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Safety Recommendation Details

Safety Recommendation A-05-031
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: Require the replacement of aileron surface position sensors installed in accordance with Supplemental Type Certificate (STC) No. ST01310NY with more reliable aileron surface position sensors within 1 year or at the next heavy maintenance check, whichever comes first, after the issuance of an approved STC. Until reliable aileron surface position sensors have been installed, require flight data recorder functional checks every 6 months and replacement of faulty sensors, as necessary.
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: The FAA previously wrote to the NTSB on August 21, 2007, concerning this recommendation. At that time, the FAA described a number of activities in progress or planned in response to the recommendation. Based on the investigation conducted by Delta Engineering (the STC holder), the FAA had concluded that the sensor problems were the result of improper installation and maintenance, causing the cable to rub on the sensor housing and leading to breakage of the cable. Delta redesigned the aileron sensor to prevent incorrect installation. On May 2, 2008, the NTSB replied that the FAA’s planned activities did not constitute an acceptable response. Our investigation of the Executive Airlines flight 5401 accident revealed a problem with the sensor, not with the installation of the cable. As described in the letter that transmitted this recommendation to the FAA, the NTSB has consistently found that potentiometers used as flight control position sensors (as with the STC) are unreliable. Delta’s planned revision to the sensor would not change the type of flight control position sensor being used. Rather than addressing what the NTSB believed to be the actual cause of these reliability problems, the FAA and Delta were accepting improper installation as the cause. The NTSB also indicated on May 2, 2008, that, although the sensor had a failure rate of over 50 percent, the revised STC would call for a 12-month inspection interval of the revised sensor. The NTSB believed that this interval was too long to allow confirmation that the revised design had provided an acceptable level of reliability. In addition, the FAA had not indicated any plans to require reporting of sensor failures to either Delta or the FAA. In the Executive Airlines flight 5401 accident, not Delta, the FAA, nor the airline was aware that Executive’s mechanics were finding failure rates of over 50 percent. The NTSB was concerned that, because the revised STC would not require inspections more frequently than once per year or require reporting to either Delta or the FAA, and because the revised design would continue to use a potentiometer as the flight control position sensor, the reliability problems would continue unnoticed until the next accident in which critical information had not been recorded by an FDR. Finally, the NTSB indicated that, although Delta had revised the instructions for continued airworthiness (ICA) for the existing sensors to call for a 6-month inspection interval as recommended, the FAA had issued only a Special Airworthiness Information Bulletin, an advisory document that does not require compliance. The NTSB was further concerned that, in the absence of a mandate to make the necessary changes, operators would continue with the longer inspection interval indicated in the original ICA and would not alter their practices even after the revised STC were issued. The FAA’s current letter states that the FAA has completed all of the actions described in its August 2007 letter but does not indicate any revisions it has made to address the concerns that the NTSB expressed in our evaluation of this response. Consequently, Safety Recommendation A-05-31 is classified CLOSED -- UNACCEPTABLE ACTION.

From: FAA
To: NTSB
Date: 9/7/2010
Response: CC# 201000358: - From J. Randolph Babbitt, Administrator: To address this safety recommendation the Federal Aviation Administration has completed the following: • On October 25, 2007, the FAA amended STC No. ST01310NY after Delta Engineering, the sensor manufacturer, redesigned the aileron surface position sensor (hereafter referred to as sensors). The FAA also approved Delta Engineering Service Bulletin (SB) No. 2301-06397-2030, dated September 26, 2008, which provides operators guidelines for replacing the existing sensors with the newly designed sensors; • On August 10, 2007, the FAA approved Delta Engineering Instructions for Continued Airworthiness (ICA) (0701-04812-2030, Revision G). This changed the inspection interval of the existing sensors from 12 months to 6 months. The 1CA requires faulty sensors identified during the inspections to be removed and replaced with the newly designed sensors (PINs 05782-501 and 05782-502). The inspection interval for these newly designed sensors is 12 months; and • On March 4, 2010, the FAA issued Special Airworthiness Information Bulletin (SAIB) NM-1 0-18 (enclosed). The SAIB recommends owners and operators of aircraft incorporating FAA STC No. ST01310NY to comply with the actions outlined in Delta Engineering SB No. 2301-06397-2030.

