Summary
We are revising an earlier proposed airworthiness directive (AD) for certain Lycoming Engines (L)O-360, (L)IO-360, AEIO-360, O-540, IO-540, AEIO-540, (L)TIO-540, IO-580, and IO-720 series reciprocating engines. That NPRM proposed to require replacing certain crankshafts of affected engine models. This action revises that NPRM by including the IO-390, AEIO-390, and AEIO-580 series engine models having affected crankshafts. We are proposing this supplemental NPRM to prevent failure of the crankshaft, which will result in total engine power loss, in- flight engine failure, and possible loss of the aircraft. Since these actions impose an additional burden over that proposed in the NPRM, we are reopening the comment period to allow the public the chance to comment on these proposed changes.