A surveying drone struck the top of a tower crane and fell 120 m to the ground at a construction site in the Cheetham Hill area of Manchester, according to 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 was identified.
In its latest bulletin, the AAIB said the drone 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, the bulletin said, but the unmanned aircraft still struck the top of the crane.
The construction company’s internal investigation found that the company and its remote pilots may not have fully understood the limitations of the obstacle avoidance software, according to the AAIB bulletin.
The account points to an operational risk around automated obstacle avoidance in complex urban sites: the feature was active, but it did not prevent contact with the crane. The AAIB did not publish further findings because no formal probe was opened.
The bulletin gives no further account of the drone operator, the extent of any damage, or whether anyone was injured. It also does not name the construction company that carried out the internal investigation.