Alitalia MD-80 near miss over Lydd, Kent (Capt. Achille Zaghetti)

Sunday, 21 April 1991. An Alitalia MD-80 was flying from Milan to London Heathrow with 57 people aboard. In command was Captain Achille Zaghetti, from Grosseto in Tuscany. Around 8 pm the airliner crossed the English coast at 22,000 feet. Below lay Lydd and Romney Marsh. And the Lydd army ranges, directly under the flight path.

A small object came across the sky. About 3 metres long. The wire reports called it brown and missile-shaped. Others remembered khaki, or beige. Zaghetti reacted at once. "At once I said: 'Look out, look out', to my co-pilot, who looked out and saw what I had seen."

The object moved east to west across their field of vision. The first reports put it about 1,000 feet above the airliner. In 2008, Zaghetti placed it to one side. "It was shaped like a cigar and passed very close, about 300 metres on the right, or 1,000ft." Nobody mentioned lights or sound. Zaghetti described no means of propulsion.

Zaghetti went straight to the radio. "As soon as the object crossed us I asked to the ACC (area control centre) operator if he saw something on his screen and he answered 'I see an unknown target 10nm (nautical miles) behind you'." Confirmation came twenty or 30 seconds later. The controller described a clear primary return behind the aircraft. According to France 24, the radar label read "cruise missile??". That evening, a local TV station reported that a 14-year-old boy had seen a low-flying missile disappear. The boy was not named.

The Civil Aviation Authority opened an airmiss inquiry. Nothing known had been in the vicinity. When the object could not be identified, the case passed to the Ministry of Defence. By 6 May 1991, the story was in The Times.

The ministry checked the Army firing ranges at Lydd. Had a missile been fired by accident? By 2 July 1991 it had an answer. No Army range was the source. British and American missiles were ruled out. So were weather balloons, space rockets and any "space-related activity". Its closing line was plain: "In the absence of any clear evidence which could be used to identify the object, it is our intention to treat this sighting like that of any other Unidentified Flying Object."

One press line called the object "consistent with a target missile used for artillery or air defence practice, but the Ministry of Defence insisted yesterday that none were in use on 21 April." To Zaghetti, it looked more like the long-range fuel tanks that fighter aircraft carry. It was "definitely not a weather balloon". He knew what a collision would have meant. "If you're flying at 700 kilometres an hour, hitting an object of 1kg is like hitting something which weighs 700kg."

The accounts do not agree on everything. Above the airliner, or on the right. Cigar-shaped, or round, in one statement issued about two weeks later. No detailed sceptical analysis of the case has come to light.

In October 2008, the Ministry of Defence released the pilot's report, the CAA airmiss report and its own correspondence to The National Archives. Zaghetti told his story again, to Nick Squires of The Telegraph. Historian David Clarke covered the case in The UFO Files in 2009. Eight weeks after Lydd, a Dan-Air Boeing 737 climbing out of Gatwick reported a "projectile" passing beneath it. The Alitalia case remains unsolved.