver to 1.5 g and pushover maneuver to 

0.5 g, and show that longitudinal control forces do not reverse.

4.9.5.1.1 High lift devices retracted configuration (or holding configuration if 

different), holding speed, power or thrust for level flight.
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4.9.5.1.2 Landing configuration, VREF for non-icing conditions, power or thrust for 

landing approach. If necessary, limit the pull-up maneuver to the point at 

which stall warning occurs.

4.10 Longitudinal Control, § 25.145.

4.10.1 No specific quantitative evaluations are required for demonstrating compliance 

with§ 25.145(b) and (c). Qualitative evaluations should be combined with the other 

testing. Review results of tests on the uncontaminated airplane for any cases of marginal 

compliance. All tests showing marginal compliance should be repeated with ice 

accretions on the airplane.

4.10.2 Acceptable Test Program.

The following specifications represent an example of an acceptable test program for 

compliance with § 25.145(a).

Maneuvers

4.10.2.1 The holding ice accretion should be used.

4.10.2.2 The airplane is at a medium to light weight, aft center-of-gravity position, 

with symmetric fuel loading.

4.10.2.3 In the configurations listed below, trim the airplane at 1.3 VSR. Reduce

speed approximately 1 knot per second using elevator control to 1 second 

past stall warning and demonstrate prompt recovery to the trim speed 

using elevator control.

4.10.2.3.1 High lift devices retracted configuration, maximum continuous power or 

thrust.

4.10.2.3.2 Maximum lift landing configuration, maximum continuous power or 

thrust.

4.11 Directional and Lateral Control, § 25.147.

To show compliance with § 25.147, applicants should combine qualitative evaluations 

with the other testing (for example, the roll tests described in paragraphs 4.9.2.3.1 and 

4.9.2.4 of this AC). Review the results of the tests on the uncontaminated airplane for 

any cases of marginal compliance. All tests showing marginal compliance should be 

repeated with ice accretions on the airplane.
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4.12 Trim, § 25.161.

4.12.1 To show compliance with this requirement, the applicant should combine qualitative 

evaluations with the other testing. Review results of tests on the uncontaminated 

airplane for any cases of marginal compliance. All tests showing marginal compliance 

should be repeated with ice accretions on the airplane. In addition, a specific check 

should be made to demonstrate compliance with § 25.161(c)(2).

4.12.2 Acceptable Test Program.

The following specifications represent an example of an acceptable test program for 

compliance with § 25.161(c)(2).

Maneuvers

4.12.2.1 The holding ice accretion should be used.

4.12.2.2 The airplane is at the most critical landing weight, with a forward center of 

gravity position and symmetric fuel loading.

4.12.2.3 In the maximum lift landing configuration, trim the airplane at the most 

critical of—

4.12.2.3.1 1.3 VSR1 at idle power or thrust, or

4.12.2.3.2 VREF with the power or thrust for a -3° flight path angle.

4.13 Stability—General, § 25.171.

To show compliance with this requirement, applicants should combine qualitative 

evaluations with the other testing. Each tendency to change speed when trimmed and a 

need for frequent trim inputs should be specifically investigated.

4.14 Demonstration of Static Longitudinal Stability, § 25.175.

4.14.1 To show compliance with § 25.175, the applicant should test each of the following 

cases. In general, it is not necessary to test in the cruise configuration at low speed 

(§ 25.175(b)(2)) or in the cruise configuration with landing gear extended 

(§ 25.175(b)(3)); nor is it necessary to test at high altitude. Maximum speed for 

substantiation of stability characteristics in icing conditions (as prescribed by 

§ 25.253(c)) is the lowest of—

• 300 knots calibrated airspeed (CAS),

• VFC, or
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• A speed at which it is demonstrated that the airframe will be free of ice accretion 

due to the effects of increased dynamic pressure.

4.14.2 Acceptable Test Program.

The following specifications represent an example of an acceptable test program for 

demonstrating static longitudinal stability.

Maneuvers

4.14.2.1 The holding ice accretion should be used.

4.14.2.2 The airplane is at a high landing weight, aft center-of-gravity position, 

with symmetric fuel loading.

4.14.2.3 In the configurations listed in paragraphs 4.14.2.3.1 through 4.14.2.3.4

below, trim the airplane at the specified speed. The power or thrust should 

be set and stability demonstrated over the speed ranges as stated in 

§ 25.175(a) through (d), as applicable.

4.14.2.3.1 Climb: With high lift devices retracted, trim at the speed for best rate of 

climb, except that the speed need not be less than 1.3 VSR.

4.14.2.3.2 Cruise: With high lift devices retracted, trim at VMO or 250 knots CAS, 

whichever is lower.

4.14.2.3.3 Approach: With the high lift devices in the approach position appropriate 

to the highest lift landing configuration, trim at 1.3 VSR.

4.14.2.3.4 Landing: With the highest lift landing configuration, trim at 1.3 VSR.

4.15 Static Lateral–Directional Stability, § 25.177.

4.15.1 Use steady heading sideslips to show compliance with the directional and lateral 

stability requirements. The maximum sideslip angles obtained should be recorded and 

may be used to substantiate a crosswind value for landing. (See paragraph 4.19 of this 

AC.) Section 25.177(c) requires directional and lateral control movements and forces to 

be substantially proportional to the angle of sideslip without reversing.

4.15.2 Acceptable Test Program.

The following specifications represent an example of an acceptable test program for 

demonstrating static directional and lateral stability.
10/27/14 AC 25-25A

4-29

Maneuvers

4.15.2.1 The holding ice accretion should be used.

4.15.2.2 The airplane is at a medium to light weight, aft center-of-gravity position, 

with symmetric fuel loading.

4.15.2.3 In the configurations listed below, trim the airplane at the specified speed 

and conduct steady heading sideslips to full rudder authority, 180 pounds 

of rudder pedal force, or full lateral control authority, whichever comes 

first:

4.15.2.3.1 High lift devices retracted configuration: Trim at best rate-of-climb speed, 

but need not be less than 1.3 VSR.

4.15.2.3.2 Lowest lift takeoff configuration: Trim at the all-engines-operating initial 

climb speed.

4.15.2.3.3 Highest lift landing configuration: Trim at VREF.

4.16 Dynamic Stability, § 25.181.

If the uncontaminated airplane has no borderline compliance test results for § 25.181,

dynamic stability tests with ice accretions on the airplane are not necessary. The 

applicant should combine qualitative evaluations with other testing. Each difficulty in 

achieving precise attitude control and each tendency to sustain oscillations in turbulence 

should be investigated.

4.17 Stall Demonstration, § 25.201/Stall Characteristics, § 25.203.

4.17.1 The applicant should conduct sufficient stall testing to demonstrate that the stall 

characteristics comply with the requirements of §§ 25.201 and 25.203. In general, it is 

not necessary to conduct a stall program that encompasses all weights, center-of-gravity 

positions, altitudes, high lift configurations, deceleration device configurations, straight 

and turning flight attitudes, and thrust or power settings. The applicant can establish a 

reduced test matrix based on a review of the stall characteristics of the uncontaminated 

airplane. However, additional tests may be necessary if—

4.17.1.1 The stall characteristics with ice accretion show a significant difference 

from those on the uncontaminated airplane,

4.17.1.2 The testing indicates borderline compliance, or
10/27/14 AC 25-25A

4-30

4.17.1.3 The activation point of a stall identification system (for example, a stick 

pusher) is reset for icing conditions.

4.17.2 Acceptable Test Program.

Turning flight stalls at decelerations greater than 1 knot per second are not required. 

Note that slow decelerations (much slower than 1 knot per second) may be critical on 

airplanes with anticipation logic in their stall protection system or on airplanes with low 

directional stability, where large sideslip angles could develop. The following 

specifications represent an example of an acceptable test program subject to the 

provisions outlined above.

Maneuvers

4.17.2.1 The holding ice accretion should be used.

4.17.2.2 The airplane should be loaded to a medium to light weight, aft 

center-of-gravity position, with symmetric fuel loading.

4.17.2.3 The tests should be conducted at the normal stall test altitude.

4.17.2.4 In the configurations listed in paragraphs 4.17.2.4.1 through 4.17.2.4.4

below, trim the airplane at the same initial stall speed factor used for stall 

speed determination. For power on stalls, use the power setting as defined 

in § 25.201(a)(2), but with ice accretions on the airplane. Decrease speed 

at a rate not to exceed 1 knot per second to stall identification and recover 

using the same recovery maneuver as for the uncontaminated airplane.

4.17.2.4.1 High lift devices retracted configuration: Straight/Power Off, 

Straight/Power On, Turning/Power Off, Turning/Power On.

4.17.2.4.2 Lowest lift takeoff configuration: Straight/Power On, Turning/Power Off.

4.17.2.4.3 Highest lift takeoff configuration: Straight/Power Off, Turning/Power On.

4.17.2.4.4 Highest lift landing configuration: Straight/Power Off, Straight/Power 

On, Turning/Power Off, Turning/Power On.

4.17.2.5 For the configurations listed in paragraphs 4.17.2.4.1 and 4.17.2.4.4

above, and each other configuration if deemed more critical, in 1 knot per 

second deceleration rates down to stall warning with wings level and 

power off, roll the airplane left and right up to 10° of bank using the 

lateral control.
10/27/14 AC 25-25A

4-31

4.18 Stall Warning, § 25.207.

4.18.1 To show compliance with § 25.207, the applicant should assess stall warning in 

conjunction with stall speed testing and stall demonstration/characteristics testing 

(§§ 25.103, 25.201, and 25.203, and paragraphs 4.2 and 4.17 of this AC, respectively), 

and in tests with faster entry rates.

