What happened
On the evening of 10 June 2023, an Arace Sirin unmanned aircraft system, registered ZT-WZR, was conducting a night-time surveillance mission for Sibanye Stillwater Protection Services in Carletonville, Gauteng. The flight was being operated under beyond visual line of sight (BVLOS) regulations.
Following a standard pre-flight inspection, the pilot launched the aircraft. Initially, the drone climbed and maintained a steady hover at approximately 5 to 10 metres. However, as the pilot attempted to transition from altitude hold mode to loiter mode to test maneuverability, the remote pilot station issued a warning regarding potential thrust loss on one of the motors. The aircraft immediately lost altitude and descended rapidly, ultimately crashing into a wall. There were no injuries resulting from the incident, though the aircraft sustained substantial damage.
The investigation
SACAA AIID examined the flight logs and hardware following the incident. The investigation focused on the discrepancy between the battery voltage readings displayed on the pilot's station and the actual voltage of the battery at takeoff. While the pilot's screen indicated a healthy 23V, physical inspection of the battery revealed a much lower voltage of 10.6V at the time of launch.
Technical analysis of the flight logs confirmed that the aircraft experienced a loss of thrust on motor 2, which triggered the rapid descent. The investigation also considered the impact of the local environment, noting that the high density altitude of the South African Highveld compared to the manufacturer's home base in Hungary can affect performance. Additionally, it was noted that the aircraft was carrying a transponder, which increased its takeoff weight beyond the standard configuration.