Air Force One was airborne before I could buckle my seat belt. The president's plane — carrying George W. Bush — had begun barreling down the runway moments after everyone was hustled aboard.

It was 9:54 a.m. on Sept. 11, 2001 — 51 minutes after the second plane hit the World Trade Center. The next few hours would be among the most intense of my life.

I was accompanying the president in Sarasota, Fla., that Tuesday as White House correspondent for USA Today. A decade later, I went to Dallas and interviewed Bush about those events and their aftermath. He told me that except for his wedding and his daughters' births, it was "the most profound moment" of his life. "It will always be vivid," he said.

Fifteen years later, I still dream about that day. Often, I wake up abruptly with a feeling that I need to hide. Although it was impossible to calculate then how much the country and the world were about to change, I knew I was witnessing consequential events. As a journalist, that was exciting. But I was terrified. This is the first time that I have written about what I personally experienced.

Mark Vancleave
Video (05:07) On Air Force One, reporter Judy Keen had a first-class seat for one of the darkest days in this nation's history.

The events in Sarasota on that steamy morning are part of history now: Bush went for an early jog on the beach in Longboat Key, then visited Emma E. Booker Elementary School to promote his education policies. He talked a lot about that topic — not foreign policy or terrorism — in the first months of his presidency.

Bush was in a second-grade classroom when White House Chief of Staff Andy Card entered and whispered in his ear, "America is under attack." Bush stayed in his seat while the youngsters finished reading. "Really good. These must be sixth-graders," he said.

Years later, Bush told me about that moment, "I, of course, remember [Card] whispering in my ear. I remember the faces of the children. … It was a moment of clarity because people were going to watch how I reacted, and I had enough experience with crises to understand that if you're head of an organization, it's important to project calm."

While Bush was in the classroom, reporters had stood in an office doorway at the school to watch TV coverage from New York after the first plane hit the tower. We saw the live image of a second plane zooming into the picture, then an orange fireball. I felt nauseous. Teachers and school staffers around me began to cry.

Bush had planned to return to Washington for a barbecue with members of Congress. Instead, after his brief remarks at the school about the horrific events in New York, journalists and White House staffers were rushed into the vans behind the presidential limousine, shepherded by tense but steely Secret Service agents.

I looked at the armed agents and thought, "I'm in the safest place I could be."

A heartbeat later, I thought, "I'm in the most dangerous place I could be."

The drive to the airport tarmac was at breakneck speed. I quickly called my editor and told her it was my turn to be on Air Force One. I said I had no idea when I'd be in touch again.

Secret Service agents stationed at the foot of Air Force One's rear stairs told everyone, including some lower-level White House staffers, to drop their gear for a security check by a bomb-sniffing dog — an unusual order, because it had all been "swept" before we entered the school.

It was my job that day to document what Bush said and did and share the information with the rest of the press corps. A small pool of about a dozen journalists always accompanies a president when he's in public: a TV reporter, producer and camera crew, a radio reporter, wire service reporters, photographers, a magazine reporter and a newspaper reporter. Pool members rotate alphabetically by their news organization's name.

I had done it dozens of times while covering three presidents. The opportunity to join Bush aboard Air Force One that day — and serve as observer and record-keeper — was an accident of the alphabet.

The media cabin is in the rear of the big plane. The galley is behind it, and the Secret Service cabin, conference room, staff seating and presidential office and bedroom are forward. Journalists can't wander out of the media cabin.

The TV in our cabin was tuned to a local TV station, and as the plane soared into the sky, we watched live coverage of the chaos in New York and at the Pentagon. Secret Service agents don't usually mingle with reporters, but a couple of them came back to our cabin. One agent, his eyes riveted to the TV screen, said that the agency's New York field office was in the World Trade Center complex.

Our cabin was mostly silent.

There were gasps when we saw the North Tower collapse at 10:28 a.m. Eventually, there were reports about Flight 93's crash in Pennsylvania.

It soon became clear that we were not returning to Washington. No one would say where we were going, but we saw no sign of the Atlantic coast. Instead, we flew over land. For a time, we knew from the sun's reappearance in the windows that we were circling.

I kept writing:

10:55 a.m.: Air Force One bolts upward, turns west. Someone said we were at 40,000 feet, much higher than normal.

11:29 a.m.: Fighter jets spotted off the wings.

Looking back, my responsibility to track what was happening minute to minute precluded — or at least delayed — emotional reactions to the scenes on the TV screen. But it felt like the Earth had shifted on its axis. Nothing seemed quite real. I was glad to be with Bush — the rest of the press corps was grounded in Florida and chartered a bus days later to return to Washington — but my heart was pounding.

Jay Carney, a Time magazine reporter who later became President Obama's press secretary, sat next to me. We exchanged phone numbers for our spouses. We didn't talk about why we thought that was necessary.

We know now that in the front of the plane there were frantic phone calls and debates over where Bush should go. No one told us anything until a White House staffer came back and said that the plane would soon land at Barksdale Air Force Base in Louisiana. Bush would speak, he said, but we couldn't say where we were — only that we were at an undisclosed military facility in the United States.

Then he said that we couldn't even turn on our cellphones, because doing so might give away our location. That's when it really hit home: The Secret Service thought the president's life was in danger. Maybe ours were, too.

Air Force One landed in Louisiana at 11:45 a.m. ET. Seconds earlier, we had heard a CBS report that casualties in New York City were "in the thousands." We watched as the fighter jets descended nearly all the way down to the tarmac with us, then swooped off into the sky.

The plane was instantly surrounded by Air Force personnel in combat gear: green fatigues, flak jackets, helmets, drawn weapons. One airman shouted to another who was standing under the tail, "Hey, hey! Get to that wing tip! Move to that wing tip NOW!" He ran to his correct position.

Bush was hurried into a blue Dodge Caravan; reporters and staff boarded a small bus. Leading the little motorcade was a military vehicle, an airman visible in its gun turret.

We were taken to an office building on the base. Bush and his top aides disappeared. We were led to a windowless conference room where we watched Air Force personnel remove plaques from a wall in preparation for the president's second televised remarks. To illuminate the dark room and show that Bush wasn't speaking from a bunker, they carried in lamps from nearby offices and positioned them just outside camera range.

We discovered that the secrecy about our location was unnecessary. A Barksdale officer had notified local media that Air Force One was on its way. We could finally use our cellphones, so I called my editor, and then I called my husband.

"When will you be home?" he asked. I told him I didn't know and pressed him to be careful; we lived and worked in downtown Washington.

Bush walked past me as he entered at 12:36 p.m. His expression was grim. On an ordinary day he might have made eye contact with me. Not that day. He looked straight ahead.

"Freedom itself was attacked this morning by a faceless coward," he began as he faced the TV cameras.

After Bush's remarks, most of us who had been with Bush that day — most journalists, including Carney and me; most White House staffers, and a congressman — were asked not to re-board Air Force One. The president would fly on to Nebraska's Offutt Air Force Base, then back to Washington, where he arrived at 6:55 p.m. Only the Associated Press remained onboard to represent the print media.

Because all commercial flights had been grounded, Bush ordered an Air Force jet to take us to Washington. When we landed at what was then called Andrews Air Force Base in Maryland (now Joint Base Andrews), the entire facility was locked down.

Carney and I filed the long pool report that we had written. Then I went to work and wrote a story about the day's events. Hours later, I finally walked home. We lived a block from FBI headquarters. Military vehicles were stationed at the corners of the impregnable building. I shuddered.

Once I was safe at home — though I didn't feel safe at all and it would be months before I did — I hugged my husband.

And then I cried.