What happened
On May 11, 2008, a Beechcraft 77 Skipper, registration EI-BHT, departed from Ireland West Airport Knock for a private flight to Weston Aerodrome. Shortly after takeoff, the pilot notified Air Traffic Control of engine vibrations and requested to return to the airport. The situation deteriorated quickly as the engine lost power, prompting the pilot to declare a PAN urgency signal.
Unable to maintain altitude, the pilot attempted an emergency landing in a field near Kilmovee, Co. Mayo. The terrain in the area was difficult, featuring an undulating surface and a steep upslope. The aircraft impacted the ground in a steep, nose-down attitude. The pilot sustained fatal injuries, while the passenger suffered serious injuries.
The investigation
Investigators examined the wreckage and the engine, an Avco Lycoming O-235-L2C. Metallurgical analysis of the engine components revealed that a fatigue fracture had occurred in the head of the number 2 inlet valve. A fragment from this fracture had migrated to the number 4 cylinder, contaminating the area. This debris, along with disrupted airflow in the inlet manifold, led to the total engine failure.
While the investigation identified overheating as the initial cause of the valve fracture, the specific reason for the overheating could not be definitively established. The investigation also noted that the aircraft's Certificate of Airworthiness had expired one week prior to the accident and that the pilot's seatbelt, a single diagonal harness, failed to adequately restrain the pilot during the impact rotation.