The US FAA plans to issue on 2 November an airworthiness directive (AD) requiring US operators of Pratt & Whitney PW4074 and PW4077-powered Boeing 777s to remove or inspect certain high pressure compressor disks from the turbine engines.
The agency says that as of 30 June, it had received maintenance reports of cracks in 53 disks from the 15th stage high pressure compressor (HPC) sections of the engines.
The cracks, located in the front rail of the load and lock slots of the disks, could lead to failure of the disks and uncontained engine failures, says the FAA.
Engineering investigations have determined that the cracks are being initiated by thermal mechanical fatigue.
The FAA estimates there are 44 of the affected engines installed on US-registered aircraft.
The proposed airworthiness directive calls on operators to replace the 15th stage HPC disks within 12,000 cycles since new.
For engines already beyond 12,000 cycles, FAA is requiring borescope and eddy current inspections of the disk rims until the disks can be replaced during normal engine maintenance cycles.