Twenty-five years ago, passengers could arrive at many US airports and walk to the departure gate accompanied by friends and relatives. Small knives were permitted in aircraft cabins, liquids were largely unrestricted and passenger screening was carried out by private contractors working for airlines.
Then came 11 September 2001.
The hijacking of four commercial aircraft and the deaths of 2,977 people transformed aviation security, triggering changes that remain part of the experience of flying today. Governments tightened access to airports and aircraft, reinforced cockpit doors, expanded baggage screening and introduced new layers of passenger checks, while international cooperation on aviation security accelerated.
A quarter of a century later, some of those measures are beginning to change again as technology improves and authorities attempt to reconcile security with a passenger experience that has become increasingly complex.
The timing could hardly be more symbolic. As reported by Travel Tomorrow, the US Transportation Security Administration (TSA) is now allowing non-ticketed visitors back into secure gate areas at 13 airports under its new Gateside programme. Approved visitors must still undergo security screening and meet strict conditions, but the initiative partially restores something that largely disappeared after 9/11: saying goodbye to someone at their departure gate or waiting there to welcome them home.
The move offers a striking illustration of how airport security has evolved over the past 25 years. The airport experience may be gradually regaining some of its pre-9/11 freedoms, but the security architecture behind it is fundamentally different.
The second plane to hit the World Trade Center on September 11, 2001 was United Airlines Flight 175 | Rare video footage | 9/11 pic.twitter.com/uEUsTccUle
— Lois (Anastasia) Mezzovenditti (@mezzovenditti) September 5, 2026
9/11 changed who was responsible for security
One of the most significant changes came in the United States itself. Before 9/11, airlines hired private contractors to operate passenger screening checkpoints. In November 2001, the Aviation and Transportation Security Act created the TSA, shifting responsibility for screening to the federal government and establishing national standards across US airports.
Other fundamental changes followed. Cockpit doors were reinforced and access to flight decks became far more restricted. Knives were prohibited from cabins, while checked baggage, air cargo and airport workers became subject to tighter security controls.
But modern airport security was not created in a single moment. Some of its foundations predate 9/11, while many of the procedures travellers associate with the post-9/11 era actually resulted from attacks and foiled plots that came afterwards.
The bombing of Pan Am Flight 103 over Lockerbie in December 1988 had already exposed vulnerabilities in checked baggage. An explosive hidden inside a radio-cassette player in an unaccompanied suitcase destroyed the Boeing 747 travelling from London to New York, killing 259 people on board and another 11 on the ground. The attack led to tighter baggage controls and greater scrutiny of luggage travelling without its owner.
After 9/11, aviation security would continue to develop in much the same way: layer by layer, with new measures introduced when attackers exposed another vulnerability.
#OTD in 1988: Lockerbie Bombing (Scotland). Pan Am Flight 103, a B-747 on a transatlantic route, explodes over the town of Lockerbie. All 259 aboard and 11 on the ground die. Attack was traced to Lybian intelligence, in retaliation from US airstrikes on the country in 1986. pic.twitter.com/fj3XyZMUhX
— Francisco Cunha – ✈️ Aviation et al (@OnDisasters) December 21, 2025
Shoes, liquids and body scanners
Just over three months after 9/11, Richard Reid boarded an American Airlines flight from Paris to Miami with explosives concealed in his shoes. He attempted to detonate them during the flight but was restrained by passengers and crew.
The failed attack eventually led to mandatory shoe screening in the United States, creating one of the most recognisable airport rituals of the post-9/11 era. Almost 24 years later, in July 2025, the US ended the general requirement for passengers to remove their shoes at TSA checkpoints.
Liquids followed a similar trajectory. In 2006, British authorities disrupted a plot to destroy transatlantic aircraft using liquid explosives concealed in drink containers. Almost all liquids were initially prohibited beyond security checkpoints before rules were adapted to allow passengers to carry limited quantities.
The attempted bombing of Northwest Airlines Flight 253 on Christmas Day 2009 exposed another weakness. Explosives had been concealed beneath the passenger’s clothing, where conventional metal detectors could not identify them. The incident accelerated the rollout of advanced full-body scanners at major airports.
Today, many airports are moving towards another generation of technology. Computed tomography scanners can produce detailed three-dimensional images of cabin baggage, potentially allowing passengers to leave liquids and electronics inside their bags, while biometrics and facial recognition are increasingly being used for identity verification.
The result is somewhat paradoxical: airport security is becoming technologically more sophisticated while some of the procedures passengers experience are becoming less intrusive.
