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 (AAIB). The incident occurred in August, the AAIB said in its latest bulletin.
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 at the time, but the aircraft still hit the crane, the bulletin said.
The AAIB was notified of the incident, but no formal investigation was launched. Neither the site nor the contractor was identified in 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. The finding points to a possible gap between reliance on automated avoidance and knowledge of how the system performs in practice.
The bulletin does not say whether anyone was injured or what damage resulted from the fall. It also does not identify the drone operator, the aircraft type or the software used.
The case highlights an operational issue for aerial survey work near cranes and other tall structures: obstacle avoidance is a support feature, and its limits need to be understood by those planning and flying the mission, according to the internal finding reported by the AAIB.