What happened
On May 6, 2019, a Piper PA28-140, registration N5542U, was destroyed after impacting the ground near Foley Municipal Airport (5R4) in Alabama. The flight was being conducted by Lightning Aviation as a Part 91 instructional flight. The crew was performing simulated engine-out emergency procedures in the airport traffic pattern.
Witnesses observed the aircraft take off from runway 3 and, approximately 300 to 400 feet above the ground, heard the flight instructor announce that the engine had quit. Following the engine failure, the aircraft was seen pitching up into a nose-high attitude and performing an aggressive left turn before descending rapidly into the ground. The accident resulted in 1 fatality (the student pilot) and 1 serious injury (the flight instructor).
The investigation
Investigators examined the wreckage and found the aircraft had sustained heavy impact damage. The left wing was separated from the fuselage, and the engine was found with a circular impact mark on the No. 4 piston, consistent with an exhaust valve strike.
Upon inspection of the engine, investigators discovered that the No. 4 cylinder exhaust valve was stuck in the valve guide due to excessive carbon deposits. Additionally, the engine-driven fuel pump showed signs of leakage, with bubbles observed around the gasket during manual actuation and loose screws found on the pump periphery.
Maintenance records indicated that another instructor had flown the aircraft the day before the accident and reported engine roughness during simulated engine-out procedures. While the spark plugs were cleaned and the engine was returned to service, no inspection for valve sticking was performed at that time.
Findings
- The engine experienced a partial loss of power because the No. 4 exhaust valve became stuck due to heavy combustion deposits.
- The flight instructor's management of the aircraft following the power loss led to an aerodynamic stall at a low altitude.
- It is possible the aircraft was trimmed in a nose-up position at the time of the engine failure, which would have contributed to the excessive pitch-up and subsequent stall.
- Had an inspection for valve sticking been conducted following the reported engine roughness the previous day, the heavy carbon deposits likely would have been detected.