What happened
On May 27, 2007, a Diamond DA40D aircraft, registration OH-FDA, performed an emergency landing in the sea near the coast of Helsinki. The flight, operated by Polyteknikkojen Ilmailukerho ry, was intended to be a flight from Helsinki-Malmi to Tallinn and back.
During the initial climb, the pilot noted power fluctuations between 80% and 100% for several seconds. While engine instruments appeared normal, the pilot sensed a lack of power. Upon engaging the autopilot, the engine suddenly began to overrev. The pilot attempted to troubleshoot the issue, suspecting a fuel supply or FADEC malfunction, but realized the aircraft could not reach land.
At approximately 700 feet, the pilot determined an emergency water landing was necessary. The aircraft was landed in the strait between Valkosaari and Katajanokka, coming to a stop about 15 meters from the Valkosaari shoreline. The pilot and two passengers successfully evacuated onto the aircraft wings and were rescued by a nearby boat and subsequently a police patrol boat. There were no fatalities and no injuries were reported.
The investigation
The investigation focused on the mechanical failure of the propeller gearbox. Upon inspection, investigators found that the friction surfaces on the clutch plate were worn. Data from the FADEC unit was analyzed by German authorities to examine engine performance and error logs. The investigation also examined the presence of oil leaks and the engine's ventilation system.
Findings
- The primary cause of the emergency landing was clutch slippage caused by oil leaking into the clutch housing.
- The leak originated from a damaged crankshaft seal, which was likely caused by high crankcase pressure.
- An external oil leak from a double oil pump had been present for approximately 1.5 months; this leak had masked the more critical crankshaft seal leak.
- The aircraft lacked a system to indicate clutch slippage to the pilot.
- The engine's propeller RPM was calculated based on a gear ratio rather than being measured directly, making it difficult to detect the slippage through standard instruments.
- The pilot did not use flaps during the water landing, which slightly increased the touchdown speed.