CANBERRA, Australia – Air safety investigators are exploring whether interference from a U.S.-Australian naval transmitter or even a passenger's laptop caused a Qantas jetliner to nose-dive twice over the Australian coast last month, an official said Friday.

Initial investigations of the midair emergency that left 13 seriously injured indicated the Oct. 7 malfunction on the Airbus A330-300 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 northwest coast at Exmouth, near where the plane made its emergency landing.

The plane was flying at 37,000 feet (11,300 meters) en route from Singapore to the western Australian city of Perth when a computer unit began transmitting wildly incorrect data to a main flight computer. The plane nose-dived 650 feet (200 meters) 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 (120 meters) in 16 seconds.

The aircrew made a mayday call to air traffic controllers after learning the extent of injuries on board, including broken bones, and detoured to the Learmonth air strip, near Exmouth. In all, 44 passengers and crew were injured.