The UK Airprox Board (UKAB) released details last week of an incident on May 2, when a West Midlands police helicopter narrowly avoided a collision with a UFO above Sandwell Valley Country Park.
The EC-135 Eurocopter pilot spotted an object with two blue/green lights some 100 metres away before he swerved to avoid contact at around 9.50pm.
The lights, according to all three on board the helicopter, then appeared to circle them, flew north, then back before finally flying off.
The pilot believed the intent was either 'sinister or just someone messing around' and thought the lights came from a radio-controlled fixed wing aircraft which was 'purposefully flown around them'.
The crew used a thermal camera but failed to identify any signs of radio-controlled activity.
'Flashing' from rotor blades was discounted by the pilot, as were internal reflections from the canopy, checked on a later flight.
A spokesperson for West Midlands Police confirmed the pilot reported the incident and said: "As far as they were concerned, nothing was picked up on Birmingham Airport radar and the object was probably a radio-controlled model aircraft.
"The helicopter was conducting a search at the time and was flying at low level."
UKAB, jointly funded by the Civil Aviation Authority and the Ministry of Defence, investigated the incident but ruled out the mystery object being a model aircraft, as the incident occurred at 1,500 feet and at night.
A laser light show was discounted due to a lack of cloud base for lights to reflect on, as was the possibility of gliders, kites and balloons due to the light and clear weather conditions.
Manny Williamson, Development Officer for the British Model Flying Association, who spoke with UKAB at the time of the investigation told the Observer: "At that time of night if you couldn't see a model aircraft, you couldn't fly it.
"To fly an aircraft at that height would be almost impossible. The maximum would be a couple of hundred feet and the lighting would need to be good. There is no way it could have been a model aircraft."
Military flights were also ruled out due to the non-appearance on radar. A spokesperson for the MOD said: "The MOD examines reports solely to establish whether UK airspace may have been compromised by hostile or unauthorised military activity.
"Unless there is evidence of a potential threat there is no attempt to identify the nature of each sighting reported."
After a thorough investigation, UKAB could not identify source of the flying lights.
The UKAB report said: "Although the possibility of a civilian clandestine flight by a microlight or similar aircraft could not be ruled out, it is thought unlikely that any pilot engaged on illegal airborne activity would orbit what could probably be identified as a police helicopter.
"Regrettably therefore, despite extensive tracing, the source of the lights could not be identified."
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