NTSB Warns of Sticking Exhaust Valves

The National Transportation Safety Board issued safety alert SA-109 on valves that can stick in piston aircraft engines.

Updated on Nov. 4, 2026 in Auto Parts

Isometric editorial illustration of a piston aircraft engine cylinder with one exhaust valve partly raised and a dark deposit visible on its stem, in oxblood, slate, and mustard. — The National Transportation Safety Board issued safety alert SA-109 after investigating 42 accidents from 2015 to 2025 in which sticking exhaust valves in piston aircraft engines contributed to power loss. AI Illustration. Upload story photo >

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The National Transportation Safety Board issued safety alert SA-109 warning about sticking exhaust valves in piston aircraft engines. The agency investigated 42 accidents from 2015 to 2025 in which a stuck valve contributed to loss of engine power.

Why it matters

The accidents resulted in five fatalities and 12 serious injuries, making the risk a concern for pilots and owners of piston-powered aircraft. Deposits on the valve stem or in the valve guide are identified as the primary cause of sticking.

The NTSB investigated 42 accidents from 2015 to 2025 in which a stuck valve contributed to power loss, causing five fatalities and 12 serious injuries. Sticking valves can disrupt the combustion cycle in reciprocating piston engines.

The players

National Transportation Safety Board (NTSB)

The U.S. federal agency responsible for investigating civil aviation accidents and issuing safety recommendations and alerts.

The details

Deposits accumulating on the valve stem or inside the valve guide are the primary cause of sticking valves, which can be aggravated by localized overheating, infrequent flying, rapid cooling, incorrect fuel-air mixture, high ambient temperatures, low-airspeed operations and high-lead fuel. A stuck valve may produce a rough-running engine, particularly during cold starts, and depending on where it sticks it can bend pushrods; piston-powered helicopters and flight school aircraft may be particularly susceptible.

Between 2015 and 2025, the NTSB investigated 42 accidents involving stuck valves.
On Oct. 29, 2026, the NTSB issued safety alert SA-109 on sticking valves.

Seasonal Patterns

The NTSB's SA-109 alert follows the agency's established use of safety alerts to flag recurring mechanical hazards across the general aviation fleet. It places a specific engine-component failure in the context of a decade of accident investigations rather than a single incident.

Owners and pilots of piston-powered aircraft should be aware that sticking valves can cause rough running, especially during cold starts, and may lead to partial power loss. Operators of piston-powered helicopters and flight school aircraft may face the greatest exposure to this hazard.

The takeaway

Routine engine care and attention to rough-running symptoms can help pilots catch a problematic valve early, since deposit buildup is the primary cause of sticking valves.