What happened
On May 9, 2002, at 14:30, a Beechcraft Be K 35 Bonanza, registration HB-EGW, was conducting a VFR flight from Figari to Lausanne. While approximately 30 nautical miles from Cannes aerodrome at flight level 65, the pilot notified Nice Information of an engine issue characterized by smoke in the cabin and the smell of oil.
As the pilot attempted to reach the airfield, the engine oil pressure dropped, and the engine ceased functioning approximately six nautical miles from the airport. During an attempt to land on runway 2cap, the aircraft struck the top of a tree and crashed into the courtyard of a residence located 220 meters from the threshold of runway 23. The accident resulted in two fatalities.
The investigation
The investigation focused on the mechanical failure of the Continental IO-470-C engine. Metallurgical examination of the engine revealed a fatigue fracture in the cylinder barrel of cylinder number one. This crack originated on the outer wall of the barrel in an area of extreme corrosion located between two cooling fins.
Investigators determined that the crack was not a recent development, noting evidence of burnt gas leaks and heavily matte surfaces on the fractured areas. The failure of the cylinder led to a progressive loss of oil from the lubrication system, which caused overheating and the eventual complete wear of the forward cylinder bearings, ultimately resulting in a total engine seizure. Additionally, a witness reported that the pilot was aware of an oil leak prior to departure from Figari but did not consider it a significant risk.
Findings
- The primary cause of the engine failure was a fatigue fracture of the cylinder barrel initiated by heavy corrosion in a difficult-to-access area.
- The loss of lubrication caused by the cylinder breach led to overheating and the complete seizure of the engine.
- The aircraft was operated despite a known, though seemingly minor, oil leak present before takeoff.