Passengers on board the first plane to be hijacked in the US terrorist attacks were told it was returning to the airport.
The hijackers were audible over the cockpit microphone as they took control of the American Airlines jet and told passengers everything would be okay.
The hijackers' words have emerged in transcripts from air traffic control recordings published in the New York Times.
Controllers were trying to contact American Airlines Flight 11 after minutes of radio silence when they heard: "We have some planes. Just stay quiet and you'll be okay. We are returning to the airport.
"Nobody move, everything will be okay. If you try to make any moves, you'll endanger yourself and the aeroplane. Just stay quiet."
A confused controller asked: "Who's trying to call me?" But all he heard were the last words audible over the microphone, as an unidentified voice said: "Nobody move please, we are going back to the airport. Don't try to make any stupid moves."
It is also revealed that the pilot of the second hijacked flight, United Airlines Flight 175, was the first to inform controllers on the ground of the hijacking on board American Airlines Flight 11.
The pilot told controllers: "We heard a suspicious transmission on our departure from Bos (Boston). Sounds like someone keyed the mike and said, 'everyone stay in your seats'."
The transmission came at 8.41 a.m. local time and within five minutes, the United plane's transponder had been turned off, pointing to it being hijacked. At 8.53 p.m., a controller said: "We have a hijack. We have some problems over here right now."
Just 10 minutes later, the plane became the second to slam into New York's World Trade Centre, hitting the south tower at an estimated 500mph.
The plane which hit the Pentagon in Washington, American Airlines Flight 77, was last heard from at 8.50 a.m. local time, soon after its transponder was switched off, meaning it had been hijacked and controllers could not work out its speed or exact height.
A controller said: "We, uh, lost track control of the guy. He's in coast track but we haven't - we don't know really where his target (radar location) is, and we can't get a hold of him."
By 9.06 a.m., the controllers had tried contacting the plane repeatedly, and used American Airlines headquarters to try to get in touch with it.
Also in the air nearby was United Flight 93, which later crashed into a field in Pennsylvania. At 8.53 a.m., realising that hijacks had happened, a text message was sent to all United planes, saying: "Beware, cockpit intrusion."
The pilot of the United jet replied with another text message, saying simply: "Confirmed."
At 9.28 a.m., the first sounds of a hijack could be heard over the radio. A source who had heard the tape told the New York Timesthere was "a very noisy sound of a confrontation was heard on the frequency, very garbled, but with some discernible phrase like, 'Hey, get out of here'."
The sound came as fighter jets were finally scrambled into the air and told to head for New York.
But the two F15s, one flown by an off-duty commercial pilot, were too late, and were only able to get the first aerial view of the devastation. And three fighters sent to Washington were also too late.
The time taken to scramble the planes meant they were too late to intercept United Flight 93, which crashed into a field in Pennsylvania. If they had been earlier, they may have been ordered to shoot down the plane.
National Guard Major General Mike Haughen said: "It kept us from having to do the unthinkable and that is to use your own weapons and own training against your own citizens."
And after the flights had all crashed, he says the pilots were given the most bizarre order they had ever heard.
General Haughen said: "A person came on the radio and identified themselves as being with the Secret Service and he said, 'I want you to protect the White House at all costs'."
PA