Men Who Killed Qantas - Matthew Benns [88]
Sixty-one passengers were seated without their seatbelts fastened and 91 per cent of them were hurt, mostly suffering head and neck injuries from slamming into the overhead lockers, and bruising to the back and legs when crashing back down. A third of the passengers who had their seatbelts on were also injured. More alarmingly, four passengers who had their seatbelts loosely fastened said the seatbelts had not restrained them. Accident investigators worked out that the belts could release if the buckle slipped off the passenger’s hip and dropped under the armrest. When the plane dropped suddenly, the latch of the buckle released itself on the armrest. This prompted official warnings to always have the seatbelt properly adjusted.
The Australian Transport Safety Bureau investigation into the incident uncovered a fault with one of the jet’s three air data inertial reference units (ADIRUs). Just before the autopilot disconnected, ADIRU 1 started sending incorrect data spikes to other parts of the aircraft’s operating systems. A check of the A330’s main computer traced the error messages, and tests of the components identified by the ADIRU found there was nothing wrong with them. The problem was compounded when the jet’s flight control computers did not filter out the data spikes about the angle of attack – the method of measuring the aircraft’s movement through the atmosphere. According to the ATSB preliminary report: ‘On the A330, angle of attack data was processed differently to other parameters and, in a very specific situation, the flight control computers could generate an undesired pitch-down elevator command.’10 The three ADIRU units from the A330 were sent to manufacturer Northrop Grumman in Los Angeles for testing.
ATSB checks found that the same Qantas jet, VH-QPA, had suffered a fault with ADIRU 1 during a flight from Hong Kong to Perth on 12 December 2006. The crew reported similar fault messages but the plane did not pitch down suddenly as it did two years later. Then, on 27 December 2008, another Qantas Airbus flying from Perth to Singapore had its autopilot automatically disconnected after it had reached its 36,000 feet cruising altitude. The crew was deluged with warning messages similar to those experienced on the flight deck of QF72 two months earlier. They decided to turn around and made a safe, overweight landing back at Perth airport without incident. Airbus identified a similar fault on another airline flight from Sydney to Saigon, which seemed to rule out the cause being electromagnetic transmissions from the Harold E. Holt Naval Communication Station near Learmouth. The ADIRU from the second Qantas flight joined the ones from the first incident for testing. The need for that testing to be done quickly was underscored by the crash of an Air New Zealand Airbus in November 2008. The A320 was on a maintenance flight when it crashed into the Mediterranean in good weather and with no emergency call, killing all seven aboard. It was not known what caused the crash.
Faulty ADIRUs had also caused problems in the past. Boeing 777 aircraft flew for six years before a fault in the ADIRU software was discovered when a Malaysian Airlines jet suddenly pitched up in a 3000-feet climb climb. The pilots raced to override the false information being sent by the ADIRU to the aircraft’s operating systems before the plane stalled. They succeeded and a bug was found in the computer software.
Qantas dealt with the passengers from the QF72 accident in its customary fashion. Not everyone in hospital was happy to receive their money back and a one-way ticket to London. A Qantas spokesman said: