Safety Recommendation A-02-051

We note that the final rule, “System Safety Assessments,” requires certification maintenance requirements to be included in the Airworthiness Limitations section of the instructions for continued airworthiness required by 14 CFR 25.1529. We also note that, on August 30, 2024, the FAA published Advisory Circular (AC) 25.1309-1B, “System Design and Analysis,” which includes guidance on assessing wear-related failures as part of a system safety assessment. Because these requirements and guidance satisfy Safety Recommendation A-02-51, the Board has voted to classify this recommendation 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 the NPRM discussed in our response to Safety Recommendations A-99-22 and -23 proposed requiring certification maintenance requirements (CMRs) to be included in the Airworthiness Limitations Section (ALS) of the instructions for continued airworthiness required by 14 CFR 25.1529. The NPRM also proposed guidance in Advisory Circular (AC) 25.1309-1B, “System Design and Analysis,” on assessing wear-related failures as part of the system safety assessment. In our March 2, 2023, comments responding to the NPRM, we informed you that requiring CMRs in the ALS and finalizing the revised guidance contained in draft AC 1309-1B would satisfy Safety Recommendation A-02-51.

We continue to support your proposed revisions to the regulations and guidance and look forward to reviewing the published final rule and AC 1309-1B. In the meantime, Safety Recommendation A-02-51 remains classified OPEN-- ACCEPTABLE RESPONSE.

-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.

The NPRM discussed in our response to Safety Recommendations A-99-22 and -23 proposes requiring certification maintenance requirements (CMRs) to be included in the Airworthiness Limitations Section (ALS) of the instructions for continued airworthiness required by 14 CFR 25.1529. The NPRM also proposes guidance in advisory circular (AC) 25.1309-1B, “System Design and Analysis,” on assessing wear-related failures as part of the system safety assessment (SSA).

In our March 2, 2023, comments responding to the NPRM, we informed you that requiring CMRs in the ALS and finalizing the revised guidance contained in draft AC 1309-1B will satisfy Safety Recommendation A-02-51. Pending timely implementation of a final rule that is consistent with the NPRM, and publication of AC 25.1309-1B, as proposed, Safety Recommendation A-02-51 is classified OPEN-- ACCEPTABLE RESPONSE.

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).

Inclusion of Wear Related Issues in System Safety Analyses In 2002, we issued Safety Recommendation A-02-51. This recommendation asked the FAA to review and revise aircraft certification regulations and associated guidance applicable to the certification of transport-category airplanes to ensure that wear-related failures are fully considered and addressed so that, to the maximum extent possible, they will not be catastrophic. The NPRM proposes a requirement to include Certification Maintenance Requirements (CMRs) in the Airworthiness Limitations Section (ALS) of the Instructions for Continued Airworthiness required by 14 CFR 25.1529.

The NPRM also contains a draft AC providing guidance on assessing wear-related failures as part of the system safety assessment. Requiring CMRs in the ALS together with the guidance contained in the draft AC would likely satisfy Safety Recommendation A 02 51. Footnote: Safety Recommendation A-02-51, which we issued as a result of our investigation of the January 31, 2000, crash of Alaska Airlines flight 261, an MD 83, is currently classified Open—Unacceptable Response based on the FAA’s lack of a timely response. For more information about the investigation’s findings, see NTSB. 2002.

-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

-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 you continue to develop a notice of proposed rulemaking (NPRM) and to revise Advisory Circular (AC) 25.1309-1A, “System Design and Analysis,” to address this recommendation. We understand that your rulemaking resources are limited and that some rulemaking projects take priority depending on congressional direction and your actions to address other NTSB safety recommendations; however, we are concerned because this recommendation is more than 13 years old and, once the NPRM is published, the final rule and revised guidance will still need to be issued.

Accordingly, pending timely issuance of the final rule and appropriate revisions to AC 25.1309-1A, Safety Recommendation A-02-51 remains classified OPEN—UNACCEPTABLE RESPONSE.

-From Michael P. Huerta, Administrator: As previously stated, the federal Aviation Administration (FAA) tasked the Aviation Rulemaking Advisory Committee (ARAC) to recommend refinements to system safety rules and guidance. In response to the ARAC's recommendations, the FAA continues to work towards issuing a revised § 25 .1309, Equipment, Systems, and Installations, Notice of Proposed Rulemaking (NPRM), concurrent with changes to Advisory Circular 25.1309-1 A, System Design and Analysis. Unfortunately, the PRM has been delayed from its July 31, 2015 publication date due to competing rulemaking priorities as determined by Congress and recommendations from the Board.

