What happened
On June 25, 2022, at approximately 15:57 UTC, a Banjo ultralight motor glider, registration OK-BKC 01, crashed at České Budějovice Airport (LKCS). The pilot had informed the AFIS dispatcher of intentions to perform a local flight over the city. Shortly after takeoff from runway 09, while climbing at an altitude of approximately 100 meters AGL, the aircraft experienced a momentary engine power loss during a left turn. This loss of power triggered a left spin.
Although airport security camera footage showed the pilot managed to stop the rotation around the longitudinal axis, the aircraft continued a steep descent at an angle of approximately 70 degrees. The aircraft entered a stall at a very low altitude and impacted the grass area near the airport perimeter. The pilot sustained fatal injuries and passed away in the hospital five days later. The aircraft was destroyed in the impact.
The investigation
The ÚZPLN investigation focused on the aircraft's modifications and stability. The investigation established that the aircraft, originally a non-motorized glider, had been retrofitted with a ZDZ 210B2-J engine. This engine is specifically designed for large-scale remote-controlled (RC) aircraft and is not intended for use in manned aviation.
The investigation examined the aircraft's center of gravity (CG) and the effects of the engine installation. It was found that the engine's thrust line, located approximately 70 cm above the CG, created significant pitching moments during power changes. To counteract a nose-down moment during power increases, the pilot had previously added 4 kg of lead weights to the rear underside of the fuselage, secured only with adhesive tape.
Findings
- The engine installation significantly compromised the longitudinal stability of the aircraft.
- The fuel system utilized a low-power electric pump that failed to provide sufficient fuel during the climb, leading to the momentary power loss.
- The addition of 4 kg of lead weight shifted the center of gravity to 48% SAT, which was 10% behind the permitted aft limit.
- The combination of the aft CG and the sudden loss of power caused a rapid increase in the angle of attack and drag, leading to a loss of airspeed and an unrecoverable spin at low altitude.