Airworthiness Directive · Amendment 39-17104 · Pratt & Whitney Turbofan Engines
Pratt & Whitney Turbofan Engines
This AD applies to Pratt & Whitney Division PW4074 and PW4077 turbofan engines with 15th stage high-pressure compressor (HPC) disks, part number (P/N) 55H615, installed.
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.
(1) For 15th stage HPC disks that have 9,865 or fewer cycles since new (CSN) on the effective date of this AD, remove the disk from service before accumulating 12,000 CSN.
(2) For 15th stage HPC disks that have accumulated more than 9,865 CSN on the effective date of this AD, do one of the following:
(i) Remove the disk from service at the next piece-part exposure, not to exceed 2,135 cycles-in-service (CIS) after the effective date of this AD.
(ii) Perform a borescope inspection (BSI) or eddy current inspection (ECI) of the front rail of the disk outer rim according to the following schedule:
(A) Within 2,400 cycles-since-last fluorescent penetrant inspection or ECI, or
(B) Within 1,200 cycles-since-last BSI, or
(C) Before accumulating 12,000 CSN, or
(D) Within 55 CIS after the effective date of this AD, whichever occurs latest.
(3) If the BSI from paragraph (e)(2)(ii) of this AD indicates the presence of a crack in the disk outer rim front rail, but you cannot visually confirm a crack, perform an ECI within 5 CIS after the BSI.
(4) If you confirm a crack in the front rail of the disk outer rim using any inspection method, remove the disk from service before further flight.
