"9/11 changed the way we fly," according to aviation expert Capt. Ron Alvarado, a pilot and former White House Marine helicopter commander.
Alvarado said the changes extended beyond airport checkpoints. Members of the public who are not traveling can no longer access airport gates and terminal areas beyond security. He also noted that responsibility for airport security shifted from private companies, primarily airlines, to the federal government.
"Security was pretty much lax at all major airports," Alvarado said.
In response to the attacks, airports expanded the use of explosive-detection X-ray machines, reinforced cockpit doors and increased the presence of armed air marshals aboard aircraft.
"So even today, you just don't know who is armed, where the air marshals are, who are the armed pilots," Alvarado said.
Alvarado said aviation security has continued to evolve in the years since the attacks. He pointed to Richard Reid's attempt to conceal an explosive in his shoe three months after 9/11, which led to passengers removing their shoes during security screenings.
He also cited an attempted bombing involving a plastic explosive hidden in a passenger's underwear on Christmas Day in 2009, which led to the introduction of full-body scanners at airports.
According to Alvarado, some aviation security measures remain out of public view.
"It's kind of like where I was at the White House, I knew a lot about the security of how we move the president, but I didn't know the full picture," he said.
Meanwhile, TSA PreCheck was established to screen passengers before travel and expedite their airport experience.
TSA Administrator David Cummins said expanding the program remains a priority.
"Our goal is to make the lanes twice the speed, and so it'll be a clear differentiation from the standard lanes. And we are hoping that will drive increased enrollment in the PreCheck program. We'd like to see another 20 million Americans enroll," Cummins said.
The TSA is also rolling out what it calls E-Gates, which will allow TSA PreCheck passengers to use facial recognition technology to pass through security without interacting with an agent, the agency said.