Safety Recommendation A-99-022

We note that, on August 27, 2024, the FAA published its final rule, “System Safety Assessments,” which amends Title 14 CFR 25.1309(b)(1)(ii) to prohibit a proposed design from allowing any single failure that could result in a catastrophic failure condition (that is, a fail-safe design requirement). The final rule also revised the requirements for safety assessments of flight control systems installations to make them consistent with the requirements for other systems regarding prohibiting catastrophic single failures. We believe the final rule is consistent with the notice of proposed rulemaking and satisfies the intent of Safety Recommendations A-99-22 and -23.

Consequently, the Board has voted to classify these recommendations CLOSED—ACCEPTABLE ACTION.

-From Michael G. Whitaker, Administrator: The FAA published the System Safety Assessments (SSA) Final Rule in the Federal Register on August 27, 2024 (89 FR 68706). This rule addresses the risk from latent failures, including control systems jams and the risk of wear-related failures, by modifying § 25.671, General, and § 25.1309, Equipment, Systems, and Installations. Additionally, the FAA has issued three new Advisory Circulars (ACs) and amended two existing ACs to provide guidance material for acceptable means, but not the only means, of showing compliance with the regulations in this final rule. These ACs are available in the public docket for this rulemaking:

• AC 25.671–1, Control Systems – General. • AC 25.901–1, Safety Assessment of Powerplant Installations. • AC 25.933–1, Unwanted In-Flight Thrust Reversal of Turbojet Thrust Reversers. • AC 25.629–1C, Aeroelastic Stability Substantiation of Transport Category Airplanes. • AC 25.1309–1B, System Design and Analysis.

The final rule addresses these recommendations by revising § 25.671(c), requiring the inclusion of certification maintenance requirements in the airworthiness limitation section, providing guidance on assessing wear-related failures as part of the SSA, and establishing guidance contained in AC 25.1309–1B.

I believe the FAA has addressed the intent of Safety Recommendations A-99-22, A-99-23, A-02- 51, and A-14-119, and consider our actions complete.

We are aware that your notice of proposed rulemaking (NPRM), “System Safety Assessments,” which was published on December 8, 2022, proposed amending Title 14 CFR 25.1309(b)(1)(ii) to prohibit a proposed design from allowing any single failure that could result in a catastrophic failure condition (that is, a fail-safe design requirement). The proposed rule would also make the requirements for safety assessments of flight control systems installations consistent with the requirements for other systems regarding prohibiting catastrophic single failures.

According to the NPRM, systems covered by the proposed 14 CFR 25.671(c) would be required to comply with the 14 CFR 25.1309 prohibition of catastrophic single failures under all operating and environmental conditions in which the airplane was approved to operate. Incorporating fail-safe design requirements across all the critical systems of the airplane would ensure consistent safety objectives are implemented.

Also, according to the NPRM, although 14 CFR 25.671(c)(3) currently allows the use of probability analysis, applicants have generally been unable to demonstrate that jamming conditions are “extremely improbable,” except for in conditions that occur during a very limited time just before landing. Therefore, the NPRM proposed revisions to 14 CFR 25.671(c) that would require that applicants’ safety assessments assume that the specified jamming conditions will occur regardless of those conditions’ probability. The proposed rule would also exclude jamming conditions that occur immediately before touchdown from the required reliability analysis if these can be shown to be extremely improbable.

-From Polly Trottenberg, Acting Administrator: The FAA published the SSA Notice of Proposed Rulemaking in the Federal Register on December 8, 2022 (87 FR 75424), and public comments closed on March 8, 2023. This 14 CFR Part 25 amendment will address the risk from latent failures, including control systems jams and the risk of wear-related failures, by modifying § 25.671, General, and § 25.1309, Equipment, Systems, and Installations. On August 30, 2022, we released the following new and revised advisory circulars (AC) for public comment:

• AC 25.1309-1B, System Design and Analysis (revised); • AC 25.629-1C, Aeroelastic Stability Substantiation of Transport Category Airplanes (revised); • AC 25.671, Control Systems (new); • AC 25.901, Safety Assessment of Powerplant Installations (new); and • AC 25.933, Powerplant Reversing Systems (new).

We anticipate publishing the SSA Final Rule and associated ACs by July 2024.

