An unmanned aircraft 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 about 120 metres to the ground, according to the latest bulletin from the Air Accidents Investigation Branch (AAIB). The incident took place in August.
The AAIB said the drone was following a pre-selected flight path over a construction site in an urban area. Its obstacle avoidance feature was enabled at the time of the flight, but the aircraft nonetheless hit the crane. The occurrence was notified to the branch, which recorded it in the bulletin without launching a formal investigation; neither the site nor the contractor has been identified.
According to the bulletin, 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.
Automated avoidance and its limits
The sequence described places the failure inside an ordinary survey workflow: a predefined route, an aircraft operated with automated obstacle avoidance, and a tall structure standing in the flight corridor. The AAIB's wording does not attribute the collision to a specific technical fault, and the company's conclusion is framed as a possibility rather than a confirmed cause.
The bulletin gives no detail on injuries, on damage beyond the aircraft's fall, on the make of the drone, on the purpose of the survey, or on the height of the crane relative to the planned path.
What the reported finding does point to is a gap between what operators expected of the avoidance software and what the system can actually handle. For site teams, pre-programmed survey routes over live construction sites depend on checking the planned corridor against the structures that stand inside it.