What happened
On 7 August 2022, a DJI Mavic 2 Enterprise was being deployed for an emergency services operation near Bangor Train Station in Gwynedd. The mission involved using the unmanned aircraft system (UAS) to locate suspects within an abandoned industrial building.
Following a rapid deployment, the pilot took off from a nearby car park. While the aircraft was hovering at an altitude of approximately 39 metres over the centre of the building, the motors suddenly ceased operation. The aircraft fell vertically without any prior warning to the remote pilot, resulting in a collision with the building's roof. The impact caused the aircraft to sustain damage to its underside, motor arms, and gimbal assembly, and the battery separated from the airframe.
The investigation
Investigators examined recorded flight data and reviewed footage from the pilot's body-worn camera. The data showed that the battery's state of charge was at 77% when the recording ended, but voltage fluctuations were noted four seconds before the loss of signal. Analysis by the manufacturer suggested an abrupt change in voltage, which is consistent with a battery disconnection.
While the body-worn camera footage showed a gap between the battery and the airframe that appeared larger than normal during pre-flight, the manufacturer could not definitively confirm if the battery was improperly seated. Physical examination of the battery revealed scuff marks, but these were determined to have occurred upon impact with the roof rather than during flight. The investigation also noted that the battery had been in use for approximately three years, though it had only completed 46 charge cycles and showed no signs of swelling or overheating.