A drone carrying out an aerial survey struck the top of a tower crane at a construction site in the Cheetham Hill area of Manchester and fell about 120 m to the ground, according to the latest bulletin from the Air Accidents Investigation Branch.
The incident took place in August. The AAIB said the unmanned aircraft was flying a pre-selected flight path over a construction site in an urban area at the time. Its obstacle avoidance feature was enabled, but the aircraft still hit the head of the crane and dropped to the ground.
The event was notified to the AAIB, which did not launch a formal investigation. Neither the site nor the contractor involved has been identified in the bulletin.
According to the AAIB account, an internal investigation by the construction company found that the company and its remote pilots may not have fully understood the limitations of the obstacle avoidance software.
The bulletin describes a flight in which an automated safety feature was active and the aircraft nevertheless collided with a structure at height. The company's own review locates the problem in how well the software's limits were understood by those operating the flight, rather than in the flight path alone.