Page last updated at 17:14 GMT, Friday, 13 March 2009

'High risk' of plane fault repeat


Footage of the Heathrow crash landing aftermath in January 2008

Experts have warned there is a "high probability" that a fault which caused a British Airways jet to crash-land at Heathrow could hit other Boeing 777s.

US air accident investigators called for a component to be redesigned after a Delta Air Lines plane reportedly encountered a similar problem.

Manufacturers Rolls-Royce say the new part should be ready within the year.

It comes after tests proved a build-up of ice in the engine was the most likely cause of the Heathrow crash.

The Boeing 777, with 152 people on board, crashed in January 2008, causing one serious injury.

The captain and co-pilot were praised for averting a major disaster.

On Thursday, a second interim report from the UK's Air Accidents Investigation Branch (AAIB) said that, during the flight from Beijing, ice may have developed in the fuel pipes.

Ice on a heat exchanger
US investigators simulated the icing on a plane's heat exchanger

Then shortly before landing, owing to factors such as turbulence or engine acceleration, a large amount of ice may have been dislodged and suddenly released into the fuel system, causing a fuel blockage.

Ten months later, it is understood a Delta Air Lines Boeing 777 was affected by a similar problem, known in the industry as an engine rollback or sudden power loss.

The plane experienced a single engine rollback while cruising over Montana while en route from Shanghai to Atlanta.

The National Transportation Safety Board (NTSB) in the US said this was because there had been a build-up of ice, from water normally present in all jet fuel, on a component known as the fuel/oil heat exchanger (FOHE). This had restricted the flow of fuel to the engine.

It has now issued an "urgent safety recommendation", calling for a redesign of the FOHE to eliminate the potential for ice build-up.

With two of these rollback events occurring within a year, we believe that there is a high probability of something happening again

US official Mark Rosenker

Mark Rosenker, acting chairman of the NTSB, said: "With two of these rollback events occurring within a year, we believe that there is a high probability of something happening again."

Rolls-Royce has said a new version of the component was already being developed and it should be ready within 12 months.

A Rolls-Royce spokesperson said there had been no issues with its equipment, adding that ice build-up in commercial "long-cold-high" routes was an industry-wide issue.

New guidelines

There are currently 220 Boeing 777s, with Rolls-Royce Trent 800 engines, in operation. The planes are used by 11 airlines and British Airways owns 15.

A Boeing spokeswoman confirmed it had issued a set of guidelines for pilots to prevent long-term build-up of ice and these procedures had been approved by the regulatory bodies.

But the NTSB report said: "While the procedures may reduce the risk of a rollback in one or both engines due to ice blockage, they add complexity to flight crew operations, and the level of risk reduction is not well established."

Pilots know how to flush the problem out
David Learmount
Aviation safety expert

An AAIB spokesman said it had not called for the planes to be grounded and neither had its US counterpart.

It joined the NTSB in recommending that Rolls-Royce should develop changes which prevent ice from causing restriction to the fuel flow.

"Operators have put in place procedures to prevent this causing another safety incident," the spokesman added.

David Learmount, safety editor for Flight International magazine, told the BBC the AAIB and the NTSB were essentially saying the same things but had a different "style" in the way they phrased them.

Both the AAIB and the NTSB acknowledged things had to be changed in the long term, he said, and both believed the problem had been resolved in the short term.

However, the NTSB had added "drama" to its warnings which Mr Learmount considered "alarmist".

Such incidents would not reoccur because it was now known how to deal with the issue, he said.

"It won't happen again because now they have systems on board and the pilots know how to flush the problem out when it doesn't make any difference - when there's no danger," he added.

Graphic of fuel system on Boeing 777

117,340 litres of fuel carried in tanks in both wings and main fuselage

Water occurring naturally in the fuel can freeze during "long-cold-high" flights such as the two examples above

Fuel/oil heat exchanger through which fuel passes on its way to engines failed to melt ice leading to build-up and blockage

In flight where fuel temperature falls below -10C pilots should make periodic climbs to a higher altitude at full throttle

If aircraft has remained at the same altitude for more than two hours prior to descending to land, and fuel temperature is below -10C, the pilot must "advance the throttle to maximum for 10 seconds" to clear any ice in the fuel system
Source: Boeing/National Transport Safety Board

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