From Lockerbie to 9/11: How attacks reshaped US airport security

Flying from a US airport today means