What happened
On January 23, 2008, a Cessna 150M, registration OO-RMU, was conducting a private flight starting from Charleroi Airport. After an initial stop at Spa airfield (EBSP), the pilot continued a flight intended to include a circuit around the Francorchamps race track. During the flight, while flying at approximately 2400 feet, the engine's RPM suddenly dropped from 2500 to 2200. Despite the pilot attempting to increase power by pushing the throttle to its maximum, the engine continued to lose power, eventually dropping to 1500 RPM.
Realizing an emergency landing was necessary, the pilot selected a suitable area for touchdown. The aircraft landed at a speed of 50 knots in the Fagnes de Malchamps, a marshy peat bog located approximately 3 km south of EBSP. Upon impact, the nose landing gear struck a tree trunk, causing the aircraft to overturn. The landing resulted in heavy damage to the airframe, including a severed main landing gear axle and a ripped-out nose gear leg. The accident also caused soil pollution due to fuel leakage.
The investigation
The AAIU(Be) examined the aircraft's maintenance records, the meteorological conditions, and the engine components. The investigation confirmed that the aircraft was well-maintained and had a valid airworthiness certificate. Meteorological data from Spa airfield indicated a high probability of carburetor icing, with temperatures at 4°C and a dewpoint of 1°C.
An inspection of the engine revealed no mechanical failures in the ignition, fuel, or air intake systems. However, the spark plugs showed evidence of an abnormally rich mixture, which is consistent with the presence of ice in the carburetor. The investigation also noted that while the pilot had used carburetor heat during the flight, the specific procedure was not applied once the engine power began to decline.
Findings
- The primary cause of the engine power loss was carburetor icing.
- The pilot did not apply the carburetor heat after the initial drop in RPM, likely due to a fear of further power loss.
- The pilot experienced a loss of situational awareness, as the aircraft was within gliding distance of EBSP when the engine trouble began.
- The choice of landing site, while appearing flat from the air, was a soft, marshy peat bog that contributed to the aircraft overturning.
- Meteorological conditions were highly conducive to ice formation.