What happened
On September 20, 2015, a Glasair RG homebuilt aircraft, registration HB-YEA, was conducting a VFR flight from Grenchen to Triengen. While cruising at approximately 3,000 feet, the aircraft experienced a sudden engine failure. Witnesses observed white and black smoke trailing from the engine as the aircraft began a rapid descent.
Unable to maintain altitude, the pilot attempted an emergency landing in a field near the A1 motorway in Kölliken. During the landing sequence, the aircraft crossed an asphalt path, which caused the plane to bounce back into the air. The aircraft then struck a roadside guardrail, which sheared off all three landing gear wheels. Immediately following this impact, the left leading edge of the wing struck a passing car on the road, causing the vehicle to flip onto its roof. A fire brokeered in the aircraft, likely caused by hot oil spraying onto the exhaust manifold during the engine failure. Although a bystander managed to pull the pilot from the cockpit, the pilot succumbed to his injuries later that evening. The driver of the car sustained significant injuries but was rescued from the overturned vehicle.
The investigation
SUST investigators examined the engine components and the aircraft's maintenance history. The investigation focused on the mechanical state of the Lycoming IO 360 engine and the circumstances of the emergency landing. Investigators also reviewed the maintenance program approved by the Federal Office of Civil Aviation (FOCA), which allowed for an extension of the engine's calendar life limit subject to specific inspections.
Findings
- The engine failure was caused by the failure of connecting rod number 3.
- The failure was attributed to micro-fatigue cracks that exhibited signs of corrosion and soot deposits.
- The pilot's decision to land in the field was appropriate given the low altitude at the time of the failure.
- The impact with the guardrail and the subsequent collision with the vehicle were unavoidable once the aircraft's path intersected the roadway.
- The fire spread rapidly due to the rupture of the main fuel tank during the collision with the car.