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Safety Recommendation Details

Safety Recommendation A-98-094
Details
Synopsis: On January 9, 1997, an Empresa Brasileira de Aeronautica, S/A (Embraer) EMB-120RT, operated by COMAIR Airlines, Inc., crashed during a rapid descent after an uncommanded roll excursion near Monroe, Michigan. The flight was a scheduled, domestic passenger flight from the Cincinnati/Northern Kentucky International Airport, Covington, Kentucky, to Detroit Metropolitan/Wayne County Airport, Detroit, Michigan. The flight departed Covington with 2 flightcrew, 1 flight attendant, and 26 passengers on board. There were no survivors. The airplane was destroyed by ground impact forces and a postaccident fire. IMC prevailed at the time of the accident, and the flight was operating on an IFR flight plan.The probable cause of this accident was the FAA's failure to establish adequate aircraft certification standardds for flight in icing conditions.
Recommendation: TO THE FEDERAL AVIATION ADMINISTRATION: 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, locations of ice accumulation, including thin amounts of very rough ice, ice accumulated in supercooled large droplet icing conditions, and tailpane icing.
Original recommendation transmittal letter: PDF
Overall Status: Closed - Acceptable Action
Mode: Aviation
Location: MONROE, MI, United States
Is Reiterated: No
Is Hazmat: No
Is NPRM: No
Accident #: DCA97MA017
Accident Reports: In-Flight Icing Encounter and Uncontrolled Collision with Terrain, Comair Flight 3272, Embraer EMB-120RT, N265CA
Report #: AAR-98-04
Accident Date: 1/9/1997
Issue Date: 11/30/1998
Date Closed: 1/19/2006
Addressee(s) and Addressee Status: FAA (Closed - Acceptable Action)
Keyword(s): Icing,

Safety Recommendation History
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. 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 research5 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.

From: NTSB
To: FAA
Date: 1/19/2006
Response: The Safety Board previously indicated that the FAA had taken the recommended action of requiring manufacturers to provide minimum maneuvering airspeeds for icing conditions. However, the Board was concerned that the FAA had not described any activities to ensure that minimum maneuvering airspeeds for nonicing conditions were readily available to pilots. Because the FAA had not addressed nonicing conditions, on July 11, 2002, Safety Recommendation A-98-94 was classified "Open-Unacceptable Response." After the February 3, 2004, meeting, the FAA provided the Board with information on activities that it had undertaken in response to this recommendation. The FAA asked aircraft manufacturers to describe how minimum airspeed information is provided to flight crews for each airplane configuration, phase of flight, and flight condition (icing and nonicing). The FAA found that manufacturers provide sufficient and accessible maneuvering speed information covering all phases of flight and airplane configurations for both icing and nonicing conditions. This information is available to pilots through flight deck displays, flight management systems, quick reference handbooks (QRH), flight crew operating manuals (FCOM), flight crew training manuals, and airplane flight manuals (AFM). The FAA's survey revealed that for airplanes with electronic speed displays (known as having a "glass cockpit"), minimum maneuvering speeds are shown on the airspeed indicator as part of a low-speed awareness bar. The Safety Board recognized that glass cockpit airplanes typically and readily display the appropriate minimum maneuvering airspeed for all airplane configurations, phases, and conditions of flight. The Board, however, was concerned with older airplanes that do not have a glass cockpit. In response to the Board's question about availability of minimum maneuvering flight speeds in these older aircraft, the FAA indicated that this information is available for all phases of flight and airplane configurations for both icing and nonicing conditions in the QRH, the FCOM, or the AFM. Based on the information supplied, the FAA has completed the recommended action. Consequently, Safety Recommendation A-98-94 is classified "Closed-Acceptable Action."

