A passenger jet coming in to land at Heathrow Airport had a near miss with a UFO, according to newly-released British Ministry of Defence files.
The captain of the Alitalia airliner was so concerned he shouted "look out" to his co-pilot after seeing the brown missile-shaped object shoot past them overhead.
The mysterious incident near Lydd in Kent in 1991 was thoroughly investigated by the Civil Aviation Authority (CAA) and the military.
But having ruled out the object being a missile, weather balloon or space rocket, the MoD closed the inquiry and left the matter unsolved.
The unexplained close encounter is one of many recounted in military UFO documents now made available online by the National Archives.
Documents show the McDonnell Douglas MD80 aircraft was en route from Milan to Heathrow at 22,000ft with 57 people on board when pilot Achille Zaghetti saw the strange object 1,000ft above him.
He recounted: "At once I said, 'look out, look out,' to my co-pilot, who looked out and saw what I had seen.
"As soon as the object crossed us I asked to the ACC (area control center) operator if he saw something on his screen and he answered 'I see an unknown target 10 nm (nautical miles) behind you'."
The files show that Southern TV broadcast a story about a 14-year-old boy who reported seeing a missile flying at low level before climbing through the cloud and disappearing on the same evening.
An unnamed Whitehall official wrote: "It is our intention to treat this sighting like that of any other Unidentified Flying Object and therefore we will not be undertaking any further investigation."
There were a number of other similar incidents recorded in the same year.
On June 17, 1991 four passengers onboard a Dan Air Boeing 737 saw a "wingless projectile" pass beneath the aircraft as it climbed from Gatwick Airport headed for Hamburg.
And on July 15 the pilot of a Britannia Airways 737 reported seeing a "small black lozenge-shaped object" travelling at speed as they approached Gatwick.