Computer glitch caused plane’s altitude to drop

Event Year: 2009 Reliability: Confirmed
Country: Australia
Industry Type: Transportation

On Qantas flight 72, the pilot switched off autopilot shortly after taking off.  One of the Airbus A330-303’s air data inertial reference units (ADIRUs) “started providing erroneous data” according to a report issued by the Austrailian Transportation Safety Bureau.  The ADIRU captures and relays air data sensor information such as position and altitude which is then fed into the flight control computers.  Two of the three AIRDU’s functioned properly, however,the plane’s flight control computers had failed to filter data regarding the wing’s motion. “The computers subsequently commanded the pitch-down movements” the report said. As soon as the autopilot system was disconnected, failure warnings started.  Soon after, the aircraft suddenly pitched nose-down and fell around 650 feet.  Shortly after correcting the 37,000 feet fall in altitude, the aircraft pitched nose down again descending 400ft.  The sudden drops in altitude cuased 11 passengers to be seriously injured.  The ATSB identified problems with two secondary computers’ ability to execute commands sent from the primary computer.  The investigation will continue.


Eleven passengers on board were seriously injured when the plane’s altitude dropped twice during the flight.