Accident investigation needs an atmosphere of calm to be effective, but the NTSB was not given that privilege

With the final publication of its investigation into the American Airlines flight AA587 accident, the US National Transportation Safety Board (NTSB) has brought to a close the most hard-fought, acrimonious accident inquiry since the American Eagle ATR 72 "Roselawn" crash.

The circumstances of the two accidents had little in common. But the accidents both happened to American Airlines or, in the American Eagle case, a feeder operator; both occurred in the USA; and the certificating authorities for - and the manufacturers of - both the aircraft were based in France.

The AA587 inquiry found the probable cause of the 12 November 2001 Airbus A300-600 accident was "the in-flight separation of the vertical stabiliser as a result of the loads beyond ultimate design that were created by the first officer's excessive and unnecessary rudder pedal inputs". For the American Eagle ATR 72 crash at Roselawn, Indiana in 1994, the NTSB probable cause stated: "The loss of control [was] attributed to a sudden and unexpected aileron hinge moment reversal that occurred after a ridge of ice accreted beyond the de-ice boots while the airplane was in a holding pattern during which it intermittently encountered supercooled cloud and drizzle/rain drops, the size and water content of which exceeded those described in the icing certification envelope."

That was not all, though; in the Roselawn case an unusually lengthy list of contributory factors made the French certificator, the manufacturer, and the US Federal Aviation Administration responsible for multiple failures, including lack of co-operation in the supply of information to the inquiry. The acrimony did not stop with the issue of the report, and years later the NTSB was persuaded to revise the wording of some of its findings. But modifications to the aircraft's de-icing systems were subsequently ordered by the FAA following the NTSB's recommendations.

The manufacturers - Airbus in the case of the A300-600 and the Franco-Italian company ATR for the ATR 72 - both insisted the main issue was that each aircraft had been subjected to circumstances for which it was neither designed nor certificated. In both cases, the NTSB made recommendations that the aircraft design should be improved. In both cases the airline was voluble in defence of its pilots and their training.

The NTSB's list of contributory factors for the AA587 accident is characteristically brief and to the point. Any argument, the manufacturer and airline have since conceded, has stopped there. As regards the NTSB recommendation that the FAA require modification to the A300-600 rudder to make it less sensitive, Airbus says: "We will be working with the FAA as they explore whether changes should be made."

The USA makes legal provision to help all parties to an accident investigation to be dispassionate. The NTSB explains:"To ensure that Safety Board investigations focus only on improving transportation safety, the board's analysis of factual information and its determination of probable cause cannot be entered as evidence in a court of law." That should remove any need by parties to be overly defensive, and persuade them to co-operate with the NTSB.

In the AA587 case, however, a slanging match was fought publicly between the airline, pilot organisations and the manufacturer. This hampered the progress of the investigation. NTSB chairman Ellen Engleman Conners, earlier this month, complained that the board had been "lobbied more than in any other investigation - from all sides" (Flight International, 11-17 January).

Pressure from the participants had "affected the timeliness of the report", Engleman Conners said. Without being specific, she said that the two parties frequently submitted depositions that did not add anything material to the information they had already supplied, thus wasting the inquiry's time.

In a thorough investigation with simple conclusions, the NTSB has fulfilled its mandate to find out the cause to reduce the chances of a similar accident happening again. But even within the NTSB all was not harmonious. Board member Carol Carmody has filed - at the end of the report - a difference over the order in which the two contributory factors appear. The order was reversed at the October meeting to approve the final draft.

Carmody says: "I support the probable cause language in the original staff draft, which listed contributing factors as the American Airlines Advanced Aircraft Manoeuvring Programme [AAMP] and characteristics of the A300-600 rudder system. I heard no reverse this order. To diminish the role of the AAMP in the accident is to downplay the role it played in the pilot's actions which caused the accident." Carmody's term as an NTSB member expired on 31 December.

The effects of the considerable external pressure on the NTSB may have shown, if subtly. Its normal style in report titles is to describe the effect of an accident on the cover and leave the details of how it happened for the body of the report. For example, the title of the report on a maintenance-caused structural failure of an aircraft's horizontal stabiliser system in a January 2000 accident begins: "Loss of control and impact with the Pacific Ocean, Alaska Airlines Flight 261, McDonnell Douglas MD-83". For the AA587, the NTSB entitles the report: "In-flight separation of the vertical stabiliser of American Airlines 587, Airbus Industrie A300-605R, N14053 Belle Harbor New York".


Source: Flight International