Skip Ribbon Commands
Skip to main content
Safety Recommendation Details

Safety Recommendation A-91-087
Details
Synopsis: ON DECEMBER 26, 1989, UNITED EXPRESS, FLIGHT 2415 (SUNDANCE 415), A BRITISH AEROSPACE BA-3101 JETSTREAM, N41OUE, CRASHED APPROXIMATELY 400 FEET SHORT OF RUNWAY 21R AT TRI-CITIES AIRPORT, PASCO, WASHINGTON. THE AIRPLANE CRASHED WHILE EXECUTING AN INSTRUMENT LANDING SYSTEM (ILS) APPROACH TO THE RUNWAY AT APPROXIMATELY 2230 PACIFIC STANDARD TIME. VISUAL METEOROLOGICAL CONDITIONS PREVAILED BENEATH THE CLOUD BASES, WHICH WERE APPROXIMATELY 1,000 FEET ABOVE GROUND LEVEL AT THE TIME OF THE ACCIDENT. THE AIRPLANE WAS DESTROYED, AND THE TWO PILOTS AND ALL FOUR PASSENGERS RECEIVED FATAL INJURIES.
Recommendation: THE NTSB RECOMMENDS THAT THE FEDERAL AVIATION ADMINISTRATION: AMEND THE ICING CERTIFICATION RULES TO REQUIRE FLIGHT TESTS WHEREIN ICE IS ACCUMULATED IN THOSE CRUISE AND APPROACH FLAP CONFIGURATION IN WHICH EXTENSIVE EXPOSURE TO ICING CONDITIONS CAN BE EXPECTED, AND REQUIRE SUBSEQUENT CHANGES IN CONFIGURATION, TO INCLUDE LANDING FLAPS.
Original recommendation transmittal letter: PDF
Overall Status: Closed - Acceptable Action
Mode: Aviation
Location: PASCO, WA, United States
Is Reiterated: No
Is Hazmat: No
Is NPRM: No
Accident #: DCA90MA011
Accident Reports: Unstabilized Approach and Loss of Controll NPA, Inc. dba United Express Flight 2415 British Aerospace BA-3101, N410UE
Report #: AAR-91-06
Accident Date: 12/26/1989
Issue Date: 11/19/1991
Date Closed: 5/2/2008
Addressee(s) and Addressee Status: FAA (Closed - Acceptable Action)
Keyword(s): Icing,

Safety Recommendation History
From: NTSB
To: FAA
Date: 5/2/2008
Response: On July 25, 2007, the FAA issued a final rule, titled Airplane Performance and Handling Qualities in Icing Conditions, which became effective October 9, 2007. On September 10, 2007, the FAA issued Advisory Circular (AC) 25-25, Performance and Handling Characteristics in the Icing Conditions Specified in Part 25, Appendix C. The AC provides detailed guidance on acceptable means of compliance with the new requirements. The Safety Board reviewed the final rule and related information in the AC and has determined that it fully meets the intent of this recommendation. Consequently, Safety Recommendation A-91-87 is classified Closed Acceptable Action.

From: FAA
To: NTSB
Date: 1/22/2008
Response: Letter Mail Controlled 1/29/2008 11:10:10 AM MC# 2080040: Robert A. Sturgell, Acting Administrator, FAA, 1/22/08 On May 10, 2006, the Board classified this recommendation Open-Acceptable Response pending issuance of the final rule and advisory material for evaluating airplane performance and handling characteristics in icing conditions. The enclosed final rule for Airplane Performance and Handling Qualities in Icing Conditions was issued July 25, 2007 and became effective on October 9, 2007. This final rule applies to transport category airplanes and becomes amendment 121 to 14 Code of Federal Regulations part 25. We also released the enclosed Advisory Circular (AC) 25-25, which provides detailed guidance on acceptable means of compliance with the new part 25 requirements. The final rule and AC also partially address Safety Recommendations A-96-56, A-96-58, and A-98-96. I will update the Board of the FAA's progress on these safety recommendations separately. I believe that the FAA has satisfactorily responded to Safety Recommendation A-91-87, and I look forward to your response.

From: NTSB
To: FAA
Date: 5/10/2006
Response: The Safety Board notes that on November 4, 2005, the FAA issued a notice of proposed rulemaking (NPRM) titled "Airplane Performance and Handling Qualities in Icing Conditions; Proposed Advisory Circular [AC] 25.21-1X, Performance and Handling Characteristics in the Icing Conditions Specified in Part 25, Appendix C." The Board reviewed this large and technically complex NPRM, and separately submitted technical comments to the docket. The NPRM is responsive to this recommendation. This recommendation is now 14 years old, and it is currently the oldest open aviation safety recommendation. The Board believes that issuance of this NPRM was delayed by important lessons learned from several significant icing accidents during the 1990s, each of which revealed new information concerning the icing problem. Before the NPRM was issued, the FAA conducted flight tests of ice contaminated tailplane stall and investigated airplanes with unpowered control systems that had been certificated without such an evaluation. For airplanes susceptible to ice contaminated tailplane stall, the FAA issued airworthiness directives (ADs) to improve tailplane stall margins. Finally, in August 2004, the FAA issued AC 23.1419 2C, "Certification of Part 23 Airplanes for Flight in Icing." The Board is pleased to see that the NPRM has been issued, and we urge the FAA to move quickly to issue the final rule. Pending issuance of a final rule revising sections of Part 25 regulations and advisory material for evaluating airplane performance and handling characteristics in icing conditions, Safety Recommendation A-91-87 remains classified "Open-Acceptable Response." Safety Recommendations A-96-54, -56, and -58 were issued to the FAA as a result of the Safety Board's investigation of an October 31, 1994, accident in which American Eagle flight 4184, an Avions de Transport Regional Model 72-212 (ATR 72-212), crashed during a rapid descent after an uncommanded roll excursion in icing conditions over Roselawn, Indiana.

