Subject: Certification of Part 23 Airplanes for Flight in Icing Conditions
Date: 9/26/02 Initiated By: ACE-100
AC No: 23.1419-2B Change:
1. PURPOSE. This advisory circular (AC) sets forth an acceptable means, but not the only means, of demonstrating compliance with the ice protection requirements in Title 14 of the Code of Federal Regulations (14 CFR) part 23. The Federal Aviation Administration (FAA) will consider other methods of demonstrating compliance that an applicant may elect to present. This material is neither mandatory nor regulatory in nature and does not constitute a regulation.
2. CANCELLATION. AC 23.1419-2A, Certification of Part 23 Airplanes for Flight in Icing Conditions, dated August 19, 1998, is canceled.
3. APPLICABILITY. The guidance provided here applies to the approval of airplane ice protection systems for operating in the icing environment defined by 14 CFR part 25, Appendix C. The guidance should be applied to new Type Certificates (TCs), Supplemental Type Certificates (STCs), and amendments to existing TCs for airplanes under Part 3 of the Civil Aviation Regulations (CAR) and part 23, for which approval under the provisions of § 23.1419 is desired.
4. RELATED REGULATIONS AND DOCUMENTS.
a. Regulations. By their adoption in Amendment 23-14, which shows their requirements are directly related, §§ 23.929, 23.1309, and 23.1419 are applicable to a part 23 airplane icing certification program regardless of the certification basis for the basic airplane; however, for those airplanes certificated in accordance with Part 3 of the CAR and part 23 through Amendment 23-13, the application of these sections may be limited to the equipment being used for ice protection. Some systems that were previously approved on the airplane may need to be modified to improve their reliability when those systems are utilized as part of that airplane's icing approval.
(1) With the adoption of Amendment 23-43, § 23.1419 was revised to do the following: to continue the current minimum ice protection requirements that have been found necessary for safe operation in icing conditions, to provide specific test requirements, to clarify the requirements for information that must be provided to the pilot, and to allow approval of equivalent components that have been previously tested and approved, and that have demonstrated satisfactory service if the installations are similar.
(2) In addition to the previously mentioned requirements (§§ 23.929, 23.1309, and
23.1419), the following sections should be applied depending upon the ice protection system design and the original certification basis of the airplane. Many of the following requirements are also applicable, even without approval for flight in icing conditions.
Date of Airplane Type Certification Application CAR/Title 14 CFR Status Icing Certification Requirements Prior to February 1, 1965 Part 3 of the CAR, (May 15, 1956, as amended through Amendment 3-8) Sections 3.85(a) and (c),
3.85a(a) and (c), 3.382,
3.383, 3.446, 3.575, (including note following
(b)), 3.652, 3.652-1, 3.665,
3.666, 3.681, 3.682, 3.685,
3.686, 3.687, 3.690, 3.691,
3.692, 3.712, 3.725, 3.758,
3.770, 3.772, 3.777, 3.778, and 3.779 On or after February 1, 1965 Recodification
Sections 23.65, 23.75, 23.77,
23.773, 23.775, 23.1301,
23.1351, 23.1357, 23.1437,
23.1541, 23.1559(b),
23.1583(h), 23.1585, and
23.1419 (boot requirement before Amendment 23-14) On or after July 29, 1965 Amendment 23-1 Add § 23.1325 to the above part 23 requirements.
On or after February 5, 1970 Amendment 23-8 Add § 23.1529 to the above part 23 requirements.
On or after December 20, 1973 Amendment 23-14 Add §§ 23.853(d), 23.929 and 23.903(c) to the above part 23 requirements.
Date of Airplane Type Certification Application CAR/Title 14 CFR Status Icing Certification Requirements On September 1, 1977
Amendment 23-20
Add §§ 23.1327 and 23.1547 to the above part 23 requirements.
On or after December 1, 1978
Amendment 23-23
Add §§ 23.863, and 23.1416 (in lieu of the boot requirement of § 23.1419 before Amendment 23-14) to the above part 23 requirements.
On or after February 17, 1987 Amendment 23-34 For commuter category airplanes, add §§ 23.67(e)(2),
23.67(e)(3), 23.997(e), and
23.1199(b) to the above part 23 requirements.
On or after February 4, 1991
Amendment 23-42
Add §§ 23.1323(e) and
23.1325(g) to the above part 23 requirements.
On or after May 10, 1993
Amendment 23-43
Add §§ 23.905(e),
23.1093(a)(6), and
23.1307(c) to the above part 23 requirements.
On or after September 7, 1993
Amendment 23-45
Add §§ 23.773(b), 23.775(f),
23.775(g), and 23.1525 to the above part 23 requirements.
