A surveying drone struck the top of a tower crane at a construction site in the Cheetham Hill area of Manchester in August and fell 120 m to the ground, according to the Air Accidents Investigation Branch.
In its latest bulletin, the AAIB said the unmanned aircraft was carrying out an aerial survey on a pre-selected flight path over a construction site in an urban area. The obstacle avoidance feature was enabled at the time, but the aircraft still hit the crane.
The incident was notified to the AAIB, but no formal investigation was launched. The site and the contractor were not identified in the bulletin, which records the event without naming the organisations involved.
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, according to the AAIB bulletin. The bulletin attributes the finding to the company rather than to a regulatory inquiry.
The account places the flight in an urban construction setting and records both the pre-selected route and the enabled avoidance function. It does not state whether the software detected the crane before impact or why the aircraft struck it. It gives the fall height but not the crane's height.