A PROPOSED airworthiness directive(AD) requiring repetitive inspection, and possible replacement, of crankshafts in certain Textron Lycoming engines has been modified to reduce its potentially serious impact on operators. The AD was prompted by failures of hollow-end crankshafts caused by corrosion-induced cracking.

The original notice of proposed rulemaking (NPRM) covered all Lycoming 235- and 290-series and certain 320- and 360-series piston engines, and required inspection of the crankshaft inner surface for corrosion and cracking.

The US Federal Aviation Administration has now revised the NPRM to limit the AD's applicability to only certain 320- and 360-series engines and to allow pitted crankshafts to remain in service as long as there is no cracking.

Source: Flight International