4.18.2 Normal Ice Protection System Operation.

The following specifications represent an example of an acceptable test program for 

stall warning in slow-down turns of at least 1.5 g and at entry rates of at least 2 knots 

per second:

Maneuvers

4.18.2.1 The holding ice accretion should be used.

4.18.2.2 The airplane should be loaded to a medium to light weight, aft 

center-of-gravity position, with symmetric fuel loading.

4.18.2.3 The test should be conducted at the normal stall test altitude.

4.18.2.4 In the configurations listed in paragraphs 4.18.2.4.1 through 4.18.2.4.3

below, trim the airplane at 1.3 VSR with the power or thrust necessary to 

maintain straight level flight. Maintain the trim power or thrust during the 

test demonstrations. Increase speed as necessary before establishing at 

least 1.5 g and a deceleration of at least 2 knots per second. Decrease 

speed until 1 second after stall warning and recover using the same 

recovery maneuver as for the uncontaminated airplane.

4.18.2.4.1 High lift devices retracted configuration.

4.18.2.4.2 Lowest lift takeoff configuration.

4.18.2.4.3 Highest lift landing configuration.

4.18.3 Stall Warning Prior to Activation and Operation of the Ice Protection System.

The following represents an acceptable means for showing compliance with 

§ 25.207(h).
10/27/14 AC 25-25A

4-32

Maneuvers

4.18.3.1 In the configurations listed in paragraphs 4.18.3.1.1 and 4.18.3.1.2 below, 

with the ice accretion specified in the requirement, trim the airplane at 1.3 

VSR.

4.18.3.1.1 High lift devices retracted configuration: Straight Flight/Power Off.

4.18.3.1.2 Landing configuration: Straight Flight/Power Off.

4.18.3.2 At deceleration rates of up to 1 knot per second, reduce the speed until 

1 second past stall warning, and demonstrate that stalling can be prevented 

using the same recovery maneuver as used for the uncontaminated 

airplane, without encountering any adverse characteristics (for example, 

rapid wing roll-off). If stall warning for the airplane with ice accretion is 

provided by a different means than it is for the airplane without ice 

accretion, the following requirements must be met:

4.18.3.2.1 Section 25.207(h)(3)(ii) requires that stalling be preventable even if the 

pilot takes no recovery action for at least 3 seconds after stall warning.

4.18.3.2.2 Section 25.207(i) requires that satisfactory stall characteristics be 

demonstrated if stall warning is provided by a different means in icing 

conditions than for non-icing conditions.

4.19 Wind Velocities, § 25.237. To show compliance with this requirement:

4.19.1 Crosswind landings with the landing ice accretion should be evaluated on an 

opportunity basis.

4.19.2 Results of the steady heading sideslip tests with landing ice may be used to establish the 

safe crosswind component of this requirement. If the flight test data show that the 

maximum sideslip angle demonstrated is similar to that shown with the uncontaminated 

airplane, and the flight characteristics (control forces and deflections, for example) are 

similar, then the non-contaminated airplane crosswind component test result is 

considered valid for icing conditions.

4.19.3 If results of the comparison discussed in paragraph 4.19.2 above are not clearly similar, 

and in the absence of a more extensive analysis, the applicant may use a conservative 

analysis based on results of the steady heading sideslip tests to establish the safe 

crosswind component value. The crosswind value may be estimated from:
10/27/14 AC 25-25A

4-33

VCW = VREF ∗

sin(sideslip angle)

1.5

Where:

VCW is the crosswind component, and

VREF is the landing reference speed appropriate to a minimum landing weight, and

Sideslip angle is that demonstrated at VREF (see paragraph 4.15 of this AC).

4.20 Vibration and Buffeting, § 25.251.

To show compliance with this requirement:

4.20.1 Combine qualitative evaluations with the other testing, including speeds up to the 

maximum speed obtained in the longitudinal stability tests. (See paragraph 4.14 of this 

AC).

4.20.2 Demonstrate that the airplane is free from harmful vibration due to residual ice 

accumulation. This may be done in conjunction with the natural icing tests.

4.20.3 Evaluate an airplane with pneumatic deicing boots up to VDF/MDF, both with the deicing 

boots operating (including deicing boot inflation cycles) and not operating. It is not 

necessary to do this demonstration with ice accretions on the airplane.

4.21 Natural Icing Conditions, § 25.1419(b).

To show compliance with this requirement, the applicant should perform additional 

flight testing.

4.21.1 Whether flight testing has been performed with artificial or simulated ice accretions or 

in natural icing conditions, additional limited flight testing described in this section 

should be conducted in the natural atmospheric icing conditions specified in part 25, 

Appendix C, and, if necessary, in the icing conditions described in Appendix O. (AC 

25-28 provides guidance on when it is necessary to perform flight testing in the natural 

atmospheric icing conditions of Appendix O). If flight testing with simulated ice 

accretions 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 the flight testing with simulated ice accretions. Validating all aspects 

of predicted ice accretions through natural icing flight tests is not required. The flight 

testing should confirm the general physical characteristics and location of the ice 

accretions and their effect on airplane performance and handling characteristics. The 

applicant should make at least a qualitative assessment to confirm that the artificial ice 

accretions are conservative relative to ice accretions resulting from natural atmospheric 

icing conditions, and that ice in natural atmospheric icing conditions does not accrete in 

unexpected places.
10/27/14 AC 25-25A

4-34

4.21.2 It is acceptable for some ice to be shed during the testing due to air loads or wing 

flexure, etc. However, the applicant should attempt to accomplish the test maneuvers as 

soon as possible after exiting the icing cloud in order to minimize atmospheric 

influences on ice shedding.

4.21.3 Acceptable Test Program.

During each of the maneuvers specified in paragraph 4.21.4 below, the behavior of the 

airplane should be consistent with that obtained with simulated ice accretions. 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.

Maneuvers

4.21.4 Ice Accretion Maneuvers.

4.21.4.1 Holding scenario.

4.21.4.1.1 The maneuvers specified in table 4-4. below should be carried out with ice 

accretions defined in paragraphs 4.21.4.1.2 and 4.21.4.1.3 below, which is 

representative of normal operation of the ice protection system:

4.21.4.1.2 Ice on unprotected parts. A target accretion thickness equivalent to the 

45-minute dry air ice accretions on an unprotected part of the wing should 

be the objective. (A thickness of 2 inches is normally a minimum value, 

unless a lesser value is agreed to with the responsible ACO).

4.21.4.1.3 Ice on protected parts. The ice accretion thickness should be that resulting 

from normal operation of the ice protection system.

4.21.4.1.4 For airplanes with control surfaces that may be susceptible to jamming 

due to ice accretion (for example, elevator horns exposed to the air flow), 

the holding speed that is critical with respect to this ice accretion should 

be used.
10/27/14 AC 25-25A

4-35

Table 4-4. Holding Scenario—Maneuvers

4.21.4.2 Approach/Landing Scenario.

4.21.4.2.1 The maneuvers specified in table 4-5 of this AC should be carried out with 

successive accretions in different configurations on unprotected surfaces.

4.21.4.2.2 Each test condition should be accomplished with the ice accretion that 

exists at that point.

4.21.4.2.3 The final ice accretion (Test Condition 3) represents the sum of the 

amounts that would accrete during a normal descent from holding to 

landing in icing conditions.

4.21.5 For airplanes with unpowered elevator controls, unless the applicant can adequately 

substantiate the critical simulated ice accretion used to demonstrate compliance with the 

controllability requirement, the pushover test of paragraph 4.9.4.3.3 should be repeated 

with a thin accretion of natural ice.

4.21.6 Existing propeller speed limits or, if required, revised propeller speed limits for flight in 

icing, should be verified by flight tests in natural icing conditions.

Airplane 

Configuration

Center-ofGravity 

Position

Trim 

Speed Maneuver

Flaps up,

Gear up

Any position 

in the aft 

range

Holding, 

except 

1.3 VSR for 

the stall 

maneuver

Level, 40° banked turn;

Bank-to-bank rapid roll, 30° - 30°;

Speedbrake extension, retraction;

Full straight stall (1 knot per second 

deceleration rate, wings level, power off)

Flaps in 

intermediate 

positions,

gear up

Any position 

in the aft 

range

1.3 VSR Deceleration to the speed reached 

3 seconds after activation of stall warning 

in a 1 knot per second deceleration

Landing flaps,

gear down

Any position 

in the aft 

range

VREF Level, 40° banked turn;

Bank-to-bank rapid roll, 30° - 30°;

Speedbrake extension, retraction (if 

approved);

Full straight stall (1 knot per second 

deceleration rate, wings level, power off)
10/27/14 AC 25-25A

4-36

Table 4-5. Approach/Landing Scenario—Maneuvers

Test 

Condition

Ice 

Accretion 

Thickness*

Airplane 

Configuration

Center-ofGravity 

Position

Trim Speed Maneuver

— First 0.5 

inch

Flaps up,

gear up

Any 

position in 

the aft 

range

Holding No specific test

1 Additional

0.25 inch

(0.75 inch 

total)

First 

intermediate 

flaps, gear up

Any 

position in 

the aft 

range

Holding, except

1.3 VSR for the 

deceleration 

maneuver

Level 40° banked turn;

Bank-to-bank rapid roll, 30°- 30°;

Speed brake extension and retraction (if approved);

Deceleration to the speed reached 3 seconds after

activation of stall warning in a 1 knot per second 

deceleration.

2 Additional

0.25 inch

(1.00 inch 

total)

Further 

intermediate 

flaps, gear up 

(as applicable)

Any 

position in 

the aft 

range

1.3 VSR Bank-to-bank rapid roll, 30° - 30°;

Speed brake extension and retraction (if approved);

Deceleration to the speed reached 3 seconds after 

activation of stall warning in a 1 knot per second 

deceleration.

