There are armed guards, checkpoints, and baggage screenings, but despite continuous efforts to fortify airports, security experts say it may ultimately be impossible to completely secure the facilities against terrorist attacks.
After suicide bombers killed 32 people in Brussels in March, gunmen with explosives strapped to their chests killed 41 people Tuesday at Turkey's Ataturk airport — both groups striking just outside the secure perimeter.
Despite additional security measures taken at airports around the world, security experts told BuzzFeed News airports continue to be targeted by terror groups because the facilities have significant vulnerabilities.
"It's impossible to lockdown, to make an airport entirely [secure] because fundamentally, the purpose is to move people to the planes and on their travel," Henry Willis, director of Rand Corporation's Homeland Security and Defense Center told BuzzFeed News.
Experts say security checkpoints at airports have created new vulnerabilities like long lines and large gatherings of people that can become open targets for attack.
“When you create a secure area, you actually create another vulnerability," he said.
While airports continue to expand their secure area — from the aircraft, to boarding and ticketing areas — groups targeting transportation hubs have merely shifted their point of attack.
“People being there, are themselves a target,” Willis said.
In recent years, terror groups have shifted their focus from more secure facilities like embassies and government buildings, to soft targets like public places with unarmed civilians.
But airports continue to pose an attractive target for terror groups because they can impact travel, the economy, and a country's morale, officials said. And some portions of airports continue to be as exposed as soft targets.
"Despite airports being hardened [secure], it has vulnerabilities, which is the real appeal for many groups," Jennifer Hesterman, a retired Air Force colonel and counterterrorism expert told BuzzFeed News.
Hesterman noted both the Brussels and Istanbul attacks targeted areas just outside the terminals, showing that heavy casualties can still be inflicted at the facilities.
"We're still focused on the wrong stuff," she said. "It's not the airplane anymore. It's the terminal."
The gunmen in Turkey, she said, also seemed to have made small but significant changes in tactics when compared to Brussels, suggesting Tuesday's attack was better planned.
In Istanbul, for example, the attackers focused on the arrivals section of the airport, which tends to be less scrutinized and less secure than departure areas.
"Anyone can walk into the baggage arrival area," she said. "Departures is usually where we're focused."
The attacks abroad have also increased concerns that similar attacks could be carried out inside the U.S. On Wednesday, CIA director John Brennan said he worried ISIS could plan a similar assault in the U.S.
"I'd be surprised if Daesh is not trying to carry out that kind of attack in the United States," he told Yahoo News, using another name for the terror group.
Officials in the U.S. have already been trying to make some changes to address that possibility.
After repeated funding and staffing cuts at the Transportation Security Administration, the Department of Homeland Security announced in May it would add 768 new agents in an effort to make security lines move faster in airports across the country.
A funding request to Congress could also make more than 2,700 part-time TSA employees full-time, and potentially further reduce crowds.
In response to the attack in Turkey, major U.S. airports deployed officers with tactical weapons to patrol the facilities, including areas outside terminals.
The issue of long lines is not just one of convenience, but security experts have for years recommended increasing personnel and cutting down wait times, pointing out that the crowd of waiting passengers poses a target for would-be attackers.
In 2004, for example, Los Angeles International Airport hired the Rand Corporation to evaluate security threats. Among the top findings was cutting down the number of people gathered at check-in and TSA checkpoint lines.
"If there aren't people waiting around to be processed, there's less targets," Willis said.
Not only would reducing lines cut the number of casualties in an attack, it could deter attackers altogether because the small number of potential casualties would not be worth the time or effort.
Rand found it would cost about $4 million to reduce crowding, but the following year, another report from another consulting company found that increasing personnel by 15% would cut down crowds by 75%.
But, the company determined, "a 75 percent decrease in lines was not worth implementing."
Some airports have already made moves to try and reduce the number of crowds. Self-service check-in counters, pre-paying for baggage and TSA pre-screening programs can help reduce gatherings in airports, where people are most vulnerable, Willis said.
Part of the problem, Hesterman said, is that security at airports is too often focused on preventing events like past assaults, while terror groups are looking for new ways to infiltrate and attack.
"We're too focused on the last attack," Hesterman said. "First we focused on airplanes being blown out of the sky, then we focused on terminal security."
Hesterman suggested airports should start their security measures outside the facility, employing technology and vehicle checkpoints to dissuade terrorists from even attempting an attack.
Adding such measures, however, could make air travel even more time consuming and inconvenient.
“There’s no easy objective answer as to whether it’s worth it or not,” Willis said. “If you want to increase security, it comes with costs, some of them economic, but some costs in convenience and intrusiveness as well.”