Our current estimated publication date is December 31, 2016.

I will keep the Board informed of the FAA"s progress on this recommendation and provide an update by March 31, 2017.

We note that you are still developing a notice of proposed rulemaking and revisions to Advisory Circular 25.1309-1, “System Design and Analysis,” to address this recommendation, although we issued it almost 12 years ago. Such long delays pose unacceptable, ongoing risks. Accordingly, pending timely issuance of the final rule and appropriate revisions being made to AC 25.1309-1, Safety Recommendation A-02-51 is classified OPEN—UNACCEPTABLE RESPONSE.

-From Michael P. Huerta, Administrator: As previously stated, the Federal Aviation Administration (FAA) tasked the Aviation Rulemaking Advisory Committee (ARAC) to recommend refinements to system safety rules and guidance. The ARAC completed its work and forwarded its recommendations to the FAA in May 2010. The ARAC determined that aging and wear were covered by§ 25.1309, Equipment, systems, and installations, and recommended changes to Advisory Circular (AC) 25.1 309-1A, System Design and Analysis, to clarify how aging and wear should be addressed to meet this regulation.

The FAA continues to process a Notice of Proposed Rulemaking (NPRM) and changes to AC 25.1309-1 A, based on the ARAC recommendations. However, the cost-benefit analysis for the NPRM has taken longer than anticipated. Therefore, we now expect to publish the NPRM for public comment by July 31, 2015, and the updated AC with the final rule.

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

The FAA anticipates issuing a notice of proposed rulemaking and revisions to Advisory Circular 25.1309-1, “System Design and Analysis,” that will address this recommendation. Pending the final rule and appropriate revisions being made to AC 25.1309-1, Safety Recommendation A-02-51 remains classified OPEN—ACCEPTABLE RESPONSE.

-From Michael P. Huerta, Acting Administrator: The FAA is continuing to process a proposal for rulemaking and associated guidance material based on the Aviation Rulemaking Advisory Committee recommendations. We estimate that the Notice of Proposed Rulemaking and revisions to Advisory Circular 25.1309-1A, System Design and Analysis, will be available for public comment sometime in 2013.

I will keep the Board informed of the FAA's progress on these recommendations and provide an update by July 31, 2013.

The FAA previously informed us that it had asked the Aviation Rulemaking Advisory Committee (ARAC) to evaluate aging- and wear-related failures. Although the ARAC did not recommend any rule changes to specifically address aging and wear, it recommended revising Advisory Circular (AC) 25.1309-1 to clarify the use of more accurate methods to calculate wear-related failure rates and probabilities in both safety assessments and maintenance planning analysis.

On January 31, 2011, we replied that, although we were encouraged by the ARAC’s recommendation, we were concerned that the proposed actions might not provide clear direction regarding whether wear should be considered as a failure mode and how design organizations should properly address aging- and wear-related safety effects in safety assessments. In its current letter, the FAA indicated that it has reviewed the planned revisions to the regulations and guidance material and believes that the revisions will respond to our concerns. Accordingly, pending appropriate revisions being made to AC 25.1309-1, Safety Recommendation A-02-51 remains classified OPEN—ACCEPTABLE RESPONSE.

From J. Randolph Babbitt, Administrator: The FAA tasked the Aviation Rulemaking Advisory Committee (ARAC) with refining system safety rules and guidance. That group completed its work and forwarded its recommendations to the FAA in May 2010. The ARAC determined that aging and wear were covered by § 25.1309 and recommended changes to Advisory Circular 25.1309-1 A, System Design and Analysis, to clarify how aging and wear should be addressed to meet this regulation. In the January 31, 2011, letter to the FAA, the Board indicated concern that the actions proposed by the FAA would not clearly stipulate the proper consideration of wear as a failure mode in safety assessments.

The Board stated: "A full response to this recommendation must include written directives that clarify when to consider and how to address wear-related failure modes when the effects of such wear could compromise continued safe night and landing, regardless of their cause (maintenance error, design error, or external sources)." The FAA considered the Board's letter while reviewing the ARAC recommendations, and we determined rulemaking was responsive to the Board's concern. We estimate issuance of a Notice of Proposed Rulemaking and related guidance material by December 2012, and publication of a final rule by June 2014.

The ARAC recommendations are available online at: http://www.faa.gov/regulations-'policies/ rulemaking/ committees/arac/ issue_areas /tae/als /medialTAE ASA.pdf. The aging and wear task is covered in Section 6.4.2, beginning on page 82 of the ARAC report, and includes the ARAC recommendations and supporting rationale. I will keep the board informed of the FAA's progress on these safety recommendations, and I will provide an update by August 31, 2012.

