What happened
On 18 June 2023, a Mavic 2 Enterprise Advanced drone, registered as ZT-YIR, was conducting a night-time surveillance mission at the Beatrix West Mine in Welkom, Free State. The operation was being performed under beyond visual line of sight (BVLOS) regulations.
The pilot had completed ten previous missions that day, noting that the battery levels had been depleting inconsistently throughout the day. During the eleventh mission, the aircraft ascended to approximately 382 feet above ground level with a full battery charge. Three minutes into the flight, the system triggered an "abnormal battery communication" warning. Despite this alert, the pilot continued the mission as the battery level remained above 50%. However, ten minutes into the flight, the aircraft experienced further battery warnings and lost its command and control (C2) link, resulting in a crash approximately one kilometer from the launch site. The aircraft sustained substantial damage upon impact, though no injuries were reported on the ground.
The investigation
SACAA AIID examined the flight logs and physical components of the ZT-YIR following the incident. The investigation reviewed the pilot's credentials, the operator's certificate, and the maintenance history of the unmanned aircraft system. Data from the flight logs revealed that the battery current had dropped to zero on multiple occasions during the flight. Physical inspection of the battery revealed that while the battery cells themselves were undamaged, the battery terminals were severely burnt.
Findings
- The primary cause of the loss of control was the disconnection from the C2 link caused by a failure in the battery power supply.
- The burnt battery terminals prevented consistent electrical contact, leading to the intermittent communication warnings and the eventual loss of power/link.
- The aircraft had flown 85.3 hours since its last mandatory periodic inspection.
Safety action
Following the investigation, the operator suggested the following preventative measures:
- Implement regular cleaning schedules for battery terminals.
- Ensure pilots do not operate aircraft using batteries that show signs of damage.