What happened
On May 6, 2016, a Scheibe SF25A motor glider, registration F-CAQV, was performing a local flight at the Oyonnax Arbent airfield. The pilot, accompanied by one passenger, was completing a landing approach on runway 22. During the final approach, the pilot observed a PA28 aircraft taxiing toward the runway threshold for takeoff. To avoid landing on the unpaved grass area, the pilot decided to execute a go-around.
After restarting the Rotax 447 engine, the pilot applied full power at an altitude of approximately 60 meters. However, the aircraft failed to climb effectively, feeling unusually heavy. The pilot attempted a turn to land on the opposite runway, but the aircraft lost altitude, entered a steep left bank, and struck trees before impacting the ground. The impact resulted in two slight injuries and the destruction of the aircraft.
The investigation
Investigators examined the wreckage of the F-CAQV and the engine components. Although the owner had partially dismantled the wreckage prior to the investigators' arrival, the BEA was able to recover the engine and fuel tank. Analysis of the engine revealed that the Rotax 447 was running on unleaded fuel without any added oil. This lack of lubrication caused superficial interference between the pistons and cylinders and deep scratches in the front cylinder, which likely led to a loss of compression and power.
Further technical analysis determined that the aircraft was approximately 55 kg over its maximum allowable mass of 485 kg. Additionally, while the pilot used a portable radio, the aircraft was not equipped with a fixed VHF radio.
Findings
- The engine was operating under improper conditions; the use of fuel without the required 2% oil mixture likely caused a partial seizure and a subsequent loss of engine power.
- The aircraft was in an overweight condition, which significantly degraded its climb performance during the go-around.
- The pilot's decision to execute a go-around was driven by the desire to avoid the unpaved runway, but the subsequent decision to attempt a landing on the opposite runway was not justified given the aircraft's altitude, performance limitations, and existing airfield traffic.