What happened
On 14 December 2003, a Cessna 172, registration ZS-JOG, departed Rand Aerodrome as part of a training flight. The flight plan involved navigating to the Johannesburg General Flying area to perform holding exercises at the GAV waypoint, followed by various aerial maneuvers, including simulated forced landings.
During one of these simulated maneuvers, while the aircraft was at an altitude of approximately 200ft AGL, the pilot attempted an overshoot. During this phase, the engine failed to accelerate beyond 2100 RPM. The pilot successfully transitioned the aircraft into an open field near Evaton, resulting in a landing with no injuries and no damage to the aircraft.
The investigation
Investigators examined the engine following the incident to determine why the power loss occurred. The inspection revealed that the exhaust valve seat of the number one cylinder had come adrift, which directly caused the reduction in engine power.
To rectify the issue, a complete, serviceable cylinder was installed. Subsequent ground testing confirmed the engine was functioning correctly. Following these repairs, the aircraft was able to return to Rand Aerodrome without further difficulty. Records indicated that the most recent Mandatory Periodic Inspection (MPI) had been completed on 4 November 2003, with 92.3 flight hours accumulated since that inspection.