FAA Issues Airworthiness Directive for Lycoming O-235, O-540, and IO-540 Engines Over Defective Piston Pins

The FAA has issued Airworthiness Directive AD 2026-17-10 covering certain Lycoming O-235, O-540, and IO-540 aircraft engines after finding defective piston pins that can cause engine failure. The agency said the piston pins contain microcracks and inclusions resulting from manufacturing process changes.

Multiple reports of piston pin failures prompted the directive. Those failures led to metal particulate contamination of engine oil and, in some cases, complete engine failure. The AD mandates replacement of the affected piston pins and inspection of engine oil for metal particulates to prevent engine failure and loss of aircraft control.

The FAA estimates the cost of compliance at between $2,200 and $2,268 per engine.

This case fits the pattern of airworthiness directives triggered by a manufacturing process change rather than by aircraft age or wear: a supplier-side shift in how a part is produced introduces a defect across a production run, and the FAA responds with a mandatory inspection-and-replacement order rather than a voluntary service bulletin.

For piston-engine operators, an AD of this kind converts a parts-quality issue into a fleet-wide, non-optional maintenance event. Engine shops and owners affected by the O-235, O-540, and IO-540 directive will need to sequence piston pin replacement and oil particulate inspection into their maintenance schedules at the estimated per-engine cost, with no substitute for compliance if the aircraft is to remain airworthy.

What remains to be seen is how many engines in service fall within the affected population and what compliance timeline the FAA sets, since neither the total engine count nor the deadline was addressed in the directive details provided here.