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Safety Recommendation Details

Safety Recommendation A-98-100
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: When the revised icing certification standards and criteria are complete, review the icing certification of all turbopropeller-driven airplanes that are currently certificated for operation in icing conditions and perform additional testing and take action as required to ensure that these fulfill the requirements of the revised icing certification standards. (Superseded by A-07-16)
Original recommendation transmittal letter: PDF
Overall Status: Closed - Unacceptable Action/Superseded
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: 2/27/2007
Addressee(s) and Addressee Status: FAA (Closed - Unacceptable Action/Superseded)
Keyword(s): Icing, Weather

Safety Recommendation History
From: NTSB
To: FAA
Date: 8/27/2010
Response: Notation 6486F: The National Transportation Safety Board (NTSB) has reviewed the Federal Aviation Administration (FAA) Notice of Proposed Rulemaking (NPRM), “Airplane and Engine Certification Requirements in Supercooled Large Drop, Mixed Phase, and Ice Crystal Icing Conditions,” published at 75 Federal Register 37311 on June 29, 2010. The FAA proposes to amend the airworthiness standards applicable to certain transport-category airplanes certificated for flight in icing conditions and the icing airworthiness standards applicable to certain aircraft engines. The NTSB initially became concerned with supercooled large droplet (SLD) conditions, including freezing rain and freezing drizzle, in the early 1980s and issued a report on September 9, 1981, titled Aircraft Icing Avoidance and Protection. This report identified the need for the FAA to review and revise the icing criteria in 14 Code of Federal Regulations (CFR) Part 25, Appendix C, to include freezing rain and for that reason issued Safety Recommendation A-81-116. On October 31, 1994, American Eagle flight 4184, ATR-72, crashed at Roselawn, Indiana. The investigation found that freezing drizzle icing conditions led to the creation of an ice ridge aft of the deice boots on the upper surface of the wing. This ridge caused the airflow over the ailerons to separate, which resulted in an uncommanded roll of the airplane. Based on its findings, the NTSB issued Safety Recommendation A-96-54, which superseded recommendation A-81-116 and 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 one of the oldest recommendations on the NTSB’s Most Wanted List of Transportation Safety Improvements and is currently classified “Open—Unacceptable Response.” The status of this recommendation highlights the NTSB’s ongoing concern that current icing certification requirements do not ensure that airplanes are tested in the most severe icing conditions, as defined in the environmental icing envelope contained in Appendix C. Accordingly, the NTSB has repeatedly stressed the need to consider the full range of icing conditions in which an airplane is authorized to operate. Additionally, the NTSB has voiced its concern that flight crews must be provided a means to recognize when an aircraft encounters conditions beyond those for which the aircraft has a demonstrated safe flight capability. In this regard, and as a result of its investigation of the Roselawn accident, the NTSB issued Safety Recommendation A-96-56 to the FAA: 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 safe operations cannot be demonstrated by the manufacturer, 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 NTSB’s Most Wanted List of Transportation Safety Improvements and is currently classified “Open—Unacceptable Response.” Since the issuance of these recommendations, the NTSB has investigated several accidents and incidents that have involved SLD conditions, including the 1997 Comair 3272 Embraer (EMB) 120 accident, which occurred in Monroe, Michigan; the 2001 Comair 5054 EMB-120 stall and loss of control event, which resulted in the flight diverting to West Palm Beach, Florida; the 2005 Circuit City Cessna 560 accident, which occurred on approach to Pueblo, Colorado; and the 2006 American Eagle flight 3008 Saab 340B in-flight upset and loss of control over Santa Maria, California. These accidents and incidents again highlighted the hazards of operating in SLD conditions, which were not required to be considered at the time of the original icing certification of these airplanes. As a result of these investigations, the NTSB stressed the need to include SLD conditions in the icing certification standards for all airplanes certificated for flight in icing conditions. These accidents and incidents demonstrated that SLD conditions can be more hazardous than those considered during current icing certification, that SLD conditions can cause ice accretions more aerodynamically detrimental than those that develop while flying within the Part 25, Appendix C, envelope, and that airplanes need to be evaluated over the full range of icing conditions for which they are authorized to operate, including a range of SLD conditions. Given the accident history described above, the NTSB is pleased that the NPRM proposes to add Section 25.1420, which would require evaluating the operation of airplanes in the SLD environment, and Appendix O, Part I, to Part 25, which expands the certification icing environment to include freezing rain and freezing drizzle by using four separate droplet size distributions and includes droplet sizes greater than 1,000 microns in one of the distributions. Additionally, the NTSB is pleased to see the inclusion of Appendix O, Part II, which states the following: The most critical ice accretion in terms of airplane performance and handling qualities for each flight phase must be used to show compliance with the applicable airplane performance and handling qualities requirements for icing conditions contained in subpart B of this part. Applicants must demonstrate that the full range of atmospheric icing conditions specified in part I of this appendix have been considered, including drop diameter distributions, liquid water content, and temperature appropriate to the flight conditions. The NTSB 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, including SLD. 