Accident Overview
On 8 January 2012, a Cessna 150M, registration ZS-MAV, operated by ZS-DOV Aircraft CC, departed from Grand Central Aerodrome (FAGC) for a Private Pilot License renewal test. The crew, consisting of a flight instructor and a private pilot (student), intended to fly to the General Flying Area south of FAGC and return for landing.
History of Flight
While on the outbound leg at 7,000 ft overhead the Emeridge Dam, the engine began running rough. The instructor and student applied carburettor heat and adjusted the mixture, but engine performance did not improve and subsequently failed. Realizing the aircraft was losing altitude at approximately 100 ft per minute and would not reach FAGC, they decided to execute a forced landing on a grass field in the Modderfontein Conservancy.
During the landing roll, the aircraft collided with an earth embankment, causing damage to the right wing and the nose wheel. The cabin remained intact, and both occupants disembarked unassisted. No injuries were reported.
Aircraft and Engine Examination
The aircraft was recovered to a local Aircraft Maintenance Organisation (AMO) for engine examination. The engine could not be rotated, so a strip inspection was conducted. The number 2 cylinder was found damaged; the exhaust valve had seized in the open position, allowing the piston to strike and bend the valve at the stem. Approximately 60 litres of fuel was drained from the tanks, considered sufficient for the flight.
Probable Cause and Contributory Factor
The investigation determined the probable cause of the accident was an unsuccessful forced landing due to an engine failure. A contributory factor was the seizure of the number 2 cylinder exhaust valve in the open position during flight.