What happened
Shortly after beginning an en route descent, the aircraft suffered a sudden and catastrophic engine failure at approximately 4,500 feet mean sea level. The pilot immediately sought a suitable location for an emergency landing and identified a nearby road. However, as he approached the roadway, a vehicle turned onto the road directly in his path. This obstruction forced the pilot to abandon the road approach and divert to a nearby field instead.
Upon touchdown in the field, the aircraft encountered significant terrain irregularities, including berms, ruts, and clumps of bushes. These obstacles contributed to the subsequent damage sustained by the airframe during the landing sequence.
The investigation
A thorough examination of the failed engine revealed that the connecting rod for the number 6 cylinder had fractured near the crankshaft end. Metallurgical analysis showed evidence of high cycle fatigue affecting approximately 60% of the material thickness, indicating a progressive failure mechanism rather than an immediate overload event.
Review of the aircraft maintenance records disclosed that since its manufacture in 1964, the airframe had accumulated a total of only 1,299 flight hours. Operational activity had been minimal, with just 109 hours flown since 1976. Further investigation into Lycoming publications indicated that the specific connecting rod part number installed on this engine had been superseded in production several times. The manufacturer explicitly stated that this particular part number was not allowed for reuse during overhaul procedures.
Findings
The manufacturer recommends an overhaul period of 1,800 hours or 10 years in service, whichever occurs first. The failure of the connecting rod was linked to its age and the specific restrictions regarding its reuse. The pilot's decision to attempt a road landing was necessitated by the sudden loss of power, but the presence of vehicular traffic prevented this option, leading to the field landing.
Safety message
Operators should ensure that all engine components comply with current manufacturer service bulletins and overhaul restrictions. Parts that have been superseded may not be reused even if they appear physically intact, as fatigue life limits may have changed or expired.