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. The proposed rule addresses these problems with the addition of Section 25.1420 by requiring that airplane operations in icing conditions do 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. In addition, the proposed addition of Part 25, Appendix O, Part II, will provide an additional margin of safety for these airplanes when operating in icing conditions by defining the ice accretions and revising the performance and handling requirements for flight in icing conditions that must be satisfied to certify an airplane for operation in Appendix O icing conditions. These requirements include, for example, requirements for takeoff performance, stall warning, and landing climb. The NTSB has stated in past NPRM comments that the full range of atmospheric conditions must be considered when evaluating icing certification, and inclusion of this provision in Part II of Appendix O will ensure that all of these conditions are addressed during the icing certification process. The NTSB has also reviewed the FAA’s proposed changes for 14 CFR Section 33.68 “Induction System Icing,” Section 33.77 “Foreign Object Ingestion – Ice,” and the addition of Appendix D, Icing Envelope Limits. The NTSB investigated three incidents of dual-engine flameouts in Hawker Beechcraft (previously identified as Raytheon) Beechjet 400A airplanes that occurred between July 12, 2004, and June 14, 2006. In one of these incidents, the pilots had to accomplish a dead stick landing after they were unable to restart either of the engines. The NTSB’s investigations of these incidents showed that all three airplanes were operating in areas near convective weather activity with high altitude ice crystals, and the flight crews had retarded the power levers. The manufacturer of the engines installed on the Beechjet conducted a study that showed the possibility that high altitude ice crystals would partially melt due to the temperature rise in the air across the fan and ice could then adhere and refreeze on the compressor inlet stator in the engine’s core, causing the engine to flame out. Hawker-Beechcraft developed procedures for the Beechjet 400A airplane prescribing activation of the engine anti-icing system when operating within specified horizontal and vertical distances from convective weather activity to prevent ice from forming inside the engine. The FAA mandated incorporation of the revised procedures into the airplane flight manual with an airworthiness directive (AD). To date, there have been no further reports of dual-engine flameouts in Beechjet 400A airplanes. While pleased with the FAA’s issuance of the AD, the NTSB has been concerned that the FAA’s action addressed Beechjet 400A aircraft only without allowing for future engine designs that could be susceptible to the deleterious effects of high altitude ice crystals. The NTSB agrees with the FAA’s proposed changes in 14 CFR 33.68 and 33.77. In particular, the NTSB supports inclusion of proposed 14 CFR 33.68(e) and the Appendix D Inflight Icing Envelope, which address mixed phase and ice crystal conditions to ensure that future engine designs are not susceptible to high altitude ice crystals. The NTSB also agrees with the proposed turbine engine icing certification requirement, which would include the icing conditions of Appendixes C and O of Part 25, and the mixed phase and ice crystal icing envelope of Appendix D of Part 33. Despite the improvements noted in this letter, the NTSB is disappointed with the proposed rule and believes that it should be expanded to include all aircraft regardless of maximum takeoff weight (MTOW) or flight control design and that the requirements should apply to both newly manufactured and currently certificated aircraft under Part 25 (transport-category airplanes) and Part 23 (normal, utility, aerobatic, and commuter airplanes). If the requirements are not expanded to include currently certificated airplanes, the NTSB believes that flight crews need additional means to positively determine when they are in icing conditions that exceed the limits of the aircraft. As described in the NPRM, the proposed rule will require that only transport-category airplanes with an MTOW of less than 60,000 pounds, or those with reversible flight controls, meet the safety standards in the expanded certification icing environment defined by Part 25 Appendix O. As a result, the proposed rule excludes numerous aircraft models that would benefit from the new requirements. The NTSB does not agree with this position, nor does the Aviation Rulemaking Advisory Committee (ARAC) Ice Protection Harmonization Working Group (IPHWG), as noted in the NPRM: The IPHWG majority … did not accept the exclusion of airplanes with the three aforementioned design features because one cannot predict with confidence that the past service experience of airplanes with these specific design features will be applicable to future designs. The IPHWG majority recommended applying the new SLD airplane certification requirements proposed in the new § 25.1420 to all future transport category airplane type designs. The IPHWG majority opposed limiting the applicability of the rule based on airplane gross weight, in part, because the ratio of wing and control surface sizes to airplane weight varies between airplane designs. Therefore, airplane takeoff weight is not a consistent indicator of lifting and control surface size or chord, which are the important parameters affecting sensitivity to a given ice accretion. In addition to its reservations concerning weight limits, the NTSB believes that this rule should apply to all airplanes regardless of their flight control system design and that the effects of SLD accretions should be considered for all aircraft with either reversible or irreversible flight control systems. However, flight control system anomalies while operating in an SLD environment comprise only one aspect of the SLD threat. Another insidious feature of ice accreted while operating in SLD conditions is that the ice may significantly reduce the angle of attack required for aerodynamic stall to occur, so much so that stall can occur prior to the stall warning, as demonstrated in the Pueblo Cessna 560 accident and five ATR-42 incidents preceding the Roselawn accident. This problem is particularly critical when the stall protection system and warning margins have been determined using Part 25 Appendix C ice accretions, but the aircraft encounters SLD icing conditions, thereby