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General Aviation Safety
This letter discusses the circumstances of several survivable accidents1 that have occurred in the last 3 years in which overhead bins and passenger service units (PSU)2 on Boeing 737 airplanes became separated from their attachments during the accident sequences, likely increasing the number of reported occupant injuries, particularly injuries to the head and face. In addition to this occupant safety hazard, the negative-g strap3 attachment bracket (used as part of the flight crew five-point restraint assembly) failed in two cases, possibly contributing to back injuries to the flight crewmembers. Findings in these investigations (some of which are ongoing) suggest that current crashworthiness test requirements do not provide an adequate basis on which to evaluate how these items will withstand impact forces during survivable accidents.
TO THE FEDERAL AVIATION ADMINISTRATION: Develop test criteria and performance measures for negative-g strap assemblies to better evaluate their real-world loading capability during accident sequences.
Original recommendation transmittal letter:
Closed - Unacceptable Action
Denver, CO, United States
Runway Side Excursion During Attempted Takeoff in Strong and Gusty Crosswind Conditions Continental Airlines Flight 1404, Boeing 737-500, NN18611
Addressee(s) and Addressee Status:
FAA (Closed - Unacceptable Action)
Safety Recommendation History
In previous correspondence and in an August 31, 2012, meeting of FAA and NTSB staff concerning these recommendations, the FAA stated that it had reviewed the information in our letter issuing these recommendations, and it had searched for related accident data to justify the actions recommended. The FAA found that, as evidenced by fuselage breaks in the accidents described in the safety recommendation letter, the seats on which the negative g strap bracket had failed had been subjected to loads that greatly exceeded their certification standards. On the basis of this review, the FAA planned not to take the recommended actions. In our November 6, 2012, letter, we replied that we believed (1) that the FAA needed to initiate a research program to understand the cause of the bracket failures and (2) that the results of such a program were needed before the FAA could appropriately decide that no further action was necessary. We regret to learn from Mr. Fazio’s letter that the FAA has not changed its position and does not believe that an appropriate low-cost research program to fully understand the nature of the problems described in our safety recommendation letter is necessary before deciding not to act further. Consequently, Safety Recommendations A-12-4, -5, and -6 are classified CLOSED—UNACCEPTABLE ACTION.
-From Tony Fazio, Director Office of Accident Investigation and Prevention: In the Board's November 6, 2012, letter, it restated that the accident investigation it conducted showed the presence of a problem concerning the failure of negative-g strap brackets, and that the FAA would have to further investigate the matter. However, as previously stated, both in our May 18, 2012, letter to the Board and our August 31, 2012, meeting with the Board, we determined that the accident aircraft were compliant with applicable regulations regarding the pilot seat negative-g strap bracket. Load factors experienced during the accidents referenced in the Board's report greatly exceeded certification standards. All the referenced accidents had fuselage breakups, and in these cases we would expect interior items to have some damage as well. Although the negative-g strap bracket failed, the other four points of the five point restraint system kept the occupant restrained and potentially prevented greater injury. Our search found no data to indicate that the negative-g strap bracket failure directly contributed to serious injury of passengers or crew. Based on this risk analysis, the FAA did not find any non-compliances with requirements, new hazards, or ineffective controls. Our assessment of the issue remains that it does not exceed an unacceptable level of safety risk. In accordance with our safety risk management process, one of the four components of a safety management system, we will continue to monitor the aerospace system for related events/data and take appropriate action to mitigate any unacceptable risk that presents itself. The FAA carefully reconsidered its actions, and we continue to find that our response to these recommendations reflects the best interests of aviation safety. Accordingly, we will take no further action in direct response to these recommendations.
As with Safety Recommendations A-12-1 and -3, the FAA indicated in the May 18, 2012, letter that it had reviewed the related accident data and found that the seats on which the negative g strap bracket had failed had been subjected to loads that greatly exceeded their certification standards. The FAA’s review found no data to indicate that failure of the negative-g strap attachment brackets had contributed to the serious injury of crewmembers. On the basis of this review, the FAA planned not to take the recommended actions. The discussion at the August 31, 2012, meeting regarding Safety Recommendations A-12-4 through -6 was the same as that regarding Safety Recommendations A-12-1 and 3: The NTSB indicated that, although the accident airplanes had experienced fuselage breaks, we did not believe this indicator alone to be an appropriate metric to determine that the accidents were not survivable. FAA staff replied that the FAA’s position was not that the accidents were not survivable, simply that the fuselage breaks made the certification standards for survivability no longer applicable. FAA staff further indicated that they could not find data from any of the accidents on which we had based these recommendations to support the need for the actions we recommended. We responded that the accident data that we had described showed the presence of a problem, but the FAA would need to do the appropriate research and analysis to fully understand why the negative-g strap attachment brackets had failed, and what could be done to address the issue. The FAA staff again replied that they did not have enough information to justify such an investigation. The NTSB believes (1) that the FAA needs to initiate a research program to understand the cause of the bracket failures and (2) that the results of such a program are needed before the FAA can appropriately decide that no action is necessary. We further believe that such a research program would be relatively low cost, and have virtually no societal impact, but would provide the FAA and seat manufacturers with appropriate information to make decisions on what further actions (if any) were necessary. Although the FAA has indicated that it considers its actions in response to these recommendations to be complete, we ask the agency to reconsider both its decision not to study the cause of the bracket failures and the consequences of potential future failures, to protect seat occupants from injury. Pending the FAA’s completing the recommended actions, Safety Recommendations A-12-4, -5, and -6 are classified OPEN—UNACCEPTABLE RESPONSE. In summary, in response to all of these recommendations except for Safety Recommendation A-12-2, the FAA indicated that it did not have sufficient information to understand and address the safety problems on which these recommendations are based. Rather than developing the needed information to understand the mitigations needed to address the safety problems, the FAA has decided that no action is warranted. We believe this to be inconsistent with fundamental principles of safety management systems (SMS). In SMSs, when there is evidence of a safety problem, the problem is evaluated and mitigations are developed, considered, and, if appropriate, implemented. This is done without waiting for an accident or serious incident to occur. We are disappointed that the FAA is not using an SMS approach in its consideration of how best to implement these recommendations.
The FAA indicated that it had reviewed the related accident data and found that the bins and PSUs that separated from their attachments had been subject to loads that greatly exceeded their certification standards. The FAA’s review found no data to indicate that the PSUs or the negative-g strap bracket failure had contributed to serious injury of either passengers or crewmembers. On the basis of this review, the FAA does not plan to take the recommended actions; however, the FAA suggested that representatives of both our agencies meet to discuss additional data that could indicate PSUs or overhead bins had contributed to passenger or crewmember injury. We agree that such a meeting would be beneficial, and this meeting is currently being scheduled. Accordingly, the NTSB will classify these recommendations after we have had an opportunity to evaluate the results of the meeting.
-From Michael P. Huerta, Acting Administrator: We reviewed the recommendations and available accident reports. We determined that the aircraft were compliant with applicable regulations regarding the PSU retention and the pilot seat negative-g strap bracket. Load factors experienced during the accidents referenced in the Board's report greatly exceeded certification standards. All the referenced accidents had fuselage breakups, and in these cases we would expect interior items to have some damage as well. Our search found no data to indicate that the PSUs or the negative-g strap bracket failure directly contributed to serious injury of passengers or crew. We welcome the opportunity to meet and discuss additional data that may indicate PSUs or overhead bins contributed to passenger or crew injury. In the absence of such data, we are unable to find the basis for continuing the evaluation. I believe that the FAA has effectively addressed these safety recommendations, and I consider our actions complete.
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