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Safety Recommendation Details

Safety Recommendation A-96-034
Details
Synopsis: ON 8/21/95, ABOUT 1253 EASTERN DAYLIGHT TIME, AN EMBRAER EMB-120, N256AS, OPERATED BY ATLANTIC SOUTHEAST AIRLINES (ASA) AS FLIGHT 529, CRASHED ON APPROACH TO THE WEST GEORGIA REGIONAL AIRPORT, CARROLLTON, GEORGIA. THE FLIGHTCREW WAS ATTEMPTING TO MAKE AN EMERGENCY LANDING FOLLOWING THE IN-FLIGHT SEPARATION OF A PROPELLER BLADE. THE CAPTAIN AND SEVEN PASSENGERS WERE KILLED, AND THE AIRPLANE WAS DESTROYED BY IMPACT FORCES AND A POSTCRASH FIRE. FLIGHT 529 WAS BEING CONDUCTED UNDER THE PROVISIONS OF TITLE 14 CODE OF FEDERAL REGULATIONS PART 135 AS A DOMESTIC, SCHEDULED PASSENGER SERVICE FLIGHT FROM ATLANTA, GEORGIA, TO GULFPORT, MISSISSIPPI. THE NTSB'S INVESTIGATION OF THIS ACCIDENT IS ONGOING.
Recommendation: THE NTSB RECOMMENDS THAT THE FAA: REQUIRE EMBRAER EMB-120 OPERATORS TO PERFORM A FLIGHT DATA RECORDER READOUT OR A POTENTIOMETER CALIBRATION TEST PER SECTION 31-31-00 OF THE EMB-120 MAINTENANCE MANUAL EVERY 6 MONTHS UNTIL FDR SENSOR DESIGN, INSTALLATION, & /OR MAINTENANCE IMPROVEMENTS ARE INCORPORATED.
Original recommendation transmittal letter: PDF
Overall Status: Closed - Acceptable Action
Mode: Aviation
Location: CARROLLTON, GA, United States
Is Reiterated: No
Is Hazmat: No
Is NPRM: No
Accident #: DCA95MA054
Accident Reports: In-flight Loss of Propeller Blade Forced Landing, and Collision with Terrain Atlantic Southeast Airlines, Inc., Flight 529 Embraer EMB-120RT, N256AS
Report #: AAR-96-06
Accident Date: 8/21/1995
Issue Date: 6/27/1996
Date Closed: 5/5/1998
Addressee(s) and Addressee Status: FAA (Closed - Acceptable Action)
Keyword(s):

