What happened
On 11 July 2020, a Cessna FR172K Hawk XP, registration EI-EZU, was performing a general aviation flight from Rathcoole Aerodrome to Tibohine Airfield. While flying near Loughrea, Co. Galway, the pilot observed a drop in engine oil pressure accompanied by oily smoke emanating from the engine cowling. Shortly thereafter, the engine failed completely.
The pilot issued a MAYDAY call to Shannon Air Traffic Control and initiated an emergency descent. While attempting to reach a suitable landing site in an agricultural field near Killimordely, the aircraft's airspeed decreased. During a maneuver to avoid an obstacle, the aircraft likely experienced a stall and a left wing drop, impacting the ground hard. The impact caused substantial damage to the aircraft and resulted in two serious injuries to the pilot and passenger. Passers-by arrived at the scene quickly to assist the occupants from the wreckage.
The investigation
The AAIU examined the wreckage and the engine components to determine the cause of the power loss. Investigators reviewed the pilot's flight logs, which indicated the frequent use of automotive gasoline (Mogas) for refueling. The investigation also analyzed cockpit photographs taken during the flight, which showed instrument readings prior to the failure. Technical examination of the engine revealed physical damage to the pistons and bearings, and investigators checked the aircraft's maintenance and airworthiness records.
Findings
- The engine failure was caused by piston damage consistent with detonation.
- The aircraft was routinely fueled with Mogas, which is not approved for this engine type and lacks the detonation resistance of Avgas.
- The engine's ignition timing was found to be advanced by 2 degrees.
- During the forced landing, the aircraft's airspeed decreased due to an increase in altitude, likely leading to a stall and wing drop.
- The occupants were wearing lap belts, but the shoulder harnesses were not in use during the flight.
- The aircraft's airworthiness and the pilot's licenses were all valid at the time of the accident.