Probe underway after Qantas jet nosedives

Two violent mid-air plunges by an airliner that seriously injured 13 passengers may have been caused by an on-board mobile phone signal, investigators said today.

They are also exploring whether interference from a naval transmitter or even a passenger’s laptop caused the Qantas flight to nose-dive over the Australian coast last month.

Initial investigations of the midair emergency indicated the malfunction on the Airbus A330-300 on October 7 was caused by a fault in a computer unit that uses sensors to detect the angle of the plane.

While that theory is still considered the most likely, investigators are looking into whether the fault could lie with electromagnetic interference from a low-frequency naval submarine communications transmitter on the Australian north-west coast at Exmouth, near where the plane made its emergency landing.

The Naval Communications Station, Harold E. Holt, was built by the US Navy in the 1960s. It provides very low frequency radio transmissions to the US and Australian navies across the western Pacific and eastern Indian oceans.

Another possible source of the interference is portable electronic devices, such as mobile phones, Australian Transport Safety Bureau director Kerryn Macaulay said. She said even those considered safe to operate during flights, such as laptop computers, are being investigated.

“Possible external sources of electromagnetic interference are being explored and assessed,” she said.

But even as investigators consider that theory, the plane’s three computer units – called air data inertial reference units, or ADIRUs – will be examined next week at manufacturer Northrop Grumman’s factory in the United States, the bureau said in a preliminary investigation report.

The electromagnetic interference “is unlikely, especially if the problem is clearly identified during the ADIRU and the system testing,” Ms Macaulay said.

Qantas said its own investigations found the likely cause of the emergency was a “manufacturer fault” in the computer unit.

The Defence Department said it agreed with the preliminary report that the transmitter was unlikely to be the cause.

The transmitter “emits very low frequency transmissions and from a significant distance from the aircraft flying overhead,” the department said in a statement.

“This indicates that it is unlikely to have caused sufficient currents in the system to have caused problems with the A330 systems,” it added.

The plane was flying at 37,000 feet from Singapore to Perth when a computer unit began transmitting wildly incorrect data to a main flight computer. The plane nose-dived 650 feet in 20 seconds before the crew brought it back to the original cruising level. The sharp drop was quickly followed by a second of about 400 feet in 16 seconds.

The aircrew made a mayday call after learning the extent of injuries on board, including broken bones.