History of Flight
The pilot, the sole occupant of the aircraft, departed Rustenburg Aerodrome (FARG) for Springs Aerodrome (FASI) on a private flight. The flight of approximately one hour was uneventful until the pilot reduced engine power slowly while on the downwind leg for landing at Springs at an altitude of approximately 6400 ft AMSL. At that point, the engine suddenly vibrated and stopped during flight. The pilot made a blind transmission on radio frequency 122.4 MHz reporting an engine failure and subsequently landed safely onto Runway 03 at Springs Aerodrome.
Damage and Investigation
The aircraft sustained no damage during the forced landing. However, upon inspection, the pilot observed damage to the engine and propeller. The engine had experienced an in-flight contained failure, resulting in distortion of the engine mounting cradle and denting of the bulkhead behind the engine. The propeller was substantially damaged when the engine stopped abruptly.
The engine was recovered to an approved maintenance organization for investigation. Examination revealed that the No. 2 cylinder head inlet valve had contacted the piston crown, and the piston crown severed from the connecting rod at the gudgeon pin holes. The No. 2 cylinder gudgeon pin had migrated forward out of its attachment hole, with strike marks on the forward side of the crankcase. One gudgeon pin retainer wire circlip was found in the engine sump, along with three pieces of the gudgeon pin. The connecting rod was bent into a U shape.
Probable Cause
The probable cause was engine failure due to mechanical failure and a successful forced landing followed. A contributory factor was that the No. 2 piston gudgeon pin wire retainer circlip became adrift, causing the gudgeon pin to migrate forward out of position and subsequently causing substantial damage to the engine that stopped abruptly.