The East Anglian Air Ambulance narrowly avoided a mid-air collision with a drone, a UK Airprox Board report has found.
UK Airprox Board investigators said the Eurocopter 145, used by the East Anglian Air Ambulance, missed the remote-controlled machine “by chance”.
The incident happened 1,900ft (579m) in August.
There had been “high risk” of a crash, “endangering the EC145 and its crew” over a busy area, the report said.
The investigation found: “That the drone was apparently being operated over a built-up area without CAA permission, was above the altitude where it could be considered in direct unaided line of sight and, if using FPV, was above the 1000ft allowed by regulation. They therefore agreed that this could be considered as endangering the EC145 and its crew in that the drone had been flown into conflict.”
It concluded: “Collision had only been narrowly avoided and chance had played a major part; they therefore determined the risk to be Category A.”
The UK Airprox Board, which probes such incidents to improve air safety, said the drone had passed within 98ft (30m) of the air ambulance, which was carrying medics.
The ambulance control room was contacted by the pilot telling them to inform the police.
The drone pilot was never found.
An EAAA spokeswoman added: “There are strict rules that drone operators must follow and it is important they are aware of their responsibilities for safe operations at all times.”