A surveying drone struck the top of a tower crane and fell about 120 metres to the ground at a construction site in the Cheetham Hill area of Manchester, according to the Air Accidents Investigation Branch (AAIB).
The incident took place in August, according to the AAIB's latest bulletin. It was notified to the branch, but no formal investigation was launched, and neither the site nor the contractor has been publicly identified.
The bulletin said the unmanned aircraft was carrying out an aerial survey along a pre-selected flight path over a construction site in an urban area. Although the obstacle avoidance feature was enabled, the aircraft struck the top of the crane and dropped 120 m.
An internal investigation by the construction company concluded that the company and its remote pilots may not have fully understood the limitations of the obstacle avoidance software, the bulletin states.
The AAIB account rests on the notified incident and the company's own review; the bulletin does not name the parties involved or indicate any further regulatory action.