causing much greater reductions of maximum lift than the system was designed for. The NTSB therefore believes that the requirements in the proposed rule should retroactively apply to all aircraft, regardless of their MTOW or the design of their flight control systems. An additional shortcoming in the proposed rule is its restriction to airplanes certificated under Part 25. As recommended in A-96-54, the NTSB believes that SLD should be considered for both Part 25 and Part 23 airplanes, which include several commuter type airplanes regularly used in passenger service. The NTSB has noted in past comments that these types of smaller aircraft typically operate at lower altitudes and are therefore more likely to encounter SLD conditions than the larger, turbine-engine aircraft certificated in Part 25, which spend less of their time operating at lower altitudes. Finally, because SLD is an atmospheric condition that can create dangerous flight conditions for the current fleet of aircraft, the NTSB believes that the proposed rule should be expanded beyond newly certificated airplanes to include all deice boot-equipped airplanes currently in service that are certificated for flight in icing conditions. The NTSB has noted that deice boot-equipped airplanes typically operate at lower altitudes more conducive to SLD encounters and must be properly tested for all icing conditions in which they are authorized to operate. The NTSB believes that the FAA should apply icing certification standards contained in this NPRM, including the provisions of Appendix O, to all deice boot-equipped airplanes currently certificated for flight in icing conditions. The NTSB stated this concern 12 years ago in Safety Recommendation A-98-100, issued to the FAA as a result of the Comair EMB-120 accident in Monroe, Michigan: When the revised icing certification standards and criteria are complete, review the icing certification of all turbopropeller-driven airplanes that are currently certificated for operation in icing conditions and perform additional testing and take action as required to ensure that these airplanes fulfill the requirements of the revised icing certification standards. This recommendation was classified “Closed?Unacceptable Action/Superseded” when Safety Recommendation A-07-16 was issued to the FAA on February 27, 2007, as a result of the February 16, 2005, Pueblo Circuit City accident. This new recommendation again stressed that revised certification requirements should apply to currently certificated deice boot-equipped aircraft, as well as new aircraft: When the revised icing certification standards (recommended in Safety Recommendations A-96-54 and A-98-92) and criteria are complete, review the icing certification of pneumatic deice boot-equipped airplanes that are currently certificated for operation in icing conditions and perform additional testing and take action as required to ensure that these airplanes fulfill the requirements of the revised icing certification standards. (A-07-16) (Open?Unacceptable Response) To summarize, the NTSB supports the Part 25 regulatory revisions proposed in this NPRM and believes that the new rule will be an essential step in improving the safety of flight for airplanes operating in icing conditions. However, the NTSB continues to believe that the proposed rule should be expanded to include all aircraft regardless of MTOW or flight control design and that the requirements should apply to both newly manufactured and currently certificated aircraft under both Parts 25 and 23. The NTSB appreciates the opportunity to comment on this NPRM.

From: NTSB
To: FAA
Date: 7/23/2007
Response: Notation 7903: The National Transportation Safety Board has reviewed the Federal Aviation Administration’s (FAA) Notice of Proposed Rulemaking (NPRM), “Activation of Ice Protection; Proposed Rule,” which was published at 72 Federal Register 20924 on April 26, 2007. The notice proposes to amend Federal Aviation Regulation (FAR) Part 25 to require a means to ensure timely activation of the airframe ice protection system (IPS) on newly certified transport category airplanes for flight in icing conditions. Specifically, the rule would require that airplane manufacturers provide one of the following methods to detect ice and to ensure that the airframe IPS is activated: • automatic activation, or • installation of an ice detection system that alerts the crew to activate the IPS, or • the identification and publication of environmental conditions conducive to icing for use by the crew to activate the IPS. The NPRM states that the proposed rule will partially address Safety Recommendations A-96-56 and A-98-91 issued by the Safety Board: 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 safe operations cannot be demonstrated by the manufacturer, operational limitation 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. (A-96-56) Require manufacturers and operators of modern turbopropeller-driven airplanes in which ice bridging is not a concern to review and revise the guidance contained in their manuals and training programs to include updated icing information and to emphasize that leading edge deicing boots should be activated as soon as the airplane enters icing conditions. (A-98-91) In reviewing the proposed rule changes, the Safety Board is pleased that the FAA agrees that the regulations regarding flight in icing conditions need to be improved. The NPRM proposes an alerting system for icing conditions that exceed the limits of aircraft certification, as recommended in part by A-96-56, by adding section 25.1419(e). The NPRM proposes to address A-07-14 in part, which supersedes A-98-91 (discussed later in this response), by requiring IPS activation as soon as the airplane enters icing conditions. However, it is only an NPRM and regulatory changes may be years away. It has been almost 11 years since the Safety Board issued Safety Recommendation A-96-56 as a result of the October 31, 1994, in-flight icing encounter and loss of control of American Eagle Flight 4184, an ATR-72, over Roselawn, Indiana (Safety Board accident DCA95MA001), and 9 years have passed since the issuance of A-98-91, issued as a result of the January 9, 1997, Monroe, Michigan, Comair EMB-120 accident (Safety Board accident DCA97MA017). The Safety Board has investigated several more accidents involving in-flight icing since then, including the following: • March 14, 1997, Detroit, Michigan, Reno Air MD-87 (accident CHI97FA083) • March 19, 2001, West Palm Beach, Florida, Comair EMB-120 (accident DCA01MA031) • February 16, 2005, Pueblo, Colorado, Circuit City Citation 560 (accident DCA05MA037) • September 8, 2006, Santa Maria, California, American Eagle SF340B (accident LAX06IA076) Ice-related accidents like these are likely to continue unless the airplane certification regulations are updated to include the icing knowledge and research developed over the past decade. The Safety Board therefore encourages the FAA to act expeditiously on ice certification regulations and IPS activation requirements, including guidance materials and training programs. The Safety Board would like to see the following issues also addressed in the proposed rule. The first issue is the ongoing disconnect between industry’s current guidance on deice boot activation and what the FAA has learned and research has shown about ice bridging and deice boot effectiveness. Information gathered from the FAA’s 1997 Airplane Deice Boot Bridging Workshop, as well as subsequent icing tunnel and flight tests, revealed that ice bridging does not occur on modern airplanes, which is contrary to what has previously been thought and why some manufacturers’ guidance addresses delayed activation of deice boots. In addition, icing tunnel tests conducted by the National Aeronautics and Space Administration have shown that thin, rough ice accumulations on the wing leading edge deice boot surfaces (like the 1/4 inch or less prescribed by some manufacturers before boot activation) can, depending on distribution, be as aerodynamically detrimental to an airplane’s performance as larger ice accumulations. As a result, deice boots should be operated at the first sign of ice. Delays intended to prevent ice bridging are inappropriate, given the results of current research, and manufacturers’ guidance to operators must be revised accordingly. For example, Cessna operating procedures for the 208 Caravan (C-208) instruct crews to wait for 1/4 to 3/4 inch of ice to accrete before activating the C 208 pneumatic boots. The NPRM, on the other hand, prescribes turning on ice protection at the first sign of ice accretion (or even before, if the conditions are right). As a result of the Safety Board’s investigation of the February 16, 2005, Cessna Citation 560 accident at Pueblo, Colorado, the Safety Board issued Safety Recommendation A-07-14, which superseded A-98-91: Require manufacturers and operators of pneumatic deice boot-equipped airplanes to revise the guidance contained in their manuals and training programs to emphasize that leading edge deice boots should be activated as soon as the airplane enters icing conditions. (A-07-14) The Safety Board encourages the FAA to address this recommendation in the final rule by addressing the ice bridging issue directly to ensure that manufacturers revise the guidance in their manuals and training programs so that operators receive clear, complete, and unambiguous guidance on deice boot activation, as set forth in Safety Recommendation A-07-14. The second issue is the need for more specific guidance with respect to the identification of environmental conditions conducive for icing, the third method of compliance offered in the NPRM. As stated in Safety Recommendation A-07-14, the Safety Board believes that the IPS should be activated “as soon as the airplane enters icing conditions,” which may include visible moisture and the requisite outside air temperature. The FAA, however, has been reluctant to support IPS activation without the presence of ice, citing concerns of reduced IPS life and airplane performance. Most recently, on April 3, 2007, the FAA issued a letter of interpretation for comment in the Federal Register (Docket No. FAA-2007-27758) seeking clarification from industry on the subject of “known icing.” In it, the FAA stated that “Permutations on the type, combination, and strength of meteorological elements that signify or negate the presence of known icing conditions are too numerous to describe….” It is the Safety Board’s position that industry cannot realistically be expected to implement the third method in the proposed rule until the FAA provides a more specific definition of “environmental conditions conducive to icing.” Understandably, industry has concerns about decreased system life and airplane performance and therefore hesitates to direct operators to activate an IPS based solely on icing potential. The FAA should use the research it has commissioned through the Aviation Rulemaking Advisory Committee to provide a more detailed description of conditions conducive to icing. Until the FAA provides specific environmental parameters and prescribed levels, the third method proposed to address activation of the IPS, despite being the most proactive solution, will not be practical. The third issue is that the proposed rule does not address operations when certain functions of the IPS are known to be inoperable. Since the proposed rule would alert crews to icing conditions, the Safety Board believes that the proposed rule should prohibit crews from operating when certain functions of the IPS are inoperable. This situation occurred on January 2, 2006, when American Eagle flight 3008, a SAAB SF340B, departed San Luis County Regional Airport, San Luis Obispo, California, with a scheduled destination of Los Angeles International Airport. The airplane encountered icing conditions during the en route climb and departed controlled flight at an altitude of about 11,500 feet mean sea level (msl), descending to an altitude of about 6,500 feet msl. During the previous inbound flight and subsequent incident flight, the airplane’s automatic deice control was inoperable due to a deicer timer light failure. According to American Eagle’s Minimum Equipment List, the crew could dispatch the airplane into known or forecast icing conditions with the automatic function of the IPS inoperable. The proposed rule does not address such operations—that is, operations with an inoperable automatic IPS. The Safety Board believes that the proposed rule should prohibit flight into known icing if certain functions of the IPS are inoperable. Finally, because ice is a major safety issue that affects all airplanes, regardless of age, the Safety Board believes