The U.S. National Transportation Safety Board wants urgent action to install a redesigned fuel/oil heat exchanger on Rolls-Royce Trent 800 engines to prevent the build-up of ice, suspected as the cause of thrust rollbacks on two Boeing 777-200ERs.
The urgent safety recommendation (read it here) is in response to two events last year: a dual-engine rollback on approach that caused the January crash of a British Airways 777 on approach to London Heathrow; and a single-engine rollback in November on a Delta Air Lines 777 in the cruise over Montana, en route from Shanghai to Atlanta.
After these events, Boeing modified the recovery procedures. These became the basis of an FAA airworthiness directive. Recognizing that Rolls-Royce is already redesigning the heat exchanger, for certification within a year, the NTSB wants the FAA and EASA to require airlines to install the new unit within 6 months of its approval.