What happened
On the night of 3 March 2023, a DJI Matrice 300 RTK drone, registered as ZT-YHM, was conducting a night-time surveillance mission at the African Explosives and Chemical Industries (AECI) facility in Modderfontein, Gauteng. The operation was being performed under beyond visual line of sight (BVLOS) regulations as part of a Part 101 mission.
After successfully completing seven previous flights that evening, the pilot launched the eighth mission at approximately 2200Z. Shortly after reaching an altitude of 656 feet, the pilot received an electronic speed control (ESC) error message. While the error initially disappeared, a series of subsequent warnings appeared on the controller, including high wind velocity, a propeller malfunction, and a notice that the aircraft was pitching sharply forward. The drone then entered an uncontrolled spiral dive, impacting the ground. The pilot attempted to execute an emergency landing and a return-to-home function, but was unable to prevent the crash. The aircraft sustained substantial damage, though no injuries were reported on the ground.
The investigation
SACAA AIID examined the flight log data and technical reports provided by the operator. The investigation confirmed that the pilot held a valid Remote Pilot Licence and a current medical certificate. The aircraft's maintenance was up to date, having been inspected in January 2023, and the operator held a valid operating certificate.
Meteorological data from the South African Weather Service indicated calm conditions, with winds at approximately 6 knots. Because the maximum wind resistance for the DJI Matrice 300 RTK is significantly higher than the recorded conditions, investigators determined that weather was not a contributing factor to the accident.
Findings
- The primary cause of the accident was the failure of the ESC due to a possible low battery voltage, which led to a loss of control and the subsequent spiral dive.
- Flight logs indicated a sequence of critical warnings, including a propeller detachment and motor issues, immediately preceding the descent.
- The pilot was able to maintain visual contact with the aircraft at the time of the failure, as the distance was approximately 400m.