Subject: CERTIFICATION OF TRANSPORT 

CATEGORY AIRPLANES FOR FLIGHT IN 

ICING CONDITIONS

Date: 5/7/04 

Initiated By: ANM-112 

AC No: 25.1419-1A

Change: 

1. PURPOSE. This advisory circular (AC) provides guidance for certification of airframe ice 

protection systems on transport category airplanes. While this is the primary focus of this AC, 

the guidance also supplements similar guidance provided in other AC’s concerning icing 

requirements for other parts of the airplane. 

2. APPLICABILITY. 

a. The guidance provided in this document is directed to airplane manufacturers, 

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

airplane type certification engineers and their designees. 

b. This material is neither mandatory nor regulatory in nature and does not constitute a 

regulation. It describes acceptable means, but not the only means, for demonstrating compliance 

with the applicable regulations. The FAA will consider other methods of demonstrating 

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. On the other hand, if 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. 

c. This material does not change, create any additional, authorize changes in, or permit 

deviations from, regulatory requirements. 

3. CANCELLATION. Advisory Circular 25.1419-1, dated 8/18/99, is canceled. 

4. ICING REQUIREMENTS. The guidance provided herein applies to the approval of the 

installation and operation of ice protection systems in the icing environment defined in 14 CFR 

part 25, Appendix C. If certification for flight in icing conditions is desired, the airplane must be 

able to safely operate throughout the icing envelope of Appendix C. Section 25.1419 sets forth 

the specific airframe requirements for demonstrating compliance with the icing conditions 

defined in Appendix C. Additionally, for other parts of the airplane (i.e., engine, engine inlet, 

propeller) there are more specific icing requirements and associated guidance defined in the 
AC 25.1419-1A 5/7/04 

ii 

referenced regulations and advisory circulars listed in paragraph 3 below. Some of the icingrelated regulations must be complied with, even if the airplane is not certificated for flight in 

icing (e.g., §§ 25.629(d)(3), 25.903, 25.975, 25.1093, 25.1323(e), and 25.1325(b)). This AC 

contains limited information on flight tests for icing certification; additional information may be 

found in Advisory Circular 25-7A, referenced in paragraph 3 of this AC. The guidance provided 

in this AC is applicable to new Type Certificates (TC's), Supplemental Type Certificates 

(STC's), and amendments to existing TC's for airplanes certified under Part 4b of the Civil 

Aviation Regulations (CAR) and Part 25, for which approval under the provisions of § 25.1419 

is desired. 

5. RELATED REGULATIONS AND DOCUMENTS. 

 a. Regulations. 

 § 25.629 - Aeroelastic stability requirements 

 § 25.773(b)(1)(ii) - Pilot compartment view 

 § 25.903 - Engines

 § 25.929 - Propeller deicing 

 § 25.975 - Fuel tank vents and carburetor vapor vents 

 § 25.1093 - Induction system icing protection 

 § 25.1323(e) - Airspeed indicating system 

 § 25.1325(b) - Static pressure systems 

 § 25.1326 - Pitot heat indication system 

 § 25.1403 - Wing icing detection lights 

 § 25.1585(a)(6) - Operating procedures 

 § 33.68 - Induction system icing 

 § 33.77 - Foreign object ingestion 

 § 33.78 - Rain and hail ingestion 

 b. Advisory Circulars. The AC's listed below may be obtained from the U.S. Department 

of Transportation, Subsequent Distribution Office, M-30, Ardmore East Business Center, 3341 Q 

75th Avenue, Landover, MD 20795: 

 AC 20-73 Aircraft Ice Protection, dated 4/21/71. 

 AC 25-7A Flight Test Guide for Certification of Transport Category 

 Airplanes, dated 3/31/98. 

 AC 25-11 Transport Category Airplane Electronic Display Systems, 

dated July 16, 1987 

 AC 25.629-1A Flutter Substantiation of Transport Category Airplanes, 

 dated 7/23/98. 
5/7/04 AC 25.1419-1A 

 iii 

 AC 25.1309-1A System Design Analysis, dated 6/21/88. 

 AC 20-117A Hazards Following Ground Deicing and Ground 

 Operations in Conditions Conducive to Aircraft 

 Icing, dated 12/17/82. 

 AC 20-115B Radio Technical Commission for Aeronautics, Inc. (RTCA) 

 Document RTCA/DO-178B, dated 1/11/93. 

 AC 120-42A Extended Range Operation with Two-Engine Airplanes 

(ETOPS), dated 12/30/88 

Note: AC 25-7A is available from the Superintendent of Documents, U.S. Government Printing 

Office, Washington D.C. 20402 (stock number 050-007-01214-4; $33.00). 

6. RELATED READING MATERIAL. 

 a. RTCA/DO-178B, “Software Considerations in Airborne Systems and Equipment 

Certification,” published December 1, 1992, provides an acceptable means of compliance for 

software used in airborne systems and equipment. This document may be obtained from the 

RTCA Inc., 1140 Connecticut Avenue NW., Suite 1020, Washington, D.C. 20036. 

 b. FAA Technical Report DOT/FAA/CT-88/8-1, "Aircraft Icing Handbook" published 

March 1991, updated September 1993, includes reference material on ground and airborne icing 

facilities, simulation procedures, and analytical techniques. This document represents all types 

and classes of aircraft and is intended as a working tool for the designer and analyst of ice 

protection systems. 

 c. FAA Technical Report ADS-4, “Engineering Summary of Airframe Icing Technical 

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

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

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

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

More usable information is now available through recent research and experience and is included 

in the Aircraft Icing Handbook referenced in paragraph b. above. 

Note: The FAA technical reports listed above can be obtained from the National Technical 

Information Service (NTIS), Department of Commerce, 5285 Port Royal Road, Springfield, 

Virginia 22161. 
AC 25.1419-1A 5/7/04 

iv 

 d. RTCA/DO160D, “Environmental Conditions and Test Procedures for Airborne 

Equipment.” This document may be obtained from the RTCA Inc., 1140 Connecticut Avenue 

NW., Suite 1020, Washington, D.C. 20036. 

/s/ Ali Bahrami 

Acting Manager, Transport Airplane Directorate 

Aircraft Certification Service 
5/7/04 AC 25.1419-1A 

 v 

Contents

Paragraph Page

1. BACKGROUND..........................................................................................................1 

 a. Civil Air Regulations (CAR)..................................................................................1 

 b. Part 25.....................................................................................................................2 

2. CERTIFICATION PLAN ............................................................................................3 

3. ANALYSIS ..................................................................................................................4 

 a. Analysis of Areas and Components to be Protected ..............................................4 

 b. The 45-Minute Hold Condition..............................................................................5 

 c. Flutter Analysis ......................................................................................................6 

 d. Power Sources ........................................................................................................6 

 e. Failure Analysis......................................................................................................6 

 f. Similarity Analysis .................................................................................................6 

 g. Impingement Limit Analysis..................................................................................7 

4. DRY AIR GROUND TESTS.......................................................................................7 

5. FLIGHT TEST PLANNING........................................................................................7 

6. COMPLIANCE TESTS (Flight/Simulation) ...............................................................8 

 a. Three Typical Stages of Icing Flight Tests............................................................8 

 b. Dry Air Flight Tests with Ice Protection Equipment Operating............................8 

 (1) Hot Air Thermal Anti-ice (TAI) Leading Edge Systems...............................8 

