FLYING Magazine
The FAA has issued an airworthiness directive for certain Lycoming O-235, O-540, and IO-540 aircraft engines due to defective piston pins that could cause engine failure.
According to the agency, AD 2026-17-10 was prompted by multiple reports of piston pin failure resulting in metal particulate contamination of the engine oil and, in some cases, engine failure.
The FAA received reports from Lycoming of metal particulates found in the engine oil during oil changes and two nondetectable engine failures of aircraft equipped with Lycoming model O-235, O-540, and IO-540 powerplants.
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Lycoming conducted an investigation and discovered that certain thin-wall piston pins were manufactured with microcracks and inclusions in the base metal due to honing and tooling process changes from the piston pin supplier, making the pins more susceptible to failure.
Piston pin failure can result in metal debris circulating throughout the engine, which can damage bearings and other cylinders and even block oil passages and lead to oil starvation.
To address this, Lycoming Engines published updated service material with a list of affected engines and instructions for replacement of the affected piston pins and inspection of the oil for metal particulates. As part of an oil change the oil filter is cut open to look for metal particulates, and an oil analysis is performed.
The FAA has issued the AD to prevent failure of the piston pins, noting “this condition, if not addressed, could result in engine failure, loss of thrust control, in-flight shutdown, damage to the airplane, and loss of control of the airplane.”
The AD applies to approximately 957 U.S.-registered engines. The engine models affected are: IO-540-A1A5, IO-540-AA1A5, IO-540-AA1B5, IO-540-AB1A5, IO-540-AC1A5, IO-540-AE1A5, IO-540-AF1A5, and IO-540-AG1A5.
“The AD requires replacement of the affected piston pin with a part eligible for installation and, for certain engines, oil change and visual inspection of the engine oil filter, oil pressure screen, and oil suction screen for metal particulates,” the FAA said. “This AD also prohibits the installation of an affected piston pin on any engine.”
The FAA estimates the cost of compliance with the AD, which takes effect September 14, to be approximately $2,200 to $2,268.