What happened
On 15 September 2019, a DJI Phantom 4 Pro was being operated near the Mangersta Stacks, Isle of Lewis, to capture cinematic footage for a television series. During the aerial work, the unmanned aircraft system (UAS) moved toward a sea stack, either through drifting or intentional maneuvering, and struck the rock formation. Following the impact, the aircraft fell into the sea and was lost. The pilot and an observer were unable to determine the exact sequence of events as the incident occurred rapidly, though the final recorded images showed the aircraft flying sideways toward the geological feature.
The investigation
The investigation relied on the aircraft accident report submitted by the pilot and an analysis of the electronic flight log. The flight log indicated that the UAS was traveling at a speed of 6.5 mph at its final recorded data point. The data showed no evidence of technical malfunctions or system errors prior to the collision. Notably, the aircraft's obstacle avoidance system failed to identify the sea stack, provide any warning to the operator, or initiate an automated avoidance maneuver. Before the collision, the UAS had demonstrated the ability to maintain its position effectively despite wind speeds reaching 15.5 knots. Because the aircraft was not recovered from the sea, a definitive physical inspection could not be performed.