3 Additional

0.25 inch 

(1.25 inch 

total)

Landing flaps, 

gear down

Any 

position in 

the aft 

range

VREF Bank-to-bank rapid roll, 30° - 30°;

Speed brake extension and retraction (if approved), 

Bank to 40°;

Full straight stall (1 knot per second deceleration 

rate, wings level, power off).

* The indicated thickness is that accumulated on the parts of the unprotected airfoil most likely to accumulate ice.
10/27/14 AC 25-25A

4-37

4.22 Failure Conditions, § 25.1309.

To show compliance with this requirement:

4.22.1 For failure conditions that are annunciated to the flightcrew, the applicant may take 

credit for flightcrew action to follow the established operating procedures provided in 

the AFM.

4.22.2 Acceptable Test Program.

In addition to a general qualitative evaluation, the applicant should carry out the 

following test program for the most critical, probable failure condition for which the 

associated procedure requires the airplane to exit the icing condition. The test program 

should be modified as necessary to reflect the specific operating procedures.

Maneuvers

4.22.2.1 The ice accretion is defined as a combination of the following:

4.22.2.1.1 Ice on unprotected surfaces. The holding ice accretion described in 

paragraph A.2.1.3 of appendix A of this AC.

4.22.2.1.2 Ice on normally protected surfaces that are no longer protected. The failure 

ice accretion described in paragraph A.3.2 of appendix A of this AC.

4.22.2.1.3 Ice on normally protected surfaces that are still protected following 

segmental failure of a cyclical deice system. The ice accretion that will 

form during the rest time of the deice system following the critical failure 

condition.

4.22.2.2 The airplane should be loaded to a medium to light weight, at aft 

center-of-gravity position, with symmetric fuel loading.

4.22.2.3 In the configurations listed in paragraphs 4.22.2.3.1 through 4.22.2.3.3

below, trim the airplane at the specified speed. Conduct 30° banked turns 

left and right with normal reversals. Conduct a pull-up maneuver to 1.5 g 

and a pushover maneuver to 0.5 g.

4.22.2.3.1 High lift devices retracted configuration (or holding configuration if 

different): Holding speed, power or thrust for level flight. In addition, 

deploy and retract the deceleration devices.

4.22.2.3.2 Approach configuration: Approach speed, power or thrust for level flight.

4.22.2.3.3 Landing configuration: Landing speed, power or thrust for landing 

approach (limit pull-up to 1.3 g). In addition, conduct steady heading 

sideslips to the angle of sideslip appropriate to the airplane type and the 

AFM landing procedure.
10/27/14 AC 25-25A

4-38

4.22.2.4 In the configurations listed in paragraphs 4.22.2.4.1 and 4.22.2.4.2 below, 

trim the airplane at the estimated 1.3 VSR. Decrease speed at 

approximately 1 knot per second until 1 second after stall warning, and 

demonstrate prompt recovery using the same recovery maneuver as for the 

uncontaminated airplane. It is acceptable for stall warning to be provided 

by a different means (for example, by the behavior of the airplane rather 

than by stick shaker) for failure cases not considered probable.

4.22.2.4.1 High lift devices retracted configuration: Straight Flight/Power Off.

4.22.2.4.2 Landing configuration: Straight Flight/Power Off.

4.22.2.5 Conduct an approach and go-around with all engines operating using the 

AFM approach and go-around procedure.

4.22.2.6 Conduct an approach and landing with all engines operating (unless the 

one-engine-inoperative condition results in a more critical probable failure 

condition) using the appropriate AFM approach and landing procedure.

4.22.3 For improbable failure conditions, flight testing may be required to demonstrate that the 

effect on safety of flight (as measured by degradation in flight characteristics) supports 

the system safety analysis, or to verify results of analyses or wind tunnel tests. The 

extent of each required flight testing should be similar to that described in 

paragraph 4.22.3 above, or as agreed to by the responsible ACO for the specific failure 

condition.
10/27/14 AC 25-25A

Appendix A

A-1

APPENDIX A. AIRFRAME ICE ACCRETIONS

A.1 Overview.

A.1.1 In accordance with § 25.1419, each airplane certified for flight in icing conditions must 

be capable of safely operating in the continuous maximum and intermittent maximum 

icing conditions of part 25, Appendix C. Therefore, at a minimum, certification for 

flight in icing conditions must include consideration of ice accretions that can occur in 

Appendix C icing conditions.

A.1.2 In accordance with § 25.1420(a)(1), each airplane with a maximum takeoff weight less 

than 60,000 pounds or with reversible flight controls certified for flight in icing 

conditions must, at a minimum, be capable of safely operating: (1) in the atmospheric 

icing conditions of part 25, Appendix C, and (2) after encountering the atmospheric 

icing conditions of part 25, Appendix O, and while subsequently exiting all icing 

conditions. Therefore, for airplanes with a maximum takeoff weight less than 

60,000 pounds or with reversible flight controls, certification for flight in icing 

conditions must consider, at a minimum, ice accretions that can occur during flight in 

Appendix C icing conditions and during detection and exiting of Appendix O icing 

conditions.

A.1.3 In accordance with § 25.1420(a)(2), an airplane with a maximum takeoff weight less 

than 60,000 pounds or with reversible flight controls may also be certified for operation 

in a portion of the atmospheric icing conditions of part 25, Appendix O. In that case, the 

airplane must also be capable of operating safely after encountering, and while exiting, 

atmospheric icing conditions in the portion of Appendix O for which operation is not 

approved. Ice accretions used for certification must consider—

A.1.3.1 Operations in Appendix C icing conditions,

A.1.3.2 Operations in the Appendix O icing conditions for which approval is 

sought, and

A.1.3.3 Detection and exiting of the Appendix O icing conditions beyond those for 

which approval is sought.

A.1.4 In accordance with § 25.1420(a)(3), in addition to being certified for flight in 

Appendix C conditions, an airplane with a maximum takeoff weight less than 60,000 

pounds or with reversible flight controls may be certified for operation throughout the 

atmospheric icing conditions of part 25, Appendix O. Certification for flight throughout 

the atmospheric icing conditions of Appendix O must consider ice accretions resulting 

from—

A.1.4.1 Operations in Appendix C icing conditions, and

A.1.4.2 Operations in Appendix O icing conditions.
10/27/14 AC 25-25A

Appendix A

A-2

A.1.5 The part 25, subpart B, airplane performance and handling characteristics requirements 

identify the specific ice accretions that apply in showing compliance. In accordance 

with Appendix C, part II(b), and Appendix O, part II(e), to reduce the number of ice 

accretions used for demonstrating compliance, the applicant may use any of the 

applicable ice accretions (or a composite accretion representing a combination of 

accretions) to show compliance with a particular subpart B requirement if that accretion 

is either the ice accretion identified in the requirement or is shown to be more 

conservative than the ice accretion identified in the requirement. In addition, the ice 

accretion with the most adverse effect on handling characteristics may be used for 

compliance with the airplane performance requirements if any difference in 

performance is conservatively taken into account. Ice accretion(s) used to show 

compliance should take into account the speeds, configurations (including configuration 

changes), angles-of-attack, power or thrust settings, etc., for the flight phases and icing 

conditions they are intended to cover.

A.1.6 The applicant should determine the most critical ice accretion in terms of handling 

characteristics and performance for each flight phase. Parameters to be considered 

include—

A.1.6.1 Flight conditions (for example, airplane configuration, speed, 

angle-of-attack, altitude), and

A.1.6.2 Atmospheric icing conditions for which certification is desired (for 

example, temperature, liquid water content (LWC), drop mean effective 

diameter (MED), and drop median volume diameter (MVD)).

A.1.7 For each phase of flight, the shape, chordwise and spanwise, and the roughness of the 

shapes considered in selection of a critical ice shape should accurately reflect the full 

range of atmospheric icing conditions for which certification. Justification and selection 

of the most critical ice shape for each phase of flight should be agreed to by the 

responsible ACO.

A.1.8 See Appendix R of AC 20-73A, Aircraft Ice Protection, dated August 16, 2009, for 

additional detailed information about determining the applicable critical ice accretion 

(shape and roughness).

A.2 Ice Accretions With an Operative Ice Protection System.

A.2.1 All Flight Phases Except Takeoff.

A.2.1.1 For unprotected parts, the ice accretion to be considered should be 

determined in accordance with part 25, Appendices C and O.

A.2.1.2 Unprotected parts consist of the unprotected airfoil leading edges and all 

unprotected airframe parts on which ice may accrete. The effect of ice 

accretion on protuberances such as antennas or flap hinge fairings need 
10/27/14 AC 25-25A

Appendix A

A-3

not normally be investigated. However, airplanes characterized by unusual 

unprotected airframe protuberances, for example fixed landing gear, large 

engine pylons, or exposed control surface horns or winglets may 

experience significant additional effects, which should therefore be taken 

into consideration.

A.2.1.3 For holding ice, the applicant should determine the effect of a 45-minute 

hold in continuous maximum icing conditions. The analysis should 

assume that the airplane remains in a rectangular “race track” pattern, with 

all turns being made within the icing cloud. Therefore, no horizontal 

extent correction should be used for this analysis. For some previous 

airplane certification programs, the maximum pinnacle height was limited 

to 3 inches. This method of compliance may continue to be accepted for 

follow-on products if service experience has been satisfactory, and the 

designs are similar enough to conclude that the previous experience is 

applicable. The applicant should substantiate the critical MED, LWC, and 

temperature resulting in the formation of an ice accretion critical to the 

airplane’s performance and handling qualities. The shape and texture of 

the ice are important and should be agreed to by the responsible ACO.

