What happened
On October 4, 1970, a Piper PA-28-180 Cherokee, registration HB-OLS, was performing a private flight from Geneva to Neuchâtel with three passengers. While flying near Concise, the pilot noticed abnormal engine noise and vibrations. Although instrument readings remained normal, the pilot attempted to rectify the issue by adjusting the throttle, but the vibrations intensified until the engine suffered a complete failure.
Faced with the loss of power, the pilot identified a recently sown field near Grandson as a potential landing site. During the final approach, the pilot observed an elevated path approximately 1 to 1.5 meters high at the end of the field and executed a 30-degree left turn to avoid the obstacle. The aircraft landed in the field and initially rolled for about 70 meters. However, the aircraft then entered a heavily plowed area where the nose wheel sank into the soft soil. This caused the nose gear to collapse, leading the aircraft to slide on its nose and eventually flip onto its back.
The investigation
The investigation examined the wreckage of the Piper PA-20-180 Cherokee and the mechanical condition of the Lycoming engine. Investigators found that the third cylinder had been torn from the engine, with a broken piston and a deformed connecting rod that had struck the engine casing. Detailed analysis of the engine revealed traces of fretting on the crankcase halves and found that the piston ring end gap was below the manufacturer's specifications. While the engine had undergone a complete overhaul in early 1970, no specific defects related to this failure were noted in the maintenance records.
Findings
- The primary cause of the accident was a forced landing on soft terrain following an engine failure.
- The exact cause of the engine failure could not be determined with certainty, though investigators noted that a seizure of the third piston was a possible trigger.
- The pilot's decision to maneuver left to avoid an obstacle at the end of the field inadvertently directed the aircraft into the plowed section of the field.
- The aircraft sustained heavy damage, including a deformed fuselage and broken engine components, and the accident resulted in two minor injuries to passengers.