BANGKOK – Safety investigators as well as manufacturer Boeing will want to know how water leaking from a galley appliance was able to jeopardise the lives of 344 passengers aboard a Qantas Boeing 747-400 descending into Bangkok on Monday.

The leakage, which shorted the aircraft's electrical system, forced the crew to ensure a safe landing after 15 minutes running on a one-hour emergency battery back-up system.

The incident has prompted a worldwide alert to Boeing 747 operators after the problem was traced to a cracked drip tray under the first-class galley.

Qantas yesterday began a fleet-wide check of its other jumbo jets.

Aviation sources said the back-up battery was likely to last for up to an hour and the problem could have been disastrous had the aircraft been travelling too far away from a suitable landing site.

The aircraft, en route from London, has been repaired and put back into service.

Airline officials are examining information from the flight data recorder to understand how the water affected the electrical system, whether any power was still getting through and what options were available to the pilots.

Qantas has denied the age of its fleet may have been a factor in Monday's incident.

Qantas executive manager John Borghetti said the 747 was 16 years old and well within its operational lifespan.

He told The Australian newspaper, "These aircraft are built to operate much longer than that and any speculation that this was related to either the engineering discussions that are going on or cost-saving is just totally wrong.

"There have been lots of discussions about waste and efficiency, of course, but never ever would there be a debate between profit and safety," he said. "It's just not on."