From cockpit doors to CT scanners: How 9/11 still shapes air travel 25 years later

Twenty-five years after the September 11 attacks, their legacy remains built into almost every stage of an airline journey.

The reinforced cockpit door, the explosives screening of checked baggage and the extensive checks conducted before some passengers reach an airport all emerged from the security transformation that followed the attacks.

Some of the most visible restrictions are now being relaxed as screening technology improves. Others are still being introduced, including a second physical barrier protecting the flight deck on newly manufactured US airliners.

On the morning of 11 September 2001, four commercial aircraft were hijacked. Two were flown into the World Trade Center in New York and another struck the Pentagon. The fourth, United Airlines Flight 93, crashed in Pennsylvania after passengers and crew attempted to regain control. Nearly 3,000 people were killed.

The attacks exposed profound weaknesses in aviation security and overturned assumptions about how a hijacked aircraft might be used. The response transformed not only airport checkpoints, but aircraft design, intelligence sharing, passenger vetting and the division of responsibility for aviation security.

How 9/11 transformed airport security

One of the first major changes was the creation of a dedicated US transportation security agency.

On 19 November 2001, the US Aviation and Transportation Security Act became law, creating the Transportation Security Administration (TSA) and placing passenger screening under federal control.

This mandated a screening programme conducted by federal officials, with 100% of checked baggage undergoing screening, as well as an expansion of the Federal Air Marshal Service and reinforced cockpit doors. 

“The agency was created to oversee security in all modes of transportation, but aviation security was at the forefront of the nation’s mind after the 9/11 attack,” said David Pekoske, former administrator for the TSA. 

Screening rules tightened a year after the attacks

By December 2002, the TSA met one of the key requirements of the Aviation and Transportation Security Act by deploying explosives detection systems across the United States to screen all bags for explosives.

The following spring, a federal flight deck officer programme was created, and the TSA began training pilots to carry firearms. The first armed pilots were put onboard commercial flights shortly after. In April 2003, all airlines met the FAA requirement to reinforce cockpit doors, protecting them even from gunfire or grenades.

There was a flurry of changes in 2006, including a requirement for passengers to remove their shoes to screen for explosives after a failed plot centred on a shoe-bomb.

The same year, the TSA deployed federal air marshals overseas and enhanced security measures to include more random employee screening, additional canine patrols, and stronger air cargo security measures.

By 2010, the TSA had begun installing full-body scanners at US airports. The units were brought in to detect non-metallic weapons, explosives and other threats that could be concealed under layers of clothing.

By the end of the year, new rules barred passengers from having printer cartridges in their carry-on baggage after intelligence about a new plot using the items to conceal explosives. 

Similar changes spread internationally. Governments strengthened passenger and baggage screening, while reinforced and locked flight deck doors became standard on commercial aircraft around the world. International aviation security standards and auditing were also tightened through the International Civil Aviation Organization.

Improving security behind the scenes

One of the less visible consequences of 9/11 has been the expansion of security beyond the passenger checkpoint.

In the years that followed the attacks, there have been enhancements to passenger vetting, employee screening, cargo security, intelligence sharing and monitoring of potential insider threats.

The TSA’s Secure Flight programme was introduced in 2009, and the agency vets transportation workers, including airport employees and airline crew, against terrorism watchlists.

Air cargo has also become a greater focus, with the TSA reporting that cargo carried on passenger aircraft departing US airports for international destinations is either screened or secured under applicable standards.

In 2018, advances in technology meant airports were beginning to see the introduction of Computed tomography scanners, a state-of-the-art, 3D screening technology which was better able to detect items such as explosives. 

CT scanners can now produce three-dimensional images of cabin baggage, allowing screeners to examine its contents in greater detail. Advanced imaging technology is used to detect both metallic and non-metallic threats, while automated systems can verify identity documents and passenger information.

Facial-recognition tools are also increasingly being used to aid with passenger-identification processes at borders and gates.

Securing the flight deck from intruders

The latest security move, which still has its roots in the 9/11 attacks, is the introduction of secondary flight deck door barriers, which are now being fitted to some aircraft. The device is a new layer of security aimed at preventing unauthorised access to the flight deck.

The additional barrier has been a long-standing demand from pilot groups, who argue that it provides essential protection when cockpit doors are opened in flight.

Southwest Airlines operated the first US commercial service using an aircraft fitted with a secondary cockpit barrier last September.

In 2023, the Federal Aviation Administration (FAA) confirmed new regulations requiring manufacturers to install secondary barriers on all newly built commercial passenger aircraft.

The requirement took effect a year ago. Under the rule, aircraft manufacturers are required to install the secondary barrier on all new commercial aircraft produced. Existing aircraft do not have to be retrofitted with the product.

Now, the remit of the TSA is much broader.

The TSA’s mission and focus “began with the urgent task of preventing another 9/11-style attack on the homeland, but its operations have expanded and evolved across the entire transportation landscape, from aviation to surface and the physical and cyber domains,” noted Pekoske.