An aerial surveying drone struck the top of a tower crane at a construction site in the Cheetham Hill area of Manchester and fell 120 m to the ground, according to a bulletin from the Air Accidents Investigation Branch.
The AAIB said the unmanned aircraft was carrying out an aerial survey on a pre-selected flight path over an urban construction site. Its obstacle avoidance feature was enabled, but the drone still hit the crane.
The incident occurred in August and was notified to the AAIB, but no formal investigation was opened. The site and the contractor were not identified in the bulletin.
The construction company carried out an internal investigation. It found that the company and its remote pilots may not have fully understood the limitations of the obstacle avoidance software, the AAIB said.
Safety expectations
The account places attention on how automated avoidance functions are planned and used around tall site equipment. The AAIB bulletin records the feature as enabled but does not say why the drone failed to avoid the crane.
It also leaves open how the flight path was selected and how the operator assessed the crane as an obstacle. Those details were not disclosed in the bulletin.
The case is a reminder that survey flights over active construction sites can involve obstacles that sit outside the assumptions of automated systems. The company's internal finding points to operational understanding and the software's limitations as areas for review. The bulletin does not provide further detail on the cause.