 (2) Hot Air Thermal Deice Leading Edge Systems .............................................9 

 (3) Pneumatic Leading Edge Boots .....................................................................9 

 (4) Electrically Heated Propeller Boots ...............................................................9 

 (5) Windshield Anti-Ice .....................................................................................10 

 (6) Pitot-Static and Static Pressure Sources.......................................................10 

 (7) Compressor Bleed Air Systems....................................................................10 

 c. Dry air Flight Tests with Predicted Artificial Ice Shapes....................................10 

 d. Icing Flight Tests ...............................................................................................12 

 (1) Instrumentation.............................................................................................12 

 (2) Simulated Icing ............................................................................................13 

 (3) Natural Icing ...............................................................................................13 

 (4) Fluid Anti-Ice/Deice Systems ......................................................................14 

 e. Performance and Handling Qualities ...................................................................15 

 f. Pneumatic Deicer Boots.......................................................................................15 

 g. Emergency and Abnormal Operating Conditions................................................15 
AC 25.1419-1A 5/7/04 

vi 

 h. Ice Detector System (Primary and Advisory)......................................................15 

7. PERFORM INTENDED FUNCTION IN ICING......................................................16 

 a. Engines and Equipment .......................................................................................16 

 b. Engine Alternate Induction Air Sources..............................................................16 

 c. Fuel System Venting ...........................................................................................16 

 d. Landing Gear ...............................................................................................16 

 e. Stall Warning ...............................................................................................16 

 f. Ice Detection Cues ...............................................................................................16 

 g. Primary and Secondary Flight Control Surfaces .................................................16 

 h. Ram Air Turbine ...............................................................................................16 

 i. Pilot Compartment View .....................................................................................17 

8. ICE DETECTION LIGHT(S) ....................................................................................17 

9. ICE-CONTAMINATED TAILPLANE STALL (ICTS) ...........................................17 

10. CAUTION INFORMATION.....................................................................................18 

11. ICE SHEDDING ...............................................................................................18 

12. AIRPLANE FLIGHT MANUAL ..............................................................................19 

 a. Operating Limitations Section .............................................................................19 

 b. Operating Procedures Section..............................................................................20 

c. Performance Information Section........................................................................20 

d. Airworthiness Directives for Severe Icing Conditions........................................20 
5/7/04 AC 25.1419-1A 

 1 

1. BACKGROUND. 

 a. Civil Air Regulations (CAR). 

 (1) Prior to 1953, airplanes were certificated under Part 04 of the CAR. Section 

04.5814 required that if deicer boots were installed, then positive means must be provided for the 

deflation of all wing boots. There were no other references to an airplane ice protection system 

in Part 04. 

 (2) Part 4b of the CAR was codified on December 31, 1953. The requirement for 

positive means of deflating deicer boots was incorporated, without change, in § 4b.640. Section 

4b.640 stated that, “When an ice protection system is installed, it shall be of an approved type. If 

pneumatic boots are used, at least two independent sources of power and a positive means for the 

deflation of the boots shall be provided.” Section 4b.351(b)(ii) provided requirements for pilot 

compartment vision in icing conditions. Section 4b.406 provided propeller-deicing 

requirements. Section 4b.461 provided induction system deicing and anti-icing requirements. 

Section 4b.612(a)(5) required that the airspeed indicating system be provided with a heated pitot 

tube or equivalent means of preventing malfunctioning due to icing. 

 (3) Amendment 4b-2, effective August 25, 1955, introduced icing envelopes similar to 

the current Appendix C to part 25. The graphs added by Amendment 4b-2 (4b-24a, 4b-24b, 4b24c, 4b-25a, 4b-25b, and 4b-25c) were identical in substance and format to the current Appendix 

C envelopes with a few exceptions. These envelopes described the liquid water content, the 

mean effective diameter of droplets, the temperature, and horizontal and vertical extent of the 

supercooled icing cloud environment. In the figures introduced by Amendment 4b-2, the units 

of the distances shown on the graphs were expressed in statute miles instead of nautical miles. 

The Liquid Water Content (LWC), however, is identical between the Amendment 4b-2 figures 

and the current Appendix C envelopes, if the correction for the difference in value between 

nautical and statute miles is made. There are two significant differences between the 

Amendment 4b-2 envelopes and the current Appendix C. The minimum mean effective diameter 

in the intermittent maximum conditions was 20 microns versus the current 15 microns, and the 

LWC/distance factor was 1.5 statute miles versus the current 0.26 nautical miles (0.3 statute 

miles). 

 (4) Amendment 4b-6, effective August 12, 1957, revised the icing envelopes to the 

current requirements and revised § 4b.461, “Induction system de-icing and anti-icing 

provisions.” The preamble to the amendment states, “There are included herein changes which 

extend the currently effective provisions governing intermittent maximum icing conditions so as 

to cover conditions which might be critical insofar as the turbine engine induction system is 

concerned. In this regard, the data are being extended in accordance with NACA Technical Note 

2738 and involve a revision of Figure 4b-25a to cover drop diameters as small as 15 microns and 

a revision of Figure 4b-25c to cover distances down to 0.3 mile. The icing conditions prescribed 

in the currently effective regulations are applicable in the main to the airframe. The changes 
AC 25.1419-1A 5/7/04 

2 

being made in section 4b.461 require the turbine powerplant to be subjected to the same icing 

conditions and require that the induction system be protected to prevent serious engine power 

loss. A similar requirement is incorporated with respect to certification of turbine engines by an 

amendment to Part 13 which is being made concurrently with this amendment.” 

 b. Part 25. 

 (1) Part 4b of the CAR was recodified into part 25, effective February 1, 1965. After 

recodification, with minor editorial changes the content of § 4b.640, Ice protection, became 

§ 25.1419; § 4b.406, Propeller deicing provisions, became § 25.929; § 4b.612(a)(5), Airspeed 

indicating systems, became § 25.1323(e); § 4b.351(b)(1)(ii), Pilot compartment view, became 

§ 25.773(b)(1)(ii). The § 4b.351 reference to the most severe icing conditions for which 

approval of the airplane is desired was changed in part 25 to reference the icing conditions 

specified in § 25.1419. Section 4b.461, Induction system deicing and anti-icing provisions, 

became § 25.1093. 

 (2) Amendment 25-5, effective July 29, 1965, revised § 25.1325(b) to require that the 

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

pressure is not changed when the airplane is exposed to the continuous and intermittent 

maximum icing conditions defined in Appendix C. 

 (3) Amendment 25-11, effective June 4, 1967, revised § 25.1585 to require that the 

Airplane Flight Manual include information on the use of ice protection equipment. 

 (4) Amendment 25-23, effective May 8, 1970, revised § 25.1419 to require that the 

effectiveness of the ice protection system and its components be shown by flight tests of the 

airplane or its components in measured natural atmospheric icing conditions. Previous to this 

amendment, flight tests in natural icing conditions were considered as one means of compliance 

but were not mandatory. Amendment 25-23 also revised § 25.1309 to include additional 

requirements for certificating equipment, systems, and installations. The regulation was revised 

to require a comprehensive systematic failure analysis, supported by appropriate test, to ensure 

that the safety objectives of the probability of occurrence decrease as the hazard of a failure 

increases. 

 (5) Amendment 25-38, effective February 1, 1977, added § 25.1403 to require a means 

for illuminating or otherwise determining the formation of ice on the parts of the wings that are 

critical from the standpoint of ice accumulation. The requirement is not applicable if the 

operating limitations prohibit operations at night in known or forecast icing conditions. 

