What happened
On the night of 9 June 2023, an Arace Sirin UAS, registered ZT-XWG, was conducting a beyond visual line of sight (BVLSO) surveillance mission over the Transnet pipelines at Watloo DSV near Mamelodi, Gauteng. The flight began without any apparent anomalies following a pre-flight inspection. The aircraft climbed to an altitude of approximately 347.6 feet above ground level.
Roughly 14 minutes into the operation, while the aircraft was 3.6 kilometers from its launch point, the remote pilot station reported a battery voltage of 17.3 volts. The pilot observed a discrepancy between the reported battery percentage and the actual voltage levels. Shortly thereafter, the system issued a warning regarding potential thrust loss across all motors. This triggered a rapid descent, resulting in a crash that caused substantial damage to the aircraft's legs and camera system.
The investigation
An investigation by the SACAA AIID examined the flight logs and the aircraft's maintenance history. Analysis of the log analysis report (LAR) confirmed that the UAS entered a land mode due to a critical battery failsafe warning. The investigation also reviewed the maintenance of the propulsion system, noting that while all four motors had been replaced during a periodic inspection earlier in the year, the aircraft had accumulated 1,045.13 total flight hours at the time of the accident.
Further inquiries with the Original Equipment Manufacturer (OEM) highlighted that atmospheric conditions in the South African highveld, which feature much higher density altitudes than the manufacturer's home base in Hungary, can impact performance. The OEM also emphasized that maintaining sufficient battery voltage is vital for motor effectiveness and recommended limiting flight times to ensure power levels do not drop below 50%.
Findings
- The aircraft was launched with a low battery voltage of 22.2 volts.
- The UAS experienced a potential thrust loss warning prior to the impact.
- There was a discrepancy between the battery percentage displayed at the pilot station and the actual voltage levels.
- Weather conditions at the time of the accident were fine and did not contribute to the crash.
Safety action
Following the incident, the operator implemented new safety protocols, including requirements that pilots verify a full battery charge prior to every takeoff. Additionally, the operator's workshop has been tasked with ensuring all Arace Sirin units are configured with a minimum arming voltage of at least 24 volts.