A.2.1.4 In accordance with the definitions of holding ice, approach ice, and 

landing ice in Appendices C and O, these flight segments are considered 

contiguous and sequential. Unless there is a procedure to deice surfaces 

that have previously accreted ice in the holding flight phase, approach ice 

is normally the same accretion as the holding ice accretion plus any 

additional ice accreted during the transition to the approach configuration. 

Similarly, unless there is a procedure to deice surfaces before landing, the 

landing ice accretion is normally the same accretion as the approach ice 

accretion plus any additional ice accreted during transition to the final 

landing configuration. A total time of 45 minutes can be used for the 

combination of hold, approach, and landing ice.

A.2.1.5 For protected parts, the ice protection systems are normally assumed to be 

operative. However, the applicant should consider the effect of ice 

accretion on or behind the protected surfaces that results from the rest time 

of a deicing cycle. Performance may be established on the basis of a 

representative intercycle ice accretion for normal operation of the deicing 

system. (The applicant should also consider effects of each residual ice 

accretion that is not shed). The average drag increment determined over 

the deicing cycle may be used for performance calculations. Consider the 

effect of—

A.2.1.5.1 Runback ice that occurs on or downstream of the protected surface 

(including deicing boots), and

A.2.1.5.2 Ice accretion prior to activation and operation of the ice protection system.

(See paragraph A.2.3 of this appendix.)
10/27/14 AC 25-25A

Appendix A

A-4

A.2.2 Takeoff Phase.

A.2.2.1 For both unprotected and protected parts, the ice accretion identified in 

part 25, Appendices C and O, for the takeoff phase may be determined by 

calculation, assuming the following:

A.2.2.1.1 Airfoils, control surfaces, and propellers if applicable are free from frost, 

snow, or ice at the start of the takeoff.

A.2.2.1.2 The ice accretion starts at the end of the takeoff distance.

A.2.2.1.3 The airplane is at the critical ratio of power/thrust-to-weight.

A.2.2.1.4 Failure of the critical engine occurs at VEF.

A.2.2.1.5 The flightcrew activates the ice protection system in accordance with an 

AFM procedure; except that after beginning the takeoff roll, no flightcrew 

action to activate the ice protection system should be assumed to occur 

until the airplane is 400 feet above the takeoff surface.

A.2.2.2 The ice accretions identified in part 25, Appendix C, for the takeoff phase 

are takeoff ice and final takeoff ice.

A.2.2.2.1 Takeoff ice: The most critical ice accretion on unprotected surfaces, and 

any ice accretion on protected surfaces appropriate to normal ice 

protection system operation, occurring between the end of the takeoff 

distance and 400 feet above the takeoff surface, assuming accretion starts 

at the end of the takeoff distance in the takeoff maximum icing conditions 

of part 25, Appendix C, part I(c).

A.2.2.2.2 Final takeoff ice: The most critical ice accretion on unprotected surfaces, 

and any ice accretion on the protected surfaces appropriate to normal ice 

protection system operation, between 400 feet and the height at which the 

transition to the en route configuration and speed is completed, or 1,500 

feet above the takeoff surface, whichever is higher, assuming accretion 

starts at the end of the takeoff distance in the takeoff maximum icing 

conditions of part 25, Appendix C, part I(c).

A.2.2.3 The final takeoff ice accretion includes the takeoff ice accretion since 

these flight segments are contiguous and sequential. For both flight path 

segments, ice begins accreting at the end of the takeoff distance. The 

reference to a height of 400 feet above the takeoff surface in these 

definitions is only used to separate the two takeoff segments. It does not 

mean that ice accreted before reaching 400 feet above the takeoff surface 

may be ignored when determining the final takeoff ice accretion.

A.2.2.4 The takeoff ice and final takeoff ice accretions for Appendix O are the 

same as those for Appendix C, except that the icing conditions are defined 

in part 25, Appendix O, part I.
10/27/14 AC 25-25A

Appendix A

A-5

A.2.3 Ice Accretion Before Activation and Effective System Operation.

A.2.3.1 When considering the ice accretion before the ice protection system has 

been activated and is performing its intended function, you should take 

into account the means of activating the ice protection system and the 

system response time. However, if artificial stall warning is provided and 

the point at which stall warning is initiated changes when the ice 

protection system is activated, then the pre-activation ice accretion used to 

evaluate the “clean” stall warning schedule does not need to include 

consideration of the ice protection system response time. System response 

time is defined as the time interval between activation of the system and 

its effective operation (for example, for a thermal ice protection system 

used for deicing, the time to heat the surface and perform its deicing 

function). If activation of the ice protection system depends on flightcrew 

recognition of icing conditions or response to a cockpit annunciation, 

appropriate delays in identifying the icing conditions and activating the ice 

protection system should be taken into account. For the icing conditions of 

Appendix C, the airplane should be assumed to be in continuous 

maximum icing conditions during the time between entering the icing 

conditions and effective operation of the ice protection system.

A.2.3.2 Section 25.1419(e) requires one of the following three methods for 

detecting icing and activating the airframe ice protection system:

A.2.3.2.1 A primary ice detection system that automatically activates or that alerts 

the flightcrew to activate the airframe ice protection system.

A.2.3.2.2 A definition of visual cues for recognition of the first sign of ice accretion 

on a specified surface combined with an advisory ice detection system that 

alerts the flightcrew to activate the airframe ice protection system.

A.2.3.2.3 Identification of conditions conducive to airframe icing as defined by an 

appropriate static or total air temperature and visible moisture for use by 

the flightcrew to activate the airframe ice protection system.

A.2.3.3 The following guidance should be used to determine the ice accretion on 

the unprotected and protected aerodynamic surfaces before activation and 

normal system operation of the ice protection system:

A.2.3.3.1 If the ice protection system activates automatically after annunciation 

from a primary ice detection system, the assumed ice accretion should take 

into account the time it takes for automatic activation of the ice protection 

system and the time it takes the system to perform its intended function. 

The assumed ice accretion can be determined as follows: (1) the ice 

accreted on the protected surfaces during the time between entry into the 

icing conditions and activation of the system, plus (2) the ice accreted

during the system response time.
10/27/14 AC 25-25A

Appendix A

A-6

A.2.3.3.2 If ice protection system activation depends on pilot action following 

annunciation from a primary ice detection system, the assumed ice 

accretion should include flightcrew delays in activating the ice protection 

system and the time it takes the system to perform its intended function. 

The assumed ice accretion should be determined as follows: (1) the ice 

accreted during the time between entry into the icing conditions and 

annunciation from the primary ice detection system, plus (2) the ice 

accreted during 10 additional seconds of operation in icing conditions, 

plus (3) the ice accreted during the system response time.

A.2.3.3.3 If ice protection system activation depends on the flightcrew visually 

recognizing the first indication of ice accretion on a reference surface (for 

example, an ice accretion probe) combined with an advisory ice detection 

system, the assumed ice accretion should take into account flightcrew 

delays in detecting the accreted ice and in activating the ice protection 

system, and the time it takes for the system to perform its intended 

function. This may be determined as follows: (1) the ice accretion on the 

aerodynamic surfaces corresponding to the ice accretion on the reference 

surface that would be easily recognizable by the flightcrew under all 

foreseeable conditions (for example, at night in clouds), plus (2) the ice 

accreted during 30 additional seconds of operation in icing conditions, 

plus (3) the ice accreted during the system response time.

A.2.3.3.4 If ice protection system activation depends on pilot identification of icing 

conditions (as defined by an appropriate static or total air temperature in 

combination with visible moisture conditions) with or without an advisory 

ice detector, the assumed ice accretion should take into account flightcrew 

delays in recognizing the presence of icing conditions and flightcrew 

delays in activating the ice protection system, and the time it takes for the 

system to perform its intended function. This may be determined as 

follows: (1) the ice accreted during 30 seconds of operation in icing 

conditions, plus (2) the ice accreted during the system response time.

A.3 Ice Accreted During Ice Protection System Failure.

A.3.1 Unprotected Parts.

The same accretion as in paragraph A.2 of this appendix is applicable.

A.3.2 Protected Parts Following System Failure.

The assumed ice accretion for failures of the ice protection system is defined as follows:

A.3.2.1 If the failure condition is not annunciated, the ice accretion on normally 

protected parts where the ice protection system has failed should be 

assumed to be the same as the accretion specified for unprotected parts.

A.3.2.2 If the failure condition is annunciated and the associated AFM procedure 

does not require the airplane to exit icing conditions, the ice accretion on 
10/27/14 AC 25-25A

Appendix A

A-7

normally protected parts where the ice protection system has failed should 

be assumed to be the same as the accretion specified for unprotected parts.

A.3.2.3 If the failure condition is annunciated and the associated AFM procedure 

requires the airplane to exit icing conditions as soon as possible, the ice 

accretion on normally protected parts where the ice protection has failed 

should be assumed to be one-half of the accretion specified for 

unprotected parts unless another value is agreed to by the responsible 

ACO.

A.4 Additional Guidance for Appendix O Ice Accretions.

A.4.1 Ice Accretion in Appendix O Conditions before those Conditions have been Detected by 

the Flightcrew.

A.4.1.1 This ice accretion, defined as pre-detection ice in Appendix O, part 

II(b)(5), refers to the ice accretion existing at the time the flightcrew 

becomes aware that they are in Appendix O icing conditions and have 

taken action to begin exiting from all icing conditions.

A.4.1.2 Both direct entry into Appendix O icing conditions and entry into 

Appendix O icing conditions from flight in Appendix C icing conditions 

should be considered.

