When automation fails: remembering Qantas flight 72
On this day 12 years ago, a software failure onboard a Qantas Airways Airbus A330 (registered as VH-QPA) almost led to the deaths of 315 occupants onboard the wide-body. The flight, saved by the heroic actions by its pilots, resulted in injuries to over 100 people and changes to safety critical-systems onboard.
The Qantas A330 departed Singapore Changi Airport (SIN) as flight 72 towards Perth, Australia at 09:32 AM local time (UTC +8) . Everything was going according to a plan, as the aircraft was cruising at 37,000 feet on its usual flight path. No weather issues were later reported by the crew, as noted by the Australian Transport Safety Bureau (ATSB). At 12:33 PM local time, Kevin Sullivan, the captain of the A330, returned from his scheduled break – six minutes after, the first officer returned to the right-hand seat, as the second officer rotated off for his own break.
At 12:40 PM, the autopilot (AP) automatically disconnected after one out of three of the aircraft air data inertial units (ADIRU) provided incorrect data to the flight computer. Following the AP disconnection, the flight crew noticed that their electronic centralized aircraft monitor (ECAM) began showing cautionary messages, warning the pilots of failures on the Airbus A330. Furthermore, the flight computer began transmitting aural messages that the aircraft was stalling and was in an Overspeed situation – a set of messages that contradicted each other.
Abrupt pitch-down movements
The flight crew canceled the initial autopilot disconnect message on the ECAM and proceeded to turn on autopilot 2, which had been on for a brief 15 seconds before the crew switched it off. In addition, the captain’s primary flight display (PFD) had started to showcase fluctuating data, while the first officer’s PFD readings were stable. From this point on, the captain used the PFD to fly the aircraft.
Two minutes following the disconnection of AP1, the second officer requested, via the cabin interphone, for the first officer to return to the flight deck as the flight was experiencing unusual issues. At the same time, the first out of two sudden pitch-down movements occurred. The maximum pitch-down angle of the first occurrence was 8.4°, according to data provided by the ATSB.
The captain proceeded to level out the aircraft. His first movement of the sidestick controller resulted in action only after a two-second delay, noted the incident investigators. The Airbus A330 was about 150 kilometers away from its nearest suitable diversion airport, Learmonth Airport (LEA), situated in the Northwest of Australia. The flight crew proceeded to deal with multiple error messages on the ECAM when the A330 once again abruptly pitched down at 12:45 PM local time, three minutes following the first pitch-down event. The maximum pitch angle of the second nose-down was recorded at 3.5°. Eerily similar to the first occurrence, the captain once again noted that his attempt to level the nose had no immediate effect and that the aircraft pitched-up only after a brief delay.
The Flight Data Recorder (FDR) later confirmed the captain’s statements. “The flight control system did not respond to flight crew inputs for at least 2 seconds, and that the aircraft descended 400 ft over 15 seconds before returning to FL370,” read the ATSB’s report. ECAM messages once again returned, including stall and Overspeed warnings. The crew noted that several messages reoccurred, including NAV IR 1, related to the ADIRU, and NAV GPS FAULT.
“The crew stated that these constant aural alerts, and the inability to silence them, were a significant source of distraction.”
Diverting to LEA
The first officer eventually returned to the flight deck, two minutes after the second pitch-down maneuver that was initiated by the aircraft itself. According to the captain of the flight, the automatic pitch trim (autotrim) function was not working – yet no indication that the aircraft was in direct law was provided to the crew on either of the PFDs. No “USE MAN PITCH TRIM” message, which would have told the pilots to manually trim the aircraft. The message only appeared when the flight was in direct law – something that Airbus would adjust following Qantas flight 72.
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