By Emmanuel Bobby
For millions of Americans, going through airport security is now an ordinary part of traveling. Passengers arrive with boarding passes, pass through federally operated screening checkpoints, remove or prepare certain belongings for inspection and carefully consider what they can pack in their carry-on luggage.
But modern airport security is the result of decades of changes. Many of the rules that travelers encounter today did not exist before a series of terrorist attacks and attempted attacks exposed weaknesses in the aviation system.
There was a time when airport security looked dramatically different. Screening checkpoints were operated by private companies hired by individual airlines rather than by a federal workforce. Travelers could take full-sized bottles of shampoo, shaving cream and other liquids through security without worrying about today’s strict limits. Friends and family members could also walk with departing passengers much farther into airports, sometimes accompanying them all the way to the gate to say goodbye.
Over time, those freedoms disappeared as authorities responded to increasingly sophisticated threats.
From the bombing of Pan Am Flight 103 over Lockerbie, Scotland, to the attacks of Sept. 11, 2001, and later attempted bombings involving shoes, liquids and concealed explosives, each major incident exposed a different vulnerability. Security agencies responded by adding new layers of screening, technology and restrictions.
Aviation security experts say the system travelers encounter today was largely built piece by piece, with major changes often coming after authorities discovered that existing safeguards were not sufficient.
“Attacks on aviation have an impact much greater than attacks on anything else because aviation commands the attention of the world as the thing that links the world,” aviation disaster attorney Mary Schiavo has said.
As the 25th anniversary of the Sept. 11 attacks approaches, the history of those changes illustrates how dramatically air travel has evolved.
September 11 changed the understanding of hijackings
Few events have had a greater impact on commercial aviation than the terrorist attacks of Sept. 11, 2001.
Nineteen al-Qaida hijackers took control of four commercial aircraft. Two planes were deliberately crashed into New York’s World Trade Center, another struck the Pentagon and a fourth crashed into a field in Pennsylvania after passengers attempted to regain control.
Before 9/11, aviation authorities generally operated under the assumption that hijackers wanted to negotiate or use an aircraft as leverage. The possibility that hijackers would deliberately turn passenger airplanes into weapons had not been treated as the central threat.
“The focus at the time, generally, was not on suicide attackers,” Schiavo said.
The attacks immediately changed that calculation.
Federal officials began imposing restrictions at airports, including limiting access beyond security checkpoints to ticketed passengers. Knives and box cutters were banned from carry-on luggage after investigators determined that the hijackers had used small cutting instruments to threaten passengers and crew members.
Congress also created the Transportation Security Administration, commonly known as TSA, and transferred responsibility for passenger and baggage screening to the federal government.
The federal legislation passed after the attacks also included requirements for reinforced cockpit doors, additional federal air marshals and screening of all checked luggage for explosives.
The changes dramatically altered the airport experience. Security lines became longer, screening became more extensive and travelers were required to arrive earlier to allow additional time for inspections.
The Lockerbie bombing exposed weaknesses in checked baggage security
The transformation of aviation security had already begun before 9/11.
On Dec. 21, 1988, Pan Am Flight 103 exploded over Lockerbie, Scotland, killing all 259 people aboard and 11 people on the ground.
Investigators determined that an explosive device concealed inside a suitcase had been placed aboard the aircraft. The luggage had originated in Malta and eventually made its way onto the Pan Am flight without being accompanied by a passenger.
The attack demonstrated that an individual did not necessarily need to carry a weapon onto an airplane personally to cause catastrophic damage.
It also exposed significant vulnerabilities involving checked baggage.
Former Federal Aviation Administration Administrator Jane Garvey later told the 9/11 Commission that the Lockerbie bombing prompted some of the most significant changes to aviation security since the early 1970s.
In response, U.S. airlines operating from airports in Europe and the Middle East were required to use X-rays or physical searches on checked luggage. Additional random inspections were introduced, and authorities sought to ensure that checked bags were associated with passengers actually traveling on the aircraft.
Security officials also increased intelligence sharing, strengthened cargo controls, developed training standards for private screening personnel and invested in technologies designed to detect explosives.
The government also conducted covert tests designed to determine whether airport and airline security systems could withstand simulated terrorist attacks.
Even with those efforts, officials recognized that aviation security could never eliminate every possible threat.
A shoe bomber leads to another major change
Just months after 9/11, another attempted attack revealed a different weakness.
On Dec. 22, 2001, Richard Reid boarded American Airlines Flight 63 traveling from Paris to Miami. He had explosives concealed inside his shoes and attempted to detonate them while the aircraft was in flight.