From: FAA
To: NTSB
Date: 9/1/2005
Response: From FAA after SWAT meeting, faxed again 9/1/05 Following up on the discussions regarding safety recommendation A-98-94 that took place during the Safety With A Team (SWAT) II meeting, we would like to provide further information to address the remaining concerns with the availability and accessibility of minimum maneuvering speed information in existing airplanes. To ensure that our response is complete and comprehensive, we requested airplane manufacturers to provide the following information: 1)In what ways is minimum airspeed speed information (including minimum maneuvering airspeeds) provided to flightcrews for each airplane configuration, phase of flight (takeoff, climb, cruise, descent, holding, approach and landing), and flight condition (icing and non-icing)? 2)How are these maneuvering speeds determined (i.e., what are they based on)? The following airplane models were covered in this survey: ManufacturerModel Airbus- -A300-600, A310, A318/319/320, A330, A340 Aerospatiale- -ATR-42, ATR-72 Boeing- -717, 737 (Classics and New Generation), 747-400, 757, 767, 777 Bombardier- -Challenger 604, Regional Jet, Learjet Models 31, 45, 60, Dash 8- 400 Cessna- -Models 550, 560, 560XL Embraer- -EMB-l20/-135/-145/-170 Gulfstream- -Gulfstream 200 The airplane manufacturers' responses are considered to be proprietary information, so a summary of this information is provided below. In all cases, we found that the manufacturers provide sufficient and accessible maneuvering speed information covering all phases of flight and airplane configurations for both icing and non-icing conditions. The means to convey the maneuvering speed information to pilots include flight deck displays, flight management systems, quick reference handbooks, flightcrew operating manuals, flightcrew training manuals, and Airplane Flight Manuals. For airplanes with electronic speed displays (except for the Bombardier Challenger and Regional Jet), minimum maneuvering speeds are shown on the airspeed indicator as part of a low speed awareness bar. The low speed awareness bar is typically composed of differently colored bands (e.g., white, amber, red) that appear In a strip next to the airspeed indication scale. Although the implementation of the bar differs slightly between airplane types, the top of the amber band generally represents the minimum maneuvering speed for the current flight condition. Minimum speeds for icing conditions are only provided when they are different from the minimum speeds for non-icing conditions. In general, the same maneuvering capability must be provided in icing conditions as for non-icing conditions. If the activation point of the stick shaker (i.e., stall warning) is different for flight in icing conditions in order to provide sufficient stall. warning margin, the minimum maneuvering speeds must be adjusted to provide an adequate maneuvering capability without encountering stall warning. A description of the minimum maneuvering speeds applicable to each flight phase and how that information is conveyed to the crew is provided below: Takeoff -Initial takeoff climb After takeoff, the minimum maneuver speed is Vz + XX (where XX varies with airplane model). If an engine fails or is shut down during the takeoff, the minimum maneuvering speed is V2. 14 Code of Federal Regulations part 25 specify the requirements that the selected V2 speed must meet. For airplanes certificated to the criteria contained in Amendment 25-108 (which includes most transport category airplanes certificated since the early 1980's), V2 must allow the pilot to use bank angles up to 30 degrees without encountering stall warning or any other characteristic that might interfere with normal maneuvering. The all-engines- operating minimum maneuvering speed, V2 + XX, must provide a 40-degree bank angle capability. For some airplanes that were not certificated to the Amendment 25-108 criteria, the maneuvering bank angle capability may be somewhat less, but it may not be less than that resulting from a V2 speed that is at least 20 percent higher than the airplane's stall speed. V2 must be provided in the AFM. V2 is also available from the flight management system (for airplanes so equipped), FCOM's, wick reference handbooks, and takeoff data tabulations produced by the operator. V2 is also shown on the airspeed display. On airplanes with electronic speed displays (except for the Learjet Models 45 and 60), a V, speed marker is automatically placed on the airspeed display. For airplanes without electronic speed displays, a speed marker is set manually by the pilot at the V2, speed. Takeoff - Flap retraction The minimum maneuvering speeds for intermediate flap configurations during flap retraction are provided in the FCOM and other documents containing airplane operating information. Although the Federal Aviation Regulations do not contain specific requirements for minimum flap retraction speeds, the standard practice is to use the same criteria in defining these speeds as are used for the all- engines-operating minimum maneuvering speed with takeoff flaps (described above) and the final takeoff segment climb speed with flaps retracted (described below). Flap retraction speeds may also be shown on the airspeed display. On airplanes with electronic speed displays (except for the Bombardier Challenger and Regional Jet, and the Learjet Models 45 and 60), flap retraction speed markers are automatically placed on the airspeed display. For airplanes without electronic speed