The National Transportation Safety Board today released the following updated information on its investigation of the November 12 crash of American Airlines flight 587 in Belle Harbor, New York, which resulted in the deaths of all 260 persons aboard and 5 persons on the ground.
Vertical Stabilizer and Rudder
The aircraft's tail section has been in NASA's Langley Research Center in Hampton, Virginia since early December. In the intervening weeks, the Safety Board has conducted a series of non-destructive tests to determine whether the vertical stabilizer and rudder had any pre-existing flaws before the accident. Some delamination has been noted, but at this time it is not known whether this occurred before impact or as a result of impact.
Contrary to recent press accounts, the Board has not ruled out either mechanical malfunction or structural defect as causing or contributing to the accident. Work at NASA Langley will take many more months and will transition to more extensive and intrusive tests of the stabilizer and rudder.
Although the flight data recorder showed significant rudder movement during the last moments of flight 587, it is not known what caused the movement - whether it was mechanically induced or pilot activated - or what role, if any, the movement played in the separation of the vertical stabilizer.
The Safety Board is surveying salvage yards for an intact A300-600 vertical stabilizer and rudder as an exemplar for potential tear down and examination. The undamaged exemplar could be helpful to investigators as they examine the accident airplane's composite materials and attachment points.
In the course of the NTSB's continuing investigation, over 350 eyewitnesses to some segment of the accident sequence have been identified. Those who have not already provided written statements or been interviewed by NTSB personnel will be contacted shortly. Some of these individuals mentioned observing fire or smoke before the plane impacted the ground, although the majority of them do not. Although at this time no physical evidence of an inflight explosion or fire has been discovered, the Board is taking into full consideration the observations of all witnesses. Witness statements will be made part of the public docket of this investigation.
As previously announced, the Safety Board has established an e-mail address (AA587wit@ntsb.gov) for eyewitness statements. All persons who can provide eyewitness testimony about this accident who have not yet been in contact with Safety Board personnel should contact the NTSB through this e-mail.
Flight Data Recorder
The flight data recorder continues to be analyzed. That process is taking a little longer in this case because signals for some parameters on this aircraft are "filtered" before they reach the flight recorder. The filtering operation is used to smooth data that drive cockpit displays so that the needle (or other indicator) does not jump around. This filtering is accomplished by averaging the data over time. When large, rapid movements are made, this averaging will distort the recorded data; rapid, extreme control movements are clipped off. As a result, 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.
In 1994, the Safety Board recommended to the FAA that such filtering systems be removed from information sent to flight data recorders. The FAA told the NTSB that its 1997 final rule amending FDR requirements "precludes the use of a filter and specifies the seconds-per-sampling interval for all parameters." Based on that information, the Safety Board closed its recommendation as "Acceptable Action" on August 9, 2000. The Safety Board has alerted Airbus and the FAA of the problem noted on the recorder recovered from American Airlines flight 587.