Summary
On 19 July 1990, at 1712 local time, a Cessna C-172 N, registration HB-CEX, experienced a total engine failure while on final approach to runway 34 at Luzern-Beromünster. The pilot, accompanied by three passengers, was returning from a private scenic flight. The aircraft contacted a power line and overturned, coming to rest inverted. The pilot and two passengers sustained minor injuries, and one passenger suffered serious injuries. The aircraft was heavily damaged, and third-party damage occurred to a power line, a building, and land.
Accident Sequence
The flight departed Luzern-Beromünster at approximately 1625 hours for a 45-minute scenic flight. The pilot reported cruising between 3,500 and 4,500 feet, adjusting the mixture. The approach to runway 34 progressed normally until final approach, after the pilot had extended full flaps. The engine began to knock. The pilot performed a final check, noting the mixture was set to rich and switching off carburetor heat, which had been applied during the approach. All engine instruments indicated within the green arc. Attempting to stabilize RPM by adding power, the engine speed decreased to a complete stop. A restart attempt failed. With the stall warning sounding, the pilot maneuvered to avoid houses. The landing gear struck a power line, causing the aircraft to flip onto its back. The pilot shut off the master switch and ignition and evacuated the passengers.
Aircraft and Engine Information
The aircraft was a Cessna C-172 N, operated by FLUBAG Flugbetriebs AG. The engine was an AVCO Lycoming 0-320-D2J, built in 1980, rated at 160 horsepower. At the time of the accident, the engine had accumulated 1,804.30 total hours, with 1,741.18 hours since its last overhaul. The last 200-hour inspection was performed on 26 June 1990. The engine had been overhauled on 2 August 1982 by IFC Industrie-Flugdienst in Munich and installed in HB-CEX on 4 April 1985.
Investigation Findings
Investigators determined that the engine failure resulted from a broken camshaft drive mechanism. Disassembly revealed three teeth fractured on the intermediate gear of the camshaft drive. The Swiss Federal Laboratories for Materials Testing and Research (EMPA) conducted fractographic and metallographic analysis, concluding that the tooth fractures were caused by fatigue. The core hardness of the gear was measured at 520 to 530 HV1, slightly above the normal limit of HG450 per DIN 50190. However, no other contributing deficiencies were identified. The investigation could not determine whether the fatigue cracks initiated due to the elevated core hardness or from prior damage during a hard stop that was not replaced during the overhaul. This type of engine failure was characterized as an isolated occurrence.
Cause
The accident was attributed to an emergency landing attempt during final approach that resulted in contact with obstacles following a total engine failure due to technical reasons, specifically a fatigue fracture of a camshaft drive gear tooth.