On or after March 11, 1996 Amendment 23-49 Add § 23.1326 to the above part 23 requirements.
b. Advisory Circulars. Copies of current editions of the following publications may be downloaded from the FAA’s Regulatory & Guidance Library (RGL) 3
<www1.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/Main Frame?OpenFrameSet> or obtained from the U.S. Department of Transportation, Subsequent Distribution Office, Ardmore East Business Center, 3341 Q 75th Avenue, Landover, MD 20785:
AC 20-73 Aircraft Ice Protection
AC 20-117 Haz ards Following Ground Deicing and Ground Operations in Conditions Conducive to Aircraft Icing
AC 23-17A Sy stems and Equipment Guide for Certification of Part 23 Airplanes
AC 23.143-1 I ce Contaminated Tailplane Stall (ICTS)
AC 23.629-1A Means of Compliance with Section 23.629, Flutter
AC 23.1309-1C Equipment, Systems, and Installations in Part 23 Airplanes
(1) Copies of the current AC may be purchased from the Superintendent of Documents, P.O. Box 371954, Pittsburgh, PA 15250-7954. Make check or money order payable to the Superintendent of Documents:
AC 23-8B Flight Test Guide for Certification of Part 23 Airplanes
5. RELATED READING MATERIAL.
a. FAA Technical Report DOT/FAA/CT-88/8, "Aircraft Icing Handbook" (March 1991), includes reference material on ground and airborne icing facilities, simulation procedures, and analytical techniques. This document represents all types and classes of aircraft and is intended as a working tool for the designer and analyst of ice protection systems.
b. FAA Technical Report ADS-4, "Engineering Summary of Airframe Icing Technical Data," and Report No. FAA-RD-77-76, "Engineering Summary of Powerplant Icing Technical Data," provide technical information on airframe and engine icing conditions, and methods of detecting, preventing, and removing ice accretion on airframes and engines in flight. Although most of the information contained in ADS-4 and FAA-RD-77-76 reports is still valid, some is outdated, and more usable information is now available through recent research and experience, and is included in the Aircraft Icing Handbook.
c. FAA Technical Report DOT/FAA/AR-01/91, "A History and Interpretation of Aircraft Icing Intensity Definitions and FAA Rules for Operating in Icing Conditions" (November 2001), provides a good reference for understanding icing operational rules.
d. FAA Technical Report DOT/FAA/AR-02/68, "Effect of Residual and Intercycle Ice Accretions on Airfoil Performance" (May 2002), details icing tunnel testing to determine intercycle and residual ice on a 23012 airfoil, and wind tunnel testing of uniform sandpaper and intercycle ice shapes.
e. The FAA technical reports listed above can be obtained from the National Technical Information Service in Springfield, Virginia 22161.
f. Policy Statement ACE-01-23.1093(b), “Compliance with Induction System Icing Protection for Part 23 Airplanes,” was published in the Federal Register on November 7, 2001, and provides the latest policy for engine induction ice protection for turbine powered part 23 airplanes.
g. The following SAE Documents can be ordered from the Society of Automotive Engineers, Inc., 400 Commonwealth Drive, Warrendale, PA 15096:
Aerospace Recommended Practice (ARP) 4761, “Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment Aerospace Information Report (AIR) 4367, “Aircraft Ice Detectors and Icing Rate Measuring Instruments” AIR 5504 “Aircraft Inflight Icing Terminology”
h. The SAE and a working group for Task 11A of the FAA Inflight Aircraft Icing Plan are developing the following documents which will be available soon from the SAE:
Aerospace Recommended Practice (ARP) 5903, “Droplet Impingement and Ice Accretion Computer Codes” ARP 5904, “Airborne Icing Tankers” ARP 5905, “Calibration and Acceptance of Icing Wind Tunnels”
6. BACKGROUND.
a. Prior to 1945, airplanes were certificated under Part 4 of the CAR. Section
04.5814 required that if deicer boots were installed, they would have a positive means of deflation. There were no other references to an ice protection system in Part 4. When separate regulations (Part 3 of the CAR) were written for normal category airplanes, this requirement for positive means of deflating deicer boots was incorporated without change in § 03.541. In 1949, § 03.541 was renumbered as § 3.712.
b. Ice protection was not addressed again until Part 3 of the CAR was revised in 1962 by Amendment 3-7. This amendment added §§ 3.772 and 3.778, which required that information be provided to the crew specifying the types of operation and the meteorological conditions to which the airplane is limited by the equipment installed.
This section gave icing as a specific example of the meteorological conditions to be 5
delineated. This change required a list of all installed equipment affecting the airplane operation limitations. The list also identified this equipment by its operational function.