A.4.1.3 The time that the applicant should assume it will take to detect Appendix 

O icing conditions exceeding those for which the airplane is certified 

should be based on the means of detection. AC 25-28 provides guidance 

for certifying the detection means. In general, we expect that the time to 

detect exceedance icing conditions may be significantly longer for a

detection means relying on the flightcrew seeing and recognizing a visual 

icing cue than it is for an ice detection system that provides an attentiongetting alert to the flightcrew.

A.4.1.4 Visual detection requires time for accumulation on the reference surface(s) 

of enough ice to be reliably identified by either pilot in all atmospheric 

and lighting conditions. Time between pilot scans of reference surface(s) 

should be included.

A.4.1.4.1 The amount of ice needed for reliable identification is a function of the

distinguishing characteristics of the ice (for example, size, shape, contrast 

compared to the surface feature that it is adhered to), the distance from the 

pilots (for example, windshield vs. engine vs. wingtip), and the relative 

viewing angle (location with respect to the pilots’ primary fields of view).

A.4.1.4.2 Pilot scan time of the reference surface(s) will be influenced by many 

factors. Such factors include phase of flight, workload, frequency of 

occurrence of Appendix O conditions, pilot awareness of the possibility of 
10/27/14 AC 25-25A

Appendix A

A-8

SLD conditions, and ease of seeing the reference surface(s). The 

infrequency of Appendix O conditions (approximately 1 in 100 to 1 in 

1000, on average in all worldwide icing encounters) and the high 

workload associated with some phases of flight in instrument conditions 

(for example, approach and landing) justify using a conservative estimate 

for the time between pilot scans.

A.4.1.4.3 In the absence of specific studies or tests validating visual detection times, 

the following times should be used for visual detection of exceedance 

icing conditions following accumulation of enough ice to be reliably 

identified by either pilot in all atmospheric and lighting conditions: (1) 

three minutes for a visual reference located on or immediately outside a 

cockpit window (for example, ice accretions on side windows, windshield 

wipers, or icing probe near the windows), and (2) Five minutes for a visual 

reference located on a wing, wing-mounted engine, or wing tip.

A.4.2 Ice Accretions for Encounters with Appendix O Conditions Beyond those in Which the 

Airplane is Certified to Operate.

A.4.2.1 Use the ice accretions in table A-1 below, to evaluate compliance with the 

applicable subpart B requirements for operating safely after encountering 

Appendix O atmospheric icing conditions for which the airplane is not 

approved, and then safely exiting all icing conditions.

A.4.2.2 These ice accretions apply when the airplane is not certified for flight in 

any portion of Appendix O atmospheric icing conditions, when the 

airplane is certified for flight in only a portion of Appendix O conditions, 

and for any flight phase for which the airplane is not certified for flight 

throughout the Appendix O icing envelope.

A.4.2.3 Table A-1 shows the scenarios to be used for determining ice accretions 

for certification testing of encounters with Appendix O conditions beyond 

those in which the airplane is certified to operate (for detecting and exiting 

those conditions).

Table A-1. Appendix O Detect-and-Exit Ice Accretions per Flight Phase

Flight Phase/

Condition Appendix O Detect-and-Exit Ice Accretion

Ground Roll No accretion

Takeoff No accretiona

Final Takeoff No accretiona
10/27/14 AC 25-25A

Appendix A

A-9

Flight Phase/

Condition Appendix O Detect-and-Exit Ice Accretion

En Route En Route Detect-and-Exit Ice

Combination of—

(1) Either Appendix C en route ice or Appendix O en route ice for which 

the airplane is approved, whichever is applicable,

(2) Pre-detection ice,

(3) Accretion from one standard cloud horizontal extent (17.4 nautical 

miles) in Appendix O conditions for which the airplane is not approved, 

and

(4) Accretion from one standard cloud horizontal extent (17.4 nautical 

miles) in Appendix C continuous maximum icing conditions.

Holding Holding Detect-and-Exit Ice

Combination of—

(1) Either Appendix C holding ice or Appendix O holding ice for which 

the airplane is approved, whichever is applicable,

(2) Pre-detection ice,

(3) Accretion from one standard cloud horizontal extent (17.4 nautical 

miles) in Appendix O conditions for which the airplane is not approved, 

and

(4) Accretion from one standard cloud horizontal extent (17.4 nautical 

miles) in Appendix C continuous maximum icing conditions.

The total time in icing conditions need not exceed 45 minutes.

Approach Approach Detect-and-Exit Ice

The more critical of holding detect-and-exit ice and the combination of—

(1) Ice accreted during a descent in the cruise configuration from the 

maximum vertical extent of the Appendix C maximum continuous icing 

conditions or the Appendix O icing environment for which the airplane is 

approved, whichever is applicable, to 2,000 feet above the landing 

surface, where transition to the approach configuration is made,

(2) Pre-detection ice, and

(3) Ice accreted at 2,000 feet above the landing surface while transiting 

one standard cloud horizontal extent (17.4 nautical miles) in Appendix O 

conditions for which the airplane is not approved and one standard cloud 

horizontal extent (17.4 nautical miles) in Appendix C continuous 

maximum icing conditions.
10/27/14 AC 25-25A

Appendix A

A-10

Flight Phase/

Condition Appendix O Detect-and-Exit Ice Accretion

Landing Landing Detect-and-Exit Ice

The more critical of holding detect-and-exit ice and the combination of—

(1) Either Appendix C or Appendix O approach and landing ice for which 

the airplane is approved, whichever is applicable,

(2) Pre-detection ice, and

(3) Ice accreted during an exit maneuver beginning with the minimum 

climb gradient specified in § 25.119 from a height of 200 feet above the 

landing surface and transiting through one standard cloud horizontal 

extent (17.4 nautical miles) in Appendix O conditions for which the 

airplane is not approved, and one standard cloud horizontal extent (17.4 

nautical miles) in Appendix C continuous maximum icing conditions.

For the purposes of defining the landing detect-and-exit ice shape, the 

Appendix C approach and landing ice is defined as the ice accreted 

during—

• A descent in the cruise configuration from the maximum vertical 

extent of the Appendix C maximum continuous icing environment 

to 2,000 feet above the landing surface,

• A transition to the approach configuration and maneuvering for 15 

minutes at 2,000 feet above the landing surface, and

• A descent from 2,000 feet to 200 feet above the landing surface 

with a transition to the landing configuration.

Ice Accretion 

Before the Ice 

Protection 

System Has Been 

Activated and is 

Performing its 

Intended 

Function

Ice accreted on protected and unprotected surfaces during the time it takes 

for icing conditions (either Appendix C or Appendix O) to be detected, 

the ice protection system to be activated, and the ice protection system to 

become fully effective in performing its intended function. (Note: If 

artificial stall warning is provided and the initiation point of that warning 

changes when the ice protection system is activated, this ice accretion 

does not need to include consideration of the time it takes for the ice 

protection system to be effective in performing its intended function.)
10/27/14 AC 25-25A

Appendix A

A-11

Flight Phase/

Condition Appendix O Detect-and-Exit Ice Accretion

Ice Accretion in 

Appendix O 

Conditions 

Before Those 

Conditions Have 

Been Detected by 

the Flightcrew 

and Actions 

Taken, in 

Accordance With 

the AFM, to 

Either Exit All 

Icing Conditions 

or Continue 

Flight in 

Appendix O Icing 

Conditions

Ice accreted on protected and unprotected surfaces during—

• The time it takes to detect and identify Appendix O conditions 

(based on the method of detection) beyond those in which the 

airplane is certified to operate, and

• The time it takes the flightcrew to refer to and act on procedures, 

including coordinating with Air Traffic Control, to exit all icing 

conditions.

A minimum time period of two minutes should be used as the time 

needed for the flightcrew to refer to and act on the procedures to exit all

icing conditions after the Appendix O icing conditions are recognized.

Failures of the Ice 

Protection 

System

No accretionb

a Intentional flight, including takeoff, is not permitted into Appendix O conditions beyond those 

in which the airplane is certified to operate.

b It is not necessary to consider an unintentional encounter with Appendix O icing conditions 

beyond those for which the airplane is certified to operate while operating with a failed ice 

protection system.

A.4.3 Ice Accretions for Encounters with Appendix O Atmospheric Icing Conditions in 

Which the Airplane is Certified to Operate.

A.4.3.1 The applicant should use the ice accretions in table A-2 to evaluate 

compliance with the applicable subpart B requirements for operating 

safely in the Appendix O atmospheric icing conditions for which the 

airplane is approved.

A.4.3.2 The decision about which ice accretions to use should include 

consideration of combinations of Appendix C and Appendix O icing 

conditions within the scenarios defined in paragraph A.4.3.3 of this 

appendix. For example, flight in Appendix O conditions may result in ice 

accumulating, and potentially forming a ridge, behind a protected surface. 

Once this accretion site has been established, flight in Appendix C icing 
10/27/14 AC 25-25A

Appendix A

A-12

conditions for the remaining portion of the applicable flight phase scenario 

may result in a more critical additional accretion than would occur for 

continued flight in Appendix O icing conditions.

A.4.3.3 Table A-2 shows the scenarios the applicant should use for determining 

ice accretions for certification for flight in the icing conditions of part 25, 

Appendix O.

Table A-2. Appendix O Ice Accretion per Flight Phase

Flight Phase/Condition Appendix O Ice Accretion

Ground Roll No accretion

Takeoff Takeoff Ice

Ice accretion occurring between the end of the takeoff 

distance and 400 feet above the takeoff surface assuming ice 

accretion starts at the end of the takeoff distance.

Final Takeoff Final Takeoff Ice

Ice accretion occurring between a height of 400 feet above 

the takeoff surface and the height at which the transition to 

the en route configuration and speed is completed, or 1500 

feet above the takeoff surface, whichever is higher, 

assuming ice accretion starts at the end of the takeoff 

distance.

