What happened
On 13 June 2017, a 3DR Solo unmanned aircraft system (UAS) was being operated for aerial work at a construction site near Kemsley Mill, Kent. The mission involved using the drone to document the site using a camera mounted on a gimbal. The flight was intended to be an autonomous mission following a pre-programmed path consisting of four waypoints, all set to an altitude of 400 ft agl.
As the aircraft climbed from its takeoff point in a nearby car park toward the first waypoint, it struck the jib of a crane. The collision occurred before the drone had reached its target altitude. The impact caused the aircraft to fall to the ground, resulting in a cracked fuselage, motor and propeller damage, and a broken gimbal. There were no injuries and no damage was sustained by the construction site.
The investigation
Investigators examined the flight plan and the circumstances surrounding the mission. It was established that the pilot had previously flown a similar mission at the same location using the same waypoint profile. However, a new crane had been introduced to the site since the previous flight.
From the pilot's position in the car park, the lack of perspective made it difficult for the pilot or the observer to identify the hazard. The investigation determined that the autonomous flight path was not updated to account for the new obstacle, and the aircraft's climb path intersected the height of the crane jib.