Qantas Flight 72
Qantas Flight 72 (QF72) is a scheduled flight from Singapore Changi Airport to Perth Airport. On 7 October 2008 the flight made an emergency landing at Learmonth airport near the town of Exmouth, Western Australia following an inflight accident featuring a pair of sudden uncommanded pitch-down manoeuvres that severely injured many of the passengers and crew. The injuries included fractures, lacerations and spinal injuries. At Learmonth, the plane was met by the Royal Flying Doctor Service of Australia and CareFlight, where 14 people were airlifted to Perth for hospitalisation, with 39 others also attending hospital. Two planes were sent by Qantas to Learmonth to collect the remaining passengers and crew. In all, one crew member and 11 passengers suffered serious injuries, while eight crew and 99 passengers suffered minor injuries. The Australian Transport Safety Bureau investigation found a fault with one of the aircraft's three air data inertial reference units and a previously unknown software design limitation of the Airbus A330's fly-by-wire flight control primary computer (FCPC).
VH-QPA, the aircraft involved pictured in 2004
|Date||7 October 2008|
|Summary||In-flight upset due to software error resulting two pitch-downs|
|Site||80NM from Learmonth |
|Aircraft type||Airbus A330-303|
|Flight origin||Singapore Changi Airport, Singapore|
|Destination||Perth Airport, Australia|
|Injuries||119 (12 serious)|
At 09:32 SST on 7 October 2008, Qantas flight 72, with 303 passengers, three flight crew, and nine cabin crew, departed Singapore on a scheduled flight to Perth, Western Australia. By 10:01, the aircraft had reached its cruise altitude of around 37,000 feet (11,000 m) and was maintaining a cruising speed of Mach 0.82.
The incident started at 12:40:26 WST when one of the aircraft’s three air data inertial reference units (ADIRU) started providing incorrect data to the flight computer. In response to the anomalous data, the autopilot disengaged automatically, and a few seconds later, the pilots received electronic messages on the aircraft ECAM, warning them of an irregularity with the autopilot and inertial reference systems, and aural stall and overspeed warnings. During this time, the captain began to manually control the aircraft. The autopilot was then re-engaged and the aircraft started to return to the prior selected flight level. The autopilot was disengaged by the crew after about 15 seconds and would remain disengaged for the remainder of the flight.
At 12:42:27 the aircraft made a sudden uncommanded pitch down manoeuvre, recording −0.8 g,[note 1] reaching 8.4 degrees pitch down and rapidly descending 650 feet (200 m) in about 20 seconds before the pilots were able to return the aircraft to the assigned cruise flight level. At 12:45:08 the aircraft then made a second uncommanded manoeuvre of similar nature, this time reaching +0.2 g[note 2], 3.5 degrees pitch down and descending 400 feet (120 m) in about 16 seconds before being returned to level flight. Unrestrained passengers and crew as well as some restrained passengers were flung around the cabin or crushed by overhead luggage as well as crashing with overhead compartments. The pilots stabilised the plane and declared a state of alert (pan-pan), which was later updated to mayday when the extent of injuries was relayed to the flight crew.
The ATSB investigation is supported by the Australian Civil Aviation Safety Authority (CASA), Qantas, the French Bureau d'Enquêtes et d'Analyses pour la sécurité de l'Aviation Civile (BEA) and Airbus. Copies of data from the aircraft's flight data recorder and cockpit voice recorder were sent to the BEA and Airbus.
The aircraft was equipped with a Northrop Grumman made ADIRU, which investigators sent to the manufacturer in the United States for further testing. On 15 January 2009 the EASA issued an emergency airworthiness directive to address the above A330 and A340 Northrop-Grumman ADIRU problem of incorrectly responding to a defective inertial reference.
The Australian Transport Safety Bureau (ATSB) identified in a preliminary report that a fault occurred within the Number 1 Air Data Inertial Reference Unit (ADIRU) and is the "likely origin of the event". The ADIRU (one of three such devices on the aircraft) began to supply incorrect data to the other aircraft systems.
The initial effects of the fault were:
- false (contradictory) stall and Overspeed warnings
- loss of altitude information on the Captain's primary flight display
- several Electronic Centralised Aircraft Monitor (ECAM) system warnings
About two minutes later, ADIRU No. 1, which was providing data to the captain's primary flight display, provided very high (and false) indications for the aircraft's angle of attack (AOA), leading to:
- the flight control computers commanding a nose-down aircraft movement, which resulted in the aircraft pitching down to a maximum of about 8.5 degrees,
- the triggering of a Flight Control Primary Computer (FCPC) pitch fault.
FCPC design limitationEdit
Angle of attack (AOA) is a critically important flight parameter, and full-authority flight control systems such as those equipping A330/A340 aircraft require accurate AOA data to function properly. The aircraft was fitted with three ADIRUs to provide redundancy and enable fault tolerance, and the FCPCs used the three independent AOA values to check their consistency. In the usual case, when all three AOA values were valid and consistent, the average value of AOA 1 and AOA 2 was used by the FCPCs for their computations. If either AOA 1 or AOA 2 significantly deviated from the other two values, the FCPCs used a memorised value for 1.2 seconds. The FCPC algorithm was very effective, but it could not correctly manage a scenario where there were multiple spikes in either AOA 1 or AOA 2 that were 1.2 seconds apart.
