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Letter from NTSB to FAA re the Filtering Problem in the Flight 587 Flight Data Recorder

by Victor Trombettas

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U.S.Read has reported previously about the filtering problem discovered on Flight 587's Flight Data Recorder. This in addition to the fact the FDR stopped recording at least 10 seconds before impact. This filtering problem, which in effect leads to inaccurate data being recorded on the FDR, has delayed the NTSB's ability to do a thorough analysis.

 

On February 6th, 2002, the NTSB Chairman, Marion Blakey, sent a letter To the FAA's Administrator addressing the issue of "vital" flight control position data that was filtered (or averaged) by the System Data Analog Converter (SDAC) before it was sent to the Digital Flight Data Recorder (DFDR) on board Flight 587. The NTSB had previously stated in their January 15th Press Release:

"the readings on the recorder show what the gauges were telling the pilots, not necessarily what was actually occurring on a real-time basis to the aircraft. This will require some aircraft testing and then further computations by Board staff to get the true readings on some parameters of interest like rudder, elevator, and aileron movement. Although this has added to the workload of investigators, it is not expected to affect the quality or the timing of the Board's final product."

The NTSB is at the point now where they are attempting to understand the characteristics of the SDAC, which filtered the data. Airbus could not provide NTSB with those characteristics so now the NTSB is bench testing the SDAC trying to figure out those characteristics on their own. Once they understand SDAC's characteristics they can move on to attempting to calculate real-time data from the averaged DFDR data.

 

In 1994, the NTSB made two safety recommendations to the FAA that filtered data not be submitted to the DFDR as accurate data. The FAA accepted this recommendation in 1997 and amended the rule related to the transmission of data to the DFDR. The NTSB therefore considered this matter "closed" in May of 2000.

 

Unfortunately, when the FAA informed the NTSB in 1996 that several airplane manufacturers were compliant with accurate FDR requirements, that list did not include Boeing and Airbus.

 

The NTSB has asked the FAA to respond within 30 days as to how they will ensure all aircraft, including Airbus A300's, are compliant with FDR rules.

 

NTSB has provided U.S.Read with a copy of the letter to the FAA:

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Please jump to the U.S.Read Home Page where you will see more links to Flight 587 stories.

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Victor Trombettas

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