This list of equipment later became known as the “Kind of Equipment List (KOEL).”
c. In 1964, Part 3 of the CAR was recodified into part 23. After recodification, § 3.712 became § 23.1419, and §§ 3.772 and 3.778(h) became §§ 23.1559 and
23.1583(h), respectively. In 1965, § 23.1325 was revised by Amendment 23-1 to take into account the effect of icing conditions on static pressure dependent instruments. This requirement applies to all airplanes regardless of whether or not they have an ice protection system approved under § 23.1419. In the latter part of 1968, the FAA instituted an extensive review of the airworthiness standards of part 23. As a result of this review, the FAA issued Amendment 23-14 (November 1973), which made several substantive changes in the interest of safety to part 23. This amendment introduced a new § 23.929, which required engine installation ice protection and completely revised § 23.1419 to establish standards for ice protection systems. It also introduced a new § 23.1309, which established reliability and noninterference requirements for installed equipment and systems. These three sections are directly related, as defined in § 21.101, to the certification of an ice protection system because of the increased reliance on this system when operating the airplane in an icing environment.
d. Specific standards for pneumatic deicer boots, which were contained in the former § 23.1419, were inadvertently omitted in Amendment 23-14. The FAA, realizing that a specific standard for pneumatic deicer boot systems was needed, issued Amendment 23-23 in 1978, which added § 23.1416, pneumatic deicer boot system. As currently configured, certification requirements are limited to those icing conditions produced by supercooled clouds as defined by part 25, Appendix C, and do not require design or proof of capability to operate in freezing rain and drizzle, snow, or mixed conditions.
e. In 1987, with the creation of the commuter category, airplanes that had weight, altitude, and temperature limitations for takeoff, en route, climb, and landing distance were being certificated. Required climb performance for commuter category airplanes is defined in § 23.67(c) and § 23.77(c).
f. With the adoption of Amendment 23-41 (effective November 26, 1990), § 23.1309 retained the existing reliability requirements adopted by Amendment 23-14 for airplane equipment, systems, and installations that are not complex and do not perform critical functions. For those cases where the applicant finds it necessary or desirable to include complex systems and/or systems that perform critical functions, Amendment 23-41, § 23.1309, provides additional requirements for identifying and certificating such equipment, systems, and installations. This amendment permitted the approval of more advanced systems having the capability to perform critical functions.
g. In 1991, with the adoption of Amendment 23-42 (effective February 4, 1991), § 23.1323(e) was added to require a heated pitot tube, or an equivalent means of preventing malfunction due to icing, and to clarify the requirement that a heated pitot 6
tube be part of the system approval for flight in icing conditions. Also, § 23.1325(g) was added to allow airplanes that are prohibited from flight in instrument meteorological conditions (IMC) to be certificated without an alternate static air source.
h. In 1993, with the adoption of Amendment 23-43 (effective May 10, 1993), § 23.905(e) was added to require that ice shed from the airplane not damage a pusher propeller. Section 23.1093(a)(6) specified ice protection requirements for fuel injection system designs with and without metering components on which impact ice may accumulate. Also, § 23.1307(c) was added to require the airplane type design to include all of the equipment necessary for operation in accordance with the limitations required by § 23.1559. Section 23.1419 was revised to do the following: to continue the current minimum ice protection requirements that have been found necessary for safe operation in icing conditions, to provide specific test requirements, to clarify the requirements for information that must be provided to the pilot, and to allow approval of equivalent components that have been previously tested and approved, and that have demonstrated satisfactory service if the installations are similar.
i. In 1993, with the adoption of Amendment 23-45 (effective September 7, 1993), the following sections were added: (1) Section 23.773(b) to provide requirements for the pilot compartment view to address the environment expected in all the operations requested for certification; (2) Section 23.775(f) to clarify the criteria for determining the cleared windshield area that is necessary to ensure safe operation in icing conditions; (3) Section 23.775(g) to require that a probable single failure of a transparency heating system may not adversely affect the integrity of the airplane cabin or danger of fire; and
(4) Section 23.1525 was revised to require the establishment and inclusion of kinds of operations authorized in the Airplane Flight Manual (AFM) as specified by § 23.1583(h).
j. In 1996, with the adoption of Amendment 23-49 (effective March 11, 1996), § 23.1325(g) was revised by exempting airplanes that are prohibited from flight in icing conditions from the requirements of § 23.1325(b)(3). Also, § 23.1326 was added to require the installation of a pitot tube heat indicating system on those airplanes required to be equipped with a heated pitot tube. Airplanes that are approved for instrument flight, or for flight in icing conditions, would be required to be equipped with a heated pitot tube and a heated pitot tube indicator by this applicability.