displays, markers may be placed manually by the pilot for the intermediate flap settings, or the maneuver speed can be determined relative to the takeoff flaps and flaps retracted maneuvering speed markers. Takeoff-Final takeoff climb The final takeoff climb speed must meet part 25 requirements. For airplanes certificated to the criteria contained in Amendment 25-108, the final takeoff climb speed must allow the pilot to use bank angles up to 40 degrees without encountering stall warning or any other characteristic that might interfere with normal maneuvering. For some airplanes that were not certificated to the Amendment 25-108 criteria, the maneuvering bank angle capability may be somewhat Less, but it may not be less than that resulting from a final takeoff climb speed that is at least 25 percent higher than the airplane's stall speed. The final takeoff climb speed represents the minimum maneuvering speed with flaps retracted. It must be provided in the AFM, and can also be obtained from the flight management system (for airplanes so equipped), FCOM's, quick reference handbooks, and other operating manuals. The final takeoff climb speed is also shown on the airspeed display. On airplanes with electronic speed displays (except fox the Bombardier Challenger and Regional Jet, and the Learjet Models 45 and 60), the flaps up speed marker is automatically placed on the airspeed display. For airplanes without electronic speed displays, a speed marker can be placed manually by the pilot. Climb. cruise. descent. and holding Recommended speeds for climb, cruise, descent, and holding are given in the FCOM and other operating manuals. Typically, minimum airspeeds for climb, cruise, and descent are not an issue since the recommended speeds are typically much higher than the flaps retracted minimum maneuvering speed. The recommended holding speed is usually the speed for minimum fuel consumption, but not less than that needed to maintain the selected maneuvering margin. Part 25 requires the buffet onset envelope to be provided in the AFM. The buffet onset envelope shows the maneuvering margin available as a function of speed, weight, and pressure altitude. Operators can use this information as an aid in selecting climb speeds and cruise altitudes. On airplanes with electronic speed displays (except for the Bombardier Challenger and Regional Jet. and the Learjet Models 45 and 60), the minimum maneuvering speed fox climb, cruise, and descent are identified as the top of the amber band of the low speed awareness bar. Below 20,000 feet, the top of the amber band corresponds to a speed that provides a 30 to 40 degree (depending on the airplane model) bank angle to stick shaker. Above 20,000 feet, the top of the amber band provides a selectable maneuver margin to stick shaker (generally 0.2 to 0.3 g margin, which is equivalent to 34 and 40 degrees of bank angle, respectively). Approach and landing Flap extension speeds for the approach phase are provided in the FCOM and other operating manuals in a similar manner to the flap retraction speeds after takeoff. Recommended approach speeds generally provide 40 to 45 degrees of bank capability without encountering stall warning. Some manufacturers recommend additional speed additives for maneuvering prior to final approach. The reference landing speed must meet part 25 requirements. For aixplanes certificated to the criteria contained in Amendment 25-108, the reference landing speed must allow the pilot to use bank angles up to 40 degrees without encountering stall warning or any other characteristic that might interfere with normal maneuvering. For some airplanes that were not: certificated to the Amendment 25- 108 criteria, the maneuvering bank angle capability may be somewhat less, but it may not be lees than that resulting from a reference landing speed that is at least 30 percent higher than the airplane's stall speed. On airplanes with electronic speed displays (except for the Bombardier Challenger and Regional Jet, and the Learjet Models 45 and 60), a reference landing speed marker is automatically placed on the airspeed display. Far airplanes Without electronic speed displays, the pilot would place a speed marker manually. We believe the above information address the remaining concerns with the availability and accessibility of minimum maneuvering speed information in existing airplanes, and consequently request that the recommendations be classified as "Closed Acceptable" 10/7/05 Email from Don Stimson, FAA Transport Standards Staff to Judy Leach, FAA, answering question posed by Jeff Marcus, NTSB Question: For older aircraft without a glass cockpit (like the EMB-120), how are minimum maneuvering airspeeds in non-icing conditions made available to operating pilots, and how has this changed? Response: For older airplanes that do not have a glass cockpit, maneuvering speed information is provided to pilots in quick reference handbooks, flightcrew operating manuals, flightcrew training manuals, and airplane flight manuals as well as winter safety bulletins and operator's pilot training programs. The content of this information and the manner in which it is conveyed to pilots has changed since the time of the Embraer 120 accident that resulted in safety recommendation A-98-94. These changes are a result of: 1) Airworthiness Directives. For example, airworthiness directives have been issued against the Embraer EMB-120 and the Cessna 560 to increase the minimum maneuvering speeds in icing conditions. 