 (6) Amendment 25-43, effective April 12, 1978, added § 25.1326 to require the 

installation of a pitot heat indication system on airplanes equipped with flight instrument pitot 

heating systems. 
5/7/04 AC 25.1419-1A 

 3 

 (7) Amendment 25-46, effective December 1, 1978, added § 25.1416 to require 

specific standards for pneumatic deicer boots. 

 (8) Amendment 25-72, effective July 20, 1990, transferred § 25.1416 to § 25.1419 for 

clarification and editorial improvement. In addition, the contents of § 25.1416(c), which 

required a means to indicate to the flightcrew that the pneumatic deicing boot system is receiving 

adequate pressure and is functioning normally, were revised to allow the use of the “dark 

cockpit” concept (i.e., a warning when failure occurs rather than continual pilot monitoring of a 

healthy system). 

2. CERTIFICATION PLAN. At the start of the design and development effort, the applicant 

should submit a certification plan to the cognizant FAA Aircraft Certification Office (ACO) for 

approval. The certification plan should include the following basic information: 

 a. A general airplane description that includes dimensions, airworthiness limitations, and 

other data that may be relevant to certification of ice protection systems. 

 b. Ice protection systems description. 

 c. A compliance checklist that addresses each section of part 25 applicable to the product. 

 d. Identification of the certification methods for each applicable section of part 25, 

including a description of analyses and tests, or references to similarity of designs, that the 

applicant intends for certification of the ice protection system. These methods of showing 

compliance should be agreed upon between the applicant and the FAA early in the certification 

program prior to conducting certification tests. 

 e. A failure hazard assessment to determine the criticality of the system. 

 f. If the ice protection or detection systems contain software, software plans, as described 

in RTCA DO-178B (or another acceptable means of compliance for software). 

 g. Projected schedules of design, analyses, testing, and reporting. 

 h. A list of any anomalous 14 CFR part 33 icing certification test results, if completed, that 

will require special operating procedures. 

 i. If the ice protection or detection systems contain complex electronic hardware (such as 

programmable logic devices (PLD) or application specific integrated circuits (ASIC)), plans for 

providing a level of design assurance of these devices commensurate with their potential 

contribution to aircraft hazards and system failures, which could result from electronic hardware 

faults or malfunctions. 
AC 25.1419-1A 5/7/04 

4 

3. ANALYSES. The applicant should prepare analyses to substantiate decisions involving the 

application of selected ice protection equipment. Such analyses should clearly state the basic 

protection required and the assumptions made, and delineate the methods of analysis used. All 

analyses should be validated either by tests or have been validated by the applicant on previous 

programs. This substantiation should include a discussion and rationale of the assumptions made 

in the analyses. To utilize a previously validated methodology, the applicant should substantiate 

that the methodology is applicable to the new program. The following is a list of analyses 

typically performed during an icing certification program: 

 a. Analysis of Areas and Components to be Protected. The applicant should examine those 

areas listed below to determine the degree of protection required: 

 (1) Leading edges of wings, winglets, and wing struts; horizontal and vertical 

stabilizer; canards; and other lifting surfaces. 

 (2) Leading edges of control surface balance areas, if not shielded. 

 (3) Accessory cooling air intakes that face the airstream and/or could otherwise 

become restricted due to ice accretion. 

 (4) Antennas and masts. 

 (5) External tanks. 

 (6) External hinges, tracks, door handles, and entry steps. 

 (7) Instruments including pitot tube (and mast), static and dynamic ports, angle-ofattack sensor, and stall warning. 

 (8)) Forward fuselage nose cone and radome. 

 (9) Windshields. 

 (10) Landing gear. 

 (11) Retractable forward landing lights. 

 (12) Ram air turbines. 

 (13) Ice detection lights, if required for compliance with § 25.1403. 

 (14) Vortex generators installed on lifting surfaces and the fuselage, and stall 

improvement devices such as strips, vortilons, and fences. 
5/7/04 AC 25.1419-1A 

 5 

 (15) Any structure that extends into the free stream such as cameras, camera mounts, 

and video equipment. 

Note 1: Ice protection of fuel tank vents, propellers, and engine inlet cowls is addressed by part 

25, subpart E – Powerplant. 

Note 2: An applicant may determine that protection is not required for one or more of these 

areas or components. If so, the applicant should include supporting data and rationale in the 

analyses for allowing those areas or components to go unprotected. The applicant should show 

that the lack of protection does not adversely affect the handling characteristics or performance 

of the airplane. Section 25.1419(b) of part 25 at amendment level 25-72 requires certain flight 

testing. However, flight test data from previous certification programs may be used as an 

integral part of a complete data package used for establishing compliance with 25.1419(b) if it 

can be shown that the flight test data is applicable to the airplane in question. This would 

generally require a similarity analysis. If a similarity analysis is used, the guidelines of 

paragraph 3(f) of this AC are applicable. If there is uncertainty about the effects of the lack of 

protection, or the similarity analysis, the manufacturer should conduct flight test demonstrations. 

 b. The 45-Minute Hold Condition. Ice shapes resulting from a 45-minute hold condition 

should be considered when developing critical ice shapes for which the overall performance and 

handling characteristics of the airplane are to be analyzed. The airplane's tolerance to continuous 

ice accumulation on the unprotected surfaces should be evaluated in accordance with the 

information provided in AC 20-73. The applicant should determine the effect of the 45-minute 

hold in continuous maximum icing conditions. It should be assumed that the airplane will 

remain 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. The applicant should 

substantiate the critical mean effective drop diameter, LWC, and temperature that result in the 

formation of an ice shape that is critical to the airplane’s performance and handling qualities. 

The critical ice shapes derived from this 45-minute hold analysis should be compared to critical 

shapes derived from other analyses (i.e., for climb, cruise, and descent) to establish the most 

critical artificial ice shapes to be used during dry air flight tests. Not only is the thickness 

important, but the shape, location, and texture may contribute to adverse aerodynamic 

characteristics. 

Note: The 45-minute hold condition will result in large ice shapes on the unprotected surfaces 

that, from visual assessment alone, would appear to have a drastic effect on airplane performance 

and handling characteristics. Operational history and wind tunnel tests have shown that the ice 

that forms on the protected and unprotected surfaces before activation and normal operation of 

the ice protection system may also have a detrimental effect on the lift and pitching moment 

characteristics of the wing and horizontal tail airfoils. Similarly, for airplanes with cyclic ice 

protection systems, the ice that accretes on the protected surfaces between cycles may have more 

than an insignificant contribution to the total effect of ice on the airplane performance and 

handling characteristics, when combined with the 45-minute holding ice accretion on the 

unprotected surfaces. 
AC 25.1419-1A 5/7/04 

6 

 c. Flutter Analysis. Advisory Circular (AC) 25.629-1A, “Flutter Substantiation of 

Transport Category Airplanes,” provides guidance for showing compliance with § 25.629. 

