AIR safety investigators say they have so far found no evidence that electronic interference from a passenger's mobile phone or laptop computer caused a Qantas Airbus to make an uncontrolled descent.

But they say such interference remains one possible cause of the incident that injured more than 70 passengers and crew during a flight from Singapore to Perth on Tuesday.

Australian Transport Safety Bureau investigations director Julian Walsh said questions about the possibility the incident was caused by such a device would be included in a survey of passengers.

He said the investigation would examine a wide range of factors that could influence the aircraft's operation.

Mr Walsh praised the crew for ensuring that the cockpit voice recording of the crucial moments was preserved.

Meanwhile, Qantas is facing the prospect of another bruising industrial fight after 1500 maintenance staff endorsed a resolution approving industrial action early next year if talks between a union and the airline break down.

Australian Manufacturing Workers Union national secretary Dave Oliver said the maintenance workers were keen to avoid drawn-out talks after talks on the last agreement took 18 months.

Workers are pushing for wage rises of 5% a year when the current deal expires at the end of this year as part of a three-year agreement.