2) Notice N8400.39. This notice reminded principal operations inspectors of the importance of aircraft manufacturers' minimum maneuvering airspeeds for various airplane configurations and phases and conditions of flight. It also noted that these minimum maneuvering airspeeds, especially for icing conditions, should be promptly incorporated in operating manuals and training programs in a clear and concise manner, regardless of the means in which the information was issued by the manufacturer. 3) Advisory circular (AC) 25.1419-1A. This AC states that the operating limitations section of the airplane flight manual should provide the minimum airspeed that should be maintained for each normal aircraft configuration whenever ice exists on the critical surfaces. This same information is conveyed in draft AC's 20-73A and 25.21-1. 4) A letter sent by the FAA to the airplane manufacturers requesting descriptions of how minimum airspeed speed information (including minimum maneuvering airspeeds) is provided to flightcrews for each airplane configuration, phase of flight (takeoff, climb, cruise, descent, holding, approach and landing), and flight condition (icing and non-icing) in order to respond to this safety recommendation. (Manufacturers made further changes as a result of this letter.) 5) Increased industry awareness of the importance of conveying minimum maneuvering speed information to pilots, especially in icing conditions. Examples of how minimum maneuvering airspeed information is conveyed to pilots of non-glass cockpit airplanes: Aerospatiale: For all ATR models, minimum airspeed and minimum maneuvering airspeed information for icing and non-icing conditions are provided to flight crews in the airplane flight manual (AFM), flightcrew operating manual (FCOM), and quick reference handbook (QRH). These speeds cover flight condition (icing or non-icing), phase of flight, and maneuvering bank angles, weight, and center-of-gravity. The minimum maneuvering/operating airspeeds for icing conditions are provided for each phase of flight and also specify a maximum bank angle. Boeing: The primary sources for operating speed information for all Boeing models, including those models without glass cockpits, are: 1. Flight Management Computer or Flight Management System 2. Flight Crew Operations Manual, including the Quick Reference Handbook 3. Airplane Flight Manual or software databases based on the AFM. In addition, the Flight Crew Training Manual provides information on speed schedules, minimum maneuvering speeds, and the maneuver margins to stick shaker for different phases of flight and airplane configurations. Bombardier: Dash 8: Detailed speed information is provided to crews via a quick reference handbook. Learjet Models 31 and 31A: Flight manuals and pilot operating handbooks (including Quick Reference Handbooks) contain recommended airspeeds for every phase of flight and airplane configuration, and are applicable to both icing and non-icing conditions. Embraer: EMB-120: Minimum airspeed information provided in the AFM and FCOM. In addition, the EMB-120 has a system to warn the flight crew if the airspeed is allowed to decay below the minimum speed while operating in icing conditions. This system will sound a horn and illuminate a "LOW SPD" visual annunciation if the airspeed is allowed to decay below 155 KIAS. Gulfstream: Minimum maneuvering speed information for all airplane configurations and icing and non-icing conditions are presented in the AFM and the airplane operating manual for all models evaluated, including the non-glass cockpit Model G-III.

From: NTSB
To: FAA
Date: 2/3/2004
Response: SWAT Meeting: This recommendation was on the Most Wanted List for several years in the icing issue area. Although the recommendation remains open-unacceptable, it was recently removed from the Most Wanted List because the FAA had satisfactorily addressed the icing issues in this recommendation. However, the recommendation explicitly asks for minimum maneuvering airspeeds in both icing and nonicing conditions, and to date the FAA has not addressed the nonicing airspeeds. The FAA indicated its concern with retroactively applying this requirement to existing airplanes. The Board noted that for some aircraft it is difficult for a pilot flying to quickly find needed information on minimum airspeeds for the conditions present. As an example, during the investigation of several accidents where the airplane’s airspeed appeared to have been below minimums, a possible cause of the accident, Board staff wanted to determine if the aircrew had made a mistake, or whether there was some other cause of failure to maintain sufficient airspeed. In order to do this analysis, Board staff needed to determine what was the appropriate (and manufacturer recommended) airspeed for the given conditions. In these accidents it has sometimes taken Board staff several weeks to locate and determine this information, clearly much longer than the time available to a pilot flying an aircraft. This recommendation seeks to put this critically needed information in an easily accessible format that pilots can quickly refer to. Results FAA will provide examples of appropriate operating speeds being effectively presented to pilots, and what the intent would be for reviewing existing airplanes concerning ease of presentation of various operating speeds. If the FAA can show that airplanes are now required to provide minimum airspeed information in an easily accessible quick reference format for pilots, this recommendation will be classified "Closed-Acceptable Action."

