By RICHARD SHEARS

Last updated at 16:38 09 January 2008

Scores of British passengers on board a Sydney-bound jumbo jet had a lucky escape after the aircraft lost all electrical power as it was approaching Bangkok airport.

In an unprecedented drama, the Qantas Boeing 747 lost vital supplies from all four of its main generators, disabling the navigation and communication system.

And if the aircraft had been any further from an airstrip when the emergency back-up batteries expired, the captain could have been faced with such drastic action as having to ditch into the sea.

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None of the passengers on board QF2 from London to Sydney were aware of the serious predicament which occurred when the jet was just 15 minutes from landing at Bangkok – with only about 30 minutes of reserve batteries remaining to provide the vital power.

"All we were told was that there was a slight power failure after the lights had flickered off and on," said 25-year-old Chloe Washbrook, who was travelling with her friend Katherine Radding - both from London - on arrival in Sydney yesterday.

"When we got off at Bangkok, we were told there might be a slight delay but then we were told we would have to be put up for the night.

"Even the new crew in Thailand didn't know what had happened to cause the delay – they were asking us what had happened on the flight into Bangkok."

Aerospace experts in Australia said today that the pilot was lucky that the failure - caused by water leaking from a galley into the plane's generator control unit - had happened when the plane was close to landing.

Qantas has never had a crash and prides itself on its safe reputation.

Julian Walsh, deputy director of the Australian Transport Safety Bureau, which is investigating the incident, said it was fortunate the fault had occurred when the jet, with 344 passengers, was only 15 minutes from Bangkok airport.

"If the aircraft was a long way from a suitable landing area, then obviously it could have resulted in the aircraft having to ditch into the ocean or do an emergency landing on to land," he said.

Colin Adams, president of the Australian International Pilots Association, said it was also lucky the aircraft landed in daylight and in good weather.

"At night or a long way from an airport, it would have been a far more serious incident because you would have lost a lot of aircraft lighting and also a lot of your instrumentation."

The seriousness of the power failure alarmed Dr Arvind Sinha, director of Aerospace at the Royal Melbourne Institute of Technology, who said the jet had "gone to the last stage of emergency power for communication and navigation".

Pointing out that the failure of all four generators on a Boeing 747 was "unheard of", Dr Sinha said that once the emergency battery power had been used it would have been "down to the skill and experience of the crew".

He added: "The engines have their own independent power source and the steering is operated by a hydraulic pump system, but the critical issues are the navigation and communication systems that you need to find your way to a runway to land."

Qantas said last night that after being subjected to stringent inspections and testing in Bangkok, the jet was cleared to fly.

The airline's entire fleet of B747-400s had also been inspected and no problems found, but the Boeing aircraft company would be informed of the incident.