The Air Accidents Investigation Branch (AAIB) said the unmanned aircraft struck the crane while documenting the site at Kemsley Mill in June last year.
The report states the pilot had previously flown the drone using four pre-programmed waypoints at the site.
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However, he did not take into account the recently erected crane, and on take-off the drone struck the jib of the new structure and crashed to the ground. There was no damage to the construction site.
The AIBB report states: "The pilot stated that the accident was caused by the incorrect programming of the autonomous waypoint mission which had not taken into account the new crane at the site.
"He stated that future missions would be planned such that the UA ascended vertically to 400 ft shortly after takeoff, in a safe corridor, before surveying the site and would avoid intersecting the working radius of any of the cranes."
(LM/MH)
