US regulators have published a final rule that prohibits filtering of certain data captured by digital flight data recorders. The rule was spurred by the November 2001 crash of an American Airlines Airbus A300-600.
The aircraft crashed after take-off from New York Kennedy airport and, after a three-year investigation, the National Transportation Safety Board determined that rudder inputs made by the pilot after wake vortex encounters were aggressive, but also highlighted the sensitivity of the A300's rudder controls.
Although the NTSB has stressed that filtered data has made several aircraft accident investigations difficult, the US Federal Aviation Administration in the final rule says that 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 accident.
The 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 it to conclude that filtering may not generate misleading information.
However, the FAA 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 digital flight data recorder 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 taking place, operators have four years from the effective date to eliminate it. 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 the FAA.
The agency recognises that most operators do not have the technical capability to conduct an engineering analysis of digital FDR systems, but says that airframers have the expertise to conduct the reviews.
"The FAA anticipates that they [manufacturers] will perform these analyses and provide the information to the certificate holders," it says.
The new regulation applies to 7,586 US-registered aircraft and 37 helicopters operated by carriers, non-scheduled aircraft operators and rotorcraft operators. The FAA estimates total compliance cost is $310,000 - almost $152,000 for manufacturers and just over $158,000 for operators.
Source: Flight International
