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Safety Recommendation Details

Safety Recommendation A-96-033
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: CONDUCT A DESIGN REVIEW OF THE EMBRAER EMB-120 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.
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: 10/21/2004
Addressee(s) and Addressee Status: FAA (Closed - Acceptable Action)
Keyword(s):

Safety Recommendation History
From: NTSB
To: FAA
Date: 10/21/2004
Response: The Safety Board notes that, in December 2002, the FAA issued a supplemental type certificate (STC) to Chippewa Aerospace that authorized the replacement of the potentiometer rudder and control column position sensors for the FDR system with rotary variable transformers. The FAA reported via e-mail on August 3, 2004, that a survey of EMB-120 commercial operators indicated that 74 of 88 airplanes have or will soon have upgraded sensors installed. The FAA reports that the 2 operators of the remaining 14 airplanes are following the manufacturer's recommended maintenance program for the potentiometers to avoid the installation costs and because of the uncertain future plans for their EMB-120 airplanes. The Safety Board appreciates the FAA's efforts to follow up on this issue. The approval of upgraded sensors appears to be an improvement in technology that will enhance the reliability of the signals provided to the FDR. The improved sensors eliminate the need for revision of the FDR system inspection procedures. It is unfortunate that two Part 135 operators are not installing the improved sensors. However, the Board believes that the actions completed, which have resulted in the majority of EMB-120 series airplanes that remain in service being equipped with the improved sensors, accomplishes the objective of these safety recommendations in an acceptable alternate manner. Accordingly, Safety Recommendation A-98-104 is classified "Closed--Acceptable Alternate Action." The development and STC approval of the rotary variable transformers have improved the design and reliability of the EMB-120 FDR system. Therefore, Safety Recommendation A-96-33 is classified "Closed--Acceptable Action."

From: FAA
To: NTSB
Date: 8/3/2004
Response: rcvd via email Here is an update on the activities for Safety Rec A-98-104. I have been performing an informal survey of EMB-120 operators for replacement of potentiometers for the FDR system. I have sent e-mails to the Part 91 operators for their input but none of them have replied. The 135 operators have been in touch and here is the information. Skywest,, as you know, operates 74 EMB-120s. They are in the process if installing the STC for the upgraded sensors. Ameriflight - They have a varied fleet but operate only 7 EMB-120 aircraft. The air carrier is aware of the STC but does not want to made the initial up front cost associated with the installation of the STC. They will continue with the EMB-120 recommended maintenance program. Great Lakes - They operate 7 EMB-120 aircraft. They are aware of the STC but are not sure how long they will continue to operate EMB-120 aircraft. They do not want to make an investment in an aircraft that they may discontinue to operate. They will continue with the EMB-120 recommended maintenance program.

From: NTSB
To: FAA
Date: 8/11/2003
Response: Since issuing these recommendations, the Safety Board has found similar failures in one or more flight control parameters for nine additional EMB-120 readouts. 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. 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: FAA
To: NTSB
Date: 6/2/2003
Response: Letter Mail Controlled 6/9/2003 4:51:51 PM MC# 2030279: On March 13,2003, the Federal Aviation Administration (FAA) issued a supplemental notice of proposed rulemaking (SNPRM) proposing to adopt an airworthiness directive (AD) applicable to all Embraer EMB-I 20 series airplanes. The SNPRM supersedes a notice of proposed rulemaking (NPRM) issued in April 20, 2001, that proposed to require replacing certain existing potentiometers with recently manufactured potentiometers, modifying the flexible couplers that attach the shafts of the potentiometers to the shafts of the primary flight controls, performing repetitive calibration tests of the potentiometers and obtaining repetitive readouts of the flight data recorder, and reporting the results to the FAA. The FAA received significant comments to the NPRM and, as a result, has made substantial changes requiring the issuance of an SNPRM in the Federal Register for comment. The primary changes in the SNPRM are: Only potentiometers with a noisy signal will be replaced as opposed to an automatic replacement of potentiometers with ones manufactured within the last 12 months.Embraer developed a procedure to detect potentiometers with a noise signal without having to remove them from the airplane, and the procedure has been incorporated into the EMB-120 maintenance manual. The SNPRM affects only those EMB-120 operators required to operate with a flight data recorder. Some EMB-120s have been converted to freighters and are not required to have flight data recorders. The initial potentiometer noise check and flight data recorder readout will be accomplished six months after the effective date of the AD. Repetitive noise checks and readouts will be done annually in accordance with the airplane maintenance manual, and the results will be reported to Embraer. The NPRM required calibration tests and readouts reported to the FAA every six months. I have enclosed a copy of the SNPRM for the Board's information. I will provide the Board with a copy of the final airworthiness directive as soon as it is issued.

