The US Aircraft Owners and Pilots Association (AOPA) is claiming victory after the Federal Aviation Administration issued a revised airworthiness directive (AD) limiting the impact of crankshaft inspections on Textron Lycoming piston engines.
AOPA says that "80% of Lycoming owners will not be affected" by the final rule - issued on 28 January. Only O-320- and O-360-series engines of 120kW (160hp) and above, with fixed pitch propellers, are affected, it says.
The AD requires inspection of the crankshaft inner diameter for corrosion pits. If no corrosion is found, the crankshaft can be re-inspected at five year intervals. If corrosion is found, however, a magnetic particle or fluorescent penetrant inspection is required to search for cracks. Cracked crankshafts must be replaced. Those with corrosion, but no cracks, can remain in service and but have to be re-inspected every 100h.
Under the revised AD, crankshafts with corrosion pits can remain in service until cracks develop. With the original proposals, AOPA says that all corroded crankshafts needed to be replaced within five years. The final rule includes a terminating action: a protective coating can be applied to a non-corroded crankshaft bore to remove the need for further inspections.
AOPA is advising owners that crankshaft corrosion is possible in Lycoming engines under 120kW, although there have been no corrosion induced crankshaft failures in these engines.
Source: Flight International