From: NTSB
To: FAA
Date: 7/11/2002
Response: Although the FAA's reported actions in response to Safety Recommendation A-98-94 meet the recommendation's intent with respect to icing conditions, the recommendation also asks for minimum maneuvering airspeed information for all airplane configurations, phases, and conditions of flight in non-icing conditions. The FAA has not indicated that it is taking any actions for conditions other than icing. The Safety Board continues to believe that minimum maneuvering airspeeds for all airplane configurations, phases, and conditions of flight (icing and non-icing conditions) should be in the flight manuals of all aircraft operated under Title 14 CFR Part 121 or Part 135. For example, the Board is aware that such minimum maneuvering airspeeds for all approach and landing configurations are in the flight manuals for the DC?9 and Boeing 727 aircraft of a major air carrier. Pending receipt and review of additional information requiring the provision of minimum maneuvering airspeed information for all airplane configurations, phases, and conditions of flight (icing and non-icing conditions) for new and currently certificated aircraft, Safety Recommendation A-98-94 is classified "Open--Unacceptable Response."

From: FAA
To: NTSB
Date: 9/21/2001
Response: Letter Mail Controlled 10/22/2001 11:44:27 AM MC# 2010866: For future airplane designs, the FAA is continuing its efforts as outlined in its letter to the Board dated September 25, 2000. These efforts include publishing the 1-g stall rule, developing 14 CFR Part 25 regulatory requirements for airplane performance and handling characteristics in icing conditions, and defining a supercooled large droplet icing environment. The 1-g stall rule is expected to be adopted in late 2001, and the proposed 14 CFR Part 25 requirements for airplane performance and handling characteristics are scheduled to be published for public comment in late 2002. The ARAC's Ice Protection Harmonization Working Group has been tasked to define an icing environment that includes supercooled large droplets (SLD). The working group determined in February 2001 that there was sufficient data for use in defining SLD certification conditions. Following development of the SLD certification conditions, a determination will be made as to what flight capabilities will be required in those conditions. For currently certificated 14 CFR Part 25 airplanes, the FAA is developing a rulemaking project to develop the following regulatory requirements to be applied retroactively: * Stall warning to be provided by a cockpit warning system at speeds appropriate for operations with ice accretions. * Operating speeds for icing conditions to provide constant speed banked-turn capability free of stall warning. * Operating speeds for icing conditions to be provided in Airplane Flight Manuals and Flightcrew Operating Manuals. I will keep the Board informed of the FAA's progress on this safety recommendation.

From: NTSB
To: FAA
Date: 3/12/2001
Response: In previous correspondence on this recommendation, the Board noted its concerns that the FAA’s actions for currently certificated aircraft would only request that manufacturers review their AFMs to ensure that appropriate speeds in icing conditions were provided. Although the actions now being taken by the FAA for new and currently certificated aircraft are responsive to the recommendation, there is no mention in FAA’s letter of any plans to develop minimum maneuvering airspeeds for flight in non-icing conditions. During its investigation of the Conair Flight 3272 accident, the Board found that guidance on minimum airspeeds was insufficient for all phases of flight, in or out of icing conditions. Therefore, the Board requests that the FAA specifically address flight in non-icing conditions and all phases of flight in response to Safety Recommendation A-98-94. Pending provision of minimum maneuvering airspeed information for all airplane configurations, phases, and conditions of flight for new and currently certificated aircraft, Safety Recommendation A-98-94 is classified Open--Acceptable Response.

