What happened
On October 11, 2019, a Beechcraft F33A Bonanza, registered as D-ETEG, departed from Zurich Airport (LSZH) following an instrument departure procedure. While climbing at approximately 3,800 ft, the pilot declared a Mayday due to a sudden engine failure. The pilot subsequently communicated an intention to land on the opposite runway and executed a left turn to return to the airport. The aircraft successfully performed an emergency landing on runway 10, though it eventually exited the runway via taxiway Juliet during the rollout.
The investigation
The investigation by SUST focused on the mechanical state of the engine and the maintenance history of the aircraft. The engine, a Continental IO-550-B, was 18 years old with 1,427 hours since its last overhaul, exceeding the manufacturer's recommended 12-year/1,700-hour interval. Investigators examined the engine's internal components and found catastrophic damage, including broken and deformed connecting rods in cylinders #1 and #3, a fractured camshaft, and a piston stuck in cylinder #1. A significant amount of metal debris was found in the oil filter.
Additionally, the investigation reviewed maintenance records, noting that the aircraft had experienced several long periods of inactivity without following manufacturer-recommended engine preservation procedures. The investigation also examined the engine monitoring data from the aircraft's EDM 800 device and various oil analysis reports.
Findings
- The engine failure was most likely caused by age-related pre-existing damage.
- Multiple oil analysis reports had previously flagged high levels of iron, aluminum, chromium, and nickel as "alarming," yet no effective corrective actions were taken.
- The engine was not properly preserved during long periods of storage, contrary to manufacturer guidelines.
- While the pilot's response to the failure was appropriate, the internal engine components had likely suffered from corrosion or wear that went undetected by standard inspections.