The tomorrow will issue a final airworthiness directive (AD) requiring operators of 11 turbofan engines to perform ultrasonic inspections of the two-spool engines every 90 days.
Although the AD also calls for U.S. operators to perform the inspections “before further flight,” GE reported that as of Sept. 18, all GEnx-1B and GEnx-2B engines in operational service had been inspected.
The directive comes after an “urgent recommendation” from the U.S.(NTSB) for immediate and repetitive inspections on the engine family, which powers the and .
The NTSB request followed an initial investigation into a contained GEnx-1B engine failure on a 787 while in ground testing in July at’s final assembly facility in Charleston, S.C. The failure involved cracks in the fan mid-shafts (FMS) of the engine’s low-pressure turbine. An inspection of a second GEnx-1B on-wing in August also turned up an FMS crack.
GE issued a service bulletin on Sept. 14 calling for initial inspections within 30 days, followed by repetitive inspections every 90 days thereafter. The engine-maker says the inspection can be done on-wing and takes “two to three hours” to complete.
While a root cause has not yet been found, the NTSB says the fractures indicate an “environmentally assisted cracking,” where crack initiation and growth “is a product of galvanic corrosion in a moist environment which may generate hydrogen.”
GE says it has introduced changes in the production process that “address environmentally assisted cracking, including changes to the dry-film coating applied to the mid-shaft at the manufacturing stage, as well as changes to the assembly lubricant used when the retaining nut is clamped to the mid-shaft.” The engine maker says the “change to a different coating, which has already been certified on other GE engines, is FAA-approved for GEnx production.”
A GEnx-2B engine failure on a 747-8F taking off in Shanghai on Sept. 11 has also been found to have damage in the low-pressure turbine, though GE says it has “not been determined whether the event involved a fracture of the fan shaft.”