that the proposed rule should be expanded beyond newly certificated airplanes to include deice boot-equipped airplanes currently certified for flight in icing conditions. The Board hopes that the FAA will apply the new certification standards to ensure timely IPS activation, developed as a result of this NPRM, to earlier recommendations related to icing certification criteria (see Safety Recommendations A-96-54 and A-98-92), so that accidents like the EMB-120 accident in Monroe, Michigan, will not reoccur. The Safety Board stated this concern 9 years ago by issuing Safety Recommendation A-98-100, as a result of the accident in Monroe, Michigan: When the revised icing certification standards and criteria are complete, review the icing certification of all turbopropeller-driven airplanes that are currently certificated for operation in icing conditions and perform additional testing and take action as required to ensure that these airplanes fulfill the requirements of the revised icing certification standards. (A-98-100) This recommendation was classified “Closed–Unacceptable Action/Superseded” with the issuance of Safety Recommendation A-07-16 to the FAA on February 27, 2007, issued as a result of the February 16, 2005, Pueblo, Colorado, Cessna Citation 560 accident. The prior recommendation addressed turbopropeller airplanes; however, the Citation 560 involved in the Pueblo accident was a deice boot-equipped turbojet. The circumstances of the Pueblo accident demonstrated that pneumatic deice boot-equipped turbojet airplanes also require review and testing to meet the expanded icing certification standards. Hence, this new recommendation, A 07-16, reiterates the point that certification requirements should apply to currently certified deice boot-equipped aircraft, as well as new aircraft: When the revised icing certification standards (recommended in Safety Recommendations A-96-54 and A-98-92) and criteria are complete, review the icing certification of pneumatic deice boot-equipped airplanes that are currently certificated for operation in icing conditions and perform additional testing and take action as required to ensure that these airplanes fulfill the requirements of the revised icing certification standards. (A-07-16) The Safety Board supports issuance of the regulatory revisions proposed in this NPRM. Ice is detrimental to airplane performance and handling qualities, and it represents a serious threat to aviation safety. The Board has investigated many accidents caused by in-flight icing. Operators need to be fully informed before entering icing conditions, and the proposed rule should help do this. However, the Board continues to believe that the issues outlined above—bridging, clearer guidance on deice activation, operation with a known inoperative IPS, and applying revised certification standards to previously certified airplanes—should be addressed in the proposed rule. The Safety Board appreciates the opportunity to comment on this NPRM.

From: NTSB
To: FAA
Date: 2/27/2007
Response: Further, icing tunnel tests conducted as part of the Comair flight 3272 accident investigation indicated that the effects of ice accretion on airplane performance could vary widely depending on the size, distribution, and type of ice accumulated on the airplane’s surfaces. However, the Board learned that manufacturers are not required to demonstrate an airplane’s flight handling characteristics or stall margins using thin, rough ice that can accrete on protected surfaces before the activation of the deice boot system or between activation cycles. As a result of its findings, the Board issued Safety Recommendation A-98-92, which asked the FAA (in cooperation with the National Aeronautics and Space Administration and other interested aviation organizations) to do the following: [C]onduct 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. The Safety Board also issued Safety Recommendation A-98-100, which asked the FAA to review the icing certification of all turbopropeller-driven airplanes currently certificated for operation in icing conditions, perform additional testing, and take action as required to ensure that these airplanes fulfill the requirements of the revised icing certification standards asked for in Safety Recommendation A-98-92. The FAA indicated in a March 6, 2006, response to Safety Recommendation A-96-54 that the ARAC IPHWG is continuing to develop a revision to Part 25 to require a demonstration that an airplane can safely operate in SLD conditions for an unrestricted time or can detect SLD and safely exit icing conditions. However, the FAA has still not received the recommendations from the IPHWG, prepared regulatory analyses, issued the NPRM, analyzed comments, or completed the many other tasks involved in issuing new regulations. The FAA indicated in an October 26, 2005, response to Safety Recommendation A-98-92 that it had completed and would shortly issue a draft revision to AC 20-73, which included the certification guidance on determining critical ice shapes, descriptions of intercycle and residual ice accretions, and the aerodynamic penalties associated with these ice shapes. Although the FAA issued AC 20-73A on August 16, 2006, it has still not provided the Safety Board with information regarding any new research conducted in response to this recommendation. Regarding Safety Recommendation A-98-100, the FAA issued a notice of proposed rulemaking (NPRM) in November 2005, which proposed 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 accumulations that must be considered for each phase of flight. Further, the FAA proposed changes to AC 25-1X, which intended to provide guidance for implementing the regulations proposed in the NPRM. In May 2006, the Safety Board expressed concern that, although it agreed with the proposed regulatory changes, the FAA had not applied the new standards to all in-service turbopropeller-driven aircraft. The FAA further indicated that no airplanes have an unsafe condition in icing environments despite a number of accidents in the 1990s that involved airplanes that had passed the certification standards. The Board stated that, to meet the intent of Safety Recommendation A-98-100, the FAA would need to formally evaluate (perhaps by conducting flight tests) all in-service turbopropeller-driven aircraft to ensure that these aircraft comply with all