The CAA have published CAP 1627, reviewing the unintentional safety risk of UAV usage.
At the time of writing there have been seven confirmed cases of direct in flight contact between drones and civil or military manned aircraft worldwide.
There have been no known collisions between small drones and manned aircraft in the UK. However, the number of occasions where pilots have reported suspected drones in proximity to their aircraft in the UK is increasing; there were 59 such occasions between April 2016 and March 2017.
Two of these involved large passenger aircraft near Heathrow, leading to concerns being voiced in Parliament, in the media and by a range of aviation bodies about the possible impact of a collision between a passenger aircraft and a drone. A further incident in July 2017, where an object believed to be a drone was seen near Gatwick, led to the runway being closed briefly and flights being diverted.
The CAA has undertaken an assessment of available information about the likelihood of an unintentional drone collision and the severity of any possible impact between an aircraft and a smaller unmanned vehicle (defined as under 2kg in this report). The findings are: