A television company filming with an unmanned ‘drone’ device have been unable to explain why the drone hit a sea stack at Mangersta and fell into the sea.

The Air Accidents Investigation Branch have concluded an investigation into the incident, which happened on 15 September last year.

The report said that the DJI Phantom 4 Pro had been flown at Mangersta sea stacks to capture cinematic shots for a television series. While it was being flown near to the sea stack, it either drifted or was flown too close to the stack and then fell into the sea below it.

The drone was not recovered so the cause could not be determined and the 38-year-old pilot stated that neither he nor the observer knew exactly what had happened.

Last recorded images showed the sea stack coming into view, with the drone flying sideways towards it. The flight log did not show any errors and there was no suggestion of a technical failure, but the obstacle avoidance system did not detect the stack, give warning of an imminent impact or automatically avoid the stack.

The pilot reported the incident immediately afterwards using an aircraft accident report form.