current icing certification criteria for new aircraft. The Board asked the FAA to provide a list of the aircraft that it had formally evaluated and a summary of the findings and resultant actions. To date, this information has not been received. The circumstances of the Comair flight 3272, American Eagle 4184, and Pueblo accidents and the icing tunnel test data show that the ice shapes used during initial certification flight tests were not adequate because the tests did not account for thin, rough ice on the wing. The 1996 ice shapes tests on the Cessna 560 were also inadequate because, although tests were conducted with ice shapes on the protected surfaces, tests were not conducted using thin, rough ice. Therefore, additional ice sizes, distribution patterns, and types need to be considered during flight testing to more adequately gauge an airplane’s performance in icing conditions. The Safety Board concludes that existing flight test certification requirements for flight into icing conditions do not test the effects of thin, rough ice on or aft of an airplane’s protected surfaces, which can cause severe aerodynamic penalties. The circumstances of this accident clearly show that the actions requested in Safety Recommendations A-96-54 and A-98-92 are needed to improve the safety of all airplanes operating in icing conditions. Therefore, the Safety Board reiterates Safety Recommendations A-96-54 and A-98-92. As noted, Safety Recommendation A-98-100 only addressed turbopropeller-driven airplanes. The circumstances of this accident clearly demonstrate that deice boot-equipped turbojet airplanes also require additional testing in an expanded Appendix C icing certification envelope, which would include thin, rough ice accumulations and intercycle and residual ice. Therefore, the Safety Board believes that the FAA should, when the revised icing certification standards and criteria are complete, review the icing certification of all pneumatic deice boot-equipped airplanes that are currently certificated for operation in icing conditions and perform additional testing and take action as required to ensure that these airplanes fulfill the requirements of the revised icing certification standards. The new recommendation (A-07-16) will supersede Safety Recommendation A-98-100 and will be classified Open Unacceptable Response. A-98-100 is classified CLOSED--UNACCEPTABLE ACTION/SUPERSEDED.

From: NTSB
To: FAA
Date: 5/10/2006
Response: In previous correspondence, the FAA has indicated that it needed to complete revisions to the icing certification standards and advisory material before it could act on this recommendation. In its current letter, the FAA states that the icing certification regulations and advisory material are now sufficiently defined to determine whether additional actions are needed. The FAA further states that no unsafe conditions exist to warrant actions beyond those that it has already completed or is in the process of completing. Among these regulatory changes completed or in process are the following: 1.Revisions to Part 25 and Part 121 Concerning Activation of Ice Protection Systems The FAA noted that it has already addressed this issue for existing turbo propeller driven airplanes through the issuance of ADs that require activation of deicing boots at the first signs of ice accumulation. 2.Revisions to Part 25 for SLD and Part 121 on Exiting Icing Conditions The FAA indicates that it has already addressed the issue of exiting severe icing conditions for existing turbo-propeller airplanes through the issuance of a series of ADs in 1999 and 2000 that require these airplanes to exit icing when the conditions exceed the capabilities of the ice protection equipment. 3.Revisions to Part 25 Airplane Performance and Handling Characteristics in the Icing Conditions of Appendix C The FAA states that the November 4, 2005, NPRM provides a comprehensive set of new certification requirements to evaluate airplane performance and handling characteristics in icing conditions, and that it has already taken action on tailplane stalls and stall warning margins in icing conditions for existing airplanes that are a concern. For airplanes with unpowered control systems, the FAA evaluated susceptibility to ice-contaminated tailplane stall, and mandated changes for airplanes found to be susceptible. The FAA also states that it will take appropriate action if unsafe conditions associated with stall warning margins are identified. 4.Proposed AC for Critical Ice Shapes The FAA states this new AC will provide guidance to FAA certification engineers and airframe manufacturers. However, the FAA does not plan to revise the aircraft certification requirements because it believes there has never been a question that the critical ice shapes should be considered during certification. The Safety Board agrees with the FAA that suitable information is now available to determine whether additional action is required for any airplanes currently certificated and in service. The Board does not agree, however, that the FAA has applied the new information to all turbo propeller airplanes in service. The FAA indicates that there are no airplanes for which an unsafe condition exists. The Board is concerned that the FAA has reached this conclusion based on the absence of accidents or serious incidents. During the 1990s, there were a number of accidents involving airplanes that had passed the certification standards and for which the FAA believed there was no unsafe condition requiring action. Lessons learned from these accidents generated new information which the FAA can now use. Before another accident or serious incident occurs, the FAA should evaluate all existing turbo-propeller driven airplanes in service using the new information available, such as critical ice shapes and stall warning margins in icing conditions. To meet the intent of this recommendation, the FAA will need to formally evaluate (perhaps by conducting flight tests) all existing turbo-propeller driven aircraft in service to ensure that these aircraft comply with all current icing certification criteria for new aircraft. The Board asks the FAA to supply a list of those aircraft that it has formally evaluated and a summary of the findings and resultant actions. Pending receipt of such a list, Safety Recommendation A-98-100 is classified "Open-Unacceptable Response."