I will keep the Board informed of the FAA’s progress on Safety Recommendations A-99-22, A-99-23, A-02-51, and A-14-119 and anticipate providing an update by May 31, 2024.

We are aware that, on December 8, 2022, you published a notice of proposed rulemaking (NPRM), “System Safety Assessments,” which proposed amending Title 14 Code of Federal Regulations (CFR) 25.1309(b)(1)(ii) to prohibit a proposed design from allowing any single failure that could result in a catastrophic failure condition (that is, a fail-safe design requirement). The proposed rule would also make the requirements for safety assessments of flight control systems installations consistent with the requirements for other systems regarding prohibiting catastrophic single failures.

According to the NPRM, systems covered by the proposed 14 CFR 25.671(c) would be required to comply with the 14 CFR 25.1309 prohibition of catastrophic single failures under all operating and environmental conditions in which the airplane was approved to operate. Incorporating fail-safe design requirements across all the critical systems of the airplane would ensure consistent safety objectives are implemented.

Also according to the NPRM, although 14 CFR 25.671(c)(3) currently allows the use of probability analysis, applicants have generally been unable to demonstrate that jamming conditions are “extremely improbable,” except for in conditions that occur during a very limited time just before landing. Therefore, the NPRM proposes revisions to 14 CFR 25.671(c) that would require that applicants’ safety assessments assume that the specified jamming conditions will occur regardless of those conditions’ probability. The proposed rule would also exclude jamming conditions that occur immediately before touchdown from the required reliability analysis if these can be shown to be extremely improbable.

The National Transportation Safety Board (NTSB) has reviewed the Federal Aviation Administration’s (FAA) notice of proposed rulemaking (NPRM) titled, “System Safety Assessments,” which was published at 87 Federal Register 75424 on December 8, 2022. We welcome the opportunity to provide comments on this NPRM, in which the FAA proposes to amend certain airworthiness regulations to standardize the criteria for conducting safety assessments for systems, including flight controls and powerplants, installed on transport-category airplanes.

According to the NPRM, the proposed action addresses a congressional mandate, safety recommendations from the NTSB, industry working groups safety analyses, and updates to regulations and provides insight to new regulations related to system safety. The NPRM also moves the United States closer to harmonizing Title 14 Code of Federal Regulations (CFR) 25.1309 with European Aviation Safety Agency Certification Specification-25. The intended effect of this proposed action is to improve aviation safety by making system safety certification requirements more comprehensive and consistent.

The NTSB has long recognized the need for system safety assessments to improve safety in aircraft design. The following comments discuss 10 safety recommendations issued to the FAA regarding issues addressed in the NPRM and accompanying draft advisory circulars (ACs).

Reliability of Flight Control Systems

In 1999, we issued Safety Recommendations A-99-22 and -23. Footnote: We issued Safety Recommendations A-99-22 and 23 (which superseded Safety Recommendations A 96 107, -109, -12, and -113) as a result of our investigation of the September 8, 1994, accident involving USAir flight 427, a Boeing 737-300, which crashed in Aliquippa, Pennsylvania, while maneuvering to land. Safety Recommendations A-99-22 and -23 are currently classified Open—Unacceptable Response based on the FAA’s lack of a timely response. More information about the recommendations referenced in this response can be found in CAROL. For more information about the USAir flight 427 investigation’s findings, see NTSB. 1999.

Uncontrolled Descent and Collision With Terrain, USAir Flight 427, Boeing 737-300, N513AU, Near Aliquippa, Pennsylvania, September 8, 1994. Aircraft Accident Report AAR-99/01. Washington, DC: NTSB. Safety Recommendation A 99-22 asked the FAA to check that future transport-category airplanes certificated by the FAA provide a reliably redundant rudder actuation system.

-From Billy Nolen, Acting Administrator: The FAA continues to prioritize the publication of the Notice of Proposed Rulemaking (NPRM) for the System Safety Assessment (SSA) rule currently in its final internal coordination with an anticipated publication date by December 31, 2022, to meet the requirements of The Aircraft Certification, Safety, and Accountability Act. The part 25 amendment will address the risk from latent failures and includes control systems jams and modifications to 14 CFR § 25.671, General, and § 25.1309, Equipment, Systems, and Installations, to address the risk of wear-related failures.

