What happened
On the night of 21 June 2023, an Arace Sirin unmanned aircraft system, registered ZT-XNK, was conducting a night-time surveillance mission over electrical infrastructure in Piet Retief, Mpumalanga. Operating under beyond visual line of sight (BVLOS) conditions, the pilot had launched the drone in stealth mode, with external lights deactivated, to inspect overhead power lines.
After successfully completing five missions, the pilot initiated a sixth flight. Approximately 15 minutes into this mission, the connection between the remote pilot station and the aircraft was severed. Because the aircraft was flying without external lights, the pilot could not immediately locate the drone. After roughly 10 minutes, the signal was restored, allowing the pilot to identify the drone's position using its lights. Upon arriving at the site, the pilot discovered the ZT-XNK suspended on electrical overhead lines between two masts, with the rotors still spinning.
In an attempt to prevent the drone from being struck by an oncoming train, the pilot attempted to maneuver the aircraft away from the wires. During this maneuver, an electric spark occurred, causing the drone to catch fire. The burning aircraft fell onto the railway tracks, where the pilot used a fire extinguisher to suppress the flames. The aircraft was destroyed in the incident, though no injuries to persons on the ground were reported and the power lines remained undamaged.
The investigation
The SACAA AIID investigation confirmed that the pilot held a valid Remote Pilot Licence with the necessary BVLOS and multirotor ratings. The aircraft was within its scheduled maintenance period, having undergone a major inspection earlier that year. The investigation established that the drone's automated failsafe—designed to return the aircraft to the launch point upon signal loss—was rendered ineffective because the drone became physically obstructed by the power lines.
Findings
- The primary cause of the loss of connection was the aircraft's impact with the railway overhead lines.
- The drone's automated return-to-home function could not execute because the aircraft was caught on the wires.
- The pilot's decision to attempt maneuvering the drone while it was suspended on live electrical lines led to an electric spark that ignited the aircraft.
- The use of stealth mode (lights off) initially hindered the pilot's ability to locate the aircraft following the signal loss.