The FAA asked its Aviation Rulemaking Advisory Committee (ARAC) to evaluate aging- and wear-related failures.

The ARAC did not recommend any rule changes to specifically address aging and wear, but did recommend revising Advisory Circular (AC) 25.1309-1 to clarify that (1) when calculating the probability of failure, both the constant and non-constant failure rates should be addressed and should be based on all causes of failure and (2) when applying a reliability analysis to determine scheduled maintenance tasks and replacement times, these maintenance tasks and replacement times should be based on the same methodology described in Title 14 Code of Federal Regulations (CFR) 25.1309 and should be documented in the “Airworthiness Limitation Section.”

Although the NTSB is encouraged by the ARAC’s recommendation that AC 25.1309-1 be revised to clarify the use of more accurate methods to calculate wear-related failure rates and probabilities in both safety assessments and maintenance planning analysis, we are concerned that the proposed actions may not provide clear direction on the issue of whether wear should be considered as a failure mode and how design organizations should properly address safety effects in safety assessments.

The NTSB understands that engineering judgment is a necessary part of the process for determining foreseeable failure modes of a system or component and that, accordingly, 14 CFR 25.1309(d)(1) is vague with regard to what modes of failure must be considered in a failure analysis, instead indicating that the analysis should consider “possible modes of failure.” However, the NTSB believes that excessive wear leading to premature wearout in a component designed to wear is a foreseeable failure mode and should be considered in any safety assessment related to the component and the system in which it is installed.

In addition, excessive wear resulting from design, installation, or maintenance errors should also be considered when significant safety effects can result. At the NTSB’s public hearing on the Alaska Airlines flight 261 accident, an FAA certification engineer stated that wear is

CC# 201000346: - From J. Randolph Babbitt, Administrator: The ARAC, as noted in safety recommendation A-02-50, also evaluated aging and wear-related failures. The ARAC did not recommend any rule changes to specifically address aging and wear, but did recommend Advisory Circular 25.1309-1 be revised to clarify the following: • When calculating the probability of failure, both the constant and non-constant failure rates should be addressed and based on all causes of failure (operational, environmental, etc.); and

• When applying a reliability analysis to determine scheduled maintenance tasks and replacement times to mitigate the risk due to aging and wear of the components, the maintenance tasks and replacement times should be established using the same methodology required to satisfy § 25.1309 (e.g. Advisory Circular 25-19) and should be documented in the Airworthiness Limitation Section as appropriate. We continue to review the ARAC recommendations to determine whether revisions to the regulations or guidance are appropriate. I will keep the Board informed of the FAA’s progress on this safety recommendation, and I will provide an updated response by October 2011.

The FAA responded that the revisions related to 14 CFR 25.1309 will include guidance that determination of failure rates utilized in calculating the “Average Probability per Flight Hour” should be estimates of the mature constant (steady-state) failure rates after infant mortality (burn-in) and prior to wear-out and that these estimates should be based on all causes of failure. The FAA indicated that, because this guidance only addresses failure rates prior to wear-out, additional measures (such as component life limits) are necessary to ensure that wear-out does not occur.

To address this issue of failures before wear-out, the FAA formed a new ARAC to refine system safety rules and guidance, including specific guidance to protect against wear-out.

On April 25, 2006, the NTSB issued a special study of the FAA’s certification processes and procedures, Safety Report on the Treatment of Safety-Critical Systems in Transport Airplanes, SR-06-02. This study evaluated the FAA’s treatment of wear issues in certification decisions and procedures. Staff from the NTSB and the FAA’s Aircraft Certification Service met and discussed this study as well as FAA activities in response to Safety Recommendation A-02-51. The FAA stated that it was conducting a certification process study (CPS) to consider the issue of wear-related failures. The FAA planned to revise aircraft certification standards regarding wear-related failures.

Although it has been 7 years since the recommendation was issued, the formation of the ARAC to study refinements to system safety rules and guidance, including specific guidance to protect against wear-out, is responsive to this recommendation. The NTSB asks the FAA to provide either a copy of the CPS, or a summary of its findings regarding wear-related failures and to describe any completed or planned revisions to its aircraft certification programs regarding wear-related failures resulting from the CPS.

Pending revisions to aircraft certification procedures and practices to ensure that wear-related failures are fully considered and addressed, Safety Recommendation A-02-51 remains classified OPEN -- ACCEPTABLE RESPONSE.

