LONDON – Alitalia pilot Achille Zaghetti thought it was a missile.

Zaghetti was at the helm of a jet from Milan to London's Heathrow Airport on the evening of April 21, 1991 when a flying object streaked across his field of vision.

"At once I said, 'look out, look out,' to my co-pilot, who looked out and saw what I had seen," Zaghetti wrote in his report. "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 nautical miles behind you.'"

An investigation later ruled out a missile — but never ruled anything in, either.

The close encounter is one of many reported UFO sightings among 19 files that Britain's National Archives posted Monday to the Web. The new material covers UFO sightings between 1986 and 1992.

While the 1,500-page batch of documents debunks a host of UFO sightings, others like Zaghetti's near-miss with a UFO remain unexplained.

Read more