Australia blames computer glitch for Airbus mishap

CANBERRA (Reuters) - An error in the automatic pilot system caused an Airbus jet to plummet last week, injuring scores of passengers on a Qantas flight from Singapore to Perth, Australia's air safety agency said on Tuesday.

The incident was an "unique event," but was serious enough to prompt Airbus to issue emergency guidelines to airlines worldwide operating the Airbus A330-300 in the event of a similar emergency, Australian Transport Safety Bureau director Julian Walsh told reporters in Canberra.

"Incorrect values led to the flight control computers commanding a nose down aircraft movement and the aircraft pitching down," Walsh said.

The aircraft, with 303 passengers and 10 crew, was cruising at 37,000 feet (11,200m) from Singapore to Perth when it suddenly gained altitude, then plummeted more than 1,000 feet in little over a minute.

The glitch occurred in an air data inertial reference unit, which feeds information to the aircraft's main computer and had never been encountered during any previous A330-300 flights, Walsh said.

The flight sensor led the computer to incorrectly determine the jet was climbing when actually in level flight, he said.

Many on board were flung around the cabin or crashed against rooftop luggage compartments before the pilots regained control and made an emergency landing, passengers said.

The aircraft landed at a remote military and mining airstrip at Learmonth, near the port of Exmouth, around 1,100 kms (700 miles) north of Perth, last Tuesday after pilots issued a "mayday" alert.

Fourteen passengers were airlifted to hospital in Perth with injuries including concussion, lacerations and broken bones. Another 60 were treated for minor bruises and did not need hospital treatment.

The ATSB last week said the jet, which was inspected by an Airbus investigator, had no structural defects causing it to drop at a sharp 8.1 degree angle, with early indications pointing to an "irregularity" it its elevator control system.

There are 247 long-haul A330-300s used by airlines around the world out of total orders for 383 of the wide body aircraft, according to the Airbus website. They can hold a maximum of 335 passengers.

Qantas, the world's 10th largest airline by market value, has been hit by a number of incidents recently and promised to refund passengers on the Perth flight.

In one, Australian air safety investigators blamed an oxygen bottle for a mid-air explosion that blew a minivan-size hole in the side of Qantas jumbo jet.

The Qantas 747-400 suffered a sudden loss of cabin pressure during a flight from Hong Kong to Melbourne on July 25, forcing the aircraft to make an emergency descent before diverting to the Philippines, where it landed safely in Manila.

The pilot landed the plane manually, with help from air traffic controllers in Manila, where all 346 passengers and 19 crew disembarked safely.

(Reporting by Rob Taylor, editing by James Regan)