What happened
On the night of 23 December 2021, a DJI Matrice 200 drone, registered as ZT-WVS, was conducting a night-time surveillance mission in the Sibanye area of Westonaria, Gauteng. The operation was being performed beyond visual line of sight (B-VLOS) under Part 101 regulations. During the tenth flight of the night, the pilot transitioned the aircraft into a fly-by-wire mode to inspect a specific location near the landing site.
While flying at approximately 330 feet above ground level, the pilot observed an orange caution alert on the control interface regarding the Inertia Measurement Unit (IMU) attitude. Immediately following this alert, the video feed began to spin violently, and the aircraft entered a rapid descent. The drone failed to execute a return-to-launch procedure. The aircraft eventually struck a tree roughly 50 feet tall, located 174 metres from the departure point. The impact resulted in the destruction of the aircraft, though no injuries or property damage were reported.
The investigation
An analysis of the post-accident flight logs revealed that a mechanical and electronic failure occurred during the mission. Investigators determined that a bearing in one of the rear motors had ceased, which triggered a failure in the electronic speed controller (ESC). This malfunction caused the rear motor to overspeed, disrupting the aircraft's stability.
The investigation also reviewed the maintenance history of the drone. A mandatory periodic inspection had been completed on 8 December 2021, which had found the motor system, cables, and installation to be in good condition. At the time of the accident, the aircraft had recorded 266.0 total flight hours.