A surveying drone struck the top of a tower crane at a construction site in the Cheetham Hill area of Manchester and fell 120 metres to the ground, according to a bulletin from the Air Accidents Investigation Branch.
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 publicly identified.
Flight on a pre-selected path
The AAIB bulletin states that 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 at the time, the bulletin says, yet the aircraft still struck the top of the crane before falling to the ground.
Internal review
An internal investigation by the construction company identified that the company and its remote pilots may not have fully understood the limitations of the obstacle avoidance software, according to the bulletin.
The published account sets out the sequence of the flight and the finding of the company's own review, and records no injury or damage on the ground.