From: FAA
To: NTSB
Date: 9/25/2000
Response: Letter Mail Controlled 10/02/2000 3:16:36 PM MC# 2001437 1.For future airplane designs, the FAA is continuing its efforts as outlined in its letter to the Board dated February 26, 1999. These efforts include publishing the 1-g stall rule, developing 14 CFR Part 25 regulatory requirements for airplane performance and handling characteristics in icing conditions, and defining a supercooled large droplet icing environment. For currently certificated 14 CFR Part 25 airplanes, the FAA had requested that manufacturers of transport-category aircraft review their Airplane Flight Manuals to ensure that appropriate operating speeds in icing conditions are provided. The FAA has reviewed the information received from these manufacturers and additional input from aircraft certification specialists. As a result of this review, the FAA is considering a rulemaking project to develop the following regulatory requirements to be applied retroactively: · Stall warning to be provided by a cockpit warning system at speeds appropriate for operations with ice accretions. · Operating speeds for icing conditions to provide constant speed banked-turn capability free of stall warning. · Operating speeds for icing conditions to be provided in Airplane Flight Manuals and Flightcrew Operating Manuals. I believe that these new actions address the Board's concerns. I will keep the Board informed of the FAA's progress on this safety recommendation.

From: NTSB
To: FAA
Date: 3/9/2000
Response: THE SAFETY BOARD BELIEVES THE ACTIONS OUTLINED ABOVE FOR DETERMINING MINIMUM MANEUVERING SPEEDS IN ALL CONFIGURATIONS AND ALL PHASES OF FLIGHT WITH AND WITHOUT ICE ACCRETIONS WILL PROVIDE SIGNIFICANT SAFETY IMPROVEMENTS IN NEWLY CERTIFICATED AIRPLANES. HOWEVER, THE SAFETY BOARD IS CONCERNED THAT FOR ALL CURRENT 14 CFR PART 25 AIRCRAFT, THE FAA WILL ONLY REQUEST THAT MANUFACTURERS REVIEW THEIR AFM'S TO ENSURE APPROPRIATE SPEEDS IN ICING CONDITIONS ARE PROVIDED. THE SAFETY BOARD EXPRESSED THE SAME CONCERN IN ITS RESPONSE TO NOTICE OF PROPOSED RULEMAKING 97-NM-46-AD, WHICH PROPOSED ESTABLISHING FOR THE EMB-120 A FLAPS-ZERO MINIMUM AIRSPEED OF 160 KNOTS FOR OPERATING IN ICING CONDITIONS. DESPITE THE SAFETY BOARD'S CONCERNS, THE FAA'S FINAL RULE, AIRWORTHINESS DIRECTIVE 97-26-06, CURRENTLY REQUIRES A 160-KNOT MINIMUM AIRSPEED FOR OPERATING THE EMB-120 IN ICING CONDITIONS. AS THE BOARD INDICATED IN THE LETTER CONTAINING A-98-94, EVIDENCE OF COMAIR FLIGHT 3272'S LOSS OF CONTROL WAS APPARENT AT 156 KNOTS--WITH A SLIGHTLY DIFFERENT ICE ACCUMULATION SCENARIO, THE LOSS OF CONTROL MAY HAVE OCCURRED EARLIER IN THE EVENT. THE SAFETY BOARD NOTES THAT AFTER THIS ACCIDENT, COMAIR ESTABLISHED A 170-KNOT MINIMUM AIRSPEED FOR OPERATING THE EMB-120 IN ICING CONDITIONS BECAUSE THE COMPANY DID NOT BELIEVE THAT A 160-KNOT AIRSPEED ENSURED AN ADEQUATE STALL MARGIN. THE SAFETY BOARD IS CONCERNED THAT IN THE ABSENCE OF A SCIENTIFICALLY DETERMINED MINIMUM AIRSPEED IN ICING CONDITIONS, OPERATORS OF CURRENTLY CERTIFICATED AIRPLANES WHO ELECT TO INCREASE THEIR MINIMUM AIRSPEEDS, LIKE COMAIR, MAY INCREASE THEM TOO MUCH, INCREASING THE RISK OF A TAILPLANE STALL. OTHER OPERATORS MAY CONTINUE TO FOLLOW FAA GUIDELINES, WHICH THE SAFETY BOARD CONSIDERS TO PROVIDE AN INADEQUATE SAFETY MARGIN. THEREFORE, A-98-94 IS CLASSIFIED "OPEN--UNACCEPTABLE RESPONSE," PENDING FAA ACTION TO PRODUCE A MORE THOROUGHLY RESEARCHED MINIMUM AIRSPEED.

