A faulty computer unit likely caused a Qantas jetliner to experience two terrifying midair plunges within minutes last week, an Australian investigator said Tuesday.

Julian Walsh, chief air investigator at the Australian Transport Safety Bureau, said an initial investigation indicated the cause was a computer unit that detects through sensors the angle of the plane against the airstream. He said one of the plane's three such units malfunctioned and sent the wrong data to the main flight computers.

The flight data recorder indicated the plane, carrying 303 passengers and 10 crew, climbed about 200 feet from its cruising level of 37,000 feet and then went into a nose-dive, dropping about 650 feet in 20 seconds, before returning to cruising level, the safety bureau said last week. The sharp drop was quickly followed by a second of about 400 feet in 16 seconds.

The problem is the latest in a series of malfunctions and near-misses for Australia's flagship carrier in recent weeks.

Australian authorities are still investigating an explosion aboard a Qantas 747-400 aircraft carrying 365 people over the South China Sea in July that ripped a hole in the fuselage. That explosion caused rapid loss of pressure in the passenger cabin but no one was injured.

Walsh said the French manufacturer Airbus had notified all operators of A330 and A340 aircraft, which are equipped with the same sensors, about how crews should respond to such a malfunction.

But aircraft are unlikely to be grounded over a malfunction that had never happened before, he said.

"It is probably unlikely that there will be a recurrence, but obviously we won't dismiss that," Walsh told reporters, saying they would investigate the problem further.

The faulty unit will be sent to the U.S. component manufacturer for testing, he said. A report on the accident is to be released next month.

Qantas said the preliminary findings showed that the fault lay with the manufacturer rather than the airline.

"This is clearly a manufacturer's issue and we will comply with the manufacturer's advice," the airline said in a statement.