From: FAA
To: NTSB
Date: 3/1/2006
Response: In its 3/1/2006 annual report to Congress, Regulatory Status of the National Transportation Safety Board's "Most Wanted" Recommendations to the Department of Transportation, the DOT wrote: The icing certification regulations and advisory material being developed by the FAA are sufficiently defined to determine whether additional actions are needed to correct unsafe conditions on currently certificated turbo-propeller-driven airplanes. The FAA has determined that no unsafe conditions exist that warrant actions beyond those which have already been completed or are in the process ofbeing completed. 1. Proposed Rule: Part 25 and Part 121 Activation of Ice Protection Systems. The FAA has already addressed the issue of activation of IPS for existing turbo-propeller-driven airplanes through the issuance of Airworthiness Directives (ADS) that require the activation of pneumatic deicing boots at the first sign of ice accumulation. 2. Proposed Rule: Part 25 Super-cooled Large Droplet and Part 121 Exiting Icing Conditions. The FAA has already addressed the issue of exiting severe icing conditions for existing turbo-propeller-driven airplanes through the issuance of ADS that require the flight crew ofthese airplanes to exit icing when the conditions exceed the capabilities ofthe ice protection equipment. 3. Proposed Rule: Part 25 Airplane Performance and Handling Characteristics in the Icing Conditions of Appendix C. Two significant safety issues addressed by the proposed rule are the susceptibility to ice-contaminated tail plane stall and the stall warning margin in icing conditions. The FAA evaluated airplanes with unpowered control systems operating under parts 121 or 135 for susceptibility to tail plane stall. The FAA mandated changes to improve tail plane stall margins for airplanes found to be susceptible. The FAA will take appropriate action if unsafe conditions associated with stall warning are identified. For example, the FAA has worked with Embraer on the EMB-I20 on the critical ice shapes which has resulted in a service bulletins to modify stall warning computers to provide adequate stall warning margin and increased operating speeds in icing conditions. The FAA plans to issue an AD to mandate incorporation of the service bulletin.

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 In the original response to this safety recommendation, the FAA agreed that after the icing certification regulations and advisory material are revised we would determine if additional actions are required to correct unsafe conditions on currently certificated turbopropeller-driven airplanes. Subsequently, the FAA has reported on the progress of various icing certification rulemaking and advisory material activities. The FAA believes the icing certification regulations and advisory material are now sufficiently defined to determine whether additional actions are needed to correct unsafe conditions on currently certificated turbopropeller-driven airplanes. Based on the information provided below, the FAA has determined that no unsafe conditions exist that warrant actions beyond those that have already been completed or are in the process of being completed. Proposed Rules - Part 25 and Part 121 Activation of Ice Protection Systems. These rules will provide the flightcrew with a means to determine when the ice protection systems must be activated. The FAA has already addressed the issue of activation of ice protection systems for existing turbopropeller-driven airplanes through the issuance of ADs that require activation of pneumatic deicing boots at the first signs of ice accumulation. The ADs address the unsafe condition of the pilot determining whether the amount of ice accumulated on the wing warrants activation of the ice protection system. The FAA acknowledges that the flightcrews' observation of ice accumulations can be difficult during times of high workload, operations at night, or when clear ice has accumulated. Therefore the proposed Part 25 and Part 121 rules will require improved ice protection activation means to address these situations. The proposed Part 121 rule will apply to all airplanes operating under Part 121, including current turbopropeller-driven airplanes that have a maximum certified takeoff weight less than 60,000 pounds. Proposed Rules - Part 25 Supercooled Large Droplet (SLD) and Part 121 Exiting Icing Conditions. The proposed Part 25 rule will require the safe operation of airplanes in SLD conditions. A proposed Part 121 rule will require flightcrews of airplanes equipped with unpowered roll controls that have not been certificated to the proposed Part 25 SLD rule to exit conditions that are conducive to the formation of ice accretion aft of the protected surfaces. The FAA has already addressed the issue of exiting severe icing conditions for existing turbopropeller airplanes through the issuance of a series of ADs issued in the 1999 and 2000 timeframe. The ADs require these airplanes to exit icing when the conditions exceed the capabilities of the ice protection equipment. The FAA acknowledges that most of the visual cues for determining the flightcrew must act to exit icing conditions are subjective and can result in varying interpretations. The proposed Part 121 rule is being written to require less subjective means of determining when the flightcrew should exit icing conditions. The proposed Part 121 rule will apply to all airplanes operating under Part 121, including current turbopropeller airplanes that have a maximum certified takeoff weight less than 60,000 pounds and are equipped with unpowered flight controls in the pitch and/or roll