A surveying drone struck the top of a tower crane during an aerial survey over a construction site in the Cheetham Hill area of Manchester, then fell 120 m to the ground, according to the Air Accidents Investigation Branch.
The incident occurred in August. It was reported to the AAIB, but the branch said no formal investigation was opened. The site and the contractor were not identified in the bulletin.
Obstacle avoidance was enabled
The AAIB’s latest bulletin said the unmanned aircraft was following a pre-selected flight path over an urban construction site. The obstacle avoidance feature was enabled when the aircraft hit the crane’s top.
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, according to the bulletin.
The internal finding points to an operational risk for drone-based site surveys: automated avoidance functions do not remove the need for route planning, site awareness and a clear understanding of system limits. The AAIB bulletin did not provide further details about the aircraft, the flight crew or the damage caused.
The bulletin gave a high-level account of the incident and did not identify the drone operator, the construction company, the equipment involved or the outcome beyond the fall.