Piper PA28 N5542U accident near Foley, Alabama

Probable cause

A partial loss of engine power due to a stuck exhaust valve and the flight instructor's exceedance of the airplane's critical angle of attack following the loss of power, which resulted in an aerodynamic stall at low altitude.

NTSB analysis

The flight instructor and student pilot were conducting simulated engine-out emergency procedures in the airport traffic pattern. About 300-400 ft above ground level after takeoff, witnesses reported that the flight instructor announced on the radio that the engine had quit. Witnesses reported that the airplane then entered a nose-high, steep left turn before pitching down and impacting the ground.

Postaccident examination of the airframe and flight controls revealed no mechanical anomalies that would have precluded normal operation. Examination of the engine revealed that the No. 4 cylinder exhaust valve was stuck in the valve guide due to excessive combustion deposits. It is likely that the stuck exhaust valve resulted in a partial loss of engine power.

A flight instructor who flew the accident airplane the day before the accident flight reported experiencing engine roughness when performing simulated engine-out procedures. Following that flight, a mechanic cleaned the sparkplugs, performed an engine run-up, and returned the airplane to service; however, maintenance records did not show that the engine valves were inspected for sticking at that time. Manufacturer service instructions suggested inspecting for valve sticking at regular intervals or sooner if sticking was suspected. If a valve inspection had been completed in accordance with engine manufacturer guidance the day before the accident following the report of engine roughness, it is likely that the heavy carbon deposits on the exhaust valve would have been detected.

Given that the flight instructor reportedly had students trim the airplane nose-up when landing, it is possible that the airplane was trimmed nose-high at the time of takeoff and the subsequent loss of engine power. Such a trim setting would have led to excessive pitch up, resulting in a rapid loss of airspeed, an exceedance of the airplane's critical angle of attack, and an aerodynamic stall at low altitude.

Text from the NTSB. Open the NTSB docket for ERA19FA164 for the full record.