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Qantas Flight 72 – Accident Investigation

May 2, 2012

Jana Langhammer

Qantas Flight 72

Synopsis
At 0932 local time (0132 UTC) on 7 October 2008, an Airbus A330-303 aircraft, registered VH-QPA, departed Singapore on a scheduled passenger transport service to Perth, Australia. On board the aircraft (operating as flight number QF72) were 303 passengers, nine cabin crew and three flight crew. At 1240:28, while the aircraft was cruising at 37,000 ft, the autopilot disconnected. From about the same time there were various aircraft system failure indications. At 1242:27, while the crew was evaluating the situation, the aircraft abruptly pitched nose-down. The aircraft reached a maximum pitch angle of about 8.4 degrees nose-down, and descended 650 ft during the event. After returning the aircraft to 37,000 ft, the crew commenced actions to deal with multiple failure messages. At 1245:08, the aircraft commenced a second uncommanded pitch-down event. The aircraft reached a maximum pitch angle of about 3.5 degrees nose-down, and descended about 400 ft during this second event.

At 1249, the crew made a PAN urgency broadcast to air traffic control, and requested a clearance to divert to and track direct to Learmonth. At 1254, after receiving advice from the cabin of several serious injuries, the crew declared a MAYDAY. The aircraft subsequently landed at Learmonth at 1350.

One flight attendant and 11 passengers were seriously injured and many others experienced less serious injuries. Most of the injuries involved passengers who were seated without their seatbelts fastened or were standing. As there were serious injuries, the occurrence constituted an accident.

Preliminary reports on the cause of the accident

Examination of flight data recorder information indicates that, while cruising at 37,000 ft the autopilot disconnected, and that it was a failure in the ADIRU 1 that led to the autopilot automatically disengaging followed by two sudden uncommanded pitch down maneuvres, according to the Australian Transport Safety Bureau (ATSB).From that time, there were many spikes in the recorded parameters from the air data reference (ADR) and IR parts of ADIRU 1. Two of the angle-of-attack spikes appear to have been associated with the uncommanded pitch-down movements of the aircraft.
It’s a faulty reading from air data sensors that caused the ADIRU 1, ATSB report stated: “Bad weather together with obstructed drainage holes in all three pitot probes were subsequently found to be the cause  of  ADIRU 1 anomaly, because it supplied an incorrect airspeed data.  Pitot and static pressure sensor information (responsible for craft’s speed and elevation) is coded to ARINC 429 data bus standard and then sent up to the ADR , which sent  these data event further to Inertial References System.  Flight Control  Computer  based on those incorrect data activated ailerons and initiated the pitch down movement

Conclusion:
Two other occurrences have been identified involving similar anomalous ADIRU behavior, but in neither case was there an in-flight upset. The ATSB also investigated an in-flight upset occurrence related to an ADIRU failure on a Boeing 777-200 aircraft, which occurred on 1 August 2005, 240 km north-west of Perth.
On August 29, 2005, the U.S. FAA issued an emergency AD (2005-18-51) to prevent the operational program software (OPS) of the air data inertial reference unit (ADIRU) of the B777 from using data from failed sensors, which could result in anomalies in the fly-by-wire primary flight control and autopilot.”
The ADR associated with the failed probe or port should be considered unreliable. The ADR associated with the failed probe or port should be considered unreliable.

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