From: NTSB
To: FAA
Date: 5/2/2008
Response: The FAA reported on activities it has been pursuing in response to this recommendation. On March 1, 2006, Delta Engineering, the holder of STC ST01310NY, released Service Alert (SA) 120105-01A, which describes a revision to the instructions for continued airworthiness (ICA) to change the inspection interval of the aileron sensors from 12 months to 6 months. On April 7, 2006, the FAA issued a special airworthiness information bulletin (SAIB) that recommends owners and operators of Aerospatiale ATR-42 and ATR-72 aircraft use the revised ICA. The FAA further reported that, based on the investigation by Delta Engineering, it has concluded that the sensor problems are the result of improper installation and maintenance. Delta believes that incorrect installation of the sensor can cause the cable to rub on the sensor housing, which causes the cable to break. To prevent incorrect installation, Delta Engineering has redesigned the aileron sensor. The FAA indicated that Delta Engineering plans to amend the STC, and that the ICA for the new sensor will call out a 12-month inspection interval with a 5-year overhaul. After issuance of the amended STC, Delta Engineering will issue a service bulletin (SB) for the removal and replacement of the old sensor with the redesigned unit, and once the SB is issued, the FAA will issue another SAIB notifying the owners/operators and flight standards inspectors of the SB and new ICA requirement. The Safety Board is disappointed by the FAA’s actions in response to this recommendation. The Board’s investigation of the Executive Airlines flight 5401 accident revealed a problem with the sensor, not with the installation of the cable. As described in the letter that transmitted this recommendation to the FAA, the Board has consistently found that potentiometers used as flight control position sensors (as with the STC) are unreliable. The Board believes that the service history has shown a potentiometer used as a flight control position sensor should not be certified, and some other type of sensor, utilizing an alternative principle of operation, must be used instead. The Board notes that problems with the reliability of potentiometers used as flight control position sensors on Embraer (EMB) 120 aircraft were not resolved by any FAA actions until the primary EMB-120 operator sought an organization to develop an STC for an altered FDR system that used a sensor with a different principle of operation. The operator was motivated to find such a system because of the unreliability of the sensors in service, not because the FAA had taken any action to address the unacceptable reliability of these sensors. For STC ST01310NY, similarly unreliable sensors are used as flight control position sensors. Rather than addressing the actual cause of these reliability problems, the FAA and Delta Engineering are accepting improper installation as the cause. The Board’s investigation of the Executive Airlines flight 5401 accident leads us to believe that the problem is not with improper installation causing cable rubbing, but instead is due to use of an inappropriate sensor. The Safety Board is also disappointed that, although the sensor had a failure rate of over 50 percent, the revised STC will call for a 12-month inspection interval. The Board believes that this interval is too long to allow confirmation that the revised design has an acceptable level of reliability. In addition, the FAA has not indicated any plans to require reporting of sensor failures to either Delta or the FAA. The Board reiterates that in the Executive Airlines flight 5401 accident, not Delta, the FAA, nor the airline was aware that Executive’s mechanics were finding failure rates of over 50 percent. The Board is concerned that because the revised STC will not require inspections more frequently than once per year, with no reporting requirement to either Delta or the FAA, and because the revised design will continue to use a potentiometer as the flight control position sensor, the reliability problems will continue unnoticed until the next accident in which critical information has not been recorded by an FDR. Finally, the Safety Board notes that Delta has revised the ICA for the existing sensors to call for the recommended 6-month inspection interval as recommended. However, rather than mandating these revisions, the FAA issued an SAIB, an advisory document that does not require compliance. Further, the FAA stated that when Delta completes its revisions for the new sensor, the FAA would again issue an SAIB only. The Board is concerned that in the absence of a mandate to make the necessary changes, operators will continue with the longer inspection interval indicated in the original ICA without making any changes even after the revised STC is issued. Pending the FAA’s issuing a requirement to replace the surface position sensors with more reliable sensors or confirmation that all operators have replaced the surface position sensors with more reliable sensors, and a requirement for 6-month functional checks until more appropriate sensors are installed, Safety Recommendation A-05-31 is classified OPEN -- UNACCEPTABLE RESPONSE.

