A Qantas flight from Melbourne to Dubai has been diverted to Sydney due to an engineering issue. Credit: Today/ Nine Network

A Qantas flight from Melbourne to Dubai has been diverted to Sydney due to an engineering issue. Credit: Today/ Nine Network

AN INVESTIGATION is underway into how a smartphone battery sparked a fire on a Qantas flight to Los Angeles.

The Australian Transport Safety Bureau is investigating the incident on June 21, on a Qantas 747 flying from Sydney to LA.

Six-and-a-half hours into the 13-hour flight a passenger’s smartphone slipped between the seats and was crushed as the owner used the reclining mechanism to try to retrieve the device.

The battery in the crushed phone then erupted into flames. Crew used a fire extinguisher to put out the blaze and the flight continued on to Los Angeles.

The ATSB confirmed the incident, and said it would seek information from Qantas as part of its investigation.

A Qantas spokeswoman revealed there had been other incidents of phones being lost and crushed - and then starting to smoulder.

“We find this tends to be more of an issue on longer flights and on our Business Class skybeds, where people might have their phone next to them as they relax and it slips down the side of the chair,” she said.

“We’re asking people to keep track of their phone in their seat, and if they do lose it down the side, to let a crew member know and to not move their seat. When the seat moves, that’s when the phone may get crushed.”

She said crew were trained to deal with such a scenario and had done “a great job on the odd occasion where we’ve had a phone break and start to smoulder”.

“But obviously, we’d much prefer if we could avoid this happening altogether,” said the spokeswoman.

Last year Qantas and other Australian airlines banned the carriage of lithium-ion batteries in cargo holds after they were found to pose an unacceptable risk of fire.

It followed tests by the US Federal Aviation Administration showing an overheating battery could cause other batteries nearby to short-circuit in a chain-reaction.

The subsequent ignition could be enough to cause an explosion strong enough to blow the door off a cargo container, resulting in fire.

Such a scenario is considered one possible cause of the MH370 mystery.

The Malaysia Airlines’ Boeing 777 was carrying 200kg of lithium ion batteries in its cargo hold when it took off from Kuala Lumpur with 239 people on board.

Shortly after the plane’s still unexplained disappearance, Malaysia Airlines imposed a ban on the bulk carriage of lithium-ion batteries.

The ATSB investigation into the June 21 incident is expected to take several months.