What happened
On 6 June 2008, a Mooney M20J, registration D-EBKB, was performing a private flight from Sjöbo, Sweden, toward Rügen, Germany. Approximately three to four minutes after takeoff, the engine began to lose power. The pilot attempted standard emergency procedures, including switching from the right fuel tank to the left, but the engine power continued to diminish gradually despite increasing the throttle.
Due to the low altitude, the pilot was forced to perform an emergency landing in an open, marshy field near Veber and Skåne County. During the landing, the aircraft struck a barbed wire fence and sustained substantial damage to the fuselage, wings, and landing gear. The pilot escaped the aircraft uninjured.
The investigation
The Swedish Accident Investigation Authority (SHK) examined the engine, fuel system, and fuel samples. Technical inspections of the engine and the fuel delivery system revealed no mechanical or electrical malfunctions. While analysis of the aircraft's fuel showed a mixture of different types of petrol, this was not determined to be the cause of the power loss.
However, investigators discovered that the fuel sample taken from the injector contained water. The investigation focused on how water entered the system, specifically examining the wing tank filler caps and the tank design. The investigation also looked into the maintenance history regarding the aircraft's fuel caps.
Findings
- The fuel at the engine injector contained water.
- The right wing tank filler cap failed to provide an adequate seal.
- The design of the fuel tanks allowed a small amount of water to collect at the bottom of the tanks, below the level of the drain valves.
- Deficient maintenance of the filler cap O-rings allowed rainwater to leak into the wing tank.
- It is believed that during taxiing and takeoff, this accumulated water entered the fuel suction line, eventually reaching the fuel servo and causing the engine to lose power.