Sticking Exhaust Valves Linked to 42 Accidents, NTSB Warns

Sticking exhaust valves caused or contributed to 42 aircraft accidents investigated by the National Transportation Safety Board from 2015 through 2025. Five people died and 12 suffered serious injuries. The agency issued a safety alert on October 29, 2026, warning pilots and mechanics that the problem can cause severe vibration and sudden engine power loss.

Low altitude makes the danger more acute. A failing cylinder can reduce power during takeoff or landing, leaving crews little time to react. Yet the NTSB says owners can often detect warning signs before flight.

Forty-two accidents reveal a recurring engine hazard

The NTSB’s Safety Alert SA-109 covers piston-powered aircraft, including training airplanes and helicopters. It identifies 42 investigated accidents involving stuck valves and engine power loss over an 11-year period.

Those cases produced five deaths and 12 serious injuries. However, the total does not represent every piston-engine accident during those years. It covers cases the agency associated with this particular failure.

Unlike a new airworthiness directive, the alert does not ground a fleet or impose a universal inspection deadline. Instead, the NTSB urges aircraft owners, operators and maintenance professionals to identify and correct problems early.

How an exhaust valve can rob an engine of power

Each engine cylinder has an exhaust valve that releases burned gases. The valve slides through a metal guide as the engine runs. Deposits on the valve stem or guide can obstruct that movement.

As a result, the cylinder may stop producing power normally. Pilots can experience rough running, strong vibration and reduced engine output. In some cases, a stuck valve also bends a pushrod, which helps operate the valve mechanism.

The NTSB identifies several conditions that promote deposits. These include local overheating, infrequent flying and sudden engine cooling. An incorrect fuel-air mixture can also contribute. High temperatures, reduced cooling airflow and lead-rich fuel are additional factors.

Flight schools and piston-powered helicopters deserve particular attention. Training aircraft often make repeated short flights, while some helicopters operate at higher engine temperatures. These conditions can increase exposure, but they do not mean every aircraft in either group has a faulty engine.

A fatal Cessna crash shows why warning signs matter

On May 25, 2022, a Cessna 172F crashed near Show Low, Arizona, during a second takeoff attempt. Both occupants died. Witnesses had heard the engine sputtering during the first attempt and subsequent taxi.

The pilot returned for another takeoff after an engine run-up. Investigators later found deposits that had caused the No. 4 cylinder’s exhaust valve to stick. The NTSB said the accident likely could have been avoided if maintenance personnel had examined the airplane before the second attempt.

A separate case involved a Piper PA-32 on May 8, 2024. It lost power after takeoff and made a forced landing. Mechanics found carbon buildup affecting exhaust valve guides in five cylinders. The pilot had reported three earlier episodes of cylinder power loss.

The Piper’s maintenance records also showed no evidence of compliance with a relevant manufacturer service bulletin. The NTSB said recommended inspections likely would have detected the deposits. These findings concern the specific accidents, not every instance of engine roughness.

Three symptoms warrant attention before takeoff

The alert identifies rough running, especially with a cold engine, as a possible warning. It also highlights unusually low exhaust gas temperature or cylinder-head temperature, often in one cylinder.

However, none of these readings proves that a valve has stuck. Other engine faults can produce similar symptoms. Pilots should follow their aircraft’s approved operating procedures and have unexplained abnormalities evaluated by qualified maintenance personnel.

For owners and operators, the NTSB recommends oil and air-filter changes at manufacturer intervals. It also advises pilots to use the approved procedures for adjusting the fuel-air mixture. Proper mixture management can help limit deposits.

Mechanics, meanwhile, should examine engine-monitoring data, check cooling baffles and follow manufacturer instructions for evaluating valves and guides. The NTSB specifically points to Lycoming and Continental technical guidance, including Lycoming Service Bulletin 388C.

What the warning changes for pilots and operators

The immediate consequence is a maintenance and decision-making warning, not a new FAA regulation. A pilot who notices rough engine operation before departure has a chance to stop, seek an inspection and avoid a problem at low altitude.

For flight schools, recurring abnormalities merit documented investigation rather than repeated acceptance as normal. Similarly, helicopter operators should consider the engine temperatures and operating patterns identified by the NTSB when following applicable manufacturer guidance.

The agency’s findings also show why accident investigations can change everyday safety decisions. AeroSillage has examined the NTSB’s reconstruction of a Colorado training-aircraft crash and a separate FAA helicopter safety oversight audit. Neither establishes a link to this valve failure.

The NTSB’s message is specific: identify suspicious engine behavior, investigate the cause and follow approved maintenance guidance before the next flight.