From: NTSB
To: FAA
Date: 2/2/2006
Response: Notation 7744A: The National Transportation Safety Board has reviewed the Federal Aviation Administration (FAA) notice of proposed rulemaking (NPRM), Airplane Performance and Handling Characteristics in Icing Conditions, published in the Federal Register (Vol. 70, No. 213) on November 4, 2005. The Safety Board has evaluated the NPRM, which applies to newly certificated designs, in light of current, open recommendations related to aircraft icing and in regard to other concerns identified during the course of its investigations. The Safety Board is providing comments on the following sections: 25.21, Proof of compliance; 25.143, General (controllability and maneuvering); 25.207, Stall warning; and Part 25, Appendix C. The Safety Board will also comment on the Aviation Rulemaking Advisory Committee (ARAC) Flight Test Harmonization Working Group findings in its comments on the relevant sections. The Safety Board has evaluated the proposed sections that detail additional rule changes specific to the phases of flight, as listed in section 25.21, and agrees that they are appropriate and acceptable to fully implement the overall regulation change in section 25.21. The Safety Board therefore will not offer individual comments on those sections. Title 14 Code of Federal Regulations (CFR) Part 25, which the NPRM proposes to revise, contains airworthiness standards for type certification of transport-category airplanes. The NPRM proposes to expand 14 CFR Part 25 to include specific certification requirements for airplane performance or handling qualities for flight in icing conditions and to specify the ice accretions that must be considered for each phase of flight. The FAA states that the proposed revisions will ensure that minimum operating speeds determined during certification of all future transport-category airplanes will provide adequate maneuvering capability in icing conditions for all phases of flight and all airplane configurations. In short, the NPRM proposes to require that the same airplane handling characteristics that apply in non-icing conditions will continue to apply in icing conditions. Additionally, the proposed revisions will harmonize U.S. and European airworthiness standards for flight in icing conditions. Previous Icing Certification Recommendations The Safety Board has been concerned for many years about the inadequacy of the existing certification regulations for flight in icing conditions, which have not required manufacturers to demonstrate an airplane’s flight handling, stall characteristics, minimum airspeeds, and stall margins under a sufficiently realistic range of adverse ice accretions. Additionally, the regulations have not required airplanes to be tested with the thin, rough ice that can accrete on protected surfaces prior to the activation of ice protection systems or between activation cycles of the ice protection systems, especially in larger water droplet environments. These issues came to light during the Board’s investigations of two accidents involving loss of control in icing conditions: United Express flight 2415, a British Aerospace BA-3101, in Pasco, Washington (December 26, 1989), and COMAIR flight 3272, an Embraer EMB-120RT, in Monroe, Michigan (January 9, 1997). United Express flight 2415 involved an ice-contaminated tailplane stall and loss of control at low altitude. Contributing to the loss of control was the accumulation of ice on the airframe, which degraded the aerodynamic performance of the airplane. The United Express 2415 investigation resulted in Safety Recommendation A-91-87: Amend the icing certification rules to require flight tests wherein ice is accumulated in those cruise and approach flap configurations in which extensive exposure to icing conditions can be expected, and require subsequent changes in configuration, to include landing flaps. [Status: “Open—Acceptable Response”] Several years later, the Safety Board investigated the Comair 3272 accident, which involved a loss of control while the airplane was maneuvering with ice accretions on the wings. The Safety Board determined that the probable cause of the accident was the following: The FAA’s failure to establish adequate aircraft certification standards for flight in icing conditions…and the FAA’s failure to require the establishment of adequate minimum airspeeds for icing conditions, which led to the loss of control when the airplane accumulated a thin, rough accretion of ice on its lifting surfaces. As a result of its investigation, the Safety Board issued Safety Recommendation A-98-94 to the FAA: Require manufacturers of all turbine-engine driven airplanes (including the EMB 120) to provide minimum maneuvering airspeed information for all airplane configurations, phases, and conditions of flight (icing and nonicing conditions); minimum airspeeds also should take into consideration the effects of various types, amounts, and locations of ice accumulations, including thin amounts of very rough ice, ice accumulated in supercooled large droplet icing conditions, and tailplane icing. [Current status: “Open—Unacceptable Response”] During the Comair 3272 accident investigation, the Safety Board also noted that the ice accretions and icing conditions considered during certification for flight in icing conditions were not representative of the most critical ice accretions that would be encountered while operating in icing conditions. The current icing certification rules required the certification applicant to demonstrate safe flight using a limited number of icing conditions within the Appendix C icing envelope. The effects of delayed ice protection system activation, intercycle ice accretions, or residual ice accretions were not addressed in the icing certification rules. Icing conditions near the edge of the Appendix C envelope, which are less likely to be encountered, can produce thin, rough ice accretions that research has shown can be as aerodynamically detrimental as the much larger ice shapes that form during flight in the more likely icing conditions. Such thin, rough ice accretions produced at the edge of the envelope icing conditions are dangerous in that they may not be noticed by the flightcrew, or they may not be perceived as a threat based on the crew’s experience accreting ice while flying in more typical, center-of-the-envelope icing conditions. As a result of these findings, the Safety Board issued Safety Recommendation A-98-92 to the FAA: With the National Aeronautics and Space Administration and other interested aviation organizations, conduct additional research to identify realistic ice accumulations, to include intercycle and residual ice accumulations and ice accumulations on unprotected surfaces aft of the deicing boots, and to determine the effects and criticality of such ice accumulations; further, the information developed through such research should be incorporated into aircraft certification requirements and pilot training programs at all levels. [Status: “Open—Acceptable Response”] This recommendation is currently on the Safety Board’s Most Wanted list of safety improvements. In addition to these loss-of-control issues, the Safety Board has addressed the need for an adequate stall warning system for operations during icing conditions. The Board found during the Comair 3272 investigation that the stall warning system installed on the airplane did not provide an adequate warning to the pilots because the system was not designed to account for aerodynamic degradation due to ice accretions or to adjust its warning to compensate for the reduced stall margin caused by ice accretions on the lifting surfaces of the airplane. The lack of a system to warn pilots of impending stall in icing conditions in this accident, and in several other similar incidents, led the Safety Board to issue Safety Recommendation A-98-96: Require the manufacturers and operators of all airplanes that are certificated to operate in icing conditions to install stall warning/protection systems that provide a cockpit warning (aural warning and/or stick shaker) before the onset of stall when the airplane is operating in icing conditions. [Status: “Open—Acceptable Response”] Following are the Safety Board’s comments on the proposed regulatory changes, presented in light of past accident and incident investigations where loss of control due to ice accretion was a factor or causal or the lack of a stall warning system was an issue. Section 25.21, Proof of Compliance The Safety Board notes that current Part 25, Subpart F, regulations for airplanes with approved ice protection state that airplanes must be able “to safely operate” in icing conditions. However, no standard set of criteria currently defines what “to safely operate” means in terms of performance and handling characteristics. The Safety Board agrees with the NPRM that a loss of control is the greatest threat to safety in icing conditions and warrants a change to the regulations to define safe operations for flight in icing conditions. Additionally, the Safety Board agrees with ARAC’s Flight Test Harmonization Working Group (FTHWG) that to ensure safe flight in icing conditions, airplanes with ice accretions should comply with Part 25, Subpart B. The NPRM seeks to address this issue by adding paragraph (g)(1) to section 25.21, which will require flight in icing conditions to comply with the same handling requirements and most of the performance requirements that are currently required for flight in non-icing conditions. The NPRM also states that compliance must be demonstrated using the ice accretions defined in Appendix C of Part 25, and assuming normal operation of the airplane and its ice protection system as specified in the Airplane Flight Manual (AFM). By referencing the AFM, this paragraph requires the AFM to include the limitations and operating procedures that are specific to operations in icing conditions. The Safety Board will comment on the use of Appendix C ice accretions for evaluating handling and performance later in these comments. The Safety Board agrees with the FAA that airplane operations in icing conditions should not diminish the safety margins, handling qualities, and performance of the airplane, and that the airplane should be as safe to operate in icing as in non-icing conditions. The Safety Board believes further that the proposed change to section 25.21, by adding specific performance and handling requirements that must be satisfied to certify an airplane for operation in icing conditions (for example, requirements for takeoff performance and landing climb performance), will provide an additional margin of safety for these airplanes. The Safety Board therefore endorses the proposed changes to the section 25.21 regulations, and the following associated sections listed in the NPRM, which will also impose the same performance and handling requirements for icing conditions as for non-icing conditions: 25.103, Stall speed; 25.105, Takeoff; 25.107, Takeoff speeds; 25.211, Takeoff path; 25.119, Landing climb: All-engines operating; 25.121, Climb: One-engine inoperative; 25.123, En route flight paths; and 25.125, Landing. The Safety Board notes that the requirements of these sections will establish minimum maneuvering speeds while in icing conditions, and will therefore satisfy that part of Safety Recommendation A-98-94 that addresses the need to provide minimum maneuvering airspeeds for all airplane configurations and phases of flight in icing conditions. Section 25.143, Controllability and Maneuverability—General This section of the NPRM addresses three issues of interest to the Safety Board: minimum control speed, tailplane stall, and visual detection of ice accretions. Minimum Control Speed. The NPRM states that it proposes to revise section 25.143 by adding a new paragraph (c) that will require a certification applicant to show that an airplane with ice accretions appropriate to the phase of flight and with the critical engine inoperative is safely controllable and maneuverable during takeoff, approach and go-around, and approach and landing. The NPRM states that the requirements proposed in paragraph (c) are intended to ensure that using the minimum control speeds for non-icing conditions will not degrade controllability and maneuverability when the same speeds are used for icing conditions. An additional paragraph, (i)(1), is also proposed, which defines the ice accretions that must be used in demonstrating compliance with 25.143. Paragraph (i)(1) states that controllability must be demonstrated with the ice accretion that proposed Appendix C defines as most critical for that particular phase of flight. The NPRM notes that by using the most critical ice accretion to determine minimum control speeds for each flight phase, certification applicants can minimize the number of ice accretions that must be tested by using one accretion that is shown to be the most critical accretion for several flight phases. The Safety Board believes that inclusion of the requirement for certification applicants to demonstrate that the minimum control speeds provide adequate controllability and maneuverability with ice accretions on the airplane [new paragraph (c)] will provide an additional level of safety for operations in icing conditions, provided that the most critical ice accretion used [new paragraph (i)(1)] is validated as such, and is tested for the respective phase of flight, as indicated in Appendix C. Section 25.143 also provides information about the thin, rough layer of ice defined as “sandpaper” ice in the proposed revision to Appendix C. The NPRM states that such ice has been shown to have a more detrimental effect on handling qualities for airplanes with unpowered control systems than larger ice accretions. In some cases, the NPRM goes on to say, a small, rough ice accretion has resulted in control surface hinge moment reversals that required the flightcrew to apply extremely high forces to the controls to regain control of the airplane. The NPRM states that certification applicants must consider sandpaper ice as a critical ice shape in showing compliance with proposed paragraph 25.143(i). The Safety Board agrees that