AD FAA-2010-1095

We are superseding an existing airworthiness directive (AD) for all Pratt & Whitney Division PW4074 and PW4077 turbofan engines. That AD currently requires removing the 15th stage high-pressure compressor (HPC) disk within 12,000 cycles since new (CSN) or using a drawdown removal plan for disks that exceed 12,000 CSN. This new AD requires the same actions and clarifies that 15th stage HPC disks that have accumulated more than 9,865 CSN require a borescope inspection (BSI) or eddy current inspection (ECI) of the disk outer rim front rail for cracks prior to accumulating 12,000 CSN. This AD was prompted by a request from an operator that we clarify our inspection schedule for 15th stage HPC disks that have accumulated more than 9,865, but less than 12,000 CSN, on the effective date of the AD. We are issuing this AD to prevent cracks from propagating into the disk bolt holes, which could result in a failure of the 15th stage HPC disk, uncontained engine failure, and damage to the airplane.