The US Federal Aviation Administration (FAA) has ordered operators of GE Aviation-powered Boeing 747-8s and 787s to avoid flying into ice crystal icing conditions.
The move formalises a warning previously issued by Boeing on the GEnx-1B engine that powers the 787 and the GEnx-2B engine onboard the 747-8.
Japan Airlines withdrew the 787 from a pair of routes to Vietnam and India as a result of the warning last week.
GEnx engine operators have reported nine instances of thrust loss at high altitude due to ice crystals forming inside the engines. In two cases, the engines recovered only to idle speed, and could not produce more power, according to the FAA rulemaking.
In other cases, the engines decelerated for about 20s, but recovered to provide normal thrust, the FAA says.
The ice crystals form inside the engines during convective thunderstorms at high altitude, which occur rarely but almost always at tropical latitudes.
They can damage the interior of the engine, which can reduce thrust and “can lead to a forced landing”, according to the FAA.
FAA also orders GEnx engine operators to inspect any engines in case the pilots inadvertently fly through ice crystal icing conditions. Such convective weather patterns are not detectable on aircraft radar, the agency says in the rulemaking.
GE Aviation, meanwhile, plans to introduce software changes to the engine’s full authority digital engine control (FADEC) system in the first quarter of next year. The new software should detect the ice crystals as they move towards the core of the engine.
At the entrance to the high pressure compressor, the FADEC will order variable bleed valve doors to open, which should divert the ice into the airflow that bypasses the engine core.