Europe changed too
Although the attacks took place in the United States, their impact on European aviation was profound. Before 9/11, the European Union had no legislative competence in aviation security, leaving responsibility to individual Member States.
The attacks prompted the creation of a common EU aviation security regime from 2002. Today, EU-wide standards cover passenger and baggage screening, airport access, aircraft security, cargo and mail, airport supplies, and the recruitment and training of staff.
Those rules have continued to evolve in response to subsequent threats. The 2006 liquid explosives plot led to additional European restrictions on liquids, while the attempted attack in 2009 involving explosives concealed on a passenger prompted further consideration of security scanners.
The EU framework also illustrates how one of the biggest consequences of 9/11 occurred largely out of sight of passengers. Aviation security became much more coordinated internationally, with governments increasingly sharing standards, intelligence and passenger information rather than treating individual airports or countries as isolated systems.
A global response
That international dimension is being emphasised by the International Civil Aviation Organization (ICAO) as the world marks the 25th anniversary.
Within two weeks of the attacks, 169 countries gathered at ICAO headquarters in Montréal and unanimously condemned the use of aircraft as weapons, pledging greater international cooperation to prevent future terrorist attacks against civil aviation.
“We must honour the victims of the 9/11 attacks – the 2,977 innocent people killed that day and the uncountable number of others who have also suffered then and now in immeasurable ways – by ensuring nothing like this can happen again,” ICAO Council President Toshiyuki Onuma and Secretary General Juan Carlos Salazar said in a joint statement marking the anniversary.
The organisation points out that the international security framework has expanded significantly since 2001, including through new treaties, security standards, audits of Member States and greater use of passenger information. But it also warns that implementation remains uneven and that aviation security cannot be treated as a finished project.
From hijackers to cyberattacks and drones
The nature of the threat is changing too. Hijacking and explosives remain security concerns, but the aviation system of 2026 faces risks that were far less prominent, or barely imaginable, in 2001.
Cyberattacks can target the increasingly interconnected digital systems used by airlines, airports and air traffic management. Drones can disrupt airport operations or potentially be used maliciously. Insider threats involve people who already possess authorised access to secure areas, while GPS interference, supply-chain vulnerabilities and conflicts can create risks far from conventional passenger checkpoints.
ICAO identifies cybersecurity, insider threats and the misuse of unmanned aircraft systems among the challenges requiring constant review, alongside navigation interference and risks arising from conflict zones.
The shift helps explain why measuring aviation security solely by what passengers experience at checkpoints can be misleading. Twenty-five years ago, preventing prohibited items from entering an aircraft was at the centre of the response. Today, protecting aviation also means securing digital infrastructure, controlling access to sensitive areas, analysing passenger information and anticipating threats that may never pass through a security lane.
Could the airport become more open again?
Against that background, the return of non-flyers to departure gates in the US is particularly significant.
The Gateside programme is far from a return to the largely unrestricted airport access of the pre-9/11 era. Participants must belong to TSA PreCheck or another eligible trusted traveller programme, apply in advance, receive approval, carry valid identification and pass through airport security.
Still, the symbolism is difficult to ignore.
The TSA says the programme will allow people to once again welcome relatives at the gate, accompany loved ones before departure, meet friends during layovers or simply use terminal restaurants and shops. Critics may question whether commercial considerations are also helping drive the change, particularly as US airports seek more non-passenger spending.
It also comes as debate continues over the future organisation of US airport security, including proposals to expand the use of private screening contractors. As Travel Tomorrow has previously reported, supporters see private participation as a way to improve efficiency, while critics warn against allowing commercial considerations to weaken a system created precisely because of the shortcomings exposed by 9/11.
Yet the Gateside experiment also suggests something broader. After 25 years of additional rules, technology and intelligence, authorities increasingly believe that security does not always have to mean imposing more visible restrictions on passengers.
That may be one of the most significant changes since 2001. The immediate response to 9/11 was necessarily about closing vulnerabilities and adding barriers. The challenge in 2026 is increasingly about maintaining those protections while deciding which barriers are still necessary.
Airport security today looks very different from the system that failed on 11 September 2001, and the threats it must confront are different too. As Onuma and Salazar noted, the framework created through years of international adjustment “remains a work in progress”.
Twenty-five years after 9/11, that may be its most enduring lesson. Aviation security cannot eliminate every risk, nor can it remain frozen in the response to the last attack. It has to continue changing before the next threat reveals where its weaknesses lie.