Concurrent with the SSA NPRM, the FAA will release the following new and revised draft advisory circulars (AC) for public comment:

• AC 25.1309-1B, System Design and Analysis (revised); • AC 25.629-1C, Aeroelastic Stability Substantiation of Transport Category Airplanes (revised); • AC 25.671, Control Systems (new); • AC 25.901, Safety Assessment of Powerplant Installations (new): and • AC 25.933, Powerplant Reversing Systems (new).

I will keep the Board informed of the FAA’s progress on safety recommendations A-99-22 and -23, A-02-51, and A-14-119, and anticipate providing an update by June 30, 2023.

We continue to believe that your plan to publish a notice of proposed rulemaking (NPRM) and revise Advisory Circular (AC) 25.1309-1A is responsive to these recommendations. We remain concerned, however, with the continued delays associated with the System Safety Assessment rulemaking project. Pending prompt publication of the NPRM and a resulting final rule, and of updates to AC 25.1309-1A that include the appropriate revisions, Safety Recommendations A-99-22 and -23 and A-02-51 remain classified OPEN-- UNACCEPTABLE RESPONSE.

-From Steve Dickson, Administrator: This is in further response to Safety Recommendations A-99-22 and -23 issued by the Board on April 16, 1999; A-02-51 issued on January 8, 2003; and A-14-119 issued on December 1, 2014, and supplements all of our previous letters. These safety recommendations are from two accidents and one incident. We have grouped these safety recommendations together to provide a consistent response to the Board because each will be addressed by the publication of the same rulemaking and guidance material.

A-99-22 and -23 were issued as a result of the accident that occurred on September 8, 1994, about 1903:23 Eastern Daylight Time, when USAir (now US Airways) flight 427, a Boeing 737-3B7 (737-300), N513AU, crashed while maneuvering to land at Pittsburgh International Airport, (PIT), Pittsburgh, Pennsylvania. Flight 427 was operating under the provisions of Title 14, Code of Federal Regulations (CFR) part 121 as a scheduled domestic passenger flight from Chicago-O’Hare International Airport, (ORD), Chicago, Illinois, to Pittsburgh. The flight departed about 1810, with 2 pilots, 3 flight attendants, and 127 passengers on board.

The airplane entered an uncontrolled descent and impacted terrain near Aliquippa, Pennsylvania. All 132 people on board were killed, and the airplane was destroyed by impact forces and fire. Visual meteorological conditions prevailed for the flight, which operated on an instrument flight rules flight plan.

A-02-51 was issued as a result of the accident that occurred on January 31, 2000, about 1621 Pacific Standard Time, when Alaska Airlines, Inc., flight 261, a McDonnell Douglas MD-83, N963AS, crashed into the Pacific Ocean about 2.7 miles north of Anacapa Island, California. The 2 pilots, 3 cabin crewmembers, and 83 passengers on board were killed, and the airplane was destroyed by impact forces.

Flight 261 was operating as a scheduled international passenger flight under the provisions of part 121 from Lic Gustavo Diaz Ordaz International Airport (PVR), Puerto Vallarta, Mexico, to Seattle-Tacoma International Airport (SEA), Seattle, Washington, with an intermediate stop planned at San Francisco International Airport (SFO), San Francisco, California. Visual meteorological conditions prevailed for the flight, which operated on an instrument flight rules flight plan.

We continue to believe that your plan to publish a notice of proposed rulemaking (NPRM) and revise Advisory Circular (AC) 25.1309-1A, as recommended by your Aviation Rulemaking Advisory Committee, are responsive to Safety Recommendations A-99-22 and -23. We remain disappointed, however, with the slow pace of progress. We point out that these recommendations are now over 20 years old, and there is still no NPRM scheduled for publication to address them, let alone a final rule.

Pending prompt publication of the NPRM and a resulting final rule, and of revisions to AC 25.1309-1A that include the recommend requirements, Safety Recommendations A-99-22 and -23 remain classified OPEN--UNACCEPTABLE RESPONSE.

Similarly, although the revisions to AC 25.1309-1A will likely satisfy Safety Recommendation A-02-51, it is already over 17 years old. Pending timely issuance of the final rule and appropriate revisions to the AC, Safety Recommendation A-02-51 remains classified “Open—Unacceptable Response.”

