But that Tuesday morning, American Airlines flight 77 was hijacked. It was a nonstop flight from Washington D.C. to Los Angeles, and terrorists crashed it into the massive building while thousands, including Applewhite, were still inside.
"It was a crisp, blue sky. I wore a blue suit that had red pin stripes in it," Applewhite recalled.
She was assigned to the Air Force Pentagon Communications Agency and worked in a classified vault with no windows, television or radio.
"You can't hear outside. Its soundproof because of what you do," she said.
It was business as usual inside room 5E278B until she received an unexpected urgent call from her husband. He informed her that the twin towers in New York City had been struck.
"And he says why don't you leave work this morning? I'm like, that's odd," Applewhite said. "I said, listen -- and I remember this moment -- I'm in the Pentagon. I'm safe."
Moments later, she went downstairs to another office that had a television in it.
"We were like, wow what is that? But regardless, we had to press on with the day. So we went back up to the office and I'm getting ready to head out," she said.
Applewhite was scheduled to leave the Pentagon for a meeting. She gave directions to her staff that she'd return in two hours. Then there was the impact, which shocked everyone in her office. It even knocked one of her staffers against the steel-wall safes.
"It was more of what I felt than what I heard," Applewhite recalled. "When it hit the building. You could feel it. Alarms in ceilings and alarms in walls. Alarms started going off. That's normally a sign that someone was trying to get in your vault, but we knew that wasn't the case."
The smell of jet fuel quickly overwhelmed the hallways, and fear set in for the Air Force veteran who knew something was terribly wrong.
She said a prayer and instructed her team to evacuate by removing classified government records from safes to take with them. The stairwells were packed with Pentagon workers desperate to escape.
"We get outside and now there's debris. We see the smoke coming from where there was impact. Jeff says, 'Ms. A that's near our office. We were literally one wing over from impact," she said. "I looked at all of them, said run. Run! And we're running with our cases. I thought the building was going to collapse."
READ MORE: 'The wounds don't close': Triangle firefighters reflect on 9/11 response
A second explosion erupting from the Pentagon struck fear into Applewhite and others around her. It was a three-hour commute home. Disbelief written all over her face as she walked into her house to a husband who hadn't heard from his wife since he told her to come home earlier.
"And he starts yelling at me. You never listen to me! I told you to get out of the building," Applewhite said.
The couple waited for their 7-year-old son, Joseph to arrive home from school. He never came. So, they headed to his school where they found him and children of other Pentagon workers having snacks and drawing peacefully.
"The principal said we knew you all would come to find your children. What we didn't want them to experience was go home and there was nobody coming home," she said. "Joseph had made a picture and he said, oh my mommy is coming home. There's no airplane going to get my mommy," she said.
Teachers described as best as they could to the children what had happened earlier that day. Applewhite returned to work two weeks later to the once-bustling Pentagon City with an eerie feeling sweeping through the walls.
"After 9/11 you could walk the halls and hear a pin drop," said Applewhite. "What a lot of people don't know is that many people didn't come back to work. Not because they were injured. They just didn't want to go back into the building."
Twenty years later, Applewhite sat down with ABC11 and called this her final interview as she closes a chapter on a moment that's already etched in history.
"There's a calling on my life," she said. "The reason why it wasn't my time to perish in the Pentagon that day."
WATCH: After 9/11, Camp Lejeune Marines recall being first responders in War on Terror
After 9/11, Marines recall being first responders in War on Terror