History of Flight
On 24 May 2013 at 1100Z, a Mooney M20E, registration ZS-CBW, departed from Springs Aerodrome (FASI) following maintenance on its engine due to high oil consumption and rough running. The pilot, a private pilot with 102.8 total flying hours, was accompanied by three passengers. The intended destination was Heidelberg Aerodrome (FAHG), the aircraft's home base.
Engine Failure and Forced Landing
Approaching Heidelberg from the north-east, the pilot opted to orbit overhead Overkruin residential area at 7,000 feet AMSL due to traffic in the circuit. While completing a right orbit, a clanking sound was heard from the engine; approximately 30 seconds later, the engine stopped. The pilot trimmed for best glide speed (100 knots) and headed for Runway 24. A mayday call was made on Heidelberg's frequency. At 500 meters from the threshold, the pilot extended the landing gear. During the forced landing, the aircraft impacted an embankment, causing the right main landing gear to detach. The aircraft skidded across a public road and came to rest 300 meters from the threshold of Runway 24 on a heading of 315°.
Damage and Injuries
The aircraft sustained substantial damage to the fuselage, propeller, landing gear, and wings. The occupants, properly restrained by safety harnesses, evacuated unassisted and reported no injuries. There was no pre- or post-impact fire.
Investigation Findings
An engine teardown revealed that manual rotation of the crankshaft was not possible. Cylinders exhibited scoring, most notably on number 4 cylinder, where the piston pin had seized in the small end bush. The number 4 bearing journal of the crankshaft was fractured, with no evidence of oil starvation. Metallurgical analysis using stereo and scanning electron microscopy identified a fatigue mode failure under high-frequency, low-load conditions, initiating in the radius area of the number 4 connecting rod big end bearing journal. The fatigue failure had progressed over an undetermined period of operation.
Probable Cause
Unsuccessful forced landing due to an engine failure in flight. Contributing factor: The engine crankshaft had failed in fatigue mode failure.