The US Federal Aviation Authority have now issued an Airworthiness Directive (AD) concerning the problems with ice in the fuel system of Boeing 777-200 and 300 airplanes fitted with Rolls Royce Trent 800 engines. The AD requires the crew to monitor the fuel temperature within 3 hours of top of descent and if it is below a certain temperature they must increase the engine power to prevent the formation of ice in the main tank fuel supply system. They can do this by stepping up to a higher altitude or increase the airspeed. There is no requirement to carry out this procedure if the aircraft is not fitted with Trent 800 engines.

There is also a procedure for the circulation of the fuel on the ground by a certified mechanic to prevent the formation of ice.

This AD is a result of the problems encountered in January 2008 by a British Airways Boeing 777 which failed to respond to a command for increased thrust while the aircraft was on approach to London Heathrow airport and landed short of the runway. the interim report suggested ice formed in the main fuel tank supply system during low fuel flow conditions in cruise flight. This ice then dislodged and caused a restriction in fuel supply during high flow conditions during approach.

No doubt there will be more measures to prevent the formation of ice from the engine and aircraft manufacturers but in the mean time the FAA are counting on this procedure to prevent the recurrence of the fuel restriction and loss of engine power.