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.

On June 17, 1991, four passengers on a Hamburg, Germany-bound Dan Air 737 spotted "a wingless projectile pass below and to the left of the aircraft" as the flight climbed out of London's Gatwick Airport.

"It would seem to have passed fairly close by as the passengers were able to see it quite clearly," the Civil Aviation Authority wrote in its report.

More disturbing was a sighting a month later by crew aboard a Gatwick-bound Britannia Airways Boeing 737, who saw "a small black lozenge-shaped object" zipping past about 100 yards (90 meters) to the left of the aircraft.

The airport confirmed seeing an object on its radar and clocked it traveling at 120 miles (190 kilometers) per hour. Air traffic controllers quickly warned the next aircraft to turn out of the object's flight path, although by then the object had disappeared from view.

Speculation centered on a weather balloon released in the area the same day, but an investigation could not determine what the UFO was.

Monday's release is the second batch of UFO files that Britain's military has put out this year. David Clarke, a UFO expert who has worked with the National Archives, said in the next few years, a total of 160 UFO-related files will be made available to the public.

Some things in the newly released files were either unhinged or unverifiable.

One correspondent tells the military he was shouted at by aliens while sleeping outdoors. Another writes in "with extraordinary news," saying the "legendary 'feathered serpents"' are waiting for permission to land on earth. One U.S. pilot's tale of being ordered to shoot down a UFO over eastern England, forwarded to the Ministry of Defense by a UFO enthusiast, was kept on file even though the military turned up no evidence of it in its official records.

Occasionally, though, officials got to the bottom of the sightings.

On a clear November afternoon in 1992, an office worker called the Ministry of Defense, saying a strange shimmering object was descending slowly over London's Regent's Park.

"As call progressed, it became clear that the object was a kite," an unidentified military staffer noted drily in his write-up.