What happened
On July 23, 2009, a Weedhopper Europa II, registration CS-UCX, operated by Aero Clube de Bragança, was involved in a technical incident near Sacoias, Bragança. The aircraft had been taken out of its hangar for a routine engine run-up following a period of approximately two months of inactivity. Although the pilot had not originally planned a flight, they decided to perform a short local flight to provide the engine with some activity after the prolonged immobilization.
While flying at an altitude of approximately 1,000 feet, about 3km from the aerodrome, the pilot experienced a partial loss of engine power accompanied by RPM fluctuations and engine surges. After unsuccessful attempts to restore power via the throttle, the pilot executed a precautionary landing in an unpaved agricultural field that had been recently harvested. During the landing roll, the aircraft struck a straw bale left in the field. The impact caused the nose gear to fracture and the left wing to strike the ground, resulting in damage to the nose wheel and the left wing.
The investigation
The GPIAAF investigation focused on the engine's performance and the aircraft's maintenance status following its long period of storage. The investigation established that the aircraft had not undergone the manufacturer-recommended preservation procedures for long-term immobilization, such as engine inhibition or fuel tank draining. The fuel mixture had remained in the tanks for over 70 days since the last significant refueling.
Findings
- The primary cause of the partial power loss was the failure to drain the fuel tanks, combined with the long-term storage of the fuel-oil mixture, which led to the deterioration of fuel quality and the formation of deposits.
- The presence of straw bales in the landing area acted as a contributing factor that led to the structural damage of the nose gear and the wing strike.
- The engine, a Rotax 582 UL, was operating on aged fuel where the two-stroke oil had likely settled, compromising the lubrication and fuel delivery.
Safety action
To prevent similar occurrences, the following actions were recommended to the Aero Clube de Bragança:
- Adherence to manufacturer-recommended preservation procedures for engines and aircraft during periods of prolonged immobilization.
- Ensuring that aircraft using two-stroke fuel-oil mixtures are refueled with fresh mixture as needed prior to flight.
- Strict execution of pre-flight inspections, specifically including the complete draining of fuel tanks to remove any accumulated water.