The incident happened while Malcolm Williams was working in air traffic control at RAF Lyneham in Wiltshire, on a night shift, just before Christmas in either 1994 or 1995, according to UFO investigator Phillip Mantle who interviewed him.
Mr Williams said he had nearly 20 years of experience at the time and was used to analysing quirks that radar can sometimes produce such as bird activity and atmospheric variation.
On the night in question, Mr Williams was guiding two C130 Hercules aircraft, that were approximately three miles from touch down.
But, he suddenly observed a very large "blob" on the radar screen, that he has been unable to explain.
Not knowing what it was, he contacted the pilots of the two Hercules aircraft and fed them around the target.
He said he then passed control of the inbound aircraft to a colleague and went upstairs to the visual control room.
Mr Williams was interviewed about the incident by UFO investigator Philip Mantle.
Mr Mantle said: "The room where he had been based had no windows so he wanted to see if he could obtain a visual sighting of this radar target.
"Mr Williams could not see anything but another radar called the DFTI (Distance from Touchdown Indicator) located in the visual control room also had this blob, which was stationary at the time, on its screen.
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