Section 25.629(d)(3) requires the consideration of inadvertent encounters with icing for airplanes 

not certificated for flight in icing conditions. 

 d. Power Sources. The applicant should evaluate the power sources in the ice protection 

system design (e.g., electrical, bleed air, and pneumatic sources). An electrical load analysis or 

test should be conducted on each power source to determine that it is adequate to supply the ice 

protection system plus all other essential electrical loads throughout the airplane flight envelope 

under conditions requiring operation of the ice protection system. The effect of an ice protection 

system component failure on power availability to other essential loads should be evaluated in 

accordance with § 25.1309. All power sources that affect engine or engine ice protection 

systems for multiengine airplanes must comply with the engine isolation requirements of 

§ 25.903(b). 

 e. Failure Analysis. Advisory Circular (AC) 25.1309-1A, “System Design Analysis,” 

provides guidance for demonstrating compliance with the requirements of § 25.1309. 

Substantiation of the hazard classification of ice protection system failure conditions is typically 

accomplished through analyses and/or testing. The failure analysis should include the potential 

contribution of complex electronic hardware faults and malfunctions to system failure 

conditions, and classify the hardware assurance level appropriately. 

 f. Similarity Analyses. 

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

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

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

in the areas of physical, functional, thermodynamic, pneumatic, aerodynamic, and environmental 

exposure. Analyses should be conducted to show that the component installation, operation, and 

the effect on the airplane’s performance and handling are equivalent to that of the previously 

approved configuration. 

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

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

consider differences affecting the airplane and the system. If there is uncertainty about the 

effects of the differences, additional tests and/or analyses should be conducted as necessary and 

appropriate to resolve the open issues. 

 (3) Engineering judgment should be used to determine if the ice protection system 

should be retested in measured natural icing conditions. The differences in the ice protection 

systems should be evaluated for their effect on the functionality of the ice protection systems and 

on safe flight in icing. If there is uncertainty about the effects of the differences, flight tests in 

measured natural icing conditions should be accomplished. 
5/7/04 AC 25.1419-1A 

 7 

Note: The applicant must possess all the data to substantiate compliance with applicable 

regulations, including the data from past certifications on which the similarity analysis is based. 

 g. Impingement Limit Analyses. The applicant should prepare a droplet trajectory and 

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

surfaces that may require icing protection. This analysis should consider the various airplane 

operational configurations and the associated angles of attack. The analysis should establish the 

upper and lower aft droplet impingement limits that can then be used to establish the aft ice 

formation limit and the ice protection coverage needed. 

4. DRY AIR GROUND TESTS. Depending upon the details of the ice protection system 

design details, some preliminary ground tests of the equipment may be warranted to verify the 

basic function of each item. Quantitative data may be obtained, as necessary, to verify the 

system designs. These data include operating temperatures of thermal devices, deicing fluid 

flow rates and flow patterns for deicing liquid devices, and operating pressures and rates of 

inflation of pneumatic components. 

5. FLIGHT TEST PLANNING. When operating any airplane in an icing environment, 

degradation in performance and flying qualities may be expected. The primary purposes for 

flight testing an airplane equipped for flight in icing conditions is to evaluate such degradation, 

and to determine that the flying qualities remain adequate and that performance levels are 

acceptable for this flight environment. 

In accordance with part 33, engine icing certification results should also be carefully reviewed 

prior to any part 25 engine or airframe icing flight tests in order to determine if there were any 

anomalous results that will require special airplane/engine operating procedures. The flight tests 

and analyses of flight tests should: 

 a. Demonstrate normal operation of the airplane with the ice protection system installed in 

non-icing flight. 

 b. Demonstrate the ability of the airplane to operate safely with critical in-flight ice shapes. 

The icing conditions specified in part 25, Appendix C, are used to determine these ice shapes. 

 c. Verify the analytical predictions that the ice protection system will perform its intended 

function throughout the icing envelope defined in Appendix C. 

 d. Verify the adequacy of the flightcrew procedures and limitations for the use of the ice 

protection system in normal, abnormal, and emergency conditions. 

 e. Demonstrate operation of the airplane in icing conditions with failed ice protection 

systems, which may include asymmetric icing. 
AC 25.1419-1A 5/7/04 

8 

 f. Confirm that the powerplant installation as a whole (engine, inlet, anti-ice system, etc.) 

performs satisfactorily while in icing conditions. In addition, the APU should be evaluated for 

performance in icing conditions if it performs essential functions. 

6. COMPLIANCE TESTS (Flight/Simulation). The following paragraphs address the major 

flight tests normally performed to show compliance with the requirement of § 25.1419 that the 

airplane must be able to safely operate in the continuous maximum and intermittent maximum 

icing conditions described in Appendix C to part 25. The airplane should be shown to comply 

with the certification requirements when all ice protection systems are installed and functioning. 

This can normally be accomplished by performing tests at those conditions found to be most 

critical to basic airplane aerodynamics, ice protection system design, and powerplant functions. 

All anti-ice and deice equipment should perform its intended function throughout the entire 

operating envelope. 

 a. Three Typical Stages of Icing Flight Tests: 

 (1) Dry air flight tests with ice protection equipment operating; 

 (2) Dry air flight tests with predicted artificial ice shapes installed; and 

 (3) Natural icing flight tests. 

 b. Dry Air Flight Tests with Ice Protection Equipment Operating. Initial dry air flight tests 

are usually the first steps conducted to evaluate the airplane with the ice protection system 

operating. The initial dry air tests are conducted to verify that the ice protection system does not 

affect the flying qualities of the airplane in clear air and to obtain a thermal profile of an 

operating thermal ice protection system. Several commonly used ice protection systems and 

components are discussed below to illustrate typical dry air flight test practices. Other types of 

equipment should be evaluated as their specific design dictates. 

 (1) Hot Air Thermal Anti-ice (TAI) Leading Edge Systems. Dry air flight tests are 

conducted to verify the system design parameters and thermal performance analyses. 

 (a) Normally, the system components are instrumented to measure the anti-icing 

mass flow rate, supply air temperature, and the surface temperatures. The dry air test plan 

generally includes the airplane operating conditions such as climb, holding, and descent phases 

of a normal flight profile. Since the presence of moisture can affect the surface temperatures, the 

tests should be conducted where the humidity is low. 

 (b) The measurements of anti-icing mass flow rate and supply air temperature 

allow the determination of heat available to the system. The adequacy of the ice protection 

system then can be demonstrated through a comparison of the measured data to the theoretical 

analysis over the entire Appendix C icing envelope. The surface temperatures measured in the 

dry air, for example, can be useful in extrapolating the maximum possible leading edge surface 
5/7/04 AC 25.1419-1A 

 9 

temperature in-flight, the heat transfer characteristics of the system, and the thermal energy 

available for the ice protection system. The supply air temperatures also may be used to verify 

that the materials of the ice protection system were appropriately chosen for the thermal 

environment. 

 (2) Hot Air Thermal Deice Leading Edge Systems. Normally the TAI system is 

designed and certified as an anti-icing system. Some airplane manufacturers may recommend 

that the system be operated as a deice system. The leading edge of the airplane airfoils are 

deiced once the pilot has detected icing through a visual cue or the deicing is initiated either 

automatically or manually after an ice detection system has sensed the presence of ice. The same 

type of testing described in paragraph (1) above should be considered for this type of system. 

 (3) Pneumatic Leading Edge Boots. Tests should demonstrate a rise and decrease in 

operating pressures, which results in the effective removal of ice. This pressure rise time, as 

well as the maximum operating pressure for each boot, should be evaluated throughout the 

altitude band defined in Appendix C (i.e., mean sea level (MSL) to 22,000 feet above MSL). 

