Summary
This action withdraws a supplemental notice of proposed rulemaking (SNPRM) that proposed a new airworthiness directive (AD) applicable to Pratt & Whitney (PW) JT9D-7R4 series turbofan engines. That action would have required the addition of initial and repetitive on-wing eddy current inspections (ECI) of affected diffuser case assembly bosses for cracks, and replacement of cracked bosses with serviceable parts. In addition, that action would have revised the initial accomplishment time for the previously proposed actions. Finally, that action would have added further etches, fluorescent penetrant inspections (FPIs), x-ray inspections, and shotpeening to the shop requirements, and would have provided an optional terminating action in the form of a redesigned diffuser case. The actions specified by the SNPRM were intended to prevent diffuser case assembly rupture, which could result in an uncontained engine failure, engine fire, and damage to the airplane. Since the issuance of the SNPRM, the FAA has reevaluated the safety risk to the fleet using the most recent fleet data , including the status of how much of the fleet has already undergone the modifications and inspections included in the proposed actions.. The drawdown period of the fleet management program that was originally proposed has been completed. All case assemblies continue to be inspected on-wing as part of normal maintenance actions. Therefore, the safety risk has been considerably reduced. As a result, the FAA has determined that an AD is no longer required, and the proposed rule is withdrawn.