What happened
On the evening of 28 May 2023, an Arace Sirin unmanned aircraft system, registered ZT-XDT, was performing surveillance duties over Transnet railway lines near Welgedacht, Gauteng. The operation was being conducted under Beyond Visual Line of $Sight$ (BVLOS) regulations.
The flight began at 1726Z with a healthy battery level. After approximately 36 minutes of patrolling at an altitude of 400 feet, the pilot noted that the battery voltage had dropped to 29% and initiated a return to the launch site. During this return leg, the pilot experienced extreme fatigue and fell asleep at the remote pilot station. Upon waking, the pilot discovered the aircraft was no longer visible on the control unit. A search conducted alongside a security official led them to the wreckage approximately 2 kilometres from the launch site, where the aircraft had sustained substantial damage, including broken landing legs.
The investigation
SACAA AIID examined the operational circumstances and the pilot's recent work schedule. The investigation confirmed that the ZT-XDT was airworthy and that the battery voltage had been sufficient to complete the return flight. The pilot held a valid Remote Pilot Licence with the necessary BVLOS ratings and a current medical certificate.
Regarding the pilot's schedule, the investigation noted that the pilot worked a rotating shift pattern (17h00Z to 01h00Z, six days a week). On the day of the accident, the pilot had just completed a shift changeover, which had provided only a single day of rest.