-From Steve Dickson, Administrator: The Federal Aviation Administration (FAA) is in the process of reviewing and coordinating a Notice of Proposed Rulemaking (NPRM) to incorporate the Aviation Rulemaking Advisory Committee (ARAC) recommendations for revising Title 14 CFR 25.671 , General, and Title l 4 CFR 25.1309, Equipment, Systems, and Installations, to address the risk from latent failures, including control systems jams, as well the risk of wear-related failures. The NPRM has been on hold due to resource constraints. We anticipate that the hold status will be lifted early 2020 and the NPRM to be published no sooner than 6 months after hold status is lifted.

In conjunction with the rule. we plan to revise Advisory Circular (AC) 25.1309-1 A. System Design and Analysis, as recommended by the ARAC. We anticipate the NPRM and draft AC to be published by December 2020.

The FAA previously added considerations of wear-related failures that could impact continued safe flight and landing throughout AC 25-l 9A, Certification Maintenance Requirements, published on October 3. 20 11. Once critical wear-related failures are identified in system safety assessments, they are controlled in a manner equivalent to controlling airworthiness limitations.

We note that, on May 11, 2010, you received the final recommendations of your Aviation Rulemaking Advisory Committee (ARAC) for revisions to 14 CFR sections 25.671 and 25.1309, and in the 7½ years since then, you have been preparing a notice of proposed rulemaking (NPRM) for these revisions. We further note that your ARAC recommended concurrent issuance of a revision to AC 25.1309-1A, “System Design and Analysis.”

The revised AC will provide guidance for showing compliance with the proposed revisions to sections 25.671 and 25.1309, as well as guidance to justify assumptions, data sources, and analytical techniques in safety assessments, and it will advise that extra conservatism be built into the analysis or design when the analytical process is variable or uncertain. The revised AC will also emphasize the importance of including safety critical assumptions in safety assessments to address new technologies that involve intrinsically hazardous equipment.

Although you originally intended to publish the NPRM in December 2012, assessing the costs and benefits of the proposed rule has taken considerably longer than you originally expected; as a result, the NPRM and AC revisions have been delayed. We note from your current letter that you are not able to provide an estimated publication date for the NPRM and draft changes to AC 25.1309-1A and that, as an interim measure, you will continue to use issue papers, as you have for many years, to apply the analysis techniques that will be in the NPRM and revised AC to assess failure conditions for all new type certification programs.

Although we believe that the NPRM, the resulting final rule, and the revisions to AC 25.1309 1A will satisfy Safety Recommendations A-99-22 and -23, we remain disappointed with the slow pace of progress. Using issue papers to apply the revisions has been an effective interim step, but these recommendations are now 19 years old and there is still no NPRM scheduled for publication to address them, let alone a final rule. Pending publication of the NPRM and a resulting final rule, and of revisions to AC 25.1309 1A that include the recommend requirements, Safety Recommendations A 99 22 and 23 remain classified OPEN--UNACCEPTABLE RESPONSE.

-From Michael P. Huerta, Administrator: As noted in our previous letters to the Board, the Federal Aviation Administration (FAA) tasked the Aviation Rulemaking Advisory Committee (ARAC) with recommending refinements to safety rules and guidance concerning these four recommendations.

In 2010. the ARAC made recommendations to the FAA to revise Title 14. Code of Federal Regulations§§ 25.671and25.1309, and associated guidance material to further mitigate the risk from latent failures, including control systems jams, as well as the risk of wear-related failures. The ARAC recommendations address the issues raised in all four safety recommendations for future new airplane designs. For existing airplane designs, we have addressed these systems failures through airworthiness directives and continuously monitor this fleet to correct any new issues that arise through our continued operational safety process.

For future airplanes and those currently being certified, the FAA applies the analysis of failure conditions to all new type certification programs through issue papers, and will continue this practice on new certification projects, as applicable, until publication of our fin al rule and guidance. We initiated a rulemaking project in 20 11 to incorporate the ARAC recommendations for revising §§ 25.671 and 25.1309, applicable to new airplane designs and significant changes to existing designs.

Assessing costs and benefits of the proposed rule took longer than expected and issuance of the Notice of Proposed Rulemaking (NPRM), entitled System Safety Assessments, and associated guidance was delayed. As a result, we cannot provide an estimated publication date for the NPRM and draft changes to Advisory Circular (AC) 25.1309- l A at this time.