As with other safety-critical systems, the development of the A330/A340 flight control system during 1991 and 1992 had many elements to minimise the risk of a design error. These included peer reviews, a system safety assessment (SSA), and testing and simulations to verify and validate the system requirements. None of these activities identified the design limitation in the FCPC’s AOA algorithm.
The ADIRU failure mode had not been previously encountered, or identified by the ADIRU manufacturer in its safety analysis activities. Overall, the design, verification and validation processes used by the aircraft manufacturer did not fully consider the potential effects of frequent spikes in data from an ADIRU.
Airbus has stated that it is not aware of a similar incident occurring previously on an Airbus aircraft. Airbus has released an Operators Information Telex to operators of Airbus A330 and A340 aircraft with procedural recommendations and checklists to minimise risk in the event of a similar incident.
After detailed forensic analysis of the FDR data, the flight control primary computer (FCPC) software and the air data inertial reference unit (ADIRU), it was determined that the CPU of the ADIRU corrupted the angle of attack (AOA) data. The exact nature was that the ADIRU CPU erroneously relabelled the altitude data word so that the binary data that represented 37,012 (the altitude at the time of the incident) would represent an angle of attack of 50.625 degrees. The FCPC then processed the erroneously high AOA data, triggering the high-AOA protection mode, which sent a command to the electrical flight control system (EFCS) to pitch the nose down.
Potential trigger typesEdit
A number of potential trigger types were investigated, including software bugs, software corruption, hardware faults, electromagnetic interference and the secondary high energy particles generated by cosmic rays. Although a definitive conclusion could not be reached, there was sufficient information from multiple sources to conclude that most of the potential triggers were very unlikely to have been involved. A much more likely scenario was that a marginal hardware weakness of some form made the units susceptible to the effects of some type of environmental factor, which triggered the failure mode.
The ATSB assessment of speculation that possible interference from Naval Communication Station Harold E. Holt or passenger personal electronic devices could have been involved was 'extremely unlikely'.
The ATSB's final report, issued on 19 December 2011, concluded that the incident "occurred due to the combination of a design limitation in the flight control primary computer (FCPC) software of the Airbus A330/Airbus A340, and a failure mode affecting one of the aircraft's three air data inertial reference units (ADIRUs). The design limitation meant that, in a very rare and specific situation, multiple spikes in angle of attack (AOA) data from one of the ADIRUs could result in the FCPCs commanding the aircraft to pitch down."
Subsequent Qantas Flight 71 incidentEdit
On 27 December 2008, a Qantas A330-300 aircraft operating from Perth to Singapore was involved in an occurrence approximately 260 nautical miles (480 km) north-west of Perth and 350 nautical miles (650 km) south of Learmonth Airport at 1729 WST while flying at 36,000 feet. The autopilot disconnected and the crew received an alert indicating a problem with ADIRU Number 1. The crew actioned the revised procedure released by Airbus after the earlier accident and returned to Perth uneventfully. The ATSB included the incident in their existing accident investigation of Flight 72. The incident again fuelled media speculation regarding the significance of the Harold E. Holt facility, with the Australian and International Pilots Association calling for commercial aircraft to be barred from the area as a precaution until the events could be better understood, while the manager of the facility claimed that it was "highly, highly unlikely" that any interference had been caused.
In the aftermath of the accident, Qantas offered compensation to all passengers. The airline announced it would refund the cost of all travel on their itineraries covering the accident flight, offer a voucher equivalent to a return trip to London applicable to their class of travel and pay for medical expenses arising from the accident. Further compensation claims would be considered on a case by case basis, with several passengers from the flight pursuing legal action against Qantas. One couple asserted that they were wearing their seatbelts at the time of the incident and questioned Qantas' handling of their cases.
Dramatisation and BookEdit
In 2018 the events of Qantas 72 were featured in "Free Fall" (Season 18, Episode 7) in the Canadian TV series Mayday. In May 2019 a book on the incident by Kevin Sullivan (the Captain of the flight) was published in Australia. In June 2019, Seven Network's Sunday Night featured the events of Qantas 72 through several passengers and crew that were onboard the flight, including Captain Kevin Sullivan, flight attendant Fuzzy Maiava, as well as US Airways Flight 1549 captain Chesley "Sully" Sullenberger.
- List of accidents and incidents involving commercial aircraft
- Lion Air Flight 610, Ethiopian Airlines Flight 302 and the subsequent Boeing 737 MAX groundings, which were caused by the possible software upsets & malfunctions of AoA (Angle of Attack) sensors and MCAS (Maneuvering Characteristics Augmentation System).
- Normal condition is +1.0 g. As an aircraft is accelerated downward (for example, by a sudden uncommanded pitch-down, as in this case), g-forces may decrease to 0.0, at which point weightlessness is experienced, and if the downward acceleration is great enough, g-forces become negative. In this case, slightly less than one full negative g was experienced—from the in-cabin frame of reference, it was similar to if gravity had "reversed" and everything "fell" upwards.
- In this second case, the downward acceleration produced by the uncommanded pitch-down was not enough to create zero or negative g forces, although it would have caused a sensation of near-weightlessness, similar to the first, highest drop on a roller coaster. +0.2 g would have made everything briefly near-weightless in the cabin, but would not have been enough to float people or objects substantially out of place or throw them around.
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