US regulators today published a final rule spurred by the November 2001 crash of an American Airlines Airbus A300-600 that prohibits filtering of certain data captured by digital flight data recorders (DFDR).
The aircraft crashed after takeoff from John F Kennedy airport in New York, and after a three-year investigation the National Transportation Safety Board (NTSB) determined that rudder inputs by the pilot after wake vortex encounters were aggressive, but also highlighted sensitivity of the A300's rudder controls.
Although NTSB has stressed that filtered data has made several aircraft accident investigations difficult, FAA in the final rule states the board "expended significant time and resources trying to recreate the performance and movements of the flight controls of the accident aircraft" involved in the American Flight 587 crash.
FAA explains that since its initial notice of proposed rulemaking in 2006, comments from industry and its increasing understanding of developments in data recording capability have led the agency to conclude that filtering in and of itself may not generate misleading information.
However, FAA still believes there are eight parameters covering flight control surface positions, flight control input positions and flight control input forces that remain too critical for accident investigation to allow them to be filtered freely.
To comply with the rule, operators have 18 months from the regulation's 20 April effective date to review their DFDR systems and produce records that indicate if the system on each aircraft is filtering data captured in the eight parameters banned from the practice.
If filtering is occurring, operators have four years from the effective date to eliminate the filtering. If an operator opts to show by test and analysis that filtered data can be reconstructed, they have 18 months from the rule's effective date to supply that information to regulators.
"The investigation following the crash of Flight 587 indicated that the issue was not that data were filtered, "but that the actual rudder movement data could not be reconstructed once processed by installed filtering devices", says FAA.
FAA recognises that most operators do not have technical capability to conduct an engineering analysis of DFDR systems, but explains airframers have the expertise to conduct the reviews.
"FAA anticipates that they [manufacturers] will perform these analyses and provide the information to the certificate holders," the agency says.
The agency explains industry sources have indicated the engineering analyses will require minimal time since most of the work related to filtering was completed during aircraft certification.
The new regulation applies to roughly 7,586 US-registered aircraft and 37 helicopters operated by air carriers, non-scheduled aircraft operators and rotorcraft operators.
FAA estimates total compliance cost is $310,000 - split between $151,694 for manufacturers and $158,406 for operators.