The security breach happened Jan. 9 between gates 2 and 3 in Sea-Tac's D concourse.
An airport spokesperson says the mentally ill man opened a glass door exit that leads to stairs, which lead to the tarmac.
Baggage handlers noticed the man and tackled him when he tried to run away from the terminal. Police arrested the suspect and took him to the King County Jail. They did not release his name or age.
He was not armed and did not make any verbal threats. Officials say he had a ticket and made it through security with no problem.
The incident raises questions about security breaches at the airport and whether passengers should be concerned.
"By tackling him they were obviously on point about what they needed to do," said Annie Salonen. "If for some reason someone does get past that then they'll be taken care of."
Port of Seattle Police Chief Colleen Wilson said while her officers are ready to react quickly to any threat, all employees are expected to challenge anybody who appears to be in a restricted area without authorization.
She applauds what the baggage handlers did.
"It's a really great example of the multiple layers of security we have built in here at the airport," she says.
Chief Wilson said it's not practical to have every doorway to the airport locked. Firefighters, for example, may need quick access to the outside in an emergency.
She said Sea-Tac has a good record when it comes to these kinds of problems.
"Thirty-three million passengers come through here every year. I would say we have very few breaches."