thin, rough ice accretions must be considered when evaluating an airplane’s controllability and performance in icing conditions. However, the Safety Board believes that the sandpaper ice used to demonstrate compliance with proposed paragraph 25.143(i) should accurately represent the thin, rough ice accreted in the most severe and edge of the-envelope icing conditions. The Safety Board believes that use of these extreme conditions should be required to evaluate critical ice shapes. Inclusion of the edge of the envelope conditions is particularly important when determining the chordwise extent of the thin, rough, sandpaper-type ice accretions. In its letter commenting on proposed Advisory Circular 25-1X, the Safety Board noted that the results of research sponsored by the FAA and NASA are currently included in Appendix R of draft AC 20-73, Aircraft Ice Protection. Appendix R includes guidance on determining critical ice shapes and their associated roughness, and descriptions of ice accreted before activation of an ice protection system and between ice protection cycles, and the aerodynamic penalties associated with these ice shapes. The Safety Board noted that by issuing the revision to AC 20-73, and by including information like that found in Appendix R, the FAA is providing useful information for better evaluating an airplane’s performance and handling capabilities in icing conditions. The Safety Board believes that, by providing examples of thin, rough ice accretions, intercycle ice accretions, and residual ice, by including paragraph 25.143(i)(1) in the regulations, and by ensuring that the most extreme conditions are examined, the FAA will satisfy the intent of Safety Recommendation A-98-92. Tailplane Stall. The NPRM proposes to add paragraph 25.143(i)(2), which would require applicants to evaluate an airplane’s susceptibility to ice-contaminated tailplane stall (ICTS) by conducting a pushover maneuver down to a zero g load factor (or the lowest load factor obtainable if limited by elevator power) with the critical ice accretion on the airplane. This issue was also described in the NPRM as an area of non-consensus in the FTHWG, as some members believed that the requirement to maintain a push force throughout the maneuver should be limited to higher values of load factor during the push down maneuver (0.5g and 0.25g were suggested alternatives). The FTHWG did agree, however, that the test should be conducted down to zero g. Safety Board investigations have shown that loss of control in icing conditions can be an extremely sudden and dynamic event. The Safety Board believes that a control force reversal, whether ice-induced or not, would be unacceptable within the flight envelope of any airplane (which includes load factors to zero g). The Safety Board supports the proposal as written in the NPRM to require a push force on the control column through the entire ICTS evaluation pushover maneuver. The Safety Board believes that incorporation of the zero-g pushover test into the regulations for flight in icing conditions will adequately address the intent of Safety Recommendation A-91-87. The Safety Board therefore endorses the inclusion of paragraph (i)(2) to the icing certification requirements of section 25.143. Visual Detection of Ice Accretion. The FAA also proposes to add paragraph 25.143(j), which would address airplane controllability from the time an airplane first enters icing conditions until the ice protection system is activated and performing as intended. This paragraph allows two different means of compliance, based on the method used to detect the icing conditions. If the means of detecting the icing conditions is dependent upon the pilot recognizing a specified amount of ice on a reference surface (for example, 1/4 inch of ice on the wing or 1/2 inch of ice on the windshield wiper), the requirements of section 25.143 must be met with the ice accretion defined in the proposed Appendix C, part II(e), and by proposed AC 25-1X, accounting for the time prior to activation of the ice protection system. If other methods are used to detect the icing conditions—initial ice accretion on an ice probe, for example—the requirements for demonstrating compliance would be less stringent for smaller ice accretions. This portion of the proposed regulation is based on the expectation that the aircraft would be in icing conditions for a brief time. The less stringent handling requirements involve the following maneuvers with the pre-activation ice shape that is expected before the ice protection system activates: (1) demonstrating controllability in a pull-up maneuver to 1.5g load factor and (2) demonstrating no longitudinal force reversal in a pushover maneuver to 0.5g load factor. The NPRM mentions that the FTHWG did not concur with the proposal to impose a different set of compliance requirements based on the means of detecting icing conditions. In the non-consensus discussion, the Air Line Pilots Association argued that any means of visual ice detection, whether trace amounts or a specified amount, relies on the flightcrew to monitor conditions outside the cockpit, and hence should be subject to the more stringent requirements. The Safety Board believes that several factors that the flightcrew may encounter during icing conditions, such as higher workload and reduced visibility, can considerably delay their recognition of icing conditions when a visual means is used, regardless of the amount of ice being observed. The flightcrew’s failure to recognize ice accretion, their perception that the ice accretion is not a threat, and the presence of clear ice have all been factors in accidents and incidents. Thin, rough ice, which can develop quickly and is difficult to detect visually, particularly that near the edge of the Appendix C icing envelope, can be enough to cause considerable aerodynamic penalty, particularly if the surface used for visual detection is a lifting surface like the wing. Hence, full controllability and maneuverability evaluation of the airplane with the ice accretion that would be expected with a considerably delayed visual detection is warranted. The Safety Board believes that for airplanes that rely on a visual means of ice detection, the more stringent rules should apply. Section 25.207, Stall Warning The NPRM proposes to revise section 25.207 to require that “the means for providing a warning of an impending stall must be the same for both icing and non-icing conditions.” Additionally, the NPRM proposes to add a paragraph to require that stall warnings in icing conditions be sufficient to allow the pilot to take corrective action to prevent stalling in both straight and turning flight, using the same recovery techniques as in icing conditions, and describes the ice accretions that must be considered in demonstrating compliance. The proposed rule also specifically addresses the time between the start of an icing encounter and activation of the ice protection system. The NPRM states that this time period is dependent upon the means of detecting the icing conditions, and if that means is dependent upon the pilot recognizing a specified amount of ice on a reference surface, the time period could be longer. The NPRM proposes that, if the pilot is visually recognizing a specific amount of ice (hence, imposing a potentially longer period before the ice protection activates), the same stall warning requirements would apply as when the ice protection system is fully active. However, if the detection of icing conditions does not depend upon the pilot recognizing a specified amount of ice on a reference surface (for example, because an ice detector is being used), the proposed rule also allows for a different method of stall warning (for example, airframe buffet) to be used while the airplane is accreting ice and before the ice protection system activates. In a case like this, a more stringent testing procedure (that is, a longer period of time prior to activation of the ice protection system) will be required to demonstrate compliance. Ensuring that all airplanes are equipped with stall warning devices that will provide adequate stall warning while those airplanes operate in icing conditions is the subject of previously described Safety Recommendation A-98-96. The Safety Board believes the proposed rules rectify a serious shortcoming in the current rules, which do not consider ice accretions on the airplane in evaluating the stall warning system. The Safety Board believes the proposed changes will satisfy the intent of this recommendation, and supports its inclusion in the certification rules. Proposed Appendix C, Part II The proposed changes to Appendix C state that the most critical ice accretions for each phase of flight must be determined considering the atmospheric conditions of part I of Appendix C and the flight conditions (such as angle of attack, configuration, and airspeed.). Ice accretions to be determined include those on the unprotected surfaces and on the protected surfaces as appropriate to normal ice protection system operation; these ice accretions must include takeoff ice, final takeoff ice, en route ice, holding ice, landing ice, and sandpaper ice. The proposed change also specifies that the ice must form before the ice protection system activates and is performing its intended function. The Safety Board believes that the proposed changes to Appendix C do not ensure that the airplane is tested in the most severe icing conditions as defined in the icing atmospheric envelope of Appendix C. As a result of its investigation of the Roselawn accident, the Safety Board issued Safety Recommendation A-96-56 to the FAA, which recommended the following: Revise the icing certification testing regulation to ensure that airplanes are properly tested for all conditions in which they are authorized to operate, or are otherwise shown to be capable of safe flight into such conditions. If the manufacturer cannot demonstrate safe operations, operational limitations should be imposed to prohibit flight in such conditions and flightcrews should be provided with the means to positively determine when they are in icing conditions that exceed the limits for aircraft certification. [Status: “Open—Unacceptable Response”] This recommendation is also on the Safety Board’s Most Wanted list of safety improvements. Although the proposed rule specifies the icing conditions that must be considered in determining the ice accretions for each phase of flight, the intent of Safety Recommendation A-96-56 is to ensure that the testing occurs in the range of conditions in which the airplane is authorized to operate—in particular, in the most hazardous icing conditions—and that the testing ensures that airplane performance is evaluated at the limits of the Part 25 Appendix C envelope for droplet size and liquid water content. The Safety Board agrees that the most critical ice shape must be determined for each phase of flight and its corresponding flight conditions, and that the resulting critical ice shape may be different for each phase of flight. The Board believes further that the additional requirements to examine the accretions for each phase of flight would be positive enhancements to the evaluation procedure for certification for flight in icing conditions. However, past Safety Board investigations of icing accidents and incidents have shown that some aircraft may not have been exposed to the full range of Appendix C conditions for all phases of flight during icing certification, and hence, have not been subject to the most critical ice shapes. The Board therefore believes that the proposed rules should also require applicants to justify their selection of the most critical ice shape for each phase of flight to ensure that the most critical shape is being used for the respective phase of flight. For each phase of flight, the applicant should be required to demonstrate that the shape, chordwise and spanwise, and the roughness of the shapes considered in selection of a critical ice shape accurately reflect the full range of Appendix C conditions that have been examined in terms of mean effective drop diameter, liquid water content, and temperature during the respective phase of flight. Additionally, the FAA should review the justification and selection of the most critical ice shape for each phase of flight. Finally, the Safety Board wishes to stress that super-cooled large droplet (SLD) conditions can be more hazardous than conditions considered during current icing certification, and accident experience has shown that SLD conditions can cause ice accretions that are more aerodynamically detrimental than those developed while flying within the Part 25 Appendix C envelope. Additionally, the accident and incident history has shown that many of the smaller turboprop airplanes spend much more of their operational time in regions of the atmosphere that are likely to contain SLD conditions than the larger, turbojet type airplanes. As a result of the Roselawn investigation, the Safety Board issued Safety Recommendation A-96-54, which requested the following of the FAA: Revise the icing criteria published in 14 Code of Federal Regulations (CFR), Parts 23 and 25, in light of both recent research into aircraft ice accretion under varying conditions of liquid water content, drop size distribution, and temperature, and recent developments in both the design and use of aircraft. Also, expand the Appendix C icing certification envelope to include freezing drizzle/freezing rain and mixed water/ice crystal conditions, as necessary. [Status: “Open—Unacceptable Response”] This recommendation is also currently on the Safety Board’s Most Wanted list of safety improvements. The proposed rules do not address this recommendation, and the Safety Board continues to await the FAA’s proposed regulatory changes to 14 CFR Part 25 in response to A 96-54 to include SLD conditions in the icing certification envelope. The Safety Board believes that the proposed rulemaking is an essential step in improving the safety of flight in icing conditions for airplanes certified under Part 25. The Safety Board appreciates the opportunity to comment on this notice of proposed rulemaking.

