What happened
On April 23, 2009, a Cessna TU206F, registration OE-KPC, was conducting a private VFR flight from Albacete to Reus when the aircraft experienced a total engine failure. While cruising at 7,000 feet near the coast, the pilot performed a "sweep turn" to check for nearby traffic. During this maneuver, the pilot noticed oil appearing on the windshield and observed a drop in oil pressure and temperature. Shortly after, the engine stopped completely, and the aircraft lost all radio communications.
During the subsequent descent, the pilot attempted to restart the engine. This attempt caused a 150A fuse to blow, which isolated the main battery from the electrical distribution system. This failure rendered the flaps inoperative, preventing the pilot from reaching a suitable landing spot on the beach. The aircraft ultimately performed a water landing near Moncofa, where it flipped upside down. The pilot and one passenger were rescued by bystanders and sustained serious and minor injuries, respectively.
The investigation
The CIAIAC examined the wreckage, the engine, and the FADEC (Full Authority Digital Engine Control) data. The investigation focused on the engine's internal condition, the electrical system configuration, and the flight manual instructions. Investigators analyzed the FADEC recordings, which revealed a series of rapid altitude and load factor changes—described as a "roller coaster" maneuver—immediately preceding the drop in oil pressure. The inspection of the engine revealed catastrophic internal damage, including destroyed connecting rods and pistons, and evidence of overheating on the crankshaft pins.
Findings
- The primary cause of the accident was the engine failure due to improper lubrication, which led to the seizure of internal components.
- A sudden maneuver (push-over and pull-up) triggered a significant drop in oil pressure, which, combined with previous periods of insufficient lubrication, caused the engine to fail.
- The attempt to restart the seized engine caused the 150A fuse to blow, which subsequently disabled the flaps and communications systems.
- The electrical system design, as approved by the STC, lacked a redundant power source for essential equipment on the main bus if the primary battery was isolated.
- The flight manual's instructions regarding in-flight restarts were insufficient, as they did not adequately warn the pilot of the potential for a total electrical failure following a blocked engine restart attempt.