The device did not successfully explode. Passengers and crew members eventually restrained Reid.
The attempted bombing nevertheless produced another major change in airport security.
Passengers were initially asked to remove their shoes voluntarily during screening. The practice eventually became mandatory, turning shoe removal into one of the most recognizable features of airport security in the United States.
For years, travelers were required to remove their footwear before walking through the checkpoint.
That policy remained in place until July 2025, when the Trump administration ended the general shoe-removal requirement for U.S. airport screening.
Liquid explosives change what passengers can bring aboard
Another major transformation came from a foiled terrorist plot involving liquid explosives.
British authorities announced in 2006 that they had disrupted a plan involving explosives concealed in beverage containers. Investigators said the suspects intended to use the devices against several transatlantic aircraft.
The discovery raised concerns that conventional airport screening procedures could be defeated by explosives disguised as ordinary drinks or other liquids.
In response, airport authorities imposed sweeping restrictions on liquids, gels and aerosols.
Passengers were initially prohibited from carrying most such substances through security checkpoints. The restrictions were later modified into the familiar “3-1-1” system.
Under the rule, travelers generally may bring liquids, gels and aerosols in containers of 3.4 ounces or less, with the containers placed in a single quart-sized clear plastic bag.
The rule remains one of the most visible examples of how a particular attempted attack can lead to a security procedure that affects millions of travelers.
The underwear bomber accelerates body-scanner technology
Another attempted attack in 2009 prompted a new technological shift.
On Christmas Day that year, Umar Farouk Abdulmutallab attempted to detonate explosives hidden in his underwear while aboard Northwest Airlines Flight 253 as it approached Detroit.
The device failed to produce the intended explosion, although it caused a fire and severely burned Abdulmutallab. He was later convicted after pleading guilty to attempting to destroy the aircraft.
The incident demonstrated another limitation in airport screening technology.
Traditional metal detectors were not designed to identify certain types of nonmetallic explosives concealed beneath clothing.
The TSA had already been testing full-body scanning technology at some airports. Following the attempted bombing, authorities accelerated the deployment of body scanners.
Today’s scanners can detect objects concealed under clothing without requiring passengers to remove all of their clothing. Travelers are typically instructed to stand in a designated position with their feet apart and their arms raised.
For many passengers, the body scanner has become as familiar as the traditional metal detector.
Airport security continues to evolve
The changes did not end with the major attacks and attempted attacks of the past several decades.
Airport security continues to evolve as officials introduce new technology and adjust procedures based on emerging threats.
One area receiving increased attention is biometric identification. Facial-recognition technology has been expanded at airports as authorities look for ways to verify passengers’ identities while potentially making the screening and boarding process more efficient.
Aircraft themselves are also being modified.
Beginning in 2026, newly manufactured passenger aircraft are required to include a secondary security barrier between the passenger cabin and the flight deck. The barrier is intended to provide an additional layer of protection whenever the main reinforced cockpit door has to be opened.
Pilot representatives have also pushed for similar secondary barriers to be installed on existing aircraft.
The broader philosophy behind modern aviation security is based on multiple layers rather than relying on a single checkpoint or piece of equipment.
Security experts acknowledge that any individual safeguard could potentially be defeated. The goal is to create enough overlapping protections that bypassing one layer does not provide an attacker with unrestricted access to an aircraft.
The airport experience is a reflection of that history
Many of today’s airport rules can seem inconvenient to travelers. Removing belongings from bags, limiting liquids, undergoing identity checks and passing through scanners are routine experiences for passengers.
Yet each procedure has a history.
Some were created after successful terrorist attacks. Others emerged following attempted attacks that exposed vulnerabilities before lives were lost on a larger scale. Still others developed as technology changed and security officials sought to address threats that had previously been difficult to detect.
The result is a system that bears little resemblance to the airport experience of several decades ago.
The restrictions can sometimes feel routine because passengers have become accustomed to them. But the modern security environment represents the accumulation of lessons learned from Lockerbie, 9/11, the shoe-bombing attempt, the liquid-explosives plot and the underwear-bombing attempt.
Aviation security is therefore not a finished system. As technology improves and potential threats evolve, authorities continue to adjust procedures and introduce new layers of protection.
The objective remains the same: prevent dangerous people or materials from reaching an aircraft while allowing millions of legitimate passengers to travel safely.
As the 25th anniversary of 9/11 approaches, the evolution of airport security offers a reminder of just how profoundly a series of attacks changed one of the most routine parts of modern life: getting on an airplane.I can also make this more newspaper-style, substantially longer, or more dramatic while keeping it factual.
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