Two decades after Sept. 11 attacks, threats to aviation have evolved. So has the system for keeping travelers safe. (2023)


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Two decades after the Sept. 11 attacks, billions of dollars have been spent on aviation security, an investment experts say has made air travel safer but not insulated from future attacks.

The security gaps that allowed 19 hijackers armed with box cutters to seize four passenger jets and attack the World Trade Center and the Pentagon have largely been addressed, as have threats that surfaced in the years since. But although terrorists have staged attacks on subways and hotels, and used truck bombs to sow fear, experts say aviation remains a prime — even if more difficult to reach — target.

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Many architects behind the 2001 attacks and subsequent plots have been killed and their networks crippled. Officials say hazards still loom as an evolving cast of players hunts for new vulnerabilities to exploit amid unrest in Afghanistan that has boosted concerns about possible threats.


“The persistence of focus by the terrorist groups that we worry about and their focus on aviation — as something that would allow them to really achieve an outsized impact on the U.S. and other Western countries — that’s been pretty much constant over the last 20 years,” said Nicholas Rasmussen, former director of the National Counterterrorism Center. “And that’s despite all the effort we’ve put into dissuading them.”

Changes to aviation are perhaps the most visible of those made in response to attacks on the World Trade Center and the Pentagon. It began with American Airlines Flight 11 striking the North Tower at 8:46 a.m. and ended with the crash of United Flight 93 in a field in Shanksville, Pa. Nearly 3,000 people died, including 265 aboard the four planes.

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Before the attacks, no identification was required to pass through airport security, shoes stayed on and anyone — not just ticketed passengers — could proceed to the gate.


Airport security was handled by private contractors with little training who were hired by airlines. Passengers went through metal detectors, but there were few restrictions on what they could carry. Checked bags and cargo weren’t routinely scanned for explosives.

In the wake of the attacks, the federal government took charge of airport security, creating the Transportation Security Administration to oversee security at more than 400 airports. The first of those security checkpoints opened at Baltimore-Washington International Marshall Airport in 2002, ushering in an era of evolving safety procedures as threats surface and technology advances.

Evolutions in passenger screening

Paul Malandrino, who served as the TSA’s federal security director at BWI from 2002 to 2006 before running Reagan National Airport, said his focus was on keeping lines moving while hundreds of new TSA officers enforced new prohibitions on items ranging from pocket knives to scissors.


But federal oversight hasn’t been a panacea. The TSA has been dogged by issues similar to those of its predecessors: low pay and high turnover. A 2015 Department of Homeland Security inspector general investigation found that federal undercover investigators carrying illegal weapons or simulated bombs penetrated airport security checkpoints in 95 percent of instances, raising alarms about the agency’s ability to protect the aviation system.

The findings led to the reassignment of the TSA’s acting director and prompted the agency to retest and reevaluate screening equipment and retrain personnel. Two years later, another inspector general report found the gaps persisted.

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TSA Administrator David Pekoske said the agency has worked to close those gaps and improve training to ensure officers are equipped to identify threats. In 2016, the agency began requiring all new hires to go through the same training program to ensure they receive consistent instruction.

“There’s no question in my mind that it’s safer,” Pekoske said, adding that more sophisticated technology has helped officers better pinpoint threats. Programs that screen cargo for anomalies and use dogs to sniff out explosives have provided additional layers of security, he said.


Most experts say that despite the TSA’s shortcomings, officers at security checkpoints are better trained than their predecessors and the aviation system is safer.

“The bottom line is that security is working,” said Brian Michael Jenkins, senior adviser to the president of the nonprofit Rand Corp. He said the 9/11 attacks “acted as a catalyst for doing a whole bunch of things and has made it even safer.”

Janet Napolitano, who served as DHS secretary from 2009 to 2013, said other elements that have tightened security include reinforced cockpit doors and the creation of the Federal Flight Deck Officer Program, which allows some pilots to carry firearms.

Pilot unions, however, have pushed for secondary barriers to be installed. In 2018, Congress approved a measure to require them on new aircraft but excluded existing aircraft. In June, the Biden administration moved the measure to its priority rulemaking list for 2021, but the Federal Aviation Administration has not yet mandated the added barriers.


John Pistole, who served as TSA administrator under Napolitano and later Jeh Johnson, said airport checkpoints may be the most visible reminder of aviation-related changes after 9/11, but they are one of many layers put in place to prevent attacks. Other elements begin before a traveler arrives at the airport, with systems that check names against federal watch lists, identifying those who should be barred from flying or who should undergo enhanced screening.

Pistole led the agency as it pivoted from similar screenings for all travelers to less stringent physical examination for those deemed lower risk. He helped oversee the rollout of TSA PreCheck, which allows fingerprinted travelers willing to undergo a background check to move more quickly through special screening lines.

“Knowing who is a known and trusted traveler really reduces the risk, allowing TSA officers to focus on those who are higher risk while expediting those who are lower risk,” Pistole said.