7. PLANNING. The applicant should submit a certification plan at the start of the design and development efforts. Refer to FAA Order 8110.4B. The certification plan should describe all of the applicant's efforts intended to lead to certification. This plan should identify, by item to be certificated, the certification methods that the applicant intends to use. It should provide for a certification checklist. Regarding § 23.1419, it should clearly identify analyses and tests, or references to similarity of designs that the applicant intends for certification of the ice protection system. These methods of showing compliance should be agreed upon between the applicant and the FAA early in the type certification program. It is imperative that the applicant obtains FAA concurrence prior to conducting certification tests. The certification plan should include the following basic information:
a. Airplane and systems descriptions, including dimensions, operating envelope and limitations, and other data that may be relevant to certification for flight in icing conditions;
b. Ice protection systems description;
c. Compliance checklist that addresses each applicable section of part 23 and the proposed methods of compliance (to be agreed upon between the applicant and the FAA early in the certification program);
d. Analyses or tests performed to date;
e. Analyses or tests planned; and
f. Projected schedules of design, analyses, testing, and reporting.
8. DESIGN OBJECTIVES. The applicant should demonstrate by analyses, tests, or a combination of analyses and tests, that the airplane is capable of safely operating throughout the icing envelope of part 25, Appendix C. The envelope can be reduced for airplanes certificated for operation where systems or performance limitations, not related to ice protection, exist. Appendix 1 lists various influence items that should be examined for their effect on safety when operating in icing conditions.
9. ANALYSES. The applicant normally prepares analyses to substantiate decisions involving application of selected ice protection equipment and to substantiate decisions to leave normally protected areas and components unprotected. Such analyses should clearly state the basic protection required, the assumptions made, and delineate the methods of analysis used. All analyses should be validated either by tests or by methods agreed to by the FAA. This substantiation should include a discussion of the assumptions made in the analyses and the design provisions included to compensate for these assumptions. Analyses are normally used for the following:
a. Areas and Components to be Protected. The applicant should examine those areas listed below to determine the degree of protection required:
(1) Leading edges of wings, winglets, and wing struts; horizontal and vertical stabilizers; 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) Fuel tank vents;
(6) External tanks, including fuel tip tanks;
(7) Propellers;
(8) External hinges, tracks, door handles, and entry steps;
(9) Instrument transducers including pitot tube (and mast), static ports, angle-of-attack sensors, and stall warning transducers;
(10) Forward fuselage nose cone and radome;
(11) Windshields;
(12) Landing gear;
(13) Retractable forward landing lights;
(14) Ram air turbines;
(15) Ice detection lights if required; and
(16) Any other external protuberance.
(a) An applicant may find that protection is not required for one or more of these areas and components. If so, the applicant should include supporting data and rationale in the analysis for allowing them to go unprotected. The applicant should demonstrate that allowing them to go unprotected does not adversely affect the handling or performance of the airplane.
b. The 45-minute Hold Condition. The 45-minute hold criterion should be used in developing critical ice shapes for which the operational characteristics of the overall 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 contained in AC 20-73, paragraphs 12a and 18b. The applicant should determine the effect of the 45-minute hold in Continuous Maximum icing conditions.
(1) A mean effective droplet diameter of 22 microns and a liquid water content of
0.5 gm/m3 with no horizontal extent correction are normally used for this analysis;
however, the applicant should substantiate the specific values used, including temperature, which represents the critical conditions for the airplane’s performance and handling qualities. The analysis should consider that the airplane would remain in an 9
icing cloud based on a rectangular course with leg lengths not exceeding the cloud horizontal extent and all turns being made within the icing cloud.
(2) The applicant may elect to use more severe liquid water contents that are more representative of expected holding altitudes. The critical ice shapes derived from this analysis should be compared to critical shapes derived from other analyses (climb, cruise, and descent) to establish the most critical artificial ice shapes to be used during dry air flight tests.
c. Flutter Analysis. A flutter investigation (see AC 23.629-1A) should be made to show that flutter characteristics are not adversely affected, taking into account the effects of mass distribution of ice accumulations. This investigation relates to unprotected surfaces and to protected surfaces where residual accumulations are allowed throughout the normal airspeed and altitude envelope; however, the effect of ice shapes on aerodynamic properties need not be considered for flutter analysis. Ice accretions due to failures of the ice protection system must also be addressed.
d. Power Sources. The applicants should evaluate the power sources in their ice protection system design. Electrical, bleed air, and pneumatic sources are normally used.
