AD FAA-2015-0787

We are adopting 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 including models with a "-3" suffix with a low-pressure turbine (LPT) 4th stage inner air seal (IAS), part number (P/N) 51N038, installed. This AD was prompted by the discovery, during routine overhaul of the LPT, of cracks in the barrel section of the LPT 4th stage IAS. This AD requires removal of the LPT 4th stage IAS, P/N 51N038, according to a prescribed schedule. We are issuing 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.