What happened
On 6 June 2023, a Condor VTOL (registration ZT-XGK) was conducting a night-time surveillance mission over the Seriti Mine in Viljoensdrif, Free State. The operation was being performed under beyond visual line of sight (BVLOS) regulations. After completing two successful flights earlier that night, the aircraft began its third mission in autonomous mode.
During the return-to-home sequence, the pilot noted that the left-side battery power had dropped to 38%. As the aircraft approached the landing zone and transitioned from fixed-wing to multirotor mode, it began to drift toward a nearby tree. The pilot observed the aircraft spinning out of control and changing direction without manual input. Although the pilot attempted to regain manual control and descend the aircraft to a safer altitude to avoid ground personnel, the drone suddenly ceased responding to commands and impacted the ground with substantial damage. No injuries were reported on the ground.
The investigation
SACAA AIID examined flight log data and the aircraft's technical specifications. The investigation reviewed the mission track, which covered approximately 150 kilometres over a period of 96 minutes. Investigators also analyzed the aircraft's power levels and the pilot's manual interventions during the final descent phase.
Findings
- The flight duration of 96 minutes exceeded the manufacturer's stated maximum endurance of 120 minutes when considering the specific power demands of the mission, and the aircraft was likely operating on critically low battery voltage.
- During the transition to landing, the system was only receiving a signal from three satellites, whereas the user manual requires at least ten for a stable 3D GPS fix.
- The pilot selected "Q Loiter" mode during the flight instability; however, the manufacturer's manual recommends using "Q Hover" mode in such scenarios, as it functions independently of a GPS fix.
- Contributing factors included an uncommanded transition during the return-to-launch phase, a loss of situational awareness, and incorrect manual inputs during the final stage of flight.