A drone carrying out an aerial survey at a construction site in the Cheetham Hill area of Manchester struck the top of a tower crane and fell about 120 metres to the ground, according to the Air Accidents Investigation Branch (AAIB).
The incident took place in August. It was notified to the AAIB, but the branch said no formal investigation was launched, and neither the site nor the contractor has been identified.
In its latest bulletin, the AAIB said the unmanned aircraft was flying a pre-selected flight path over a construction site in an urban area. The obstacle avoidance feature was enabled at the time, the bulletin states, yet the aircraft still struck the crane.
Internal review findings
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 AAIB account does not name the drone model or the operator, describe the purpose of the survey, or report the extent of any damage or injury on the ground. Its findings on pilot understanding rest on the company's own internal review rather than on an AAIB investigation.
The bulletin sets out no safety recommendations. It records that obstacle avoidance was enabled and the aircraft still hit the crane, while the company's internal review pointed to possible gaps in how well the software's limits were understood.