Flight Sequence
On the morning of 1 April 1997, a student pilot departed Lugano-Agno Airport for a training flight in preparation for his private pilot license exam. The flight proceeded normally through the first circuit. After a touch-and-go landing, during the climb over the lake at approximately 150 meters, the engine stopped abruptly and the propeller locked. The student pilot radioed the tower, declared an emergency, and began looking for a landing spot. He spotted a field to his right and headed towards it, shutting off the fuel valve, magnetos, master switch, and lowering full flaps. During the final glide, the right wingtip struck the roof of a house and hit a chimney. The impact caused the aircraft to spin 360°, reducing its speed. It then fell from about 10 meters onto the grass in front of the house, where the nose wheel absorbed some of the impact. The aircraft came to a stop 20–30 meters from the house. The pilot was uninjured but suffered severe shock. The aircraft was destroyed. The house roof was damaged; the grass field and minor fuel spillage did not cause further damage.
Findings
The pilot held a valid student pilot license and had 43 hours total flight time. A breath alcohol test was negative. The instructor, monitoring from the ground, heard the mayday call but received no response to his instructions. The aircraft's mass and balance were within limits. The airworthiness certificate was valid. The seatbelt was used and held. The aircraft had no ELT. Routine inspections had been performed. Before impact, the pilot had closed the fuel valve, magnetos, and master switch; flaps were fully extended. The left fuel tank, intact, contained about 20 liters; the right tank was destroyed but held about 7 liters. Maintenance records showed a history of engine issues: in December 1996, aluminum filings were found in the oil filter, leading to cylinder replacement and overhaul. After repair, a test pilot noted the propeller stopped after one rotation. The mechanic attributed this to a tight engine. Subsequent complaints of hard propeller rotation when hot led to further checks, but no problems were found. A 200-hour inspection on 3 March 1997 revealed no issues. At the time of the accident, the engine had 1,783 hours.
Technical Analysis
A technical examination by the Swiss Aircraft and Systems Enterprise (SF) at Lodrino found:
- The crankcase had a hole in the lower right side caused by connecting rod No. 3 separating from the crankshaft.
- Connecting rods 1, 2, and 4 showed no overheating; rod No. 3 was broken with clear signs of overheating on both the rod and crankshaft.
- Main bearing No. 3 was in an abnormal position with evidence of vibration and axial sliding.
The engine stoppage was due to the failure of connecting rod No. 3. The rod failure was caused by excessive friction from the rod bearing on the crankshaft due to lack of lubrication. The dark coloration indicated severe overheating originating at the rod bearing. The lubrication failure occurred because oil flow to the rod bearing was blocked when main bearing No. 3 shifted out of its seat, misaligning the oil holes. The bearing shift was caused by wear of the contact surfaces of the crankcase halves at the No. 3 bearing support, consuming a total of 0.15 mm of material. This wear allowed the bearing to move; axial sliding marks were evident. Radial movement was limited by the locating tab, whose recess was visibly eroded.
Cause
The accident resulted from an emergency landing on difficult terrain (residential area) necessitated by an engine failure.