What happened
On 21 January 2022, at approximately 1752Z, a DJI Matrice 200 (M200), registration ZT-WAX, was conducting a surveillance mission at the Glencore Tweefontein Coal Mines in the Emalahleni District of Mpumalanga. The operation was being performed by a pilot stationed at the Glencore Tweefontein complex offices under Part 101 regulations.
While utilizing the aircraft's infrared camera to investigate an unusual heat signature, the pilot descended closer to the object, which was identified as a bale of hay. During this maneuver, the drone lost its connection to the controller and began to spiral downward, ultimately crashing. The wreckage was recovered by the pilot from a localized area within five meters of the impact site.
The investigation
Technical analysis of the post-accident troubleshooting report established that the aircraft suffered an electronic speed control (ESC) failure. This malfunction caused an imbalance in motor speeds, with one or more motors either overspeeding or dropping speed, which induced the uncontrolled descent.
Investigators noted that the drone's ground proximity sensors and default return-to-origin functions failed to prevent the uncommanded landing because the specific attitude of the aircraft during the descent overrode the sensor capabilities. The investigation also noted that this specific hardware failure had been observed in other drones of the same model, which were already being phased out of service since early 2021.
Findings
- The primary cause of the accident was an electronic speed control (ESC) failure.
- The failure created a speed imbalance among the motors, leading to a loss of flight stability and a spiral descent.
- The aircraft's descent angle and attitude prevented the ground proximity sensors from successfully triggering an automated avoidance maneuver.
- The specific drone model had a known history of similar ESC-related malfunctions.