Summary
This supplemental NPRM revises an earlier proposed airworthiness directive (AD), applicable to CFM International, S.A. CFM56-5B1/P; -5B2/P; -5B3/P; -5B3/P1; -5B4/P; -5B4/P1; -5B5/P; -5B6/P; -5B7/P; -5B8/P; and -5B9/P turbofan engines. That proposed AD would have required initial and repetitive eddy current inspections (ECIs) of certain part number (P/N) low-pressure (LP) turbine rear frames. That proposed AD resulted from a refined lifing analysis by the engine manufacturer that shows the need to identify initial and repetitive inspection thresholds for inspecting certain LP turbine rear frames. This supplemental NPRM revises the proposed AD to add two LP turbine rear frame P/Ns to the applicability, to add 11 engine models to the applicability, and to clarify the commercial and corporate engines/LP turbine rear frames applicability. This supplemental NPRM results from CFM International, S.A. revising the service information to add LP turbine rear frame P/Ns and engine models,and from comments received on the proposed AD. This supplemental NPRM also results from a refined lifing analysis by the engine manufacturer that shows the need to identify initial and repetitive inspection thresholds for inspecting certain LP turbine rear frames. We are proposing this AD to detect low- cycle-fatigue cracks in the LP turbine rear frame, which could result in an engine separating from the airplane, causing damage to, and possibly leading to loss of control of, the airplane.