What happened
On the night of 10 July 2023, an Arace Sirin unmanned aircraft system (UAS), registered ZT-YFW, was performing a beyond visual line of and sight (BVLOS) surveillance mission near Dipaleseng, Mpumalanga. The flight was being conducted under Part 101 regulations for the purpose of monitoring pipeline servitudes.
Following a successful pre-flight inspection and launch with nearly full battery power, the aircraft climbed to an altitude of 394 feet above ground level. Approximately 16 minutes into the mission, while roughly 9.7 kilometers from the launch site, the pilot observed a disturbance in the video feed. Shortly thereafter, the ZT-YFW struck a power line pole. The pilot subsequently located the aircraft, which had crashed on the ground. The impact caused minor aircraft damage, specifically to the right front landing gear, but resulted in zero injuries or property damage on the ground.
The investigation
The SACAA AIID investigation examined the flight parameters, the aircraft's technical specifications, and the environmental conditions. The investigation confirmed that the pilot held a valid Remote Pilot Licence with the necessary BVLOS ratings and a current medical certificate. The operator also held a valid UAS Operating Certificate and the specific aircraft had a valid Letter of Approval.
Investigators analyzed the terrain and the flight path, noting that the mission took place in an area with rising elevation. While the aircraft was operating within its design specifications for wind resistance, the investigation focused on the relationship between the flight altitude and the physical landscape.
Findings
- The aircraft struck high-tension electrical power lines that crossed its flight path.
- The flight plan failed to account for rising terrain, which caused the ground elevation to increase relative to the aircraft's altitude.
- Although the aircraft was flying at 394 feet above ground level, the increasing elevation of the landscape meant the drone's altitude was insufficient to clear the overhead power line infrastructure.
Safety action
To prevent similar occurrences, it is recommended that UAS operators and pilots performing missions in undulating or rising terrain must incorporate varying ground elevations into their flight planning to ensure adequate clearance of all obstacles.