Summary
The FAA proposes to adopt a new airworthiness directive (AD) for Pratt & Whitney (PW) PW4090 and PW4090-3 turbofan engines with front turbine hub, part number (P/N) 53L601, installed. This proposed AD would reduce the published life limit of those front turbine hubs from 12,000 cycles-since-new (CSN) to 9,370 CSN. This proposed AD would also remove from service those front turbine hubs using a drawdown schedule. This proposed AD results from PW updating the low-cycle- fatigue (LCF) life analysis for front turbine hubs, P/N 53L601. We are proposing this AD to prevent an uncontained failure of the front turbine hub, resulting in an in-flight engine shutdown and possible damage to the airplane.