From: FAA
To: NTSB
Date: 2/26/1999
Response: THE NEW 1-G STALL SPEED REQUIREMENTS REPRESENT THE CULMINATION OF A MULTIYEAR HARMONIZATION EFFORT TO DEFINE STALL SPEEDS THAT WILL PROVIDE CONSISTENT MANEUVERING CAPABILITY FOR ALL 14 CFR PART 25 AIRPLANES IN ALL CONFIGURATIONS AND ALL PHASES OF FLIGHT. FOR THE UNCONTAMINATED AIRPLANE, THE FAA ANTICIPATES AMENDING 14 CFR PART 25 TO DEFINE 1-G STALL SPEEDS. ONE ELEMENT OF THAT AMENDMENT WILL BE A NEW RULE REQUIRING A FLIGHT DEMONSTRATION OF CONSTANT SPEED TURNING MANEUVERS IN TERMINAL AREA AIRPLANE CONFIGURATIONS (I.E., TAKEOFF, FINAL TAKEOFF, APPROACH, AND LANDING). THE FLIGHT DEMONSTRATION WILL ENSURE THAT STALL WARNING WILL NOT BE ENCOUNTERED AT THE SCHEDULED OPERATING SPEEDS--THIS NEW REQUIREMENT WILL ENSURE THAT THE OPERATING SPEEDS IN THE AFM PROVIDE ADEQUATE MANEUVERING CAPABILITY FOR THE AIRPLANE WITHOUT ICE ACCRETIONS IN NORMAL FLIGHT OPERATIONS. FOR FLIGHT IN THE ICING CONDITIONS OF APPENDIX C, THE FLIGHT TEST HARMONIZATION WORKING GROUP IS PROPOSING A REGULATORY AMENDMENT. THE AMENDMENT WILL REQUIRE COMPLIANCE WITH THE SAME MANEUVERING REQUIREMENTS WITH THE ICE ACCRETION APPROPRIATE TO THE AIRPLANE CONFIGURATION AND PHASE OF FLIGHT AS FOR THE AIRPLANE WITHOUT ICE ACCRETIONS (REFERENCE THE 1-G STALL SPEED REQUIREMENTS DESCRIBED IN THE PRECEDING PARAGRAPH). CONSEQUENTLY, THE PROPOSED REGULATIONS WILL RESULT IN AFM OPERATING SPEEDS THAT PROVIDE ADEQUATE MANEUVERING CAPABILITY FOR THE AIRPLANE, WITH OR WITHOUT ICE ACCRETIONS, IN ALL CONFIGURATIONS AND PHASES OF FLIGHT. COMPLETION OF THE FLIGHT TEST HARMONIZATION WORKING GROUP PROJECT IS SCHEDULED FOR DECEMBER 2000 AND WILL COMPLETE A TASK OUTLINED IN THE FAA'S IN-FLIGHT AIRCRAFT ICING PLAN PUBLISHED IN APRIL 1997. IN SPECIFYING ICE SHAPES APPROPRIATE TO THE PHASE OF FLIGHT, THE FLIGHT TEST HARMONIZATION WORKING GROUP HAS INCLUDED INTERCYCLE ICE ON PROTECTED SURFACES. THE WORKING GROUP IS ALSO DEVELOPING MATERIAL RELATED TO AN ICE ACCRETION THAT WOULD FORM ON BOTH THE UNPROTECTED AND PROTECTED SURFACES PRIOR TO NORMAL OPERATION OF THE ICE PROTECTION SYSTEM (I.E., THIN, ROUGH ICE). THE FLIGHT TEST HARMONIZATION WORKING GROUP IS ALSO PROPOSING A 14 CFR PART 25 REQUIREMENT TO INVESTIGATE AN AIRPLANE'S SUSCEPTIBILITY TO TAILPLANE STALL OVER THE OPERATING SPEED RANGE FOR THE CRITICAL AIRPLANE CONFIGURATION. THE TASKS DESCRIBED IN THIS AND THE PRECEEDING PARAGRAPHS RELATE TO THE ENVIRONMENTAL CONDITIONS OF APPENDIX C OF 14 CFR PART 25 ONLY. APPLICABILITY OF THE PRODUCTS OF THE FLIGHT