From: NTSB
To: FAA
Date: 2/2/2006
Response: The National Transportation Safety Board has reviewed the Federal Aviation Administration (FAA) notice of proposed rulemaking (NPRM), Airplane Performance and Handling Characteristics in Icing Conditions, published in the Federal Register (Vol. 70, No. 213) on November 4, 2005. The Safety Board has evaluated the NPRM, which applies to newly certificated designs, in light of current, open recommendations related to aircraft icing and in regard to other concerns identified during the course of its investigations. Previous Icing Certification Recommendations The Safety Board has been concerned for many years about the inadequacy of the existing certification regulations for flight in icing conditions, which have not required manufacturers to demonstrate an airplane's flight handling, stall characteristics, minimum airspeeds, and stall margins under a sufficiently realistic range of adverse ice accretions. Additionally, the regulations have not required airplanes to be tested with the thin, rough ice that can accrete on protected surfaces prior to the activation of ice protection systems or between activation cycles of the ice protection systems, especially in larger water droplet environments. These issues came to light during the Board's investigations of two accidents involving loss of control in icing conditions: United Express flight 2415, a British Aerospace BA-3101, in Pasco, Washington (December 26, 1989), and COMAIR flight 3272, an Embraer EMB-120RT, in Monroe, Michigan (January 9, 1997). United Express flight 2415 involved an ice-contaminated tailplane stall and loss of control at low altitude. Contributing to the loss of control was the accumulation of ice on the airframe, which degraded the aerodynamic performance of the airplane. The United Express 2415 investigation resulted in Safety Recommendation A-91-87: Amend the icing certification rules to require flight tests wherein ice is accumulated in those cruise and approach flap configurations in which extensive exposure to icing conditions can be expected, and require subsequent changes in configuration, to include landing flaps. [Status: "Open-Acceptable Response"] Several years later, the Safety Board investigated the Comair 3272 accident, which involved a loss of control while the airplane was maneuvering with ice accretions on the wings. The Safety Board determined that the probable cause of the accident was the following: The FAA's failure to establish adequate aircraft certification standards for flight in icing conditions ... and the FAA's failure to require the establishment of adequate minimum airspeeds for icing conditions, which led to the loss of control when the airplane accumulated a thin, rough accretion of ice on its lifting surfaces.

