What happened
On April 1, 1997, a student pilot was conducting a flight training session at Lugano-Agno airport, performing circuit patterns and precision landings. During a climbing turn over a lake at approximately 150 meters altitude, the engine of the Reims/Cessna RA F152, registration HB-CGV, abruptly stopped, causing the propeller to cease rotation after only one revolution.
Recognizing the emergency, the pilot notified the control tower and immediately began searching for a suitable landing site. The pilot identified a meadow to the right and initiated an emergency descent, performing necessary procedures such as closing the fuel valve, turning off the magnetos and master switch, and extending the flaps. During the final glide, the right wingtip struck a chimney on a house, which caused the aircraft to spin 306 degrees and significantly reduced its forward speed. The aircraft then dropped from about 10 meters onto the meadow, coming to rest approximately 20 to 30 meters from the building. The aircraft was destroyed in the impact, and the house roof sustained damage, but the pilot escaped without injury.
The investigation
Technical experts examined the Lycoming 0-235 L2C engine to determine the cause of the sudden power loss. The investigation revealed that the engine's third connecting rod had detached from the crankshaft. This failure was traced back to excessive friction and overheating at the third main bearing.
Further analysis of the engine crankcase showed that the bottom right section had been punctured by the detached connecting rod. The investigation also noted that the third main bearing had shifted from its original position due to significant wear on the contact surfaces of the engine'set halves. This displacement caused the oil passages to become misaligned, effectively blocking the flow of lubricant to the connecting rod bearing.
Findings
- The primary cause of the engine failure was the failure of the third connecting rod.
- This failure was driven by a lack of lubrication to the third connecting rod bearing.
- The lubrication failure occurred because the third main bearing moved out of its seat, which obstructed the oil delivery path.
- The displacement of the bearing was caused by excessive wear (totaling 0.15 mm) on the mating surfaces of the engine crankcase halves.
- The pilot demonstrated significant composure and followed emergency procedures effectively during the engine failure and subsequent landing.