TEST HARMONIZATION WORKING GROUP AND CHANGES TO 14 CFR PART 25 WILL ALSO BE CONSIDERED FOR APPLICATION TO TURBINE ENGINE-POWERED AIRPLANES CERTIFICATED UNDER 14 CFR PART 23 ACCOUNTING FOR RELEVANT DIFFERENCES SUCH AS SCALE, COMPLEXITY, SIZE, AND MASS. WITH REGARD TO OPERATIONS IN SUPERCOOLED LIQUID DROPLET ICING ENVIRONMENTS, ONE ELEMENT OF THE FAA'S IN-FLIGHT AIRCRAFT ICING PLAN PUBLISHED IN APRIL 1997 CALLS FOR TASKING THE ARAC WITH A LONG-TERM HARMONIZATION PROJECT. THE HARMONIZATION PROJECT WILL DEVELOP CERTIFICATION CRITERIA AND ADVISORY MATERIAL FOR SAFE OPERATION OF AIRPLANES IN SUPERCOOLED LARGE DROPLET ICING CONDITIONS BEYOND THE CURRENT APPENDIX C ENVELOPE. THIS TASK WAS ASSIGNED TO THE ICE PROTECTION HARMONIZATION WORKING GROUP IN DECEMBER 1997. THE WORKING GROUP WILL BEGIN DISCUSSIONS ON THE DEFINITION OF THE SUPERCOOLED LARGE DROPLET ICING ENVIRONMENT IN FEBRUARY 1999. FOR CURRENTLY CERTIFICATED 14 CFR PART 25 AIRPLANES, THE FAA ISSUED LETTERS ON 10/1/98, REQUESTING MANUFACTURERS OF TRANSPORT-CATEGORY AIRCRAFT TO REVIEW AFM'S TO ENSURE THAT APPROPRIATE OPERATING SPEEDS IN ICING CONDITIONS ARE PROVIDED. IF SUCH SPEEDS WERE NOT IN THE AFM'S, THE MANUFACTURERS WERE REQUESTED TO PROVIDE A SCHEDULE FOR REVISION OF THE AFM'S. THE LETTERS ALSO INFORMED THE MANUFACTURERS THAT THE REVISIONS MAY BE USED IN MANDATORY ACTIONS TO BRING THE INFORMATION TO THE ATTENTION OF FLIGHTCREWS. IN JANUARY 1999, FAA SPECIALISTS MET TO REVIEW THE STATUS OF THE AFM'S AND TO REACH A PRELIMINARY POSITION ON WHETHER MANDATORY ACTIONS ARE WARRANTED. THE FAA HELD A CONFERENCE WITH AIRFRAME MANUFACTURERS, AIRLINE OPERATORS, WORLDWIDE CIVIL AVIATION AUTHORITIES, AND OTHER AVIATION ORGANIZATIONS FEBRUARY 2, 1999. AT THE CONFERENCE, INFORMATION WAS EXCHANGED ON VARIOUS TOPICS INCLUDING THE INCLUSION OF MINIMUM OPERATING SPEEDS IN ICING CONDITIONS IN THE AFM. FOLLOWING THE CONFERENCE, THE FAA WILL REACH A FINAL POSITION ON WHETHER MANDATORY ACTION SHOULD BE TAKEN.

From: NTSB
To: FAA
Date:
Response: At the 1997 Board meeting addressing the NTSB’s Most Wanted List of Transportation Safety Improvements (MWL), the Board voted to place Safety Recommendations A-96-54 through A-96-56, A-96-62, and A-96-69 on the MWL under the issue category “Airframe Structural Icing.” The Board voted to add Safety Recommendations A-98-92, A-98-94, A-98-95, A-98-99, A-98-100, A-07-14 at later dates. Safety Recommendation A-07-16 was added to the MWL upon its adaptation because it supersedes Safety Recommendation A-98-100.