Software redesign following investigation of an in-flight upset to an American Airlines Airbus Industrie A300-600R has been recommended by the US National Transportation Safety Board (NTSB). The aircraft's airspeed was allowed to decrease dangerously when it levelled out at 16,000ft (4,900m) during descent, before the stall-warning sounded and the aircraft rolled left and right, rapidly descending more than 3,000ft.
Although the cause of the incident, on 12 May, 1997, is still under investigation, the NTSB believes that the Federal Aviation Administration should act immediately on two items.
During the upset, electronic flight-instrument system (EFIS) displays controlled by symbol generator unit (SGU) computers were lost for several seconds, leaving the crew with standby instruments. The NTSB wants modifications to the A300's SGU software and its autothrottle system.
Airbus has said that during the upset, the SGUs underwent an automatic reset and self-test to detect unreliable data. The Safety Board feels that the SGU software should be modified so that "an unreliable-data reset of the EFIS will not occur during an upset."
Concern about the autothrottle system (ATS) is based on the fact that it was definitely engaged during descent from 24,000ft, but when the crew levelled-off at 16,000ft it was not.
The NTSB concluded that the airspeed was allowed to decrease to the stall, which caused the upset, but post-flight testing found no evidence of ATS malfunction.
Source: Flight International
