FAA Airworthiness Directive Targets Lycoming Piston Pin Defects

The FAA has issued an airworthiness directive for certain Lycoming O-235, O-540, and IO-540 aircraft engines. AD 2026-17-10 follows reports of defective piston pins that could cause engine failure. Multiple piston pin failures produced metal particulate contamination of engine oil and, in some cases, engine failure.

Lycoming received reports of metal particulates found during oil changes and two nondetectable engine failures on aircraft with the affected models. The company traced the problem to certain thin-wall piston pins manufactured with microcracks and inclusions in the base metal, the result of honing and tooling process changes by the piston pin supplier.

A failed piston pin can release metal debris that circulates through the engine, damaging bearings and cylinders or blocking oil passages and causing oil starvation. Lycoming published updated service material listing affected engines and providing instructions for pin replacement and oil inspection. The FAA said the condition, if not corrected, could result in engine failure, loss of thrust control, in-flight shutdown, and loss of control of the airplane.

The AD applies to about 957 U.S.-registered engines across multiple IO-540 model variants.