What happened
On 2 June 2023, an Arace Sirin unmanned aircraft system, registered as ZT-XOA, was performing railway line surveillance near Doornpoort, Gauteng. The operation was being conducted at night under beyond visual line of sight (BVLOS) regulations. During the mission, the pilot observed anomalies in the video feed at the remote pilot station. In response, the pilot initiated the return-to-home (RTH) function.
As the aircraft began its automated return, it started to descend unexpectedly. The pilot took manual control and increased the throttle, successfully bringing the aircraft up to 410 feet above ground level. Upon landing and subsequent inspection, it was discovered that the aircraft had sustained minor damage, including a damaged gimbal front plate and propeller damage. No injuries were reported on the ground.
The investigation
SACAA AIID examined the mechanical state of the aircraft and the credentials of the personnel involved. The investigation confirmed that the pilot held a valid Remote Pilot Licence with the necessary BVLOS ratings and a current medical certificate. The operator held a valid RPAS Operating Certificate, and the maintenance technician involved in previous repairs was properly licensed.
Technical inspections revealed that a mandatory periodic inspection had been completed recently, during which a faulty battery had been replaced. The investigation also noted that weather conditions, specifically wind, were not a factor in the flight instability. Furthermore, while the flight occurred near Wonderboom Airport, the aerodrome was closed at the time of the incident.
Findings
The investigation established that the failure of the tracking device enclosure was the primary cause of the incident. The 3D-printed housing for the Bidtracker device failed, allowing the device to become loose and move freely against the aircraft's fuselage. This loose device repeatedly struck the rotating propeller blades, creating an imbalance that prevented the UAS from maintaining its automated flight path and necessitated manual intervention by the pilot.