Boeing has completed flight tests of a modified fuel-metering unit and fuel-oil heat-exchanger (FOHE) on a new British Airways Rolls-Royce Trent 800-powered 777-200ER. The modified system is designed to prevent the buildup of ice, which was suspected as the cause of a crash-landing of a BA 777 at London Heathrow Airport in January 2008, and an engine rollback on a Delta Air Lines 777 last November. The redesigned unit has also been mandated by the European Aviation Safety Agency, which says operators must fit the redesigned FOHE by the end of next year or within 6,000 flight hours.