From: NTSB
To: FAA
Date: 8/16/2001
Response: The Safety Board is pleased that the FAA is taking the necessary steps to comply with this safety recommendation. Pending the issuance of the AD, Safety Recommendation A-96-33 remains classified "Open--Acceptable Response."

From: FAA
To: NTSB
Date: 6/4/2001
Response: Letter Mail Controlled 06/08/2001 7:15:15 PM MC# 2010480: On April 20, 2001, the Federal Aviation Administration (FM) issued a notice of proposed rulemaking (NPRM) proposing to adopt an airworthiness directive (AD) requiring EMB-120 operators to replace all potentiometers for the flight control position indications with potentiometers manufactured within the past year. This will ensure that the potentiometers have recently been factory-verified as fully functional. The NPRM proposes to require operators to apply locktite to the pertinent couplers to prevent noisy or loose couplers. The NPRM also proposes to require operators to perform a flight data recorder readout and a potentiometer calibration test in accordance with the EMB-120 Maintenance Manual, Section 31-30-00, every 6 months and to report the results to the FM. The FAA plans to gather the results of the readout for a period of 2 years to ensure that the potentiometers are working properly. Based on the results of the readouts, the FM will determine if the procedures specified in Embraer Service Newsletter 120-31-0009 and Service Bulletin 120-31-0038 correct noisy signals, loose couplers, and/or improper calibration problems associated with the potentiometers on the EMB-120. I have enclosed a copy of the NPRM for the Board's information. I will provide the Board with a copy of the AD as soon as it is issued.

From: NTSB
To: FAA
Date: 8/11/2000
Response: THE ACTIONS BEING TAKEN BY THE FAA COMPLY WITH THE INTENT OF THE RECOMMENDATION. PENDING ISSUANCE OF THE NPRM AND THE RECEIPT AND REVIEW OF THE AD, A-96-33 REMAINS CLASSIFIED "OPEN--ACCEPTABLE RESPONSE."

From: FAA
To: NTSB
Date: 5/30/2000
Response: Letter Mail Controlled 06/05/2000 3:31:04 PM MC# 2000711 THE FAA PLANS TO ISSUE A NOTICE OF PROPOSED RULEMAKING (NPRM) PROPOSING TO REQUIRE EMB-120 OPERATORS TO REPLACE ALL POTENTIOMETERS FOR THE FLIGHT CONTROL POSITION INDICATIONS WITH POTENTIOMETERS MANUFACTURED WITHIN THE PAST YEAR. THIS WILL ENSURE THAT THE POTENTIOMETERS HAVE RECENTLY BEEN FACTORY-VERIFIED AS FULLY FUNCTIONAL. THE NPRM WILL PROPOSE TO REQUIRE OPERATORS TO APPLY LOCKTITE TO THE PERTINENT COUPLERS TO PREVENT NOISY OR LOOSE COUPLERS. THE NPRM WILL ALSO PROPOSE TO REQUIRE OPERATORS TO PERFORM A FLIGHT DATA RECORDER READOUT AND A POTENTIOMETER CALIBRATION TEST IN ACCORDANCE WITH THE EMB-120 MAINTENANCE MANUAL, SECTION 31-30-00, EVERY 6 MONTHS AND TO REPORT THE RESULTS TO THE FAA. THE FAA PLANS TO GATHER THE RESULTS OF THE READOUT FOR A PERIOD OF 2 YEARS TO ENSURE THAT THE POTENTIOMETERS ARE WORKING PROPERLY. BASED ON THE RESULTS OF THE READOUTS, THE FAA WILL DETERMINE IF THE PROCEDURES SPECIFIED IN EMBRAER SERVICE NEWSLETTER 120-31-0009 AND SERVICE BULLETIN 120-31-0038 CORRECT NOISY SIGNALS, LOOSE COUPLERS, AND/OR IMPROPER CALIBRATION PROBLEMS ASSOCIATED WITH THE POTENTIOMETERS ON THE EMB-120. IT IS ANTICIPATED THAT THE NPRM WILL BE ISSUED BY AUGUST 2000. I WILL PROVIDE THE BOARD WITH A COPY OF THE NPRM AS SOON AS IT IS ISSUED.

From: NTSB
To: FAA
Date: 5/5/1998
Response: THE BOARD APPRECIATES THE FAA'S EFFORTS IN THIS MATTER & HAS CLASSIFIED A-96-33 "OPEN--ACCEPTABLE RESPONSE," PENDING RECEIPT & REVIEW OF THE AIRWORTHINESS DIRECTIVE.

From: FAA
To: NTSB
Date: 12/5/1997
Response: THE FAA, BRAZIL AVIATION AUTHORITY, CENTRO TECHNICO AEROSPACIAL, & EMBRAER CONDUCTED A DESIGN REVIEW OF FLIGHT DATA RECORDER (FDR) MALFUNCTIONS. AS PART OF THE OVERALL DESIGN REVIEW, EMBRAER SURVEYED EIGHT EME-120 AIRCRAFT & REPORTED THAT A CALIBRATION ERROR ON ONE AIRCRAFT RESULTED FROM A LOOSE BOLT ON THE FLEXIBLE COUPLING, WHICH ATTACHES THE POTENTIOMETER TO THE MECHANISM. IT WAS DETERMINED, HOWEVER, THAT THE BOLT IS CAPABLE OF BEING TIGHTENED TO REMOVE THE CALIBRATION ERROR. THE DESIGN REVIEW DID NOT IDENTIFY ANY PARTICULAR DESIGN FLAWS THAT REQUIRE CORRECTION. THE DESIGN REVIEW DID IDENTIFY A NOISE IN THE ELECTRICAL SIGNAL EMANATING FROM ONE OF THE RUDDER POTENTIOMETERS. SINCE THE DESIGN REVIEW, THE POTENTIOMETER MANUFACTURER HAS FOUND OTHER OCCURRENCES OF NOISY POTENTIOMETERS. THE NOISE IS BELIEVED TO BE DUE TO A SLIGHT OXIDE FILM FORMING ON THE WINDING SURFACE. TO ADDRESS THIS PROBLEM MORE FREQUENT CHECKS OF THE SYSTEM & A SPECIFIC CHECK FOR THE EXISTENCE OF OXIDE FILM ARE NEEDED.

From: NTSB
To: FAA
Date: 10/15/1996
Response: EMBRAER HAS INITIATED A DESIGN REVIEW FOCUSING ON THE POTENTIOMETERS & ASSOCIATED ATTACHING HARDWARE, & THE FAA WILL DETERMINE A COURSE OF ACTION WHEN THE REVIEW IS COMPLETED. PENDING FINAL ACTION, A-96-33 IS CLASSIFIED "OPEN--ACCEPTABLE RESPONSE."

From: FAA
To: NTSB
Date: 9/5/1996
Response: EMBRAER HAS INITIATED A DESIGN REVIEW FOCUSING ON THE POTENTIOMETERS & ASSOCIATED ATTACHING HARDWARE. THE FAA WILL DETERMINE A COURSE WHEN THE REVIEW IS COMPLETED.