Investigation of the American Airlines Airbus A300-600 crash on 12 November is being slowed by "filtered" information from the flight data recorder (FDR), according to the US National Transportation Safety Board (NTSB).

The accident investigation organisation believes that it will find out what caused the crash just after take-off from New York Kennedy, but it will take longer than is usual.

The problem, says the NTSB, is that the system feeding the FDR is the same as that feeding the pilot's flight and engine instruments. The data feed to these is filtered to take out transient peaks and troughs to give the pilots steadier data displays - it is an averaging-out process, the NTSB adds. But in a case like this one, in which some crucial evidence may consist of very brief but sharp control-surface movements or loadings, filtering might be hiding important data, says the accident investigators.

In 1994, the NTSB recommended that the data to FDRs should not be filtered, and the US Federal Aviation Administration accepted the recommendation in 1997. The NTSB says that it "has alerted Airbus and the FAA to the problem noted on the recorder recovered from Flight 587".

Meanwhile, the board says it is looking for the tailfin of a "salvage" A300-600 on which it can carry out stress and "tear-down" tests to try to determine why the fin of the American Airlines aircraft broke away from its mountings without, according to data recovered so far, being under very great stress. The composite fin recovered from the crashed aircraft shows "some signs of delamination", says the NTSB, but it is unclear whether the problem predated the crash or was caused by it.

Source: Flight International