We note that, on May 11, 2010, you received the final recommendations of your Aviation Rulemaking Advisory Committee for revisions to 14 CFR Sections 25.671 and 25.1309, and since then have been preparing a notice of proposed rulemaking (NPRM) for these revisions. We further note that, although you had intended to publish the NPRM in December 2012, this date has been revised to July 2015 so that you can address concerns about the potential costs and benefits of implementing the recommended requirement.

Your letter discussed how the NPRM would address issues related to aging and wear, which are not the subject of either Safety Recommendation A-99-22 or -23; your staff clarified that the NPRM will also address rudder reliability and continued safe flight after the jamming of a flight control.

Although we believe that the NPRM and resulting final rule will satisfy Safety Recommendations A-99-22 and -23, we remain disappointed with the slow pace of progress. These recommendations are 16 years old without an NPRM being published to address them, let alone implementation of a final rule. In view of the continuing delay, pending publication of the NPRM and a resulting final rule that includes the recommend requirement, Safety Recommendations A 99-22 and -23 remain classified OPEN—UNACCEPTABLE RESPONSE.

-From Michael P. Huerta, Administrator: As stated in our May 13, 2011, letter, the Federal Aviation Administration (FAA) received the final Aviation Rulemaking Advisory Committee (ARAC) recommendations for changes to 14 CFR §§ 25.671 and 25.1 309. The ARAC determined that aging and wear were covered by § 25.1309, Equipment, systems, and installations, and recommended changes to Advisory Circular (AC) 25.1309-1 A, System Design and Analysis, to clarify how aging and wear should be addressed to meet this regulation.

The FAA initiated a Notice of Proposed Rulemaking (NPRM) to address the Board's recommendations. However, due to concerns about the potential costs and benefits of the proposed rule, the NPRM was delayed from its original expected issue date of December 2012. We expect to publish the NPRM for public comment by July 31, 2015, and the updated AC with the subsequent final rule.

I will keep the Board informed of the FAA's progress on these safety recommendations and provide an update by October 31, 2015.

The NTSB notes the FAA’s ongoing efforts to address these recommendations. We are aware that, on May 11, 2010, the FAA received the Aviation Rulemaking Advisory Committee’s (ARAC) final recommendations for changes to the CFRs and that the FAA intends, in light of the ARAC’s recommendations, to revise the CFRs. Although we are pleased that the FAA plans to act as recommended, these recommendations are now over 12 years old, and we remain disappointed with the slow pace of progress. Accordingly, pending the completion of these revisions, Safety Recommendations A-99-22 and -23 remain classified OPEN—UNACCEPTABLE RESPONSE.

CC# 201100210: - From J. Randolph Babbitt, Administrator: As noted in our October 3, 2010 response to the Board, we received on May 11, 2010 the final Aviation Rulemaking Advisory Committee (ARAC) recommendations for changes to 14 CFR 25.671 and 25.1309. We also indicated previously that the ARAC recommendations would serve as the basis for a rulemaking action to address these safety recommendations. We are currently developing a notice of proposed rulemaking, which we plan to issue by December 2012. I will keep the board informed of the FAA's progress on these recommendations and provide an updated response by June 30, 2012.

The FAA originally referred these recommendations to two Aviation Rulemaking Advisory Committees (ARAC), one concerned with 14 CFR Section 25.1309, “Equipment, Systems, and Installations,” and the other with 14 CFR Section 25.671, “Control Systems–General.” On April 29, 2003, the FAA published a notice of availability of the ARAC-recommended changes to the airworthiness standards for transport-category airplanes. This notice of availability also indicated that the ARAC-recommended changes could be used in current airplane certification programs.

The ARACs also proposed revisions to advisory circular (AC) 25.1309-1A, “System Design and Analysis,” which provides guidance on how to analyze the reliability of aircraft systems. In an October 24, 2008, letter, the FAA stated that it had not yet incorporated the ARACs’ recommendations into the CFRs because it wanted to gather further information and recommendations from the ARACs regarding a number of regulations that involve system safety, to establish standardized criteria and guidance for conducting airplane-level safety assessments of “specific risks.”

Although the ARACs’ recommendations had not yet been incorporated into the CFRs, the FAA stated that airplane manufacturers had been applying these standards to the analysis of failure conditions on all new type certificates, and the FAA expected that airplane manufacturers would continue to do so. Therefore, the FAA believed that the intent of Safety Recommendations A-99-22 and -23 had been fully addressed through application of the revised guidance material. The FAA did not believe that the rulemaking that awaited further ARAC recommendations would revise any of the standards and guidance developed by the ARACs in response to these recommendations.

