A police helicopter crew was put in danger when a drone passed under their aircraft, the National Police Air Service (NPAS) has said.
Drone user Sergej Miaun - the first person to be prosecuted under UK drone laws - also disrupted the crew's mission to find a missing person.
The crew filmed the drone passing underneath and guided police to Miaun's house at Guyhirn, near Peterborough.
He was convicted of two offences and fined by Peterborough magistrates.
Miaun, 37, of High Road, had been charged with failure to maintain direct, unaided visual contact with a small unmanned aircraft and flying it when not reasonably satisfied that the flight can be safely made.
The NPAS said the case "provides absolute clarity that flying a drone in this way is unacceptable and dangerous."
The helicopter crew were involved in a search and rescue operation on 9 December when the drone passed underneath.
It was then seen to land in Miaun's garden.
Cambridgeshire Police then found the drone in the house and arrested Miaun under the Air Navigation Order 2016.
James Cunningham, head of aviation safety for the NPAS, said: "This is the first case of conflict between one of our helicopters and a small unmanned aircraft.
"Not only did it put our crew in danger, it disrupted our search for a vulnerable missing person."
The Civil Aviation Authority's assistant director, Jonathan Nicholson, said: "Anyone operating a drone must do so responsibly and follow the rules and regulations which are designed to keep all airspace users safe."
It is illegal to fly a drone above 400ft (122m) or within 1km (0.6m) of an airfield boundary.