From: NTSB
To: FAA
Date: 1/3/2006
Response: Notation 7744: The National Transportation Safety Board has reviewed the Federal Aviation Administration (FAA) proposed Advisory Circular (AC) 25.21-1X, Performance and Handling Characteristics in the Icing Conditions Specified in Part 25, Appendix C, published in the Federal Register (Vol. 70, No. 213) on November 4, 2005. The Safety Board has evaluated the proposed AC in light of current, open recommendations related to aircraft icing and in regard to other concerns identified during the course of its accident and incident investigations. The intent of the proposed AC is to provide acceptable methods of compliance with proposed certification requirements for performance and handling characteristics of transport-category airplanes affected by flight in the icing conditions defined in Appendix C of Title 14, Code of Federal Regulations (CFR) Part 25. The AC states that the means of compliance in this document are intended to provide guidance to supplement the engineering and operational judgment that must form the basis of any compliance findings relative to handling characteristics and performance in Appendix C icing conditions. The AC also states that it provides one means, but not the only means, of complying with the airworthiness standards revisions proposed in Notice No. 05-10, titled “Airplane Performance and Handling Qualities in Icing Conditions,” published in the same edition of the Federal Register. The Safety Board is closely evaluating this notice of proposed rulemaking (NPRM), which contains the changes to the CFR requirements that must be adhered to by applicants. The Safety Board will comment on Notice No. 05-10 separately. The materials contained within the AC, commented upon in this letter, are a strictly advisory means of compliance for the applicants. The notice of the proposed AC states that the AC is based on recommendations submitted to the FAA by the Aviation Rulemaking Advisory Committee (ARAC), which was tasked by the FAA to provide advice and recommendations on “harmonizing” certain sections of Part 25 (including section 25.21) with the counterpart standards contained in Joint Aviation Requirements (JAR). The goal of the “harmonization tasks” is to ensure the following: 1. Where possible, standards and guidance do not require domestic and foreign parties to manufacture or operate to different standards for each country involved; and 2. The standards and guidance adopted are mutually acceptable to the FAA and the foreign aviation authorities; 3. The guidance contained in the proposed AC has been harmonized with that of the Joint Aviation Authority (JAA), and provides a method of compliance that has been found acceptable to both the FAA and JAA. The Safety Board has issued several recommendations to the FAA regarding performance and handling in icing conditions that pertain to the proposed AC. These include Safety Recommendation A-91-87, which recommended the following to the FAA: Amend the icing certification rules to require flight tests wherein ice is accumulated in those cruise and approach flap configurations in which extensive exposure to icing conditions can be expected, and require subsequent changes in configuration, to include landing flaps. The flight testing described in the proposed AC describes flight testing with simulated ice accretions as the primary means for showing compliance with the regulations, and states that the objective of the natural atmospheric icing testing is to corroborate the handling characteristics and performance results obtained in flight tests with simulated ice accretions. The natural atmospheric icing condition testing described in paragraph 3u(2)(b) of the proposed AC would include accreting ½ inch ice in flight while at the trimmed holding speeds with the airplane configured with flaps and gear retracted. The airplane configuration would then be changed by subsequent flap deployment positions and further accretions of ice while at each new flap setting. After the ice accreted an additional ¼ inch, several maneuvers, including bank-to-bank rolls and decelerations to the speed reached 3 seconds after the activation of a stall warning, would be performed. This testing would conclude with ice accreting while the airplane was configured with the landing flap setting in the landing gear down position. The handling maneuvers would then start with the airplane flying at the VREF trim speed. The testing specified in the AC guidance is of the type that the Safety Board recommended as mandatory in Safety Recommendation A-91-87. The proposed testing guidelines for approach and landing with successive ice accretions in different airplane configurations address in part Safety Recommendation A-91-87. However, the Safety Board notes that the proposed AC does not address scenarios when ice is accreted with flaps deployed, and with flaps subsequently retracted. The Safety Board is concerned with this type of ice accretion scenario, which played a role in the 1994 ATR-72 accident in Roselawn, Indiana. Also in reference to Safety Recommendation A-91-87, the Safety Board notes that the zero-g pushover flight test maneuver, described in paragraph 3i(3)(a) of the proposed AC, is a reasonable means for evaluating an airplane’s susceptibility to ice-contaminated airplane stall. Additional flight testing with simulated ice shapes is described to evaluate the potential for ice-contaminated tailplane stall while operating in a sideslip. The Safety Board believes that the types of flight tests mentioned above would adequately address the intent of regulations recommended in A-91-87. The Safety Board also notes that paragraph 3i(2)(g) describes an additional acceptable flight test program using simulated ice accretion shapes that would include the evaluation of an approach and landing, wherein satisfactory controllability should be demonstrated during a landing conducted at an airspeed of VREF minus 5 knots, using a heavy airplane weight and forward center of gravity. The Safety Board believes this is a useful way to evaluate airplane performance during maneuvers that may be performed at less than the minimum reference speed. During the Comair 3272 accident, which occurred in Monroe, Michigan, the Safety Board issued recommendation A-98-92, which recommended the following to the FAA: With the National Aeronautics and Space Administration and other interested aviation organizations, conduct additional research to identify realistic ice accumulations, to include intercycle and residual ice accumulations and ice accumulations on unprotected surfaces aft of the deicing boots, and to determine the effects and criticality of such ice accumulations; further, the information developed through such research should be incorporated into aircraft certification requirements and pilot training programs at all levels. This recommendation is currently on the Safety Board’s Most Wanted list of safety improvements. The results of research sponsored by the FAA and NASA are currently included in Appendix R of draft AC 20-73. Appendix R is also referenced in Appendix 1, Airframe Ice Accretion, and Appendix 2, Simulated Ice Shapes, of proposed AC 25.21-1X. Appendix R includes guidance on determining critical ice shapes and their associated roughness, and descriptions of ice accreted in the time prior to activation of an ice protection system, intercycle ice accretions, and the aerodynamic penalties associated with these ice shapes. The Safety Board notes that by issuing the revision to AC 20-73, and including information like that found in Appendix R, the FAA is providing useful information for better evaluating an airplane’s performance and handling capabilities in icing conditions. The Safety Board is aware that research by other agencies, universities, and entities is ongoing in the area of in-flight ice accretions and their effects on aircraft, and encourages the FAA to continue to incorporate into the advisory materials additional information and results from ongoing research as they become available. The intent of A-98-92 would be partially met with the inclusion of Appendix R in AC 20-73, which has not yet been issued. The importance of Appendix R is further enhanced by its repeated reference in draft AC 25.21-1X. The Safety Board will be evaluating the associated NPRM to determine how this information will be integrated with the proposed certification requirements. In addition to the testing described above, the Safety Board is concerned that the proposed AC does not ensure that the airplane is tested in the most severe icing conditions that are defined in the icing design envelope (Appendix C). As a result of its investigation of the Roselawn accident, the Safety Board issued Safety Recommendation A-96-56 to the FAA, which recommended the following: Revise the icing certification testing regulation to ensure that airplanes are properly tested for all conditions in which they are authorized to operate, or are otherwise shown to be capable of safe flight into such conditions. If the manufacturer cannot demonstrate safe operations, operational limitations should be imposed to prohibit flight in such conditions and flightcrews should be provided with the means to positively determine when they are in icing conditions that exceed the limits for aircraft certification. This recommendation is also on the Safety Board’s Most Wanted list of safety improvements. Whereas the proposed AC provides guidance on several flight-testing procedures that can be used to evaluate the performance and handling qualities of an airplane in icing conditions, the intent of Safety Recommendation A-96-56 is to ensure that the testing occurs in the range of conditions in which the airplane is authorized to operate—in particular, in the most hazardous icing conditions—and that the testing ensures evaluation at the limits of the Part 25 Appendix C envelope. The Safety Board notes that Appendix 1 of the proposed AC states that the most critical ice accretion in terms of handling characteristics and/or performance should be determined. The parameters to be considered should include the flight conditions (for example, airplane configuration, speed, angle of attack, altitude) and the icing conditions of Appendix C (for example, temperature, liquid water content, mean effective drop diameter). Similarly, Appendix 2 of the proposed AC provides guidance for using simulated ice accretions and states that the simulated ice accretions used for flight testing should be those that have the most adverse effects on handling characteristics. The simulated accretions should represent natural icing conditions in terms of location, general shape, thickness, and texture. The Safety Board agrees that the most critical ice shape must be determined for each phase of flight and its corresponding flight conditions, and that the resulting critical ice shape may be different for each phase of flight. Past Safety Board investigations of icing accidents and incidents have shown that some aircraft may not have been exposed to the full range of Appendix C conditions for all phases of flight, and hence, have not been subject to the most critical ice shapes during icing certification. Appendix 1 of the proposed AC specifies that icing conditions of Appendix C be considered in developing the critical ice accretions used in certification testing, and states the applicant should substantiate the conditions that result in the formation of the critical ice accretion. The Safety Board believes that the proposed AC should also provide means for applicants to justify their selection of the most critical ice shape for each phase of flight to ensure that the most critical shape is the one being used for the respective phase of flight. For each phase of flight, the applicant should ensure the shape, chordwise and spanwise, and the roughness of the shapes, considered in selection of a critical ice shape, accurately reflect the full range of Appendix C conditions that have been examined in terms of mean effective drop diameter, liquid water content, and temperature during the respective phase of flight. Additionally, the FAA should review the justification and selection of the most critical ice shape for each phase of flight. The proposed AC specifies that icing conditions of Appendix C be considered in developing the critical ice accretions used in certification testing. However, means are not provided to ensure that the full range of Appendix C conditions are examined by the applicant in determining the most critical ice shape for each phase of flight. The Safety Board therefore notes that the intent of A-96-56 will not be met, and is awaiting the proposed changes to 14 CFR Part 25 in response to Safety Recommendation A-96-56, as well as proposed changes to 14 CFR Part 25 in response to recommendation A-96-54 to include regulatory requirements that an airplane can safely operate in super-cooled large droplets (SLD) or detect and safely exit the SLD conditions. Finally, the Safety Board wishes to stress that SLD conditions can be more hazardous than those considered during current icing certification, and accident experience has shown that SLD conditions can cause ice accretions more aerodynamically detrimental than those developed while flying within the Part 25 Appendix C envelope. Additionally, the accident and incident history has shown that many of the smaller, turboprop airplanes spend much more of their operational time in regions of the atmosphere that are more likely to contain SLD conditions than the larger, turbojet type airplanes. As a result of the Roselawn investigation, the Safety Board issued recommendation A-96-54, which requested the following of the FAA: Revise the icing criteria published in 14 Code of Federal Regulations (CFR), Parts 23 and 25, in light of both recent research into aircraft ice accretion under varying conditions of liquid water content, drop size distribution, and temperature, and recent developments in both the design and use of aircraft. Also, expand the Appendix C icing certification envelope to include freezing drizzle/freezing rain and mixed water/ice crystal conditions, as necessary. This recommendation is also currently on the Safety Board’s Most Wanted list of safety improvements. The proposed AC does not address this recommendation, and the Safety Board continues to await the FAA’s proposed regulatory changes to 14 CFR Part 25 in response to A 96-54. The Safety Board appreciates the opportunity to comment on this proposed AC.

From: FAA
To: NTSB
Date: 10/26/2005
Response: Letter Mail Controlled 10/27/2005 2:12:40 PM MC# 2050501 Marion C. Blakey, Administrator, FAA, 10/26/05 The Federal Aviation Administration is continuing its efforts to revise the 14 CFR Part 25 requirements and related advisory material to introduce new requirements for evaluating airplane performance and handling characteristics of transport-category airplanes for flight in the icing conditions of 14 CFR Part 25, Appendix C. There has been a delay in the publication of these documents and it is now anticipated that they will be published for comment by October 2005. Although the proposed notice of proposed rulemaking (NPRM) and advisory circular (AC) have been delayed, the FAA has been responsive to the safety issue addressed in this safety recommendation. The FAA has been conducting flight test evaluations for susceptibility to ice-contaminated tailplane stall for all airplanes approved for flight in icing conditions since the mid-1990s. The FAA has also investigated airplanes with unpowered control systems operating under 14 CFR Parts 121 and 135 operating rules that had been certificated without such an evaluation. For those airplanes found to be susceptible to ice-contaminated tailplane stall, the FAA mandated changes through airworthiness directives (AD) to improve tailplane stall margins. Also, AC 23.1419-2C, Certification of Part 23 Airplanes for Flight in Icing, was issued in August 2004 and guidance on ice accretions in the landing configuration has been added. The proposed NPRM will provide a comprehensive set of new certification requirements to evaluate airplane performance and handling characteristics in icing conditions in order to improve the level of safety for operation in icing conditions. One of the proposed certification requirements will be to conduct a flight test maneuver that is designed to evaluate airplanes for susceptibility to ice-contaminated tailplane stall. This evaluation takes into account lessons learned from analyses of icing accidents that have occurred sincc the accident that generated this safety recommendation. Therefore, it will address more potential causes of ice-contaminated tailplane stall than the single concern identified in this safety recommendation. In addition to the concern identified in the safety recommendation, this evaluation considers changes in flight conditions (for example, a high approach speed resulting in an increased flap downwash angle, gusts, maneuvering, or changes to engine power setting, as well as lateral airflow effects like a sideslip or a lateral wind gust). An accompanying AC will provide detailed guidance on acceptable means of compliance with the new requirements. The proposed AC will include several flight test maneuver conditions with ice being progressively accreted while the airplane configuration changes from flaps and gear retracted with the airplane trimmed at the recommended holding speed to flaps and gear fully extended with the airplane trimmed at the landing reference speed. I will provide the Board with copies of the NPRM and AC as soon as they are published for comment.