En Route En Route Ice

Ice accreted during the en route phase of flight.

Holding Holding Ice

Ice accreted during a 45 minute hold with no reduction for 

horizontal cloud extent (that is, the hold is conducted 

entirely within the 17.4 nautical mile standard cloud extent).
10/27/14 AC 25-25A

Appendix A

A-13

Flight Phase/Condition Appendix O Ice Accretion

Approach Approach Ice

More critical ice accretion of—

(1) Ice accreted during a descent in the cruise configuration 

from the maximum vertical extent of the Appendix O icing 

environment to 2,000 feet above the landing surface, 

followed by—

• Transition to the approach configuration, and

• Maneuvering for 15 minutes at 2,000 feet above the 

landing surface; and

(2) Holding ice (if the airplane is certified for holding in 

Appendix O conditions).

Landing Landing Ice

More critical ice accretion of—

(1) Approach ice plus ice accreted during descent from 

2,000 feet above the landing surface to 200 feet above the 

landing surface with—

• A transition to the landing configuration, followed by 

• A go-around maneuver beginning with the minimum 

climb gradient specified in § 25.119 from 200 feet to 

2,000 feet above the landing surface,

• Holding for 15 minutes at 2,000 feet above the 

landing surface in the approach configuration, and

• A descent to the landing surface in the landing 

configuration; and

(2) Holding ice (if the airplane is certified for holding in 

Appendix O conditions).

Ice Accretion Before the Ice 

Protection System has been 

Activated and is Performing its 

Intended Function

Ice accreted during the time it takes for the flightcrew to 

recognize icing conditions and activate the ice protection 

system, plus the time for the ice protection system to 

perform its intended function.
10/27/14 AC 25-25A

Appendix A

A-14

Flight Phase/Condition Appendix O Ice Accretion

Ice Accretion in Appendix O 

Conditions Before those 

Conditions have been Detected 

by the Flightcrew and Actions 

Taken, in Accordance With the 

AFM, to Either Exit All Icing 

Conditions or Continue Flight in 

Appendix O Icing Conditions

Ice accreted during the time it takes for the flightcrew to 

detect Appendix O conditions and refer to and initiate 

associated procedures, and any time it takes for systems to 

perform their intended functions (if applicable). Predetection ice need not be considered if there are no specific 

crew actions or systems changes associated with flight in 

Appendix O conditions.

Failures of the Ice Protection 

System

Same criteria as for Appendix C (see paragraph A.3 of this 

appendix), but in Appendix O conditions.
10/27/14 AC 25-25A

Appendix B

B-1

APPENDIX B. SIMULATED ICE ACCRETIONS

B.1 Overview.

B.1.1 In general, the simulated ice accretions used for flight testing should be those that have 

the most adverse effects on handling characteristics. However, if analytical data show 

that other reasonably expected ice accretions could be generated that could have a more 

adverse effect on performance, then the ice accretion having the most adverse effect on 

handling characteristics may be used for performance tests only if each difference in 

performance can be conservatively taken into account.

B.1.2 Simulated accretions should be representative of natural icing conditions in terms of 

location, general shape, thickness, and texture. The determination of the form and 

surface texture of the ice accretion (see paragraph B.2 below) should be agreed to by the 

responsible ACO as being representative of natural ice accretion.

B.1.3 Sandpaper ice is addressed in paragraph B.3 below.

B.2 Shape and Texture of Simulated Ice Accretion.

B.2.1 The shape and texture of the simulated ice accretion should be established and 

substantiated by agreed-upon methods. Common practices used to accomplish this 

include—

• Use of computer codes,

• Flight in measured natural icing conditions,

• Icing wind tunnel tests, and

• Flight in a controlled simulated icing cloud (for example, from an icing tanker).

B.2.2 Unless another texture is substantiated by the applicant and agreed to by the ACO, the 

applicant should use an ice accretion roughness height of 3 mm with a particle density 

of 8 to 10/cm2.

B.3 Sandpaper Ice.

B.3.1 Sandpaper ice is the most critical thin, rough layer of ice. Carborundum sandpaper 

No. 40 (40-grit carborundum sandpaper) has been used in past certification programs to 

represent sandpaper ice. However, as detailed in Appendix R of AC 20-73A, the 

uniformly distributed roughness of carborundum grit may not result in aerodynamic 

effects similar to those of the actual intercycle ice surface roughness. The applicant 

should validate use of uniformly distributed roughness to simulate sandpaper ice, 

particularly for intercycle ice accretions.
10/27/14 AC 25-25A

Appendix B

B-2

B.3.2 Because sandpaper ice must be considered in the basic icing certification within the 

Appendix C environmental icing envelope, it does not need to be considered for 

certification of flight in Appendix O icing conditions.

B.3.3 The spanwise and chordwise coverage of simulated ice should be consistent with the 

areas of ice accretion determined for the conditions of part 25, Appendix C, except that, 

for the zero-g pushover maneuver of paragraph 4.9.4.3.3 of this AC, the sandpaper ice 

may be restricted to the horizontal stabilizer if this can be shown to be conservative.

B.3.4 Appendix C, part II(a) requires applicants to use the most critical ice accretion to show 

compliance with the applicable subpart B airplane requirements for performance and 

handling characteristics in icing conditions. When determining the most critical ice 

accretion, the applicant must consider the full range of atmospheric icing conditions of 

Appendix C, part I, as well as the characteristics of the ice protection system, in 

accordance with § 25.21(g)(2) and Appendix C, part II(a). This would include 

consideration of sandpaper ice (as well as any other type of ice accretion that may occur 

in the applicable atmospheric icing conditions), taking into account the operating 

characteristics of the ice protection system and the flight phase. Sandpaper ice can be

particularly critical for showing compliance with either § 25.143(i)(2) or (j)(2). If 

sandpaper ice can be present, it must be considered in showing compliance with both of 

these requirements.
10/27/14 AC 25-25A

Appendix C

C-1

APPENDIX C. DESIGN FEATURES

C.1 Airplane Configuration and Ancestry.

An airplane’s size is an important design characteristic that can affect performance, 

controllability, and maneuverability in icing conditions. The safety record of the 

airplane’s closely related ancestors is another aspect that may be taken into 

consideration.

C.1.1 Size.

The size of an airplane determines the sensitivity of its flight characteristics to ice 

thickness and roughness. The relative effect of a given ice height (or ice roughness 

height) decreases as airplane size increases.

C.1.2 Ancestors.

If a closely related ancestor airplane was certified for flight in icing conditions, that 

airplane’s safety record may be used on a similarity basis when evaluating the subject 

airplane’s general capabilities for flight in icing conditions.

C.2 Wing.

Design features of a wing that can affect performance, controllability, and 

maneuverability include airfoil type, leading edge devices, and lateral control system 

effectiveness.

C.2.1 Airfoil Type.

Aerodynamic effects of ice accretions result mainly from the effects of the ice accretion 

on the behavior of the airfoil’s boundary layer. The boundary layer is the layer of air 

close to the surface of the airfoil that is moving across the airfoil at a velocity lower 

than the freestream velocity, that is, the velocity of the airfoil. Ice accretions that occur 

in areas favorable to keeping the boundary layer attached to the aircraft surface will 

result in effects that are less aerodynamically adverse than ice accretions that occur in 

areas less favorable to attached boundary layer conditions. Ice shapes that build up in 

areas of local airflow deceleration (positively increasing surface pressure), or result in 

conditions unfavorable to keeping attached flow conditions, as the airflow negotiates 

the ice surface, will result in the most adverse effects.

C.2.2 Leading Edge Devices.

The presence of a leading edge device (such as a slat) reduces the percentage decrease 

in the maximum lift coefficient (CLMAX) due to ice by increasing the overall level of the 

lift coefficient (CL). Movement of a slat so that a gap forms may improve the situation 

further. Leading edge devices can also reduce loss in angle-of-attack at stall due to ice.
10/27/14 AC 25-25A

Appendix C

C-2

C.2.3 Lateral Control System Effectiveness.

The applicant can evaluate effectiveness of the lateral control system in icing conditions 

by comparing it with the lateral control system in closely related ancestor airplanes, 

with consideration of the design of aerodynamic balance surfaces.

C.3 Empennage.

The effects of size and airfoil type also apply to the horizontal and vertical tails. Other 

design features include tailplane design philosophy, horizontal stabilizer design, control 

surface actuation, control surface size, and vertical stabilizer and rudder design. Since 

tails are usually not equipped with leading edge devices, the effects of ice on tail 

aerodynamics are similar to those on a wing with no leading edge devices. However, 

these effects usually result in changes to airplane handling and/or control characteristics 

rather than degraded performance.

C.3.1 Tailplane Design Philosophy.

The tailplane may be designed and sized to provide full functionality in icing conditions 

without ice protection, or it may be designed with a deicing or anti-icing system.

C.3.2 Horizontal Stabilizer Design.

Cambered airfoils and/or trimmable stabilizers may reduce the susceptibility to and 

consequences of elevator hinge moment reversal due to ice-induced tailplane stall.

C.3.3 Control Surface Actuation.

Hydraulically powered irreversible elevator controls are usually not affected by 

ice-induced aerodynamic hinge moment reversal.

C.3.4 Control Surface Size.

For mechanical elevator controls, the size of the surface significantly affects the control 

force resulting from an ice-induced aerodynamic hinge moment reversal. Small surfaces 

are less susceptible to control difficulties for given hinge moment coefficients.

C.3.5 Vertical Stabilizer and Rudder Design.

