A drone carrying out an aerial survey over a construction site in the Cheetham Hill area of Manchester struck the top of a tower crane and fell 120 metres to the ground, according to the Air Accidents Investigation Branch (AAIB).
The incident happened in August. It was notified to the AAIB, but no formal investigation was launched, and neither the site nor the contractor has been identified. The details appeared in the branch's latest bulletin.
The AAIB said the unmanned aircraft was operating on a pre-selected flight path over a construction site in an urban area. Although its obstacle avoidance feature was enabled, the aircraft hit the top of the crane and dropped 120 m.
Software limits questioned
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 states.
The account points to the gap between an automated safeguard being switched on and operators knowing what it can and cannot handle. On a crowded urban site where cranes rise well above surrounding buildings, the feature appears to have acted as an aid rather than a guarantee. The bulletin does not give further detail on the flight, the equipment used or any consequences beyond the fall.