What happened
On the early morning of 10 May 2023, an Arace Sirin unmanned aircraft system, registered as ZT-YHR, was deployed from a launch pad in Balfour, Mpumalanga. The mission, conducted under beyond visual line of sight (BVLOS) regulations, was intended for security surveillance. After an initial climb to 410 feet and approximately 55 minutes of flight, the aircraft began its return leg to the takeoff site.
During the return flight, the remote pilot observed an 'EKF3 lane switch' warning, indicating the system had transitioned to a secondary GPS module to maintain position estimation. Shortly after this alert, the link between the aircraft and the remote pilot station was lost. The pilot used strobe lights to locate the aircraft and discovered it on the ground roughly 1-0 metres from the launch pad. The impact resulted in substantial damage to the landing legs, fuselage, and camera gimbal, though no injuries to persons on the ground were reported.
The investigation
SACAA AIID examined the operational parameters and the technical state of the aircraft. The investigation confirmed that the pilot held a valid Remote Pilot Licence with the necessary BVLOS ratings and that the operator held a valid UAS Operating Certificate. Maintenance records showed that a mandatory periodic inspection had been completed recently, and the technician responsible for previous repairs was properly licensed.
Technical analysis focused on the flight telemetry and the battery status at the time of the incident. The investigation established that the aircraft's flight endurance had reached nearly 60 minutes, at which point the battery level had dropped to a critical state.
Findings
- The aircraft triggered an automated landing mode following the EKF3 lane switch warning.
- At the time the landing sequence was initiated, the battery level was at 10%, which is significantly below the operator's standard operating procedure (SOP) requirement to land with at least 25% capacity remaining.
- The unsuccessful landing mode was triggered by the combination of the GPS sensor transition and the depleted battery level.