Effectiveness of the vertical stabilizer and rudder in icing conditions can be evaluated 

by comparison with the vertical stabilizer and rudder in closely related ancestor 

airplanes, with consideration of the design of aerodynamic balance surfaces.

C.4 Aerodynamic Balancing of Flight Control Surfaces.

C.4.1 The aerodynamic balance of unpowered or boosted reversible flight control surfaces is 

an important design feature to consider. The applicant should carefully evaluate the 

design to account for effects of ice accretion on flight control system hinge moment 

characteristics. Closely balanced controls may be vulnerable to overbalance in icing. 

The effect of ice in front of the control surface, or on the surface, may upset the balance 

of hinge moments, leading to either increased positive or negative force gradients.
10/27/14 AC 25-25A

Appendix C

C-3

C.4.2 The aerodynamic balancing of unpowered or boosted reversible flight control surfaces 

is particularly important with respect to lateral flight control systems when large aileron 

hinge moments are balanced by equally large hinge moments on the opposite aileron. 

Any asymmetric disturbance in flow that affects this critical balance can lead to a 

sudden uncommanded deflection of the control. This auto deflection, in extreme cases, 

may be to the control stops.

C.5 Ice Protection/Detection System.

The ice protection/detection system design philosophy may include design features that 

reduce ice accretion on the wing and/or tailplane.

C.5.1 Wing Ice Protection/Detection.

C.5.1.1 A primary ice detection system that automatically activates a wing deicing 

system may ensure that there is no significant ice accretion on wings that 

are susceptible to performance losses with small amounts of ice.

C.5.1.2 If portions of the wing leading edge are not protected, the part that is 

protected may be selected to provide good handling characteristics at stall, 

with an acceptable performance degradation.

C.5.2 Tail Ice Protection/Detection.

C.5.2.1 A primary ice detection system may automatically activate a tailplane 

deicing system on airplanes that do not have visible cues for system 

operation.

C.5.2.2 An ice protection system on the unshielded aerodynamic balances of 

airplanes with unpowered reversible controls can reduce the risk of iceinduced aerodynamic hinge moment reversals.
10/27/14 AC 25-25A

Appendix D

D-1

APPENDIX D. EXAMPLES OF AIRPLANE FLIGHT MANUAL LIMITATIONS AND 

OPERATING PROCEDURES FOR OPERATIONS IN SUPERCOOLED LARGE DROP ICING

CONDITIONS

D.1 Airplane Approved for Flight in Appendix C Icing Conditions but not Approved 

for Flight in Appendix O Icing Conditions.

D.1.1 AFM Limitations.

Intentional flight, including takeoff and landing, into supercooled large drop (SLD) 

icing conditions, which includes freezing drizzle or freezing rain, is prohibited. If 

freezing drizzle or freezing rain conditions are encountered, or if {placeholder for 

applicant to insert description of pilot cues here}, immediately request priority handling 

from air traffic control to facilitate a route or altitude change to exit all icing conditions. 

Stay clear of all icing conditions for the remainder of the flight, including landing, 

unless it can be determined that ice accretions no longer remain on the airframe.

D.1.2 AFM Operating Procedures (Normal Procedures Section).

Supercooled large drop (SLD) icing conditions, including freezing drizzle and freezing 

rain conditions, are severe icing conditions for this airplane. Intentional flight, including 

takeoff and landing, into SLD icing conditions is prohibited. A flight delay or diversion 

to an alternate airport is required if these conditions exist at the departure or destination 

airports.

{Placeholder for applicant to insert description of pilot cues here} is one indication of 

severe icing for this airplane. If severe icing is encountered, immediately request 

priority handling from air traffic control to facilitate a route or altitude change to exit all 

icing conditions. Stay clear of all icing conditions for the remainder of the flight, 

including landing, unless it can be determined that ice accretions no longer remain on 

the airframe.

D.1.3 Flightcrew Operating Manual Operating Procedures.

Warning: Hazardous icing effects may result from environmental conditions outside of 

those for which this airplane is certified. Flight into unapproved icing conditions may 

result in ice build-up on protected surfaces exceeding the capability of the ice protection 

system, or in ice forming aft of the protected surfaces. This ice might not be shed when 

using the ice protection systems, and may seriously degrade performance and 

controllability of the airplane.

Operations in icing conditions were evaluated as part of the certification process for this 

airplane. Supercooled large drop (SLD) icing conditions, including freezing drizzle and 

freezing rain, were not evaluated and are considered severe icing conditions for this 

airplane.

Intentional flight, including takeoff and landing, into SLD icing conditions, including 

freezing drizzle or freezing rain, is prohibited. A flight delay or diversion to an alternate 

airport is required if these conditions exist at the departure or destination airports. 

{Placeholder for applicant to insert description of pilot cues here} is an indication of 
10/27/14 AC 25-25A

Appendix D

D-2

severe icing conditions that exceed those for which this airplane is certified. If severe 

icing is encountered, immediately request priority handling from air traffic control to 

facilitate a route or altitude change to exit all icing conditions. Stay clear of all icing 

conditions for the remainder of the flight, including landing, unless it can be determined 

that ice accretions no longer remain on the airframe.

D.2 Airplane Approved for Flight in Appendix C Icing Conditions and Freezing 

Drizzle Conditions of Appendix O but not Approved for Flight in Freezing Rain 

Conditions of Appendix O.

D.2.1 AFM Limitations.

Intentional flight, including takeoff and landing, into freezing rain conditions is 

prohibited. If freezing rain conditions are encountered, or if {placeholder for applicant 

to insert description of pilot cues here}, immediately request priority handling from air 

traffic control to facilitate a route or altitude change to exit all icing conditions. Stay 

clear of all icing conditions for the remainder of the flight, including landing, unless it 

can be determined that ice accretions no longer remain on the airframe.

D.2.2 AFM Operating Procedures (Normal Procedures Section).

Freezing rain conditions are severe icing conditions for this airplane. Intentional flight, 

including takeoff and landing, into freezing rain conditions is prohibited. A flight delay 

or diversion to an alternate airport is required if these conditions exist at the departure 

or destination airports.

{Placeholder for applicant to insert description of pilot cues here} is one indication of 

severe icing for this airplane. If severe icing is encountered, immediately request 

priority handling from air traffic control to facilitate a route or altitude change to exit all 

icing conditions. Stay clear of all icing conditions for the remainder of the flight, 

including landing, unless it can be determined that ice accretions no longer remain on 

the airframe.

D.2.3 Flightcrew Operating Manual Operating Procedures.

Warning: Hazardous icing effects may result from environmental conditions outside of 

those for which this airplane is certified. Flight into unapproved icing conditions may 

result in ice build-up on protected surfaces exceeding the capability of the ice protection 

system, or may result in ice forming aft of the protected surfaces. This ice might not be

shed when using the ice protection systems, and may seriously degrade the performance 

and controllability of the airplane.

Operations in icing conditions, including freezing drizzle, were evaluated as part of the 

certification process for this airplane. Freezing rain conditions were not evaluated and 

are considered severe icing conditions for this airplane.

Intentional flight, including takeoff and landing, into freezing rain conditions is 

prohibited. A flight delay or diversion to an alternate airport is required if these 

conditions exist at the departure or destination airports. {Placeholder for applicant to 

insert description of pilot cues here} is an indication of severe icing conditions that 
10/27/14 AC 25-25A

Appendix D

D-3

exceed those for which this airplane is certified. If severe icing is encountered, 

immediately request priority handling from air traffic control to facilitate a route or 

altitude change to exit all icing conditions. Stay clear of all icing conditions for the 

remainder of the flight, including landing, unless it can be determined that ice 

accretions no longer remain on the airframe.

D.3 Airplane Approved for Flight in Appendix C and Appendix O Icing Conditions 

Except for En Route and Holding Flight Phases in Appendix O Icing Conditions.

D.3.1 AFM Limitations.

Intentional holding or en route flight into supercooled large drop (SLD) icing 

conditions, including freezing drizzle or freezing rain, is prohibited. If SLD icing 

conditions, including freezing drizzle or freezing rain, are encountered during a hold (in 

any airplane configuration) or in the en route phase of flight (climb, cruise, or descent 

with high lift devices and gear retracted), or if {placeholder for applicant to insert 

description of pilot cues here} is present, immediately request priority handling from air 

traffic control to facilitate a route or altitude change to exit all icing conditions. Stay 

clear of all icing conditions for the remainder of the flight, including landing, unless it 

can be determined that ice accretions no longer remain on the airframe.

D.3.2 AFM Operating Procedures (Normal Procedures Section).

Supercooled large drop (SLD) icing conditions, including freezing drizzle and freezing 

rain, encountered during a hold (in any airplane configuration) or in the en route phase 

of flight (climb, cruise, or descent with high lift devices and gear retracted) are severe 

icing conditions for this airplane. Intentional holding or en route flight in SLD icing 

conditions, including freezing drizzle or freezing rain, is prohibited.

{Placeholder for applicant to insert description of pilot cues here} is one indication of 

severe icing for this airplane. If severe icing is encountered, immediately request 

priority handling from air traffic control to facilitate a route or altitude change to exit all 

icing conditions. Stay clear of all icing conditions for the remainder of the flight, 

including landing, unless it can be determined that ice accretions no longer remain on 

the airframe.

D.3.3 Flightcrew Operating Manual Operating Procedures.

Warning: Hazardous icing effects may result from environmental conditions outside of 

those for which this airplane is certified. Flight into unapproved icing conditions may 

result in ice build-up on protected surfaces exceeding the capability of the ice protection 

system, or in ice forming aft of the protected surfaces. This ice might not be shed when 

using the ice protection systems, and may seriously degrade the performance and 

controllability of the airplane.

