What happened
On 4 November 2000, an Enstrom F-28A, registration G-BWOV, was conducting a private flight from Bishops Waltham toward Goodwood. Shortly after the pilot began a gentle climb near Waterlooville, a vibration was felt in the cyclic controls. This was immediately followed by a loud bang, smoke entering the cabin, and a significant yaw to the right.
Recognizing the emergency, the pilot initiated an autorotative descent and turned the aircraft away from built-up areas to avoid populated zones. The pilot successfully performed a run-on forced landing in a large field. There were no injuries to the pilot during the incident.
The investigation
Investigators examined the Lycoming HIO-360-C1A engine and recovered fragments from the engine tray. The analysis revealed that the big end of the No.2 connecting rod had failed, causing it to break out of the top of the crankcase.
While the crankshaft journals showed no signs of lubrication loss, the examination of the No.2 connecting rod big end components identified high cycle fatigue in the cap. The failure of the cap bolts and the rod itself were attributed to high strain and bending overloads. Furthermore, the manufacturer identified evidence of galling on the big-end cap, a type of surface damage typically caused by engine overspeeding.
Findings
- The primary cause of the engine failure was a tensile fatigue failure of the connecting rod big end cap.
- The presence of galling on the cap suggests the engine may have experienced an unreported overspeed event after its last major inspection.
- This galling likely acted as the initiation point for the fatigue crack.
- The failure of the cap subsequently caused the connecting rod and bolts to fail due to extreme secondary loads.