Boots should be operated in flight at the minimum envelope temperature (-22 o

F) of Appendix C, 

to demonstrate adequate performance throughout the entire flight envelope and to demonstrate 

that no damage occurs during inflation and deflation. The appropriate speed and temperature 

limitation (if any) on boot activation should be included in the Airplane Flight Manual (AFM). 

The inflation of the boots should have no hazardous effect on airplane performance and handling 

qualities. 

 (4) Electrically Heated Propeller Boots. For compliance with the provisions of 

§§ 25.901(c), 25.903(b), 25.929, and 25.1419(c): 

 (a) When flight testing in dry air, the following system parameters should be 

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

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

ensure that adequate power is applied to the deicers. Surface temperature measurements should 

be made during dry air tests. These surface temperature measurements are useful for correlating 

analytically predicted dry air temperatures with actual temperatures, and as a general indicator 

that the system is functioning and that each deicer is heating. 

 (b) The system operation should be checked throughout the full r.p.m. and 

propeller cyclic pitch range expected during flight in icing. Any significant vibrations should be 

investigated. 

 (c) Consideration should be given to the maximum temperatures that a composite 

propeller blade may be subjected to when the deicers are energized. It may be useful to monitor 

deicer bond-side temperatures. When performing this evaluation, the most critical conditions 

should be investigated (e.g., airplane on the ground; propellers non-rotating) on a hot day with 

the system inadvertently energized. 
AC 25.1419-1A 5/7/04 

10 

 (5) Windshield Anti-Ice. Section 25.773(b)(ii) requires that the airplane must have a 

means to maintain a clear portion of the windshield in icing conditions specified in § 25.1419, if 

certification with ice protection provisions is requested. Dry air flight tests should be conducted 

to verify the thermal analysis. Both inner and outer windshield surface temperature 

measurements of the protected area may be needed to verify the thermal analysis. Thermal 

analysis should substantiate that the windshield surface temperature is sufficient to maintain antiicing capability without causing structural damage to the windshield. An evaluation of the 

visibility, including distortion effects through the protected area, should be made for both day 

and night operations. In addition, the size and location of the protected area should be reviewed 

for adequate visibility, especially during the approach and landing phases of flight. 

 (6) Pitot-Static and Static Pressure Sources. Section 25.1323(e) requires a heated pitot 

tube or an equivalent means of preventing malfunction due to icing for each airspeed indicating 

system; § 25.1325(b) requires that static pressure ports be designed and located such that the 

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

pressure is not affected when the airplane encounters icing conditions defined in Appendix C; 

and § 25.1326 requires an indication system be provided to indicate to the flightcrew when a 

pitot heating system is not operating. An acceptable indication system may consist of separate 

lights or crew alert indication on an electronic display for each pitot source. Additional guidance 

on an acceptable means of compliance with § 25.1326 is provided in AC 25-11. Component 

surface temperature evaluations should be performed to verify thermal analyses. 

 (7) Compressor Bleed Air Systems. The effects of any bleed air extraction on engine 

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

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

climb, cruise, hold, and descent. Temperature measurements may be necessary to verify the 

thermal analyses. In accordance with the provisions of § 25.939(a), the effects of the maximum 

bleed air for ice protection should have no detrimental effect on engine operation throughout the 

engine’s power range. 

 c. Dry Air Flight Tests with Predicted Artificial Ice Shapes. The installation of artificial 

ice shapes on the test airplane allows airplane performance and handling characteristics to be 

evaluated in stable dry air conditions with the critical ice shape remaining a constant (i.e., no 

change of ice accretion due to erosion, shedding, sublimation, etc., as can occur with natural ice 

shapes). Dry air flight tests with artificial ice shapes installed also result in a considerable 

reduction in the amount of flight testing that would otherwise be required to accumulate the test 

ice shapes in natural icing conditions and then evaluate their effects on airplane performance and 

handling characteristics in stable air. 

 (1) The shape and texture of artificial ice shapes should be developed and substantiated 

using methods found acceptable to the FAA. Common practices include: use of computer codes 

for droplet impingement limits and ice shape predictions, flight in measured natural icing 

conditions, icing wind tunnel tests, and flight in a measured controlled simulated icing cloud 

(e.g., behind an icing tanker). These methods should be conservative and should address the 
5/7/04 AC 25.1419-1A 

 11 

conditions associated with the icing envelope of part 25, Appendix C, that are critical to the 

airplane's performance and handling qualities. It is not intended that natural icing flight tests 

validate all aspects of predicted ice shapes. Flight testing should be conducted in measured 

natural icing conditions (within the part 25, Appendix C icing envelope) to corroborate the 

general physical characteristics and location of the artificial ice shapes, and, in particular, their 

effect on airplane handling characteristics. 

Note: The 45-minute hold condition will result in large ice shapes on the unprotected surfaces 

that, from visual assessment alone, would appear to have a drastic effect on airplane performance 

and handling characteristics. Operational history and wind tunnel tests have shown that the ice 

that forms on the protected and unprotected surfaces before activation and normal operation of 

the ice protection system may also have a detrimental effect on the lift and pitching moment 

characteristics of the wing and horizontal tail airfoils. Similarly, for airplanes with cyclic ice 

protection systems, the ice that accretes on the protected surfaces between cycles may have more 

than an insignificant contribution to the total effect of ice on the airplane performance and 

handling characteristics, when combined with the 45-minute holding ice accretion on the 

unprotected surfaces. 

 (2) The effects of the ice shapes on stall speeds and airplane climb performance should 

be determined. Stall warning margins and maneuvering capability should also be evaluated. 

Operating speeds, stall warning speeds, and AFM performance information should be adjusted, if 

necessary, to provide adequate performance capability and stall warning margins. The 

determination of the effects of ice on airplane performance should include the decrease of engine 

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

general, the effects on any system that utilizes bleed air should be determined. This information 

should appear in the AFM. 

 (3) Handling characteristics should be investigated to determine that an acceptable 

level of safety exists. The results of these tests may be used in preparing specific AFM operating 

procedures and limitations for flight in icing conditions. 

 (4) The effects on pitot-static, pressure sources, stall warning, and angle-of-attack 

sensors may need to be confirmed by dry air testing with shapes installed at critical locations that 

are not protected from ice accumulation. It should be confirmed that any ice formed on the 

airframe in the vicinity of the sensors does not adversely affect the sensor’s operation. 

Note: Effects on the sensors are typically evaluated in natural icing conditions. 

 (5) Testing with ice shapes should be approached with extreme caution. A suitable 

buildup program to the full span ice shape configuration should be considered if sufficient 

analysis or similarity to other designs does not provide full confidence in the performance and 

handling qualities of the airplane with full-span ice shapes installed. 
AC 25.1419-1A 5/7/04 

12 

 d. Icing Flight Tests. Flight tests in measured natural icing and the use of simulated icing 

tools, such as icing tankers and icing wind tunnels, are normally employed to demonstrate that 

the ice protection system performs during flight as predicted by analysis or other testing. They 

are also used to confirm the analyses used in developing the various components (e.g. ice 

detectors) and ice shapes and, in the case of natural icing tests, to confirm the conclusions 

reached during flight tests conducted with artificial ice shapes. Testing should be accomplished 

within the icing envelope of part 25, Appendix C, to verify the analytically predicted location 

and general physical characteristics of the ice accretions and, in particular, to corroborate the 

general nature of the effects on airplane handling characteristics and performance determined 

with artificial ice shapes. 

