A surveying drone struck the top of a tower crane at a construction site in Manchester before falling 120 m to the ground, according to the Air Accidents Investigation Branch (AAIB).
The incident happened in August at a site in the Cheetham Hill area of the city. It was notified to the AAIB, but no formal investigation was opened, and neither the site nor the contractor was identified in the bulletin.
Pre-selected flight path
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 obstacle avoidance feature was enabled, but the aircraft still struck the top of the crane and fell 120 m.
Internal investigation
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 does not confirm a cause, and no formal investigation was opened.
The case centres on the performance of an obstacle avoidance system at an urban construction site. The bulletin states that the feature was enabled, while the company's internal review raises a question over how far its limits were understood. It does not provide further detail on the flight, the equipment or the aftermath of the fall.