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A Qantas plane - Source: ONE News
Australia's air safety watchdog is now investigating two in-flight system malfunctions on Qantas jets.
In the latest incident, on December 27, a Qantas Airbus A330-300 destined for Singapore was forced to return to Perth after the autopilot disconnected.
The malfunction occurred while the jet was cruising at 36,000 feet about 500km north-west of Perth.
"The crew elected to return to Perth and an uneventful overweight landing was conducted," the Australian Transport Safety Bureau (ATSB) said in a statement.
It says the incident is "similar" to one that occurred in
October last year and will be investigated as part of the
inquiry
into that emergency.
On October 7, 2008, 70 of the 313 people on board a Qantas Airbus A330 travelling from Singapore to Perth were injured, with 44 needing hospital treatment, after the aircraft suddenly plunged, hurling passengers around the cabin.
The aircraft was cruising at 37,000 feet when the fault occurred, causing it to descend up to 650 feet in seconds.
The pilot made an emergency landing at Learmonth in north-western WA.
A preliminary report into the October incident by the ATSB, released in November, found there was a possibility transmissions from the Harold E Holt naval communications station interfered with aircraft onboard systems.
The bureau is also investigating the possibility passenger electronic devices aboard the aircraft caused the problem.
It regards both as unlikely but says it cannot rule either out yet.
The air safety watchdog is focusing on a flight computer system component called an ADIRU - air data inertial reference unit.
When the autopilot disconnected on December 27, the crew received a message indicating a problem with the plane's number 1 ADIRU.
They then followed revised guidelines from Airbus issued after the October emergency.