From: FAA
To: NTSB
Date: 8/21/2007
Response: Letter Mail Controlled 8/27/2007 4:14:38 PM MC# 2070437: - From Marion C. Blakey, Administrator: 8/21/07 The Federal Aviation Administration has been working with Delta Engineering, the holder of Supplemental Type Certificate (STC) No. ST01310NY, regarding the redesign of the current aileron surface position sensors. On March 1, 2006, Delta Engineering issued the enclosed Service Alert (SA) 120105-01A. The SA notifies the owners and operators of a revision to their instructions for continued airworthiness (ICA) to change the inspection interval of the aileron sensors from 12 months to 6 months. On April 7, 2006, we issued a special airworthiness information bulletin (SAIB) to recommend that owners and operators of Aerospatiale ATR-42 and ATR-72 aircraft use the inspection interval established in the revised ICA to mitigate the risk of recording invalid data on the aileron surface position. A copy of the SAIB is enclosed for your information. As a result of the Delta Engineering investigation, the FAA has concluded that the sensor problems are the result of improper installation and maintenance. Incorrect installation of the sensor can result in the cable rubbing on the sensor housing causing the cable to break. To prevent incorrect installation Delta Engineering has redesigned the aileron sensor. Delta Engineering Plans to proceed with an amendment to STC No. ST01310NY. The ICA for the new sensor will call out a 12-month inspection interval with a 5-year overhaul. Following the issuance of the amended STC, Delta Engineering will issue a service bulletin (SB) for the removal and replacement of the old sensor with the redesigned unit. Once the SB is issued, the FAA will issue another SAIB notifying the owners/operators and flight standards inspectors of the SB and new ICA requirement.

From: NTSB
To: FAA
Date: 2/15/2007
Response: The Safety Board notes that the FAA is working with the holder of the STC, which is in the process of redesigning the sensors, and is planning to commence testing of the redesigned sensor soon. The FAA’s work has focused on (1) redesigning the aileron surface position sensors; (2) amending the STC to install the new aileron surface position sensor; and (3) issuing a service alert to reduce the inspection interval from 12 months to 6 months, to perform FDR parameter readout or a potentiometer calibration test every 6 months, to conduct an FDR functional check every 6 months, and to replace faulty sensors as necessary. Pending completion of the recommended actions, Safety Recommendation A-05-31 is classified OPEN -- ACCEPTABLE RESPONSE. We would appreciate receiving updates on FAA progress on this safety recommendation.

From: FAA
To: NTSB
Date: 12/21/2005
Response: Letter Mail Controlled 1/3/2006 12:11:35 PM MC# 2060009 - From Marion C. Blakey, Administrator: The FAA is working closely with Delta Engineering who is the holder of Supplemental Type Certificate (STC) No. ST01310NY. Delta Engineering is aware of the incident and has indicated that it is in the process of redesigning the sensors and is planning to commence the testing phase soon. Our discussion with Delta Engineering focused around the following areas: a redesign of the aileron surface position sensors; amending STC ST013lONY to install the new aileron surface position sensor; and issuing a service alert to reduce the inspection interval from 12 months to 6 months, to perform FDR parameter readout or a potentiometer calibration test every 6 months, conduct an FDR functional check every 6 months, and replacement of faulty sensors as necessary. Preliminary review shows that the aileron surface position sensors were installed in accordance with STC No. ST01310NY. However, the FAA is conducting an investigation and has requested an action plan with projected milestone dates from Delta Engineering. After review of the information from Delta Engineering, the FAA will take appropriate action.