Safety Recommendation History
From: NTSB
To: FAA
Date: 8/11/2003
Response: SNPRM 6698A comment Safety Recommendation A-96-34 was closed in 1998 with an acceptable status because the original NPRM and the Federal Aviation Administration (FAA) Flight Standards Handbook Bulletin for Airworthiness 97-14 EMBRAER EMB-120 Flight Data Recorder Test directed potentiometer calibration testing every 6 months. Unfortunately, the FAA has reversed its position on these inspections in the SNPRM by requiring annual inspections only. The annual inspection prescribed by the AD, which is the typical inspection cycle for FDR systems, will not provide timely, frequent feedback on the effectiveness of this or any other corrective action and could result in a failed sensor remaining in place for a full year. In addition, removal of the requirement to report inspection results and readouts to the FAA will eliminate the opportunity for a fleetwide evaluation of this continuing problem. Therefore, the Safety Board reiterates its opinion that the repetitive testing interval should occur at least every 6 months as originally proposed in the NPRM and in Safety Recommendation A-96-34. In conclusion, the Safety Board believes that the proposed corrective action (that is, replacement of the noisy potentiometers with sensors of the same make and model that are less than 12 months old and requiring only an annual inspection) will not resolve the sensor reliability problem. However, the Board notes that, if the AD is revised as proposed, the only way to properly evaluate the effectiveness of the proposed corrective action is to require an FDR readout and evaluation every 6 months for 2 years and submit the results to the FAA for evaluation, as prescribed in the original AD and in Safety Recommendation A-96-34. Notation 6698A: The National Transportation Safety Board first encountered problems with flight control parameter readouts for the EMB-120 flight data recorder (FDR) in 1990. After noting similar flight control parameter failures in six of seven other EMB-120 FDR readouts conducted from 1990 through 1996, the Safety Board issued Safety Recommendations A-96-33 and -34: Conduct a design review of the Embraer EMB-120 flight data recorder system, with emphasis on potentiometer failures, and mandate design, installation, and/or maintenance changes, as necessary, to ensure that reliable flight control data are available for accident/incident investigation. (A-96-33) Require Embraer EMB-120 operators to perform a flight data recorder readout or a potentiometer calibration test per section 31-31-00 of the EMB-120 Maintenance Manual every 6 months until FDR sensor design, installation and /or maintenance improvements are incorporated. (A-96-34) Since issuing these recommendations, the Safety Board has found similar failures in one or more flight control parameters for nine additional EMB 120 readouts. The supplemental notice of proposed rulemaking (SNPRM), which reopens comment on a proposed revision to the airworthiness directive (AD) that is intended to address these recommendations, implies that the sensor reliability problem will be solved by replacing the noisy potentiometers with new sensors (that is, sensors that are less than 12 months old) of the same make and model, and by applying locktite to the flexible coupler attachment screw. The Safety Board is not convinced that this corrective action will solve the problem. The fact that one or more flight control parameters failed in 16 of the 17 EMB-120 FDR readouts conducted by the Safety Board since 1990 suggests that EMB-120 FDR problems may be systemic and may require a more robust sensor and/or installation. The Board doubts that all of the failures were caused by storing the sensors for more than 12 months, which the airplane and sensor manufacturers claim caused an oxide film to form on the sensor, resulting in the noisy signal. The Safety Board has found that, with the exception of the EMB-120, noisy sensors are rare and the few sensor-related problems that do occur are generally associated with poor maintenance or an improperly executed FDR retrofit Supplemental Type Certificate. Our experience has shown that factory-installed sensors almost never fail. Although the Safety Board agrees that only noisy sensors need to be replaced, it does question how effectively the proposed AD procedure, which also calls for an annual adjustment of the sensor followed by a noise check and FDR readout, will identify problem sensors. The Board has found that sensor failures can be intermittent and that a one-time check may not reveal a problem. The Board suggests that a more effective procedure would be to conduct the FDR readout and evaluation just prior to the airplane’s scheduled maintenance with emphasis on observing parameter performance during in-flight and ground operations. The Board suggests further that the most direct way to detect a sensor failure or out-of-calibration condition would be for a qualified analyst to periodically evaluate FDR data from a number of flights and to conduct a calibration check and make any necessary sensor replacements and adjustments during scheduled maintenance. Safety Recommendation A-96-34 was closed in 1998 with an acceptable status because the original NPRM and the Federal Aviation Administration (FAA) Flight Standards Handbook Bulletin for Airworthiness 97-14 EMBRAER EMB-120 Flight Data Recorder Test directed potentiometer calibration testing every 6 months. Unfortunately, the FAA has reversed its position on these inspections in the SNPRM by requiring annual inspections only. The annual inspection prescribed by the AD, which is the typical inspection cycle for FDR systems, will not provide timely, frequent feedback on the effectiveness of this or any other corrective action and could result in a failed sensor remaining in place for a full year. In addition, removal of the requirement to report inspection results and readouts to the FAA will eliminate the opportunity for a fleetwide evaluation of this continuing problem. Therefore, the Safety Board reiterates its opinion that the repetitive testing interval should occur at least every 6 months as originally proposed in the NPRM and in Safety Recommendation A-96-34. In conclusion, the Safety Board believes that the proposed corrective action (that is, replacement of the noisy potentiometers with sensors of the same make and model that are less than 12 months old and requiring only an annual inspection) will not resolve the sensor reliability problem. However, the Board notes that, if the AD is revised as proposed, the only way to properly evaluate the effectiveness of the proposed corrective action is to require an FDR readout and evaluation every 6 months for 2 years and submit the results to the FAA for evaluation, as prescribed in the original AD and in Safety Recommendation A-96-34. The Safety Board appreciates this opportunity to comment on the SNPRM and will support the FAA’s efforts to identify and correct this problem.

From: NTSB
To: FAA
Date: 5/5/1998
Response: A-96-34 ASKED THE FAA TO REQUIRE EMBRAER EMB-120 OPERATORS TO PERFORM AN FDR READOUT OR A POTENTIOMETER CALIBRATION TEST PER SECTION 31-31-00 OF THE EMB-120 MAINTENANCE MANUAL EVERY 6 MONTHS UNTIL FDR SENSOR DESIGN, INSTALLATION, &/OR MAINTENANCE IMPROVEMENTS ARE INCORPORATED. THIS ACTION IS FULLY RESPONSIVE TO THE RECOMMENDATION. ACCORDINGLY, A-96-34 HAS BEEN CLASSIFIED "CLOSED--ACCEPTABLE ACTION."

From: FAA
To: NTSB
Date: 12/5/1997
Response: ON 9/16/97, THE FAA ISSUED FLIGHT STANDARDS HANDBOOK BULLETIN FOR AIRWORTHINESS 97-14, EMBRAER EMB-120 FLIGHT DATA RECORDER TEST. THE BULLETIN DIRECTS PRINCIPAL AVIONICS INSPECTORS TO REQUIRE AFFECTED EMB-120 OPERATORS TO PERFORM AN INITIAL & RECURRING POTENTIOMETER CALIBRATION TEST EVERY 6 MONTHS UNTIL THE FDR SENSOR DESIGN & INSTALLATION HAVE BEEN ENHANCED. THE BULLETIN ALSO REQUIRES THAT AN INITIAL INSPECTION OF THE AFFECTED OPERATOR'S TOTAL FLEET BE ACCOMPLISHED WITHIN 60 DAYS AFTER RECEIPT OF THIS BULLETIN.

From: NTSB
To: FAA
Date: 10/15/1996
Response: THE FAA HAS INDICATED THAT IT WILL CONTACT THE MANUFACTURER & COORDINATE THE NECESSARY MAINTENANCE INSTRUCTIONS WITH AN APPROPRIATE INSPECTION INTERVAL. PENDING FINAL ACTION, A-96-34 IS CLASSIFIED "OPEN--ACCEPTABLE RESPONSE."

From: FAA
To: NTSB
Date: 9/5/1996
Response: THE FAA WILL CONTACT THE MANUFACTURER & COORDINATE THE NECESSARY MAINTENANCE INSTRUCTIONS WITH AN APPROPRIATE INSPECTION INTERVAL.