A commercial UAV crashed due to poor planning and overshoots caused by bad weather, according to an investigation.
The Air Accident Investigation Branch (AAIB) released a report stating that the collision, which took place in July last year in Somerset during a foreshore survey, was the result of winds causing the drone to overshoot on turns and collide with a crane.
The 48-year-old pilot, which flew a fixed-wing survey drone at 35kt and 200ft using a flight plan of pre-programmed waypoints, selected a flight plan with tracks running across the wind with into-wind turns.
At the time of planning the weather forecast was fine and the wind was from the east-north-east at 7 to 13kt, but at the time of the survey the weather conditions had changed and the first four downwind turns caused the UAV to overshoot the waypoints by approximately 125m.
During the model’s final turn it descended to 200ft, as planned, when it collided with the horizontal beam of a tower crane and fell to the ground.
While there was ‘extensive damage’ to the UAV, the AAIB has confirmed that no one was injured.
In its investigation report, the AAIB stated: “The pilot commented that the main cause of the accident was poor flight planning. The overshoot and collision could have been prevented by aligning the flight legs east/west instead of north/south and maintaining 400ft near the construction site.
“The pilot did not do this because optimum imaging uses crosswind legs, in this case north/south. Also the position of the tower cranes, outside the planned flight area, were not fully considered during the planning stage due to their more remote location. Additionally, the pilot did not intervene and initiate a climb before the collision because the distance and height of the cranes were difficult to perceive.”
Since the incident last year, the operator has implemented procedural changes to minimise the probability of collisions with high obstacles.
The new procedures outline that construction site staff will be contacted, prior to launch, to check the height of the highest structure to ensure that sufficient clearance can be met, any flights that have the potential to overfly the construction site will be flown at 400ft and manual corrective action will be taken to manoeuvre a UAV in the event of deviations from the flight plan.