U.S. transportation regulators are questioning the safety of some Boeing 777s built with Rolls-Royce engines. The National Transportation Safety Board (NTSB) is not convinced that procedures recently adopted by airlines flying Boeing 777s will prevent a potentially catastrophic power loss related to a defect in the Rolls-Royce engine. According to reports, Boeing 777s with Rolls-Royce engines could lose power in freezing weather due to accumulation of ice in the fuel supply. This engine defect has already been implicated in two accidents. One incident occurred last January when a British Airways flight lost power in both engines during final approach and crashed at London’s Heathrow Airport. The aircraft’s landing gear was ripped off. Only one passenger suffered serious injury. In the second incident a Delta Air Lines Boeing 777 suffered a similar loss of engine power while flying between Shanghai and Atlanta in November. The pilot followed a standard procedure to recover engine power and landed the jet safely at its planned destination. Following the two incidents, Boeing issued new procedures to help prevent ice accumulation, and to recover thrust in cases of ice blockage. The NTSB said that while the mandatory procedures did reduce the risk of ice blocking the fuel supply, the added burden placed on pilots who have to implement them might cause other hazards. The NTSB is recommending that the Federal Aviation Administration require Rolls-Royce to redesign the engine’s heat exchanger to prevent ice from restricting fuel flow. It is also recommending the redesigned part be installed within six months of its certification to fly or during an aircraft’s next scheduled maintenance. Yet despite the urgent nature of its recommendation, the NTSB has not called for the grounding of Boeing 777s with Rolls-Royce engines That means that around 220 Boeing 777s with the potentially deadly engine flaw will stay in the air.