A DJI Matrice M210 Version 1, quadcopter unmanned aircraft (UA) was being flown during a police operation when the wind at 400 ft exceeded the forecast wind, the manufacturer's wind limit and the maximum restricted speed of the UA. The UA drifted beyond visual line of sight and then communication with it was lost. When the battery level was low it entered an auto-land mode but collided with the wall of a house, damaging its propeller blades before coming to rest on a balcony.
The investigation revealed that shortly after takeoff one of the UA's two batteries had disconnected which resulted in its maximum speed being restricted, but this restriction is not referenced in the user manual and neither the remote pilot nor operator were aware of it. When the UA detected that the manufacturer's wind limit had been exceeded, the message triggered on the pilot's controller display was 'Fly with caution, strong wind' instead of advising the pilot that the limit had been exceeded and that the UA should be landed as soon as possible.
Three Safety Recommendations are made to the UAS manufacturer and one to the CAA on Visual Line of Sight guidance.