Letter Mail Controlled 6/16/2009 12:43:06 PM MC# 2090364: - From Lynne A. Osmus, Acting Administrator: FAA Comment. In addition to the inclusion of the “no single failure” requirement in the changes to § 25.1309, the revised version of AC 25.1309-1A includes the following guidance related to wear: “The individual part, component, and assembly failure rates utilized in calculating the ‘Average Probability per Flight Hour’ should be estimates of the mature constant failure rates after infant mortality and prior to wear-out and should be based on all causes of failure (operational, environmental, etc.).” We recognize that this guidance only addresses failure rates prior to wear-out.

We believe that additional measures, such as component life limits, are necessary to ensure wear-out does not occur. A new ARAC group, referred to as the Airplane-level Safety Analysis Working Group, was formed and continues the process of refining system safety rules and guidance, including specific guidance to protect against wear-out. This group’s final recommendations to the FAA are expected no later than December 2009.

The FAA indicated that it is reviewing existing certification regulations and guidance. Based on the results of this review and of those being performed in response to items (2) and (3) of Safety Recommendation A-02-49, the FAA will make appropriate revisions to aircraft certification regulations, policies, procedures, and guidance to ensure (1) that new horizontal stabilizer trim control system designs are not certified if they have a single-point catastrophic failure mode and (2) that wear-related failures are fully considered and addressed so that such failures will not be catastrophic.

The FAA noted that for airplane models currently being type certificated, it has raised the issue of avoiding new horizontal stabilizer trim control system designs with a single-point catastrophic failure mode as a special attention item. Pending the results of the FAA’s review and implementation of appropriate revisions, Safety Recommendations A-02-50 and -51 remain classified OPEN -- ACCEPTABLE RESPONSE.

Letter Mail Controlled 8/2/2006 1:47:14 PM MC# 2060350: - From Marion C. Blakey, Administrator: The FAA is reviewing the existing regulations and guidance material. The result of this review and the result of the engineering reviews in response to parts (2) and (3) of safety recommendation A 02 49 will form the basis for revision of the aircraft certification regulations, policies, procedures or guidance materials as requested in this safety recommendation.

The FAA indicated that it agrees with this recommendation and will evaluate the certification requirements for consideration of wear-related failures and the methods by which maintenance considerations for wear issues are disseminated to the operators and implemented. The FAA also indicated that it would implement any changes to certification policy, guidance, or regulations that are determined to be necessary or appropriate. At the June 2, 2004, meeting, the FAA clarified that it believes it is inappropriate to consider the consequences of a total lack of maintenance.

The Safety Board requests that the FAA provide a copy of the results of its review, and the revisions that will be recommended as a result. Pending the results of the review and implementation of appropriate revisions, Safety Recommendation A-02-51 is classified OPEN -- ACCEPTABLE RESPONSE.

Letter Mail Controlled 12/30/2003 2:35:04 PM MC# 2030612 - From Marion C. Blakey, Administrator: The FAA agrees with the intent of this safety recommendation. A preliminary assessment of the Certification Process Review Study indicates that the concerns expressed in this safety recommendation may have broader implications than stabilizer pitch trim systems. The FAA will evaluate the certification requirements for consideration of wear-related failures and the methods by which maintenance considerations for wear issues are disseminated to the operators and implemented.

The FAA will conduct a review of the existing certification regulations, policy, and guidance material pertinent to establishing, identifying, and disseminating wear-related maintenance items. The FAA will evaluate the implementation of recommended maintenance practices in service and identify areas for regulatory change, policy guidance, and advisory material that will address this safety recommendation. The FAA will also implement any changes to certification policy, guidance, or regulations that are determined to be necessary or appropriate.

Any changes to policy, guidance, and regulations, and their planned application and implementation will be included in the Airframe and System Core Job Function Training Courses. These changes will also be disseminated to the engineering community through the recurring designee training system.

I will keep the Board informed of the FAA's progress on this safety recommendation. Meeting with FAA on Alaska Air Recommendations, 6/2/2004 Minutes attached.

This letter was handled by phone by Elaine Weinstein on September 22, 2003, in a conversation with Steve Wallace, FAA. The FAA is sending a more complete response.

Letter Mail Controlled 6/5/2003 4:40:51 PM MC# 2030272: - From Marion C. Blakey, Administrator: As a followup to your discussion with Deputy Administrator Sturgell, we are reviewing these safety recommendations to determine the best possible approach to addressing these important safety issues. The Federal Aviation Administration is committed to provide a substantive response as soon as the review is completed. You should expect a complete response by the end of June.