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

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

encountered. The following parameters should be considered: 

 (a) Altitude, airspeed, and engine power level or speed, as well as propeller speed 

and pitch (if applicable). 

 (b) Static air, engine component, electrical generation equipment, surface, 

interlaminate, and any other key temperatures that could be affected by ice protection equipment, 

by ice accumulation, or are necessary for validation of analyses. 

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

instrument or other equivalent means. 

 (d) Median volume droplet diameter. This can be approximately determined by 

using a drop slide device. A gelatin oil or soot slide is exposed to supercooled liquid water and 

the resultant impact craters are measured with a microscope. Median volume diameter may also 

be measured using more sophisticated equipment such as a laser-based droplet measuring and 

recording instrument. Trained personnel should confirm that the equipment is properly 

calibrated and functioning during the tests. 

 (e) A means to measure ice accumulation, such as a rod mounted on the airfoil and 

the use of black paint on the airfoil. 

 (2) Simulated Icing. 

 (a) Testing in simulated icing environments, such as icing tunnels or behind icing 

tankers, represents one way to predict ice protection capabilities of individual elements of the ice 

protection equipment. Due to limited volume of the simulated icing environment, testing is 

usually limited to components having small exposed surfaces, such as heated pitot tubes, 

antennas, air inlets including engine induction air inlets, empennage, and other surfaces having 

small leading edge radii and windshields. 
5/7/04 AC 25.1419-1A 

 13 

 (b) A simulated icing exposure may be obtained by using onboard spray nozzles 

forward of the component under examination or by flying the test airplane in the cloud generated 

by an icing tanker. It may be difficult to obtain small droplet sizes with some spray nozzles; 

therefore, these methods could produce larger ice build-ups and different ice shapes than those 

observed in natural icing conditions within the icing envelope of part 25, Appendix C. 

Simulated icing tests should be evaluated to ensure the conditions of concern are accurately 

simulated. 

 (3) Natural Icing. Flight tests in measured natural icing conditions are required by 

§ 25.1419 to verify the ice protection analysis, to check for icing anomalies, and to demonstrate 

that the ice protection system and its components function as intended. Advisory Circular 20-73 

(paragraph 25) provides additional information that is useful for planning a natural icing flight 

test program. At least one exposure to icing conditions within the part 25, Appendix C, 

continuous maximum icing envelope should be obtained. The exposure should be sufficiently 

stabilized to obtain valid data. It is often difficult to obtain temperature stabilization during brief 

exposures. Additional exposures may be required to allow extrapolation to the envelope critical 

conditions by analysis. Test data obtained during these exposures may be used to validate the 

analytical methods used and the results of any preceding simulated icing tests. 

 (a) Past experience indicates that flight testing in natural intermittent maximum 

icing conditions may be accompanied by severe turbulence and possible hail encounters that 

could extensively damage the test airplane. When design analyses show that the critical ice 

protection design points (i.e., heat loads, critical ice shapes, accumulation, and accumulation 

rates, etc.) are adequate under these conditions, and sufficient ground or flight test data exist to 

verify the analysis, the flight test in intermittent maximum icing conditions may not be 

necessary. 

 (b) During natural icing flight tests, ice accumulation on unprotected areas should 

be observed, where possible, and sufficient data taken to allow correlation with dry air tests 

using artificial ice shapes. Remotely located cameras either on the test airplane or on a chase 

airplane have been used to document ice accumulations on areas that cannot be seen from the 

test airplane’s flightdeck or cabin. A limited test program should be conducted in natural icing 

conditions to show a general correlation with the results of flight tests conducted with artificial 

ice shapes in dry air. In addition, flying qualities and performance should be qualitatively 

evaluated with the ice accumulations existing just prior to operation of deice (as opposed to antiice) components. The ice protection systems are to be activated by the flightcrew when icing 

conditions exist in accordance with AFM procedures proposed by the applicant. However, for 

anti-ice components, tests should also be conducted that simulate inadvertent icing encounters in 

which the pilot may not recognize that the airplane has entered an icing condition and the antiice component may not be activated until actual ice build-up is noticed. A delay in the activation 

of the ice protection system should be used in these tests to represent the flightcrew's failure to 

recognize that they are in icing conditions. The delay should be based on the icing recognition 

means available to the flightcrew for the particular airplane (e.g., visual observation of ice 

accumulations or an ice detector) and the recommended crew procedures. An ice accretion 
AC 25.1419-1A 5/7/04 

14 

should be determined that would accumulate in the continuous maximum icing conditions of part 

25, Appendix C, during the time period that represents the recognition delay, plus the time it 

takes for the ice protection system to perform its intended function. Handling qualities should 

remain acceptable to the test pilot, and the airplane should be capable of operating safely with 

this ice accretion. 

 (c) To use a thermal deice system as the ice protection system, the applicant may 

be required to demonstrate the effectiveness of the deice operation either in simulated icing 

conditions or during the natural icing flight test certification program. The tests usually 

encompass the measurements of the surface temperature time history. This time history includes 

the time the system is activated, the time the surface reaches an effective temperature, and the 

time the majority of ice is shed from the leading edge. It should be demonstrated that the effect 

of ice accretions resulting from any delay between the onset of icing conditions and the removal 

of ice on the affected airplane surface does not result in an unacceptable degradation in airplane 

performance and handling characteristics. The data should be recorded in the flight test report. 

 (4) Fluid Anti-Ice/Deice Systems. Flight testing should include evaluation of fluid 

flow paths to confirm that adequate and uniform fluid distribution over the protected surfaces is 

achieved. Fluid flow paths should be determined when the fluid is mixed with impinging water 

during system operation. In cold temperatures, fluid flow paths determined without the 

impinging water may result in the anti/deice fluid freezing on the surface to be protected. A 

means of indicating fluid flow rates, fluid quantity remaining, etc., should be evaluated to 

determine that the indicators are plainly visible to the pilot and that the indications provided can 

be effectively read. A shutoff valve should be provided in systems using flammable fluids. The 

fluid anti-ice/deice systems may be used to protect propellers and windshields as well as leading 

edges of airfoils. The fluid for windshield fluid anti-ice systems should be tested to demonstrate 

that it does not become opaque at low temperatures. The Airplane Flight Manual should include 

information so the flightcrew will know how long it will take to deplete the amount of fluid 

remaining in the reservoir. 

 e. Performance and Handling Qualities. Airplane performance and handling qualities are 

degraded by ice accumulations in various ways depending upon the type, shape, size, and 

location of these accumulations. Because of these variations in degradation, it is difficult to 

establish a standard method of demonstrating satisfactory performance with such degradations. 

However, certain minimum tests should be used to demonstrate that the airplane does not have 

unsafe features or characteristics that prevent it from operating safely in the part 25, Appendix C, 

icing envelope. A minimum set of flight tests for determining the effects of ice accretions on 

airplane performance and handling characteristics is presented in AC 25-7A, “Flight Test Guide 

for Certification of Transport Category Airplanes.” 

 f. Pneumatic Deicer Boots. Many AFM's specify a minimum ice accumulation thickness 

prior to activation of the deicer boot system. This practice originates from the belief that a 

bridge of ice could form if the boots are operated prematurely. Although the ice may not shed 

completely with one cycle of the boots, this residual ice will usually be removed during 
5/7/04 AC 25.1419-1A 

 15 

subsequent boot cycles and does not act as a foundation for a bridge of ice to form. The AFM 

procedure for boot operation should be to operate the boots at the first sign of ice and not wait 

for a specific amount of ice to accumulate. 