A load analysis or test should be conducted on each power source to determine that the power source is adequate to supply the ice protection system, plus all other essential loads throughout the airplane flight envelope under conditions requiring operation of the ice protection system.
(1) The effect of an ice protection system component failure on power availability to other essential loads should be evaluated, and any resultant hazard should be prevented on multi-engine designs and minimized on single-engine designs. The applicant should show that there is no hazard to the airplane in the event of any power source failure during flight in icing conditions. Two separate power sources (installed so that the failure of one source does not affect the ability of the remaining source to provide system power) are adequate if the single source can carry all the essential loads.
(2) Two-engine airplanes require two sources in accordance with § 23.1309(c). If a single source system is planned, additional reliability evaluation of the power source under system loads and environmental conditions may be required. All power sources that affect engine or engine ice protection systems for multi-engine airplanes must comply with the engine isolation requirements of § 23.903(c).
e. Failure Analysis. AC 23.1309-1C provides guidance and information for an acceptable means, but not the only means, for showing compliance with the requirements of § 23.1309(a) and (b) (Amendment 23-49) for equipment, systems, and installations in 14 CFR part 23 airplanes. The regulatory requirements are in § 23.1309. Substantiation of the hazard classification of ice protection system failure conditions is typically accomplished through analyses and/or testing. It has been standard industry practice to 10
assign a probability of encountering icing conditions of “one” for an airplane certificated for flight in icing.
(1) During the analyses, each identifiable failure within the system should be examined for its effect on the airplane and its occupants. Examples of failures that need to be examined include:
(a) Those that allow ice to accumulate beyond design levels; or
(b) Those that allow asymmetric ice accumulation.
(2) A probable malfunction or failure is any single malfunction or failure that is expected to occur during the life of any single airplane of a specific type. This may be determined on the basis of past service experience with similar components in comparable airplane applications. This definition should be extended to multiple malfunctions or failure when:
(a) The first malfunction or failure would not be detected during normal operation of the system, including periodic checks established at intervals that are consistent with the degree of hazard involved; or
(b) The first malfunction would inevitably lead to other malfunctions or failures. A procedure requiring a pilot to exit icing conditions would not be acceptable after any failure condition that would become catastrophic within the average exposure time probability it takes to exit icing conditions.
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 for physical, functional, thermodynamic, pneumatic, aerodynamic, and environmental areas. Analyses should be conducted to show that the component installation and operation is equivalent to the previously approved installation.
(2) Similarity requires an evaluation of both the system and installation differences that may adversely affect the system performance. An assessment of a new installation should consider differences affecting the aircraft and the system. Similarity may be used as the basis for certification without the need for additional tests provided:
(a) Only minimal differences exist between the previously certificated system and installation, and the system and installation to be certificated; and
(b) The previously certificated system and installation have no unresolved icing related service history problems.
(c) FAA Order 8110.4B should be consulted regarding the use of previously approved FAA data.
(d) If there is uncertainty about the effects of the differences, additional tests or analyses, or both, should be conducted as necessary and appropriate to resolve the open issues.
g. Impingement Limit Analyses. The applicant should prepare a droplet trajectory and impingement analysis of the wing, horizontal and vertical stabilizers, propellers, and any other leading edges that may require protection. This analysis should consider the various airplane operational configurations and associated angles of attack. This analysis is needed to establish the upper and lower aft droplet impingement limits that can then be used to establish the aft ice formation limit and the protective coverage needed.
Typically, 40-micron droplets for maximum continuous icing conditions and 50 micron drops for Intermittent Maximum icing conditions are used to establish the aft impingement limits. More specific information can be found in AC 20-73, Aircraft Ice Protection.
h. Induction Air System Protection. The induction air system for turbine engine airplanes is certificated for icing encounters in accordance with § 23.1093(b). These requirements are for all airplanes even those not certificated for flight in icing conditions.
Thus ice protection systems installed on previously type certificated airplanes to protect the engine induction air system should be adequate and need not be re-examined, unless being modified.
10. FLIGHT TEST PLANNING. When operating any airplane in an icing environment, degradation in performance and flying qualities may be expected. The primary purposes for flight testing an airplane equipped for flight in icing conditions is to evaluate such degradation, determining that the flying qualities remain adequate, and that performance levels are acceptable for this flight environment.
a. The flight tests and analyses of flight tests should:
(1) Demonstrate normal operation of the airplane with the ice protection system installed in non-icing flight.
(2) Demonstrate operation of the airplane with anticipated in-flight accumulations of ice.
(3) Verify the analyses conducted to show adequacy of the ice protection system throughout the icing envelope of part 25, Appendix C.