A surveying drone struck the top of a tower crane at a construction site in the Cheetham Hill area of Manchester in August, then fell around 120 m to the ground, according to a bulletin from the Air Accidents Investigation Branch.
The incident was notified to the AAIB, but the branch did not open a formal investigation, and neither the site nor the contractor has been publicly identified.
In its latest bulletin, the AAIB said the unmanned aircraft was “carrying out an aerial survey using a pre-selected flight path over a construction site in an urban area”.
The bulletin states that the drone’s obstacle avoidance feature was enabled during the flight, yet the aircraft still struck the top of the crane.
Internal review findings
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”, according to the bulletin.
The account centres on how the survey flight was planned and supervised rather than on a single technical fault: the route had been set in advance over an urban site containing tall plant, and the automated avoidance function did not prevent contact with the crane.
The bulletin does not identify the drone’s make or model, the height of the crane or the damage caused where the aircraft came down, and it does not report any injuries.