What happened
On August 23, 2020, a crew conducting PPL(A) flight training was performing navigation exercises that included arrivals and landings at the controlled Wrocław Airport (EPWR). During the initial departure from runway 29, the aircraft reached an altitude of approximately 500 to 600 feet when the engine RPM dropped by 200 to 300 revolutions per minute. The crew declared an emergency and requested to land on runway 11. The landing was completed without incident.
After taxiing to the parking apron, the crew inspected the engine parameters and found them to be within normal operating limits. Following coordination with Wrocław Tower, the decision was made to attempt a second departure from runway 29. During this second climb, once the aircraft reached an altitude of approximately 400 to 500 feet, a second drop in engine RPM of 200 to 330 revolutions per minute occurred. The crew again elected to land on runway 11, and the second landing was also completed without further consequence.
The investigation
The investigation focused on the mechanical performance of the engine following the two power loss events. A subsequent inspection of the engine revealed that an exhaust valve in cylinder number 4 had burned out.
Findings
- The primary cause of the engine power fluctuations was the burned exhaust valve in cylinder number 4.
- The failure of the valve led to a loss of combustion chamber sealing and a reduction in compression during the compression stroke, which directly resulted in the observed decrease in engine RPM.