Operators of Boeing 787s powered by upgraded General Electric GEnx-1Bs are grinding out additional space in their engine fan cases to prevent contact with the fan blades in the event of shedding ice or some other contact with a foreign object.
The work is mandated by an April 22 FAA airworthiness directive (AD), which GE says will require rework on 336 GEnx-1B Performance Improvement Package-2 (PIP2) engines that power 168 787-8 and 787-9s. The work, scheduled to be completed by September, can be done on-wing, but will entail up to 16 hr. of grinding per powerplant.
The FAA’s mandate requires rework of “at least” one engine on aircraft with two affected engines. It also gives operators until Oct. 1 to comply.
The AD was prompted by an inflight shutdown that occurred after an aircraft flew through icing conditions at 20,000 ft. on Jan. 29. The FAA said the engine encountered “a significant fan rub event . . . apparently caused by partial fan ice shedding and a resulting fan imbalance that in turn caused substantial damage to the engine and an inflight non-restartable power loss.”
GE, Boeing and the FAA believe the problem was caused by the fan rebounding forward into the abradable seal after shedding the ice and that this will be prevented by opening up slightly more space between the fan and forward seal. The affected engines will therefore require the grinding out of extra depth—less than 0.10 in.—of the abradable seal material running along the interior of the fan case immediately forward of the fan blades. The profile of this seal is slightly different in the PIP2 from earlier GEnx-1Bs, but GE said any performance losses resulting from increasing the slight opening will be “immeasurable.”
GE issued a service bulletin on April 1 recommending the modifications. The manufacturer’s plan calls for most of the work to be done during regularly scheduled A checks, meaning minimal operational disruption. The engine rework will mitigate potential buildups experienced during standard airframe and engine icing events and is not related to the higher-altitude engine core icing issues experienced primarily by the GEnx-2B engine variant on the Boeing 747-8.
The AD, which is based on GE’s bulletin, also mandates revisions to the fan-ice removal procedure and crew briefing in the 787 flight manual. These will now call for crews, when in icing conditions above 12,500 ft. and with indications or warnings of engine icing, to repeatedly clear the blades of ice from each engine every 5 min. They will do this by increasing N1 (fan speed) momentarily to a minimum of 85% before resuming normal operations. The AD also prohibits operators from dispatching the aircraft unless at least one ice detector and engine anti-ice indicator is operational.