Note: Activation of the deicing boots typically results in one cycle of inflation and deflation of 

all boots, but not necessarily at the same time. Some systems are designed such that a complete 

cycle of the boots does not occur (i.e., some boots are not inflated) if the ice protection system is 

“selected off” before the cycle is complete. For these systems the AFM should include 

information to warn the flightcrew to select the ice protection system on for at least one complete 

cycle of the deicing boots. This note is equally applicable to other deicing systems that similarly 

do not activate all portions of the deicing systems simultaneously. 

 g. Emergency and Abnormal Operating Conditions. Flight tests should be conducted to 

demonstrate continued safe flight and landing, using appropriate AFM abnormal and/or 

emergency operating procedures, following failures in the ice protection system. These 

demonstrations should be conducted with anticipated residual ice accumulation on normally 

protected surfaces. 

 h. Ice Detector System (Primary and Advisory). Ice detector systems either directly detect 

the presence of ice on the airplane surface or detect that the airplane is in icing conditions. In the 

latter case, flight testing is typically performed to correlate the detected icing conditions and the 

presence of ice on the airplane. The primary system is the prime means used to determine when 

the ice protection system should be activated. The activation of the ice protection system may be 

automatically or manually activated. An advisory system is not the prime means used to 

determine if the ice protection system should be activated. Typically, when there is an advisory 

system installed on an airplane, the flightcrew is the primary means for determining when the ice 

protection system should be activated. 

7. PERFORM INTENDED FUNCTION IN ICING. All systems and components of the basic 

airplane should continue to function as intended when operating in an icing environment 

including, for example: 

 a. Engines and Equipment. Engines and equipment (such as generators and alternators 

operating under maximum ice protection load) should be monitored during icing tests for 

adequate cooling (§ 25.1041) and be found acceptable for this operation (§§ 25.1093 and 

25.1301). 

 b. Engine Alternate Induction Air Sources. Engine alternate induction air sources should 

remain functional in an icing environment. 

 c. Fuel System Venting. Fuel system venting should not be adversely affected by ice 

accumulation. 
AC 25.1419-1A 5/7/04 

16 

 d. Landing Gear. A retractable landing gear should operate as intended following an icing 

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

 e. Stall Warning. Ice could form on stall warning and angle-of-attack sensors if these 

devices are not protected. Therefore, the sensors’ functions should be evaluated for operation in 

the icing conditions of Appendix C. Adequate stall warning (aerodynamic or artificial) should 

be provided with ice accumulations on the airplane. Ice accumulations that should be considered 

are those on unprotected surfaces, those that occur prior to the initial activation of the ice 

protection system, those that occur between the ice protection activation cycles, and those that 

remain after one cycle of the ice protection system. The activation points of artificial stall 

warning and stall identification systems, if installed, may need to be reset for operations in icing 

conditions to provide adequate stall warning margins and to prevent inadvertent stalling or loss 

of control, respectively. 

 f. Ice Detection Cues. Ice detection cues that the pilot relies on for timely operation of ice 

protection equipment should be evaluated in anticipated flight attitudes. 

 g. Primary and Secondary Flight Control Surfaces. Primary and secondary flight control 

surfaces should remain operational after exposure to icing conditions. Demonstrate that 

aerodynamic balance surfaces are not subject to icing throughout the airplane's operating 

envelope (weight, center of gravity, and speed) or that any ice accumulation on these surfaces 

does not interfere with or limit actuation of the control for these surfaces, including retraction of 

flaps for a safe go around from the landing configuration. 

 h. Ram Air Turbine. The ram air turbine should remain operational. It does not need to be 

tested in natural icing conditions if tested in the icing wind tunnel. 

 i. Pilot Compartment View. In support of compliance with § 25.773, Pilot compartment 

view, any obstruction of the pilots’ view due to ice accumulation should be noted. 

8. ICE DETECTION LIGHT(S). Unless operations at night in known or forecast icing 

conditions are prohibited by an operating limitation, § 25.1403 requires that a means be provided 

for illuminating or otherwise determining the formation of ice on the parts of the wings that are 

critical from the standpoint of ice accumulations. 

 a. If the wings cannot be observed by the flightcrew, one acceptable means of compliance 

with this regulation would be the installation of an ice evidence probe located in a position 

where the flightcrew can observe the ice accumulation. Formation of ice on the device should be 

shown to precede or occur simultaneously with the formation of ice on the wings. Consideration 

should be given to the need for illumination of the ice evidence probe. 

 b. Ice detection lights should be evaluated both in and out of clouds during night flight to 

determine that adequate illumination of the component of interest is available without excessive 

glare, reflections, or other distractions to the flightcrew. These tests may be conveniently 
5/7/04 AC 25.1419-1A 

 17 

accomplished both in and out of clouds during the airplane certification flight tests. Typically, 

airplane-mounted illumination has been used as a means of compliance with this regulation. Use 

of a hand-held flashlight has not been considered acceptable due to the associated workload. 

The appropriate manual should identify the ice characteristics the flightcrew is expected to 

observe and the flightcrew action associated with the observation. 

9. ICE-CONTAMINATED TAILPLANE STALL (ICTS). This phenomenon occurs due to 

airflow separation on the lower surface of the tailplane. This can occur if the angle-of-attack of 

the horizontal tailplane exceeds the stall angle-of-attack, which can be reduced by even small 

quantities of ice on the tailplane leading edge. The increase in tailplane angle-of-attack can 

result from airplane configuration (e.g., increased flap extension increasing the downwash angle 

or trim required for the center-of-gravity position) and flight conditions (e.g., a high approach 

speed resulting in an increased flap downwash angle, gusts, maneuvering, or changes to engine 

power setting). ICTS is characterized by a reduction or loss of pitch control or stability while 

operating in, or after recently departing from, icing conditions. 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 draw the 

control column forward with a level of force that is beyond the combined efforts of the pilot and 

copilot to overcome. On some airplanes, ICTS has been caused by a lateral flow component 

coming off of the vertical stabilizer, as may occur in sideslip conditions or due to a gust with a 

lateral component. Aerodynamic effects of reduced tailplane lift should be considered for all 

airplanes, including those with powered controls. An evaluation should be made to determine if 

this unsafe flight condition is likely to occur. Airplanes susceptible to this phenomenon are 

those having a near zero or negative tailplane stall margin with tailplane icing contamination. 

An acceptable flight test procedure for determining susceptibility to ICTS is presented in AC 25-

7A. 

10. CAUTION INFORMATION. Section 25.1419(c) requires that caution information be 

provided to alert the flightcrew when the ice protection system is not functioning normally. 

Caution information should be provided if the failure condition of the ice protection system can 

result in a hazardous airplane condition. It should be assumed that icing conditions exist during 

the failure event. The decision to provide the caution information should not be based on the 

numerical probability of the failure event (i.e., even if a numerical probability analysis indicates 

the system failure is improbable or extremely improbable, the caution information should be 

provided if the failure could result in a hazardous condition). 

 a. The placement of the sensor(s) used to identify a failure condition should be evaluated 

to ensure that the sensors are properly located to obtain accurate data on the failure of the ice 

protection system. 

 b. The applicant should submit data to substantiate that the indication system does not give 

a false indication that the system is functioning normally. For example, if a pneumatic deicing 

system (boots) requires a specific minimum pressure and pressure rise rate to adequately shed 
AC 25.1419-1A 5/7/04 

18 

ice, then caution information should be provided if the minimum pressure and pressure rise rate 

are not attained. If this caution information is not provided, the flightcrew may erroneously 

believe that the boots are operating normally when, in fact, the boots might not be inflating with 

sufficient pressure or rate of inflation to adequately shed the ice. The need for caution 

information should also be considered for the case of ice forming in the pneumatic system that 

can result in low pneumatic boot pressures or an inadequate pressure rise rate. 

