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Safety Recommendation Details

Safety Recommendation A-05-032
Details
Synopsis: On May 9, 2004, about 1450 Atlantic standard time, Executive Airlines (doing business as American Eagle) flight 5401, an Avions de Transport Regional (ATR) 72-212, N438AT, skipped once, bounced hard twice, and then crashed at Luis Muñoz Marin International Airport, San Juan, Puerto Rico. The airplane came to a complete stop on a grassy area about 217 feet left of the runway 8 centerline and about 4,317 feet beyond the runway threshold. The captain was seriously injured; the first officer, 2 flight attendants, and 16 of the 22 passengers received minor injuries; and the remaining 6 passengers received no injuries. The airplane was substantially damaged. The airplane was operating under the provisions of 14 Code of Federal Regulations (CFR) Part 121 as a scheduled passenger flight. Visual meteorological conditions prevailed for the flight, which operated on an instrument flight rules flight plan.
Recommendation: TO THE FEDERAL AVIATION ADMINISTRATION: Conduct a review of all flight data recorder systems that have been modified by a supplemental type certificate to determine the reliability of all sensors used as flight control surface position sensors. If the review determines that a sensor does not provide reliable flight control surface position data, require that the sensor be replaced with a more reliable sensor.
Original recommendation transmittal letter: PDF
Overall Status: Closed - Unacceptable Action
Mode: Aviation
Location: San Juan, PR, United States
Is Reiterated: No
Is Hazmat: No
Is NPRM: No
Accident #: DCA04MA045
Accident Reports: Crash During Landing, Executive Airlines Flight 5401, Avions de Transport Regional 72-212, N438AT
Report #: AAR-05-02
Accident Date: 5/9/2004
Issue Date: 9/26/2005
Date Closed: 1/11/2011
Addressee(s) and Addressee Status: FAA (Closed - Unacceptable Action)
Keyword(s): Maintenance, Recorders

Safety Recommendation History
From: NTSB
To: FAA
Date: 1/11/2011
Response: This recommendation was issued because of high failure rates in flight control position sensors that have hindered NTSB investigations when a critical FDR signal has been lost. Our experience has been that FAA certification of FDR systems does not ensure the reliability of these systems nor do airline maintenance systems or FAA oversight detect high failure rates in the critical components of these systems. The FAA uses advisory circulars (AC) in certification reviews and considerations, and in its previous letter proposed, as an alternate response to this recommendation, that the next revision to AC 20-141 contain emphasis and additional guidance on FDR sensor reliability monitoring. On May 2, 2008, the NTSB stated this would constitute an acceptable alternate response provided that the revisions were completed in a timely manner and that they addressed the following specific concerns: • String pot potentiometers should never be used as flight control surface position sensors because this type of sensor has a service history indicating it to be unreliable and unsuitable for this application. • The maintenance program for sensors and other FDR components should track the failure rates of these components, and, if elevated failure rates are encountered by an operator (a defined numerical limit for this rate should be part of the certification/STC application), the FAA and the certificate/STC holder should be informed. The operator should take steps to correct the situation and bring the failure rate back to the standard developed by the certificate holder. • When the design of an FDR system is certified, consideration must be given to its ability to reliably perform its intended purpose. On December 8, 2008, the FAA published AC 20-141A, a revision including paragraph 2-4.m, which the FAA believes specifically addresses the NTSB’s concerns. The NTSB reviewed AC 20-141B, the most current version of this AC, issued August 17, 2010. Paragraph 2-4.m directs manufacturers of FDR systems and FAA certification personnel reviewing such systems to use care when selecting sensor types for particular applications because all sensor types are not equally reliable in all applications. The AC uses the example that potentiometers have historically been unreliable on flight control surface applications and notes that potentiometers should be avoided in all cases for retrofit flight recording system design. AC 20-141B addresses the first specific concern raised in our May 2, 2008, letter, and provides some guidance addressing our third concern. However, the AC does not address the fundamental problem that is the basis for our second concern: that FAA certification of FDR systems does not ensure the reliability of the systems nor do airline maintenance systems or FAA oversight detect high failure rates in the critical components of these systems. Unreliable FDR systems that are not discovered to be such until critical information for an accident investigation cannot be accessed defeat the basic purpose of having an accident flight recorder. Accordingly, without requirements being included in the AC for continuous maintenance monitoring of recorder systems, the FAA’s action is not acceptable. Consequently, Safety Recommendation A-05-32 is classified CLOSED -- UNACCEPTABLE ACTION.

From: FAA
To: NTSB
Date: 9/7/2010
Response: CC# 201000358: - From J. Randolph Babbitt, Administrator: In a letter dated, August 21, 2007, the FAA stated that occasionally flight data recorder (FOR) sensors do not perform as reliably as expected. Operators, airplane/equipment\ manufacturers, and overseeing FAA staff should be alert and identify and correct such cases when they occur. The FAA proposed that the next revision to Advisory Circular (AC) 20-141 contain emphasis with additional guidance on FOR sensor reliability monitoring. In a letter dated May 2, 2008, the Board classified this safety recommendation as "Open-Acceptable Alternate Response" citing that appropriate and timely revisions to AC 20-141 may be an acceptable alternative response to this recommendation provided that the revisions address the Board's concerns. On December 8, 2008, the FAA published AC 20-14IA, specifically, paragraph 2-4.m (enclosed). I believe that the FAA has effectively addressed these safety recommendations, and I consider our actions complete.

From: NTSB
To: FAA
Date: 5/2/2008
Response: This recommendation was issued because of high failure rates in flight control position sensors hindering Safety Board investigations when a critical FDR has been lost. Despite known problems, the Board’s experience has been that FAA certification of FDR systems does not ensure the reliability of the systems, nor do FAA oversight or airline maintenance systems detect high failure rates in the critical components of these systems. The FAA has previously indicated that there is no ready means to identify which types of sensors are installed on aircraft, as recommended, and the type of review recommended would entail a time-consuming and labor-intensive effort that the FAA believes is unlikely to produce any useful benefits. During a meeting with FAA staff, the FAA indicated that it was unlikely that any changes to certification policies, standards, or procedures for FDR systems were possible, but that improved guidance for FAA inspectors might address the problem. In its current letter, the FAA acknowledged that there may be occasions when FDR sensors do not perform as reliably as expected and that operators, airplane/equipment manufacturers, and overseeing FAA staff should be alert to identify and correct such cases when they occur. The FAA proposes as an alternative response to this recommendation that the next revision to Advisory Circular (AC) 20-141 contain emphasis and added guidance for all parties (FAA, manufacturers, and operators) on FDR sensor reliability monitoring. Appropriate and timely revisions to AC 20-141 may be an acceptable alternative response to this recommendation provided that the revisions address the Safety Board’s concerns. The AC was issued in 1999 in response to Safety Recommendation A-97-30 to address the need for documentation necessary to read an FDR. The Board believes that, as currently written, the AC is focused primarily on documentation, not on design or reliability issues. As the FAA uses ACs in certification reviews and considerations, revisions to AC 20-141 may represent an acceptable alternative. The Safety Board offers the following suggestions as the FAA considers revisions to the AC: ·String pot potentiometers should never be used as flight control surface position sensors because this type of sensor has a service history indicating it to be unreliable and unsuitable for this application. ·The maintenance program for sensors and other FDR components should track the failure rates of these components, and if elevated failure rates are encountered by an operator (a defined numerical limit for this rate should be part of the certification/STC application), the FAA and the certificate/STC holder should be informed. The operator should take steps to correct the situation and bring the failure rate back to the standard developed by the certificate holder. ·When the design of an FDR system is certified, consideration must be given to its ability to reliably perform its reasonably intended purpose. The Safety Board also believes that if the FAA revises the AC, it will need to make plans to ensure that the appropriate FAA personnel, such as certification staff reviewing FDR systems and inspectors who oversee the maintenance of these systems, receive training in these revisionsThe Board would appreciate the opportunity to review and comment on the revised AC prior to its issuance. Pending timely revisions and issuance of a revised AC that addresses the points made above, Safety Recommendation A-05-32 is classified OPEN -- ACCEPTABLE ALTERNATE RESPONSE.

From: FAA
To: NTSB
Date: 8/21/2007
Response: Letter Mail Controlled 8/31/2007 8:37:02 AM MC# 2070437: - From Marion C. Blakey, Administrator: The FAA shares the Boards concern with flight data recorder (FDR) sensor reliability. The FAA recognizes that there may be occasions when FDR sensors do not perform as reliably as expected and that operators, airplane/equipment manufacturers, and overseeing FAA inspectors and engineers should be alert to identify and correct such cases when they occur. Pursuant to discussions with the Board, the FAA proposes an alternative response to this recommendation. Accordingly, the FAA proposes that the next revision to FAA Advisory Circular 20-141 will contain emphasis and added guidance for all parties (FAA, manufacturers, and operators) on FDR sensor reliability monitoring.

From: NTSB
To: FAA
Date: 2/15/2007
Response: In its letter, the FAA indicates that it disagrees with this recommendation and believes that the FDR problem in this accident is not indicative of an endemic problem across all models of airplanes. The FAA further notes that 14 CFR Parts 121.373 and 135.431 require operators to monitor their maintenance programs continually and to correct any deficiencies that are found. The FAA believes that these regulations and their application are adequate, and that the recommended review would be expensive and time consuming for both the FAA and operators, and unlikely to result in any substantive findings and/or changes to installed FDR systems. The Safety Board disagrees with the FAA. We believe that the results of the Board’s investigation of the Executive Airlines flight 5401 accident clearly contradict the FAA’s beliefs. As documented in the letter that transmitted this recommendation to the FAA, during a 3 1/2 year period, there were 47 flight control position sensor failures discovered during maintenance checks of Executive Airlines’ fleet of 41 ATR aircraft (for which STC No. ST01310NY had been performed). Thus, out of the 82 aileron position control sensors in Executive Airlines’ ATR fleet (2 per airplane), 47 failed; this is a failure rate of 56 percent. Despite this very high failure rate, which made significant portions of the FDR data unavailable, neither the FAA, the airline, nor the STC holder were aware of this problem until the Board’s investigation. During the investigation, the airline indicated to the Board that sensor failures and replacements were not tracked in the maintenance system and that, therefore, the time from installation to failure was unavailable. The Board further notes that at the time of the accident, Executive Airlines only performed functional checks of the FDR system every 3,000 flight cycles, a potential interval of 1 1/2 years. With such an inspection schedule, there is no way to tell for what period of these 1 1/2 years the sensor may have not been functioning properly. As a result of the information revealed during the Executive Airlines investigation, the Board disagrees with the FAA’s conclusion that 14 CFR Part 121.373 and 135.431 requirements to monitor maintenance programs continually and to correct deficiencies ensure that FDR systems are maintained such that the intended reliability is achieved. The systems in place did not detect the problem, and so, the FDR system did not have the needed reliability. On March 20, 2006, a teleconference was held with staff from the FAA and the Safety Board to discuss this recommendation. During this teleconference, Board staff discussed the problem of high failure rates in flight control position sensors hindering Board investigations when critical FDR is lost. Board staff also indicated that despite these types of known problems, FAA certification of FDR systems focuses on the FDR systems’ not endangering safety of flight, but does not ensure the reliability of the systems, nor does FAA oversight or airline maintenance systems detect high failure rates in critical components of these systems. FAA staff indicated that there was no ready means for them to identify which types of sensors were installed on aircraft, and they repeated that the type of review recommended would entail a time-consuming and labor-intensive effort that they did not feel was likely to produce any useful benefits. Board staff asked the FAA if they could suggest any activities that would end the unacceptably high failure rates encountered with flight control position sensors. The FAA staff indicated that they believed it unlikely that any changes to certification policies, standards, or procedures for FDR systems were possible, but that improved guidance for FAA inspectors might address the problem. The FAA agreed to revise such guidance and submit it to the Board for consideration of whether this would be an acceptable alternative response to this recommendation. To date, the Board has not been able to learn of any further FAA activities in response to this recommendation. The letter that transmitted this recommendation to the FAA also noted that the Board has encountered difficulties with FDR data on Embraer EMB-120 aircraft that have similar FDR flight control position sensors. The Board issued this recommendation because of this demonstrated history with more than one model aircraft of undetected problems with flight control position sensors’ making FDR data unusable in accident investigations. The Board believes that existing FAA oversight and airline maintenance programs are not doing an acceptable job of detecting these problems and correcting the fundamental problem with the FDR system before the data is needed for an accident or incident investigation, and the FAA therefore needs to analyze flight control position sensors to determine why these serious problems exist. The Board asks the FAA to reconsider its position on this recommendation. Pending the FAA’s taking action that meets the intent of the recommendation, Safety Recommendation A-05-32 is classified OPEN -- UNACCEPTABLE RESPONSE.

From: FAA
To: NTSB
Date: 12/21/2005
Response: Letter Mail Controlled 1/3/2006 12:11:35 PM MC# 2060009: - Marion C. Blakey, Administrator: From The FAA has reviewed the safety recommendation, as well as the circumstances that precipitated the issuance of the recommendation. The FAA realizes that the sensors necessary for investigation of this incident had failed between maintenance cycles, which hindered the investigation. The FAA shares the Board’s concern regarding the necessity for reliable flight data recording. However, the FAA does not agree that this incident is indicative of an endemic problem across all models of airplanes operated under 14 CFR arts 121 and 135. 14 CFR 121.373 and 135.431 require each operator to monitor their maintenance programs continually and to correct any deficiencies that are found. This requirement is in place to assure that the airplane and associated systems are maintained in such a manner that the reliability intended by the rules is achieved. The FAA believes that this regulation and its application are adequate. Consequently, the FAA cannot support the recommended review, which would be expensive and time consuming for both the FAA and operators and unlikely to result in any substantive findings and/or changes to installed FDR systems. I believe that the FAA has satisfactorily addressed this safety recommendation, and I look forward to your response.