Why did jet with pristine safety record crash?

London: Accident investigators yesterday focused on why one of the safest jets in the history of aviation apparently lost all power in the final phase of an otherwise routine flight.

The most likely cause of the Boeing 777's crash landing appears to be a catastrophic electrical failure that struck without warning 20 seconds before it was due to touch down.

Pilots said that would be consistent with the tilting of the plane witnessed by onlookers as pilot Peter Burkill struggled to keep it under control.

The power loss would have left him with only a handful of key flight deck instruments run from a battery, such as the altimeter, to guide the plane in.

A similar electrical failure was suffered by a Qantas 747 last week on a flight from London to Sydney. It had to make an emergency landing at Bangkok, relying on a standby generator to get it on the ground.

But that came at cruising height. Burkill would have had only seconds to react if his plane had suffered a similar "black-out".

Alternatively, the computer could have initiated an "involuntary flight control command" that could have accounted for the nose lifting in the final moments of the descent.

However, this has only been recorded as ever happening once before. The pilot will have been trained to glide a plane into land with double engine failure. However, the reliability of modern jet engines means most pilots will only encounter even a single engine loss a few times in their career.

A double simultaneous failure is regarded as an incredibly remote possibility with odds of many millions to one.

However, some experts suggested it could have been caused by a massive bird strike with the plane possibly flying through a flock of geese on the final approach, disabling both Rolls-Royce Trent 895 engines.

But there were no eye-witness reports of large movements of birds in the area and no passengers have spoken of seeing any. A British Mediterranean flight from Heathrow to Beirut was forced to make an emergency landing last October after a bird strike on take-off.

Another theory is that the plane encountered violent wind-shear - strong down-draughts responsible for a number of major crashes near airports.

Although cross-winds were relatively light at Heathrow yesterday there were thunderstorms. But Boeing 777s are all equipped with a predictive wind shear system, which would normally delay the approach.

One other possibility is the plane ran out of fuel after being asked to stack because of congestion. Airlines have been accused of cutting safety margins to save money.

Most crashes usually involve some element of pilot error but it seems unlikely that a senior pilot with 20 years' flying experience could have made such a blunder on a routine approach.

Pilots were yesterday full of praise for Burkill. One said: "It was a fantastic bit of flying. He had to get the plane down and he did. In that situation you have to convert any speed you have got into height and that is what he did. That is why he lifted the nose. The cockpit workload in the final approach is huge anyway. When something like this happens you have got no time at all to react. You have got to do it all instinctively."

Investigators from the Department for Transport's Air Accident Investigation Branch will release an initial report within 48 hours.

The Boeing 777 has not been involved in a single fatal crash since launch in 1995, giving it one of the best safety records.

Twelve short haul flights within Britain and Europe were cancelled yesterday as the southern runway was still operating on limited capacity. A BAA spokesman said the rest of the 1,300 flights were due to take off and land as planned.