11. ICE SHEDDING. Ice shedding from forward airplane structures may damage or erode 

engine or powerplant components as well as lifting, stabilizing, and flight control surface leading 

edges. Fan and compressor blades, impeller vanes, inlet screens and ducts, as well as propellers, 

are examples of powerplant components subject to damage from shedding ice. For fuselagemounted turbojet engines (and pusher propellers that are very close to the fuselage and well aft 

of the airplane's nose), ice shedding from the forward fuselage and from the wings may cause 

significant damage. Ice shedding from components, including antennas, of the airplane should 

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

engines and propellers (compliance with § 25.1093). Consideration should also be given to 

airplane damage that can occur due to ice shedding from the propellers. 

Control surfaces such as elevators, ailerons, flaps, and spoilers are also subject to damage, 

especially those constructed of thin metallic, nonmetallic, or composite materials. Trajectory 

and impingement analyses may not adequately predict such damage. Unpredictable ice shedding 

paths from forward areas such as radomes and forward wings (canards) have been found to 

negate the results of these analyses. For this reason, a damage analysis should consider that the 

most critical ice shapes will shed and impact the areas of concern. 

12. AIRPLANE FLIGHT MANUAL (AFM). The AFM should provide the pilot with the 

information needed to operate the ice protection system, including the following: 

 a. Operating Limitations Section. 

 (1) The minimum airspeed that should be maintained for each normal airplane 

configuration whenever ice exists on the critical surfaces. 

 (2) Instructions to activate the engine anti-ice system if Instrument Meteorological 

Conditions (IMC) are encountered at an altitude near or above the freezing level. 

 (3) Landing weight limitations should be presented for flight in icing that reflect any 

effects on lift, drag, thrust, and operating speeds related to operating in icing conditions. These 

weight limitations may be presented in the Performance Information Section of the AFM and 

included as limitations by specific reference in the Limitations Section of the AFM. 

 (4) Limitations on operating time for ice protection equipment, if these limitations are 

based on fluid anti-ice/deice systems capacities and flow rates. 
5/7/04 AC 25.1419-1A 

 19 

 (5) Speed limitations (if any) and minimum temperature for deicing boot operation for 

airplanes equipped with boots. 

 (6) Environmental limitations for equipment operations as applicable (e.g., minimum 

temperature for boot operation or maximum altitude for boot operation). 

 (7) Minimum engine speed if the airframe ice protection system does not function 

properly below this speed. 

 (8) A list of required placards. 

 (9) For airplanes with unpowered roll controls and pneumatic deicing boots, a warning 

should be provided for severe icing that may result from environmental conditions outside the 

icing envelope established as the basis of the approval defined in Appendix C (reference the 

AFM information in paragraphs 12d(3) and (4)). 
AC 25.1419-1A 5/7/04 

20 

 b. Operating Procedures Section. 

 (1) Section 25.1585(a)(6) requires that the pilot be provided with recommended 

procedures for the use of ice protection equipment. This should include any preflight action 

necessary to minimize the potential of enroute emergencies associated with the ice protection 

system. The system components should be described with sufficient clarity and depth that the 

pilot can understand their function. Unless flightcrew actions are accepted as normal 

airmanship, the appropriate procedures should be included in the FAA-approved AFM, AFM 

revision, or AFM supplement. These procedures should include proper pilot response to cockpit 

warnings, a means to diagnose system failures, and the use of the system(s) in a safe manner. 

 (2) Procedures should be provided to optimize airplane operation during penetration of 

icing conditions, including climb, holding, and approach configurations and speeds. The AFM 

should define when the ice protection equipment should be activated. 

 (3) Emergency or abnormal procedures, including procedures to be followed when ice 

protection systems fail and/or warning or monitor alerts occur, should be provided. 

 (4) For fluid anti-ice/deice systems, information and method(s) for determining the 

remaining flight operation time should be provided. 

 (5) For airplanes that cannot supply adequate electrical power for all systems at low 

engine speeds, load-shedding instructions should be provided to the pilot for approach and 

landing in icing conditions. 

 c. Performance Information Section. Data should be provided so that the maximum 

landing weight, as limited by approach and landing climb performance (§§ 25.121(d) and 25.119 

respectively) can be determined in icing conditions. These data should include the effect of drag 

due to residual ice on protected and unprotected surfaces, the power extraction associated with 

ice protection system operation, and any changes in operating speeds due to icing. The effect on 

landing distance due to revised approach speeds, and/or landing configurations, should be 

shown. 

 d. Airworthiness Directives for Severe Icing Conditions. 

 (1) In October 1994, an accident involving a transport category airplane occurred in 

which severe icing conditions were reported in the area. During extensive testing the accident 

profile was replicated by ice shapes developed from testing in an icing cloud having droplets in 

the size range of freezing drizzle at a temperature near freezing. This condition created a ridge 

of ice aft of the deicing boots and forward of the ailerons, which resulted in uncommanded 

motion of the ailerons and rapid roll of the aircraft. 

 (2) Following this accident the FAA determined that flightcrews are not currently 

provided with the information necessary to determine when the airplane is operating in icing 
5/7/04 AC 25.1419-1A 

 21 

conditions that have been shown to be unsafe and for which the airplane is not certificated; or 

what action to take when such conditions are encountered. Therefore, the FAA determined that 

flightcrews must be provided with such information, and must be made aware of certain visual 

cues that may indicate when the airplane is operating in atmospheric conditions that are outside 

the part 25, Appendix C icing envelope. 

 (3) The FAA is particularly concerned with airplanes that are equipped with pneumatic 

deicing boots and non-powered roll control systems, since non-powered roll flight controls do 

not have the physical advantage of hydraulic or electrical power to assist the pilot in overcoming 

the large control forces that may exist from differential pressure resulting from flow separation 

over the roll control surfaces. The FAA issued a series of Airworthiness Directives (AD’s) in 

April 1996 and February 1998 on airplanes equipped with pneumatic deicing boots and nonpowered roll control systems. The AD’s require revising the Airplane Flight Manual (AFM) to 

provide the flight crew with recognition cues for, and procedures for exiting from, severe icing 

conditions, and to limit or prohibit the use of various flight control devices. Other similarly 

equipped aircraft should also include this information in the AFM. 

 (4) The limitations and procedures specified in Airworthiness Directive (AD) 96-09-25 

are an acceptable means of providing this information. These limitations and procedures 

include, but are not limited to, the following: 

 (a) Visual cues that the airplane is in severe icing conditions; 

 (b) Prohibition on the use of the autopilot when the visual cues are observed; 

 (c) All icing detection lights operative prior to flight into icing conditions at night; 

 (d) Immediate exiting of the severe icing conditions; and 

 (e) If the flaps are extended, do not retract them until the airframe is clear of ice. 

Note: The retraction of the flaps is contingent upon the existence of a means to determine if the 

airframe is clear of ice.