The anchorage of major load-bearing composite structures to the metal aircraft body is likely to come under scrutiny

Airframe structural design rules may need reappraisal in the light of information emerging from the inquiry into the American Airlines Airbus A300-600 crash in a New York suburb last week.

For the first time, a major aerodynamic component made of composite material has been torn from an airliner in flight. Also for the first time, an Airbus type has lost its engines in flight. The US Federal Aviation Administration has ordered that the fin mountings on all US-registered A300-600s be checked.

Flight AA587 was carrying 251 passengers and nine crew. All were killed, along with several people on the ground, when the flight crashed into a residential area close to New York's Kennedy airport. There was 2min 6s between the start of the take-off roll and the point at which one of the pilots spoke about loss of control, 19s later the data recorders stopped. The pilots had carried out the airlines "recovery from extreme attitudes" training programme.

National Transportation Safety Board (NTSB) investigators say that, although the sequence of events leading to the 12 November accident began with the A300 encountering wake vortices from a Japan Air Lines Boeing 747-400 which took off just less than 2min ahead, the side acceleration forces applied by the vortices did not exceed 0.1g.

The bigger side forces following this event - "0.3g, 0.4g, then 0.3g opposite" - were "coincident with...large rudder deflections... which appear to be consistent with pilot control inputs", the NTSB says. Details on pilot input should be revealed by more extensive flight data recorder (FDR) analysis, according to the Board.

The elapsed time from the first wake encounter to the point at which the cockpit voice recorder (CVR) stopped recording was 28s. In the last seconds, the CVR recorded a "significant rattle". At some point in the sequence of increasing side accelerations the vertical fin broke away from the aircraft at its mounting points.

During the last 2.5s of the FDR operation, the NTSB reports, the rudder displacement information "becomes unreliable", but the side acceleration peaked at 0.8g. "During the last few seconds of the FDR data we see the following," said NTSB chairman Marion Blakey: "Side acceleration increases from 0.3g to about 0.8g. The aircraft heading changes at about 10í/s to the left. The bank angle is increasing through 25í, left wing down with control wheel to the right."

As the recording ends, the NTSB says, the vertical acceleration was reading "over 2g". Both engines detached from the wing in flight, presumably under the gyroscopic forces generated by the rapid heading and pitch changes associated with the high lateral g acceleration. The A300-600 was the first airliner with a composite fin. All Airbus airliners other than early A300s have composite fins, as do some Boeings.

The economic impact of the crash is viewed as uncertain, more marked in its industry-wide effects as its effects on American.

While some analysts estimate the crash will cause a $200-$250 million revenue loss to AMR, the airline itself remains strong. "With $2.3 billion in cash as of 30 September, and $8 billion of unsecured aircraft to use as potential collateral, AMR and American face no near-term liquidity problems," says Standard & Poor analyst Philip Baggaley. He adds though that the longer-term financial consequences "remain to be determined". Salomon Smith Barney analyst Brian Harris says "historical data suggests customer avoidance" of an airline that has suffered a crash "rarely extends past two quarters". Deutsche Bank Alex Brown analyst Susan Donofrio says the impact could force tottering carriers such as America West out of business.

Source: Flight International