On May 12, 2009, the NTSB replied that, although we were disappointed that it had taken 10 years to reach this point, the revisions recommended by the ARACs were responsive to these recommendations, and the application of these standards and practices to new certification programs before the CFRs could be revised constituted a responsive interim action. However, we stated that the revisions would also need to be incorporated into the CFRs before the recommendations could be closed.

CC# 201000379: - From J. Randolph Babbitt, Administrator: In previous responses we outlined our plans for changes to 14 CFR 25.671 and 25.1309. We noted that we were awaiting further recommendations from the Aviation Rulemaking Advisory Committee (ARAC). On May 11, 2010, we received the final ARAC recommendations for changes to these and other rules (enclosed). Based on the ARAC recommendations, the FAA intends to address these safety recommendations via rulemaking. I will keep the Board informed of the FAA's progress on these safety recommendations and provide an update by July 2011.

On October 23, 2000, the FAA informed the NTSB that it had referred the issues in these recommendations to two Aviation Rulemaking Advisory Committees (ARACs), one concerned with 14 CFR Section 25.1309, Equipment, Systems, and Installations, and the other with 14 CFR Section 25.671, Control Systems General. On April 25, 2001, the NTSB responded that referral of an issue to an ARAC did not necessarily indicate that the recommended action was being taken and that, without knowing the ARACs’ recommendations or whether the FAA would adopt the ARACs’ recommendations, the NTSB was unable to determine the status of these recommendations.

Pending further correspondence and action to address the recommendations, Safety Recommendations A-99-22 and A-99-23 remained classified Open Unacceptable Response.

In its current letter, the FAA stated that it had received material from the ARACs regarding revisions to Sections 25.1309 and 25.671 as well as a proposed revision to Advisory Circular (AC) 25.1309-1A, System Design and Analysis. The AC provides guidance on how to analyze the reliability of aircraft systems. On April 29, 2003, the FAA published a notice of availability of the ARAC-recommended changes to the airworthiness standards for transport-category airplanes. This notice of availability indicated that the ARAC-recommended changes could be used on current airplane certification programs.

The FAA further indicated that the proposed revision to AC 25.1309-1A has been, and continues to be, widely used in recent certification programs. The AC indicates that aircraft systems are not acceptable if they have a single?point catastrophic failure mode such as a rudder system that is not reliably redundant. The ARAC recommendations for

Letter Mail Controlled 11/6/2008 12:13:58 PM MC# 2080675: - From Robert A. Sturgell, Acting Administrator: On October 23, 2000, the Federal Aviation Administration informed the Board that the FAA was working in cooperation with the Aviation Rulemaking Advisory Committee (ARAC) to revise FAA regulations and guidance material to address the Board’s safety recommendations. The two primary regulations associated with the issues raised by the Board are Q 25.1309, Equipment, systems, and installations, which addresses all systems, and Q 25.67 1 , Control systems - General, which specifically addresses flight control systems.

Through the ARAC process, the Systems Design and Analysis Harmonization Working Group, and the Flight Controls Harmonization Working Group, were established to provide recommendations necessary to revise the rules and advisory material for QQ 25.1309 and 25.671 , respectively. The FAA has received the recommendations from these two working groups. These recommendations are available at the following Web address: http://www.faa.gov/regulationsqolicies/rulemaking/committees/arac/issue-areas/ The FAA believes the ARAC recommendations and the FAA’s planned rulemaking and advisory material will address the Board’s recommendations.

On April 29,2003, the FAA published a notice of availability of the ARAC-recommended proposed changes to the airworthiness standards for transport category airplanes regarding equipment, systems, and installations, and Advisory Circular (AC) 25.1309-1A (68 FR 22636). This notice of availability indicates that the ARAC-recommended proposed changes may be used on current airplane certification programs through a request for an equivalent level of safety finding.

The proposed revised version of AC 25.1309- 1 A, System Design and Analysis, (often referred to as the “Arsenal” version) has been and continues to be widely used by industry during recent certification programs, and specifically prohibits single catastrophic failures. The ARAC recommendations for 3 25.671 include changes to the current failure and jamming criteria for flight controls, as well as a new advisory circular. Although the above ARAC recommendations have not been codified, transport airplanes manufacturers have recognized their value as improved standards.