From: NTSB
To: FAA
Date: 7/31/2003
Response: The Safety Board is pleased that the FAA is responding positively to this recommendation, but feels compelled to note that it has been 11 1/2 years since it was issued. The Board is aware that several prominent aviation accidents occurred during the 1990s in which icing was a factor and from which important lessons were learned. The Board believes that analyses of these accidents should result in a more complete response to this recommendation. Pending publication of the NPRM by June 2004 and adoption of a final rule, Safety Recommendation A-91-87 remains classified "Open--Acceptable Response."

From: FAA
To: NTSB
Date: 5/5/2003
Response: Letter Mail Controlled 5/13/2003 10:57:31 AM MC# 2030238 The Aviation Rulemaking Advisory Committee has drafted recommended changes to 14 CFR Part 25 requirements and related advisory material to introduce new requirements for evaluating airplane performance and handling characteristics of transport-category airplanes for flight in the icing conditions of 14 CFR Part 25, Appendix C. The Federal Aviation Administration (FAA) will publish a notice of proposed rulemaking (NPRM) based on these recommendations. It is anticipated that the NPRM will be issued by June 2004. The recommendations include a proposed regulatory amendment that contains a flight test maneuver to evaluate airplanes for susceptibility to ice-contaminated tailplane stall. The advisory material provides detailed flight test guidance, including consideration of critical ice accretions that may be accumulated during extensive exposure to icing conditions, and evaluated in the most critical landing configurations. I will keep the Board informed on the FAA's progress on this safety recommendation.

From: NTSB
To: FAA
Date: 1/4/2001
Response: THE SAFETY BOARD IS CONCERNED ABOUT THE LENGTH OF TIME IT HAS TAKEN TO COMPLETE WORK ON THIS RECOMMENDATION. THE BOARD NOTES THAT IT HAS BEEN ABOUT 9 YEARS SINCE THIS RECOMMENDATION WAS ISSUED. HOWEVER, THE BOARD ALSO NOTES THAT SEVERAL PROMINENT AVIATION ACCIDENTS OCCURRED DURING THE 1990'S IN WHICH ICING WAS AN IMPORTANT CONSIDERATION AND FROM WHICH IMPORTANT INFORMATION WAS LEARNED. THEREFORE, ALTHOUGH THE BOARD UNDERSTANDS THE REASONS FOR THE DELAY IN COMPLETING THIS WORK, THE BOARD ALSO BELIEVES THAT THE FAA SHOULD COMPLETE THIS WORK SOON. PENDING AMENDMENT OF THE ICING CERTIFICATION RULES, A-91-87 REMAINS CLASSIFIED "OPEN--ACCEPTABLE RESPONSE."

From: FAA
To: NTSB
Date: 8/29/2000
Response: Letter Mail Controlled 09/01/2000 1:25:45 PM MC# 2001200 ON 4/29/94, THE FAA ISSUED A POLICY MEMORANDUM TO ALL CERTIFICATION OFFICES DESCRIBING THE TAILPLANE STALL PHENOMENON AND DEFINING A FLIGHT TEST MANEUVER (ZERO-G PUSHOVER MANEUVER) TO IDENTIFY SUSCEPTIBILITY TO ICE-CONTAMINATED TAILPLANE STALL. ON 3/31/98, THE FAA ISSUED ADVISORY CIRCULAR (AC) 25-7, FLIGHT TEST GUIDE FOR CERTIFICATION OF TRANSPORT CATEGORY AIRPLANES. THE AC INCLUDES GUIDANCE MATERIAL DEFINING ZERO-G PUSHOVER MANEUVER FOR SHOWING COMPLIANCE WITH 14 CFR 25.143, CONTROLLABILITY AND MANEUVERABILITY. COPIES OF THE POLICY MEMORANDUM AND THE AC WERE PROVIDED TO THE BOARD. THE FLIGHT TEST HARMONIZATION WORKING GROUP HAS NOW COMPLETED THE TECHNICAL CONTENT OF PROPOSED 14 CFR PART 25 REGULATIONS AND ADVISORY MATERIAL FOR EVALUATING AIRPLANE PERFORMANCE AND HANDLING CHARACTERISTICS IN THE ICING CONDITIONS OF APPENDIX C AND IS CURRENTLY DEVELOPING ITS PROPOSALS. THESE PROPOSALS INCLUDE A REQUIREMENT TO INVESTIGATE AIRPLANE SUSCEPTIBILITY TO ICE-CONTAMINATED TAILPLANE STALL. THE FAA WILL PUBLISH A NOTICE OF PROPOSED RULEMAKING (NPRM) AFTER THE ARAC COMPLETES ITS WORK. IT IS ANTICIPATED THAT THE NPRM WILL BE PUBLISHED IN EARLY 2002. I WANT TO EMPHASIZE THAT UNTIL THE RULEMAKING EFFORT IS COMPLETED, THE FAA WILL REVIEW EACH SIGNIFICANT PROJECT RELATED TO ICING TO ENSURE THROUGH THE PROVISIONS OF 14 CFR 21.21(B)(2) THAT NO UNSAFE CONDITION EXISTS. I WILL KEEP THE BOARD INFORMED OF THE FAA'S PROGRESS ON THIS RECOMMENDATION.