Two decades later in the midst of a global pandemic that has stoked different fears about air travel, officials say some travelers might not recall the anxious months and years that followed 9/11. Even as air travel resumed, many remained uneasy about boarding a plane.

“People have forgotten, I think, about how serious the threat was, not only immediately during the run-up to 9/11, obviously, but in the decade-plus after,” said Javed Ali, a former DHS senior intelligence analyst who teaches public policy at the University of Michigan. “Even in the 2010s, it wasn’t like the threat went away.”

Security threats bring added restrictions

Several incidents — the first just months after the Sept. 11 attacks — have served as reminders that the aviation system continues to be a target. But they also demonstrate how improvements in the gathering and sharing of intelligence enable officials to respond more quickly to potential threats.


In December 2001, British drifter Richard C. Reid tried to detonate bombs concealed in his shoes while on board an American Airlines flight from Paris to Miami. Reid caught the attention of a flight attendant, who detected a burning smell in the cabin, then saw Reid try to light a fuse protruding from his hiking boots. He was the first admitted member of al-Qaeda sentenced in the United States after 9/11.

The incident, combined with other intelligence, eventually led to new security protocols. In 2006, the TSA began requiring travelers to take off their shoes as they moved through airport security.

That same year, after British police uncovered a plan to use liquid explosives to blow up airliners over the Atlantic Ocean, TSA officials banned passengers from bringing liquids and gels in carry-on bags. The ban eventually was relaxed, leading to the current rule’s limit of 3.4 ounces in a clear, quart-size plastic bag.


Three years later, a Nigerian student tried to ignite explosives sewn into his underwear on a Northwest Airlines flight from Amsterdam to Detroit. Umar Farouk Abdulmutallab, who authorities say was trained by an al-Qaeda affiliate in Yemen and became known as the “Underwear Bomber,” was sentenced in 2012 to life in prison.

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Napolitano said Abdulmutallab’s attempt exposed gaps in the system and led to improvements in information-sharing among federal agencies. It also led to tighter screening at international airports to help identify travelers who may pose a threat before boarding a U.S.-bound flight.

Those incidents were followed by other plots, including one involving bombs concealed in printer cartridges aboard cargo planes from Yemen that officials say were intended to go off during flights to the United States. The improvised explosive devices were intercepted by authorities in Britain and the United Arab Emirates.

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The most recent TSA restrictions, in 2017, were spurred by reports that terrorists might use portable electronic devices to conceal bombs, leading to a ban on some larger devices in cabins on flights from eight majority-Muslim countries. The ban was rescinded for airports and carriers that met improved screening standards but led to requirements that many electronics be placed in separate bins during screening.

That same year, Australian officials uncovered a plot involving two brothers with links to Islamic State operatives in Syria who tried to plant a bomb in a meat grinder on an Etihad Airways flight from Sydney to Abu Dhabi. Experts said the incident highlighted new strategies by terrorist networks to get around security protocols.

In December, the Justice Department unsealed an indictment against Cholo Abdi Abdullah, a Kenyan national who allegedly was plotting a 9/11-style attack at the direction of senior al-Shabab leaders. Abdullah was arrested in the Philippines, where he had gone for flight training, according to the indictment.

“I know some of these schemes that the terrorists are coming up with are fantastical, but it’s still on their minds,” said Jenkins, the Rand Corp. analyst. “It’s still in their playbook.”

‘Hard to imagine us stepping back’

Americans have mostly grown accustomed to the post-9/11 security protocols.

“Most people have adapted pretty well to the TSA regimen that we all go through,” said Rasmussen, the former director of the National Counterterrorism Center. “It doesn’t mean everybody loves it, but I just think people understand that it has become a feature of our system and it’s pretty hard to imagine us stepping back.”

Napolitano said the nation’s willingness to invest in aviation security is often driven by the perception of risk. Through the ebbs and flows, she said, the challenge for the TSA is to continue to develop better ways of moving people through airports and on to planes.

In a 2017 report, the Government Accountability Office said the TSA needs to be more “systematic” about measuring the effectiveness of the myriad security measures it deploys. Measuring effectiveness can prove challenging but is necessary to ensure the investment in security is yielding results, the report concluded.

Experts caution against becoming complacent after an absence of recent high-profile aviation threats, saying that’s the result of a mostly effective security system. But they also note that events in Afghanistan have raised concerns about a possible resurgence in terrorist activity.

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“The concern, of course, is that with the Taliban taking over, Afghanistan becomes once more a terrorist haven … a haven in the sense that attacks on other countries, including the U.S., can be hatched there,” Napolitano said. “I think we’re going to have to be very mindful and very careful and have to figure out some way to be able to monitor what’s happening in Afghanistan.”

Ali, the former DHS analyst, said one event is enough to spark worry across the travel industry and the globe. Although systems in place over two decades have largely suppressed those concerns, he said, Americans shouldn’t become overly confident that they are impenetrable.

“As past history has demonstrated, all it takes is another attempted attack to kick-start the conversation about are we doing enough to protect ourselves,” Ali said.

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