Summary
This notice revises an earlier proposed airworthiness directive (AD), applicable to certain Teledyne Continental Motors (TCM) IO-360, TSIO-360, LTSIO-360, IO-520, and TSIO-520 series reciprocating engines. Airworthiness directive 87-23-08 currently requires ultrasonic inspection for subsurface fatigue cracks in crankshafts installed in TCM IO-520 and TSIO-520 series engines and replacement of the crankshaft if a crack is found. The proposed AD would have superseded AD 87-23-08 by expanding the applicability of the AD to include IO-360, TSIO-360 and LTSIO-360 series engines, requiring the removal of all crankshafts manufactured using the airmelt process on all of the affected engine models and replacement with crankshafts manufactured using the vacuum arc remelt (VAR) process. That proposal was prompted by reports of crankshaft failures due to subsurface fatigue cracking on engines that had been inspected in accordance with the current AD. This action revises the proposed rule by superseding AD 87-23-08, making the new AD applicable to TCM IO-360, TSIO-360, LTSIO-360, IO-520, LIO-520, TSIO-520, LTSIO-520 and Rolls-Royce, plc IO-360 and TSIO-360 series engines, incorporating new ultrasonic inspection criteria in the AD and revising the economic impact analysis. The proposed action would still require removal of crankshafts manufactured using the airmelt process and replacement with crankshafts manufactured using the VAR process. The actions specified by this proposed AD are intended to prevent crankshaft failure and subsequent engine failure.