Summary
The FAA proposes to adopt a new airworthiness directive (AD) for certain Pratt & Whitney Division (PW) PW4164, PW4164-1D, PW4168, PW4168-1D, PW4168A, PW4168A-1D, and PW4170 model turbofan engines. This AD was prompted by several reports of low pressure turbine (LPT) 4th stage vane cluster assemblies leaning back and notching into the rotating LPT 4th stage blades, causing some blades to fracture and release. An investigation by the manufacturer into those reports determined that the leaning back of the LPT 4th stage vane cluster assemblies was caused by damage to the LPT 4th stage air sealing ring segment assemblies. This proposed AD would require initial and repetitive replacements of the LPT 4th stage air sealing ring segment assemblies with parts eligible for installation. This proposed AD would also require initial and repetitive dimensional inspections of the LPT case for bulging and, depending on the results of the dimensional inspection, repair or replacement of the LPTcase. The FAA is proposing this AD to address the unsafe condition on these products.