Crash investigators identified the potentially fatal flaw in Rolls-Royce Trent 800 engines by using a laboratory to recreate the extremely cold conditions through which the BA Boeing 777 had flown.

The Air Accidents Investigation Branch (AAIB) found that ice accumulated in fuel delivery pipes. This ice could be dislodged suddenly when fuel flow increased or during turbulence and be washed along the pipes to a component known as the fuel/oil heat exchanger.

The inlet to the exchanger is like a colander, with hundreds of tiny holes that can be blocked by ice crystals. With too little fuel passing through the exchanger, both engines lost thrust within seconds of each other.

The revelation that a single component could cause both engines to fail undermines the aviation industry’s oft-repeated claim that every safety critical system on a modern aircraft is duplicated. The AAIB is not absolutely certain that the exchanger is where the critical blockage occurred. It says: “It has not been possible, due to limitations in the available recorded data, totally to eliminate the possibility that a fuel restriction, from ice, formed elsewhere in the fuel system.”

This raises the possibility that, even after Rolls-Royce modifies the exchanger, the same problem could occur elsewhere in the fuel system on long flights passing close to the poles.

The AAIB calls for a study into the feasibility of using antiicing additives in fuel, as already happens on some military and business jets. However, airlines will be reluctant to do this as it will require expensive changes to fuelling systems at airports. Aircraft may also have to undergo more regular maintenance.

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