What happened
On June 12, 2019, at approximately 17:30 UTC, a Cessna C-150 was conducting a cross-country training flight at an altitude of 1,500 ft near Nowe Miasto Airport (EPNM). During the flight, the student pilot reduced engine RPM to decrease the airspeed to 90 kt. Following this reduction, the engine began to run unevenly, and the RPM dropped from 2,500 to 2,000 despite engine parameters remaining within normal operating ranges.
In an attempt to rectify the issue, the student pilot engaged the carburetor heat. While this stabilized the RPM at approximately 2,100, the aircraft suffered a loss of power and descended 100 ft, maintaining a speed of 70 kt. Following instructions from the flight instructor, the student pilot executed a simulated engine-out landing procedure and successfully landed the aircraft without further incident.
The investigation
The investigation examined the mechanical performance of the engine following the power loss and the subsequent flight maneuvers. The inquiry focused on the cause of the engine's uneven operation and the drop in RPM during the reduction of power.
Findings
- The primary cause of the engine malfunction was a fractured exhaust valve rocker arm.
- The engine's uneven operation and subsequent power loss were directly linked to this mechanical failure within the cylinder.