Airworthiness Directives; Pratt & Whitney JT9D-7R4 Series Turbofan Engines

This amendment adopts a new airworthiness directive (AD), that is applicable to Pratt & Whitney JT9D-7R4 series turbofan engines. This amendment requires initial and repetitive fluorescent penetrant inspection (FPI) of the high pressure turbine (HPT) 1st stage disk aft lugs, and if the aft lug(s) are cracked, replacement of the HPT 1st stage disk and HPT 1st stage airseals. Also, for certain configuration HPT disk assemblies, this amendment requires replacement of the HPT 1st stage airseals with newly designed airseals at the next accessibility. This amendment is prompted by reports of cracks in HPT 1st stage disk firtrees and failure of firtree lugs. The actions specified by this AD are intended to prevent 1st stage HPT disk firtree fracture, which could result in an uncontained engine failure, and damage to the airplane.