Summary
We propose to adopt a new airworthiness directive (AD) for all Pratt & Whitney Division (PW) PW4164, PW4168, PW4168A, PW4164C, PW4164C/B, PW4164-1D, PW4168-1D, PW4168A-1D, PW4170, PW4164C-1D, PW4164C/B-1D, PW4050, PW4052, PW4056, PW4060, PW4060A, PW4060C, PW4062, PW4062A, PW4152, PW4156, PW4156A, PW4158, PW4160, PW4460, PW4462, and PW4650 turbofan engines with a low-pressure turbine (LPT) 4th stage inner air seal (IAS), P/N 51N038, installed. This proposed AD was prompted by the discovery, during routine overhaul of the LPT, of cracks in the barrel section of the 4th stage IAS. This proposed AD would require removal of the LPT 4th stage IAS, P/N 51N038, according to a prescribed schedule. We are proposing this AD to prevent failure of the LPT 4th stage IAS, which could lead to an uncontained IAS release, damage to the engine, and damage to the airplane.