Summary
The FAA proposes to adopt a new airworthiness directive (AD) for Rolls-Royce Corporation (RRC) (formerly Allison Engine Company) 501-D22A, 501-D22C, and 501-D22G turboprop engines. This proposed AD would require a onetime inspection for proper metal hardness of certain 1st stage, 2nd stage, 3rd stage, and 4th stage turbine wheels. This proposed AD results from a report of a turbine wheel found to be over dimensional limits, caused by improper metal hardness. We are proposing this AD to prevent uncontained turbine wheel failure, leading to damage of the airplane and total loss of engine power.