The pilot looked at me as though I was a fool. "Eighteen months? You think it takes 18 months to learn how to fly a Boeing 757 once it's in the air?'' Far below us the clouds of northern Europe passed like a white screen. "I can teach you how to fly this plane in two minutes. At least I can teach you all you need to know in order to become a hijacker."
We had already been through all that is wrong on a commercial airliner. The pilot's cabin door is a flimsy sheet of metal, easy to break open with a shoulder if the pilot should have locked it. Even now, most pilots keep the door unlocked, slipping out from time to time - when the co-pilot is flying - to talk to passengers or go to the toilet. "There's one thing we have to defend ourselves and that's this," the pilot said, pointing to a pouch on the wall. It was the emergency escape axe at the back of the flight deck. "The problem is, hijackers can use this on us if they get in quickly enough."
The flight deck crew had made up their mind about what happened on the four hijacked airliners in the US. They were convinced that the killers had cut the throats of the pilots with their box cutters. "We should have reinforced iron doors with bars that go across to prevent access, and use the floor emergency hatch to leave the aircraft," he said. "Why should we have to allow access from the cabin?"
The co-pilot had laid the maps across his lap. His colleague tut-tutted. "A hijacker doesn't need these maps,'' he said. "All he needed to do was code in the exact location of the World Trade Centre twin towers. On automatic pilot, the plane will follow those instructions, he switches off the transponder [which identifies the aircraft for ground control], this knob - and the plane will head for his chosen destination.'' The pilot leaned forward. The code word for the setting was punched in as "FISK" along with a series of numbers - the imaginary co-ordinates of down-town Manhattan (in this case, 123456789) - so that the plane would fly itself to its "target".
"The hijacker probably couldn't put an airliner through a take-off - but he doesn't have to," the pilot said. "The hijackers in America let the flight deck crew do that. They wait until the 757 is at its cruising altitude, say 35,000ft, then they burst into the cabin, murder the pilot and take over. Most of their work has already been done for them."
A pattern of lit-up towns emerge in the darkness below us. "Your hijacker has now reached the area west of New York, and he lets the plane take him to within sight of the city," The pilot continues. "Then he just presses this button to cut the automatic pilot and flies the plane himself. He can see the twin towers. In broad daylight it's easy - every pilot into New York would see the trade centre. Then he pushes the wheel forward and starts his dive."
European pilots have already discussed the last moments of the two aircraft to hit the twin towers. They have studied the photographs, listened to the videotapes. On the flight deck of the plane on which I was travelling, the crew had a set of magazine photos of the last moments of the two American airliners.
"On the videotape that was made of the first plane to hit, you can clearly hear the twin engines," the pilot says. "They are so loud that someone in the street looks up. They are overpowered, they were never meant to be flying the plane that fast, they are under immense pressure," and he makes a noise like a jet through his teeth. "The way the plane is plunging - he's pushing it down with the wheel [control stick] remember, it's now flying way forward of its permitted speed. I reckon that first aircraft hit the tower at maybe 900, even 1,000kph."
The co-pilot suddenly asks: "You know why these people suddenly jumped from the windows of the building? That wasn't gasoline that had burned into the buildings, the kind you use in a car. That jet was carrying around 20,000 gallons of aviation fuel which is the same as kerosene.
"Ordinary gasoline will burn you, but kerosene burns so ferociously, it's much hotter ... They jumped because of the pain.''