axis. Proposed Rule - Part 25 Airplane Performance and Handling Characteristics in the Icing Conditions of Appendix C. As reported in response to Safety Recommendation A-91-87, the proposed rule 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. Two significant safety issues addressed by the proposed rule are susceptibility to ice-contaminated tailplane stall and the stall warning margin in icing. The FAA has already taken action on both issues for existing airplanes that are a concern. For airplanes with unpowered control systems operating under the Parts 121 or 135 operating rules, the FAA evaluated the airplanes for susceptibility to ice-contaminated tailplane stall. The FAA mandated changes to improve tailplane stall margins for airplanes found to be susceptible. As reported in response to Safety Recommendation A-98-96, the FAA will take appropriate action if unsafe conditions associated with stall warning are identified. The update cited the critical ice shape work done by Embraer on the EMB-120 that has resulted in a service bulletin to modify stall warning computers to provide adequate stall warning margin and increase operating speeds in icing conditions. The FAA plans to issue an AD to mandate incorporation of the service bulletin. Proposed Advisory Circular Material for Critical Ice Shapes. As reported in response to Safety Recommendation A-98-92, the FAA has completed draft advisory material that provides guidance to FAA certification engineers and airframe manufacturers. This guidance material will be utilized by FAA certification engineers and airframe manufacturers and will be available as guidance during icing certifications and icing investigations. The FAA does not plan on revising the aircraft certification requirements since there has never been a question that the critical ice shapes should be considered during certification. As noted above, the FAA plans to mandate changes to the EMB-120 minimum operating speeds and stall warning computers for operation icing conditions to reflect refined critical ice shapes.

From: FAA
To: NTSB
Date: 2/1/2005
Response: In its 2/1/2005 annual report to Congress, Regulatory Status of the National Transportation Safety Board's "Most Wanted" Recommendations to the Department of Transportation, the DOT wrote: The FAA is issuing a draft rule to address certain currently certificated turbo-propellerdriven airplanes. This draft rule would introduce requirements for operating speeds that provide adequate maneuver capability in icing conditions. It would also require stall warning to be provided by a warning device in the flight deck. Upon completion of its efforts to address Safety Recommendation A-98-92, -94, and -96, the FAA will evaluate the need for additional actions related to critical ice shapes on currently certificated turbo-propeller airplanes.

From: NTSB
To: FAA
Date: 7/11/2002
Response: The Safety Board recognizes that the FAA's actions in response to this recommendation are contingent on the FAA's action in response to Safety Recommendation A-98-92. Pending completion of action on that recommendation and the development and application of revised icing certification standards to currently certificated aircraft, Safety Recommendation A-98-100 remains classified "Open--Acceptable Response."

From: FAA
To: NTSB
Date: 9/21/2001
Response: Letter Mail Controlled 10/22/2001 11:44:27 AM MC# 2010866: As discussed in response to Safety Recommendations A-98-94 and A-98-96, the FAA is developing a regulatory project to address currently certificated 14 CFR Part 25 airplanes. The proposed regulatory action will introduce requirements for operating speeds in icing conditions that provide adequate maneuver capability and for stall warning to be provided by a warning device in the flightdeck. Upon completion of the efforts to address Safety Recommendation A-98-92, the FAA will evaluate the need for additional actions related to critical ice shapes on currently certificated turbopropeller airplanes. I will keep the Board informed of the FAA's progress on this safety recommendation.

From: NTSB
To: FAA
Date: 3/12/2001
Response: The FAA indicates that, after the icing certification regulations and advisory material are revised in response to Safety Recommendations A-98-92, -94, and -96, it will determine whether additional actions are required to correct unsafe conditions on currently certificated turbopropeller-driven airplanes. Pending development and application of revised icing certification standards and criteria to currently certificated aircraft, Safety Recommendation A-98-100 remains 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 After the icing certification regulations and advisory material are revised in response to Safety Recommendations A-98-92, -94, and -96, the FAA will determine if additional actions are required to correct unsafe conditions on currently certificated turbopropeller-driven airplanes. I will keep the Board informed of the FAA's progress on this safety recommendation.

From: NTSB
To: FAA
Date: 3/9/2000
Response: PENDING THE FAA'S REVIEW OF ALL NEW MATERIALS AND ITS SUBSEQUENT ACTION, A-98-100 IS CLASSIFIED "OPEN--ACCEPTABLE RESPONSE."

From: FAA
To: NTSB
Date: 2/26/1999
Response: AFTER THE ICING CERTIFICATION REGULATIONS AND ADVISORY MATERIAL ARE REVISED, THE FAA WILL DETERMINE IF ADDITIONAL ACTIONS ARE REQUIRED TO CORRECT UNSAFE CONDITIONS ON CURRENTLY CERTIFICATED TURBOPROPELLER-DRIVEN AIRPLANES. I WILL INFORM THE BOARD OF THE FAA'S COURSE OF ACTION TO ADDRESS THIS RECOMMENDATION UPON COMPLETION OF THE ICING CERTIFICATION REGULATIONS AND ADVISORY MATERIAL.

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.