From: NTSB
To: FAA
Date: 3/16/2000
Response: ON 3/16/00 THE SAFETY BOARD REQUESTED AN UPDATE ON THE STATUS OF THIS RECOMMENDATION.

From: NTSB
To: FAA
Date: 3/1/1999
Response: THE BOARD NOTES THE CHANGES IN AC 25-7A AS THEY PERTAIN TO FLIGHT TESTING IN ICING CONDITIONS. THESE CHANGES OFFER GUIDANCE IN TESTING FLIGHT OPERATIONS IN ICING CONDITIONS, AND THE EXPECTED NEW RULES THAT MAY RESULT FROM THE ACTIONS OF THE ARAC PROCESS SHOULD PROVIDE UPDATED GUIDANCE IN THIS CRITICAL FIELD. A-91-87 IS CLASSIFIED "OPEN--ACCEPTABLE RESPONSE," PENDING THE ACTIONS OF THE ARAC EFFORT.

From: FAA
To: NTSB
Date: 12/11/1998
Response: Letter Mail Controlled 02/19/1999 10:03:45 AM MC# 981470 ON 4/29/94, THE FAA ISSUED A POLICY MEMORANDUM TO ALL CERTIFICATION OFFICES DESCRIBING THE TAILPLANE STALL PHENOMENA AND DEFINING A FLIGHT TEST MANEUVER (ZERO-G PUSHOVER MANEUVER) TO IDENTIFY SUSCEPTIBILITY TO ICE CONTAMINATED TAILPLANE STALL. ON 3/31/98, FAA ISSUED ADVISORY CIRCULAR (AC) 25-7, FLIGHT TEST GUIDE FOR CERTIFICATION OF TRANSPORT CATEGORY AIRPLANES. THE AC INCLUDES GUIDANCE MATERIAL ON ZERO-G PUSHOVER MANEUVER FOR COMPLIANCE WITH 14 CFR 25.143, CONTROLLABILITY AND MANEUVERABILITY. I HAVE ENCLOSED A COPY OF THE AC FOR THE BOARD'S INFORMATION. AN AVIATION RULEMAKING ADVISORY COMMITTEE (ARAC) PROJECT TO HARMONIZE REGULATORY AND ADVISORY MATERIAL FOR EVALUATING AIRPLANE PERFORMANCE AND HANDLING CHARACTERISTICS IN THE ICING CONDITIONS OF APPENDIX C TO 14 CFR PART 25 WILL ALSO ADDRESS THE TAILPLANE STALL ISSUE. THE RESULTS OF THE ARAC EFFORT WILL BE PUBLISHED AS NEW REGULATIONS AND ADVISORY MATERIAL.

From: NTSB
To: FAA
Date: 7/19/1996
Response: THE BOARD NOTES THAT ON 4/29/94, THE FAA ISSUED A POLICY MEMORANDUM TO ALL CERTIFICATION OFFICES DESCRIBING THE TAILPLANE STALL PHENOMENA & DEFINING A FLIGHT TEST MANEUVER (ZERO-G PUSHOVER MANEUVER) TO IDENTIFY SUSCEPTIBILITY TO ICE-CONTAMINATED TAILPLANE STALL. THE BOARD ALSO NOTES THAT THIS INTERIM GUIDANCE MAY BE INCLUDED IN A PROPOSED REVISION TO ADVISORY CIRCURLAR 25-7, "FLIGHT TEST GUIDE FOR CERTIFICATION OF TRANSPORT CATEGORY AIRPLANES." ALSO, A "TERMS OF REFERENCE" DOCUMENT HAS BEEN DRAFTED & HAS BEEN SUBMITTED TO THE AVIATION RULEMAKING ADVISORY COMMITTEE FOR REVIEW & HARMONIZATION OF ICE PROTECTION STANDARDS FOR TRANSPORT-CATEGORY AIRPLANES. PENDING THE BOARD'S REVIEW OF THE REVISION TO AC 25-7, & THE FAA'S REVIEW OF APPENDIX C OF 14 CFR PART 25 & ANY RULEMAKING TO REVISE PARTS 23 & 25, A-91-87 IS CLASSIFIED "OPEN--ACCEPTABLE ALTERNATE RESPONSE."

From: FAA
To: NTSB
Date: 2/13/1996
Response: ON 4/29/94, THE FAA ISSUED A POLICY MEMORANDUM TO ALL CERTIFICATION OFFICES DESCRIBING THE TAILPANE STALL PHENOMENA & DEFINING A FLIGHT TEST MANEUVER (ZERO-G PUSHOVER MANEUVER) TO IDENTIFY SUSCEPTIBILITY TO ICE CONTAMINATED TAILPLANE STALL. THIS INTERIM GUIDANCE IS BEING CONSIDERED FOR INCLUSION IN A PROPOSED REVISION TO ADVISORY CIRCULAR 25-7, FLIGHT TEST GUIDE FOR CERTIFICATION OF TRANSPORT CATEGORY AIRPLANES.

From: NTSB
To: FAA
Date: 4/10/1992
Response: In response to Safety Recommendation A-91-87, which asked the FAA to amend icing certification rules, we note that the FAA will publish advisory material to address icing certification procedures for 14 CFR Parts 23 and 25 category airplanes. Although the Safety Board does not agree that the current language in 14 CFR 25.1419 specifically addresses the change of configuration following the accumulation of ice, the inclusion of this certification procedure in an appropriate document, such as the Engineering Flight Test Guide, may satisfy the Safety Board's concern. Thus, pending our further review, this safety recommendation is classified as "Open- Acceptable Alternate Response."

From: FAA
To: NTSB
Date: 1/31/1992
Response: THE FAA BELIEVES THAT THE CURRENT CERTIFICATION REQUIREMENTS OF 14 CFR 25.1419 CONTAIN THE STANDARDS REQUESTED BY THIS SAFETY RECOMMENDATION. SECTION 25.1419 (B) STATES, IN PART, THAT THE AIRPLANE OR ITS COMPONENTS MUST BE FLIGHT TESTED IN THE VARIOUS OPERATIONAL CONFIGURATIONS IN MEASURED NATURAL ATMOSPHERIC ICING CONDITIONS IN ACCORDANCE WITH APPENDIX C. THE REGULATIONS ALSO DESCRIBE OTHER TESTS THAT MUST BE PERFORMED "AS FOUND NECESSARY ." ADDITIONALLY THE FAA BELIEVES THAT SINCE THE ICING CERTFICATION RULES UNDER 14 CFR 23.1419 (B) REFER TO APPENDIX C OF 14 CFR PART 25, THESE REGULATIONS ADEQUATELY ADDRESS THE ICING CERTIFICATION REQUIREMENTS. AS AN ALTERNATE ACTION, THE FAA WILL PUBLISH ADVISORY MATERIAL TO ADDRESS ICING CERTIFICATION PROCEDURES FOR 14 CFR PARTS 23 25 CATEGORY AIRPLANES.