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 about 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, but the aircraft still hit the top of the crane and fell 120 m.
The incident was notified to the AAIB, but no formal investigation was launched, and neither the site nor the contractor was 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.
What the bulletin records
The AAIB account is confined to the circumstances described: an urban site, a pre-planned survey route and an avoidance system that did not prevent contact with the crane. The bulletin does not set out findings on the cause, and it does not identify the equipment or the operator.
The case points to a practical question for operators flying automated survey missions near tall structures: whether the limits of onboard avoidance systems are understood by those planning and supervising the flight. The company's internal review raised that point directly, stating that understanding of the software's limitations may have been incomplete.