The Safety Board notes that referral of an issue to ARAC does not necessarily indicate that the recommended action is being taken. Without knowing ARAC's recommendations or whether the FAA will adopt ARAC's recommendations, the Board is unable to determine the status of the Board's recommendations. Pending receipt of further correspondence, and FAA action to address the recommendations, Safety Recommendations A-99-22 and A-99-23 remain classified OPEN -- UNACCEPTABLE RESPONSE.

Letter Mail Controlled 10/26/2000 4:59:28 PM MC# 2001592 - From Jane F. Garvey, Administrator: The FAA agrees with this recommendation. Existing regulations are intended to ensure reliability and redundancy in all flight control systems. The two primary regulations that apply are 14 CFR 25.1309, which addresses all systems, and 14 CFR 25.671, which specifically addresses flight control systems. The basic objective of these regulations is to ensure that an airplane is capable of continued safe flight and landing following any single failure, and following any combination of failures not shown to be extremely improbable.

The FAA is currently working to revise 14 CFR 25.671 and 14 CFR 25.1309 in cooperation with the Aviation Rulemaking Advisory Committee (ARAC). Through this process, the Systems Design and Analysis Harmonization Working Group and the Flight Controls Harmonization Working Group were established to provide rule and advisory material recommendations for 14 CFR 25.1309 and 14 CFR 25.671, respectively. While the basic objective of the requirements will not change, the FAA believes that with improved rules and advisory material, it will be better able to ensure that this objective is met.

The Systems Design and Analysis Harmonization Working Group has provided its recommendations to the ARAC, which has forwarded them to the FAA. This includes changes to

In response to each of these three Safety Recommendations (A-99-20, A-99-21, and A- 99-22), the FAA notes that it has convened an engineering test and evaluation board to conduct an in-depth failure analysis of the 737 rudder system. The FAA states that the engineering board will examine all of the issues specified in A-99-21 and, in addition, will also focus on any malfunction that could affect lateral/directional control. The FAA states that the engineering board consists of representatives from the FAA, Boeing, the Safety Board, the National Aeronautics and Space Administration, the Department of Defense, the Air Line Pilots Association,

the Air Transport Association of America, and also includes engineers from the Ford Motor Company and from Iluyshin Aviation Complex (a Russian aircraft manufacturing company).

The Safety Board supports the establishment of the engineering board and has been impressed with the results of its work to date. The engineering board has developed a substantial amount of additional information about failure modes in the 737 rudder system that were previously identified by the Safety Board, and has identified numerous additional potential failure modes. The engineering board's identification of these additional potential failure modes confirms the validity of the concern, expressed by the Safety Board in its report on the USAir flight 427 accident, that although two identified failure modes associated with rudder reversal had been

eliminated by design changes to the 737 rudder system, additional unidentified failure modes might still exist. Therefore, pending receipt of the engineering board's final report, Safety Recommendation A-99-21 is classified "Open Acceptable Response."

The engineering board's findings have reinforced the fact that the current 737 rudder system, even with its recent modifications, is not reliably redundant and that design changes are necessary. With regard to Safety Recommendation A-99-20, the FAA states that the engineering board will provide valuable insights, information, and data to determine an appropriate course of action. The Safety Board recognizes that some of the information being developed by the engineering board may be useful in connection with redesigning the 737 rudder system. However, the engineering board was not charged with and has not been, developing a reliably

redundant rudder system for the 737 and, therefore, the establishment of the engineering board does not meet the intent of this recommendation. Waiting until the engineering board completes its work and publishes a report will only unnecessarily delay action that has already been demonstrated to be needed and that should have been undertaken as a parallel effort: the provision of a reliably redundant rudder actuation system on 737s.

Letter Mail Controlled 6/30/99 3:02:35 PM MC# 990699: - From Jane F. Garvey, Administrator: The FAA has convened an engineering test and evaluation board to conduct a failureanalysis of the Boeing 737 rudder system. It is expected that this group will provide the FAA with valuable insights, information, and data for the Boeing 737 and other rudders of similar design to determine an appropriate course of action.

I will keep the Board informed of the FAA's progress on this safety recommendation.