Operations in icing conditions were evaluated as part of the certification process for this 

airplane. En route (climb, cruise, and descent with high left devices and gear retracted) 

and holding flight (in any airplane configuration) in supercooled large drop (SLD) icing 
10/27/14 AC 25-25A

Appendix D

D-4

conditions, including freezing drizzle and freezing rain, were not evaluated and are 

considered severe icing conditions for this airplane.

Intentional holding or en route flight in SLD icing conditions, including freezing drizzle 

or freezing rain, is prohibited. {Placeholder for applicant to insert description of pilot 

cues here} is an indication of severe icing conditions that exceed those for which the 

airplane is certified. If severe icing is encountered, immediately request priority 

handling from air traffic control to facilitate a route or altitude change to exit all icing 

conditions. Stay clear of all icing conditions for the remainder of the flight, including 

landing, unless it can be determined that ice accretions no longer remain on the 

airframe.

D.4 Airplane Approved for Flight in Appendix C Icing Conditions and a Portion of 

Appendix O Icing Conditions.

D.4.1 AFM Limitations.

Intentional flight, including takeoff and landing, into {Placeholder for applicant to 

insert pilot usable description here} conditions is prohibited. If {insert pilot usable 

description here} conditions are encountered, or if {insert cue description here}, 

immediately request priority handling from air traffic control to facilitate a route or 

altitude change to exit all icing conditions. Stay clear of all icing conditions for the 

remainder of the flight, including landing, unless it can be determined that ice 

accretions no longer remain on the airframe.

D.4.2 AFM Operating Procedures (Normal Procedures Section).

{Placeholder for applicant to insert description for pilots to use here} are severe icing 

conditions for this airplane. Intentional flight, including takeoff and landing, into {insert 

pilot usable description here} conditions is prohibited. A flight delay or diversion to an 

alternate airport is required if these conditions exist at the departure or destination 

airports.

{Placeholder for applicant to insert description of pilot cues here} is one indication of 

severe icing for this airplane. If severe icing is encountered, immediately request 

priority handling from air traffic control to facilitate a route or altitude change to exit all 

icing conditions. Stay clear of all icing conditions for the remainder of the flight, 

including landing, unless it can be determined that ice accretions no longer remain on 

the airframe.

D.4.3 Flightcrew Operating Manual Operating Procedures.

Warning: Hazardous icing effects may result from environmental conditions outside of 

those for which this airplane is certified. Flight into unapproved icing conditions may 

result in ice build-up on protected surfaces exceeding the capability of the ice protection 

system, or may result in ice forming aft of the protected surfaces. This ice might not be

shed when using the ice protection systems, and may seriously degrade the performance 

and controllability of the airplane.
10/27/14 AC 25-25A

Appendix D

D-5

Operations in icing conditions were evaluated as part of the certification process for this 

airplane. {Placeholder for applicant to insert description for pilots to use here} were 

not evaluated and are considered severe icing conditions for this airplane.

Intentional flight, including takeoff and landing, into {Placeholder for applicant to 

insert description for pilots to use here} is prohibited. A flight delay or diversion to an 

alternate airport is required if these conditions exist at the departure or destination 

airports. {Placeholder for applicant to insert description of pilot cues here} is an 

indication of severe icing conditions that exceed those for which this airplane is 

certified. If severe icing is encountered, immediately request priority handling from air 

traffic control to facilitate a route or altitude change to exit all icing conditions. Remain 

clear of all icing conditions for the remainder of the flight, including landing, unless it 

can be determined that ice accretions no longer remain on the airframe.
10/27/14 AC 25-25A

Appendix E

E-1

APPENDIX E. RELATED REGULATIONS AND ADVISORY CIRCULARS

E.1 Regulations.

The following sections of Title 14, Code of Federal Regulations (14 CFR) part 25 are 

referenced in this AC. The full text of these regulations can be downloaded from the

U.S. Government Printing Office e-CFR. A paper copy may be ordered from the 

Government Printing Office, Superintendent of Documents, Attn: New Orders, PO Box 

371954, Pittsburgh, PA, 15250-7954.

Table E-1. Related Regulations

14 CFR Title

§ 25.21 Proof of compliance

§ 25.23 Load distribution limits

§ 25.25 Weight limits

§ 25.27 Center of gravity limits

§ 25.29 Empty weight and corresponding center of gravity

§ 25.31 Removable ballast

§ 25.33 Propeller speed and pitch limits

§ 25.101 Performance—General

§ 25.103 Stall speed

§ 25.105 Takeoff

§ 25.107 Takeoff speeds

§ 25.109 Accelerate-stop distance

§ 25.111 Takeoff path

§ 25.119 Landing climb: All-engines-operating

§ 25.121 Climb: One-engine-inoperative

§ 25.123 En route flight paths
10/27/14 AC 25-25A

Appendix E

E-2

14 CFR Title

§ 25.125 Landing

§ 25.143 Controllability and Maneuverability—General

§ 25.145 Longitudinal control

§ 25.147 Directional and lateral control

§ 25.161 Trim

§ 25.171 Stability—General

§ 25.175 Demonstration of static longitudinal stability

§ 25.177 Static lateral-directional stability

§ 25.181 Dynamic stability

§ 25.201 Stall demonstration

§ 25.203 Stall characteristics

§ 25.207 Stall warning

§ 25.231 Longitudinal stability and control

§ 25.233 Directional stability and control

§ 25.235 Taxiing condition

§ 25.237 Wind velocities

§ 25.251 Vibration and buffeting

§ 25.253 High-speed characteristics

§ 25.255 Out-of-trim characteristics

§ 25.1309 Equipment, systems, and installations

§ 25.1329 Flight guidance system

§ 25.1419 Ice protection

§ 25.1420 Supercooled large drop icing conditions

§ 25.1581 Airplane Flight Manual—General
10/27/14 AC 25-25A

Appendix E

E-3

14 CFR Title

§ 25.1583 Operating limitations

§ 25.1585 Operating procedures

§ 25.1587 Performance information

Part 25, Appendix C

Part 25, Appendix O Supercooled Large Drop Icing Conditions

E.2 Advisory Circulars.

The following ACs are related to the guidance in this AC. Table E-2 identifies the latest 

version of each AC at the time of publication. If any AC is revised after publication of 

this AC, you should refer to the latest version for guidance. You can find the latest 

version at the FAA website.

Table E-2. Related Advisory Circulars

Number Title Date

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

AC 25-7C Flight Test Guide for Certification of 

Transport Category Airplanes

October 16, 2012

AC 25.1309-1A System Design and Analysis June 21, 1988

AC 25.1329-1C Approval of Flight Guidance Systems October 27, 2014

AC 25.1419-2 Compliance with the Ice Protection 

Requirements of §§ 25.1419(e), (f), (g), 

and (h)

October 27, 2009

AC 25-28 Compliance of Transport Category 

Airplanes with Certification Requirements 

for Flight in Icing Conditions

October 27, 2014
10/27/14 AC 25-25A

Appendix F

F-1

APPENDIX F. ACRONYMS

Table F-1. Acronyms, Terms, and Definitions

Acronym/Term Definition

AC Advisory Circular

ACO Aircraft Certification Office

AFM Airplane Flight Manual

ATTCS Automatic Takeoff Thrust Control System

CAS Calibrated Airspeed

CFR Code of Federal Regulations

FAA Federal Aviation Administration

ICTS Ice-Contaminated Tailplane Stall

KIAS Knots Indicated Airspeed

LWC Liquid Water Content

MED Mean Effective Diameter

MVD Median Volume Diameter

CL Lift Coefficient

CLMAX Maximum Lift Coefficient

SLD Supercooled Large Drop

Trim A flight condition in which the aerodynamic moment acting 

about the axis of interest is zero. In the absence of an 

external disturbance, no control input is needed to maintain 

the flight condition.
10/27/14 AC 25-25A

Appendix F

F-2

Acronym/Term Definition

V1 The maximum speed in the takeoff at which the pilot must 

take the first action (for example, apply brakes, reduce 

thrust, deploy speed brakes) to stop the airplane within the 

accelerate-stop distance. V1 also means the minimum speed 

in the takeoff, following a failure of the critical engine at 

VEF, at which the pilot can continue the takeoff and achieve 

the required height above the takeoff surface within the 

takeoff distance.

V2 Takeoff Safety Speed. (The target speed to be reached by 

the time the airplane is 35 feet above the takeoff surface.)

V2MIN Minimum Takeoff Safety Speed

VCW Crosswind Component of Wind Speed

VDF/MDF Demonstrated Flight Diving Speed

VEF Engine Failure Speed. The speed at which the critical 

engine is assumed to fail during takeoff.

VFC Maximum Speed for Stability Characteristics

VFE Maximum Flaps Extended Speed

VMO Maximum Operating Limit Speed

VREF Landing Reference Speed

VS 1-g 1-g Stall Speed. The calibrated airspeed at which 

aerodynamic forces alone can support the airplane in 1-g 

flight.

VSR Reference Stall Speed. VSR may not be less than VS 1-g. For 

airplanes with a device that abruptly pushes the nose down 

at a selected angle of attack (for example, a stick pusher), 

VSR may not be less than 2 knots or 2 percent, whichever is 

greater, above the speed at which the device operates.

VSR1 Reference Stall Speed in a Specific Configuration
Advisory Circular Feedback 

If you find an error in this AC, have recommendations for improving it, or have suggestions for 

new items/subjects to be added, you may let us know by (1) emailing this form to 9-AWA-AVSAIR500-Coord@faa.gov or (2) faxing it to the attention of the Aircraft Certification Service 

Directives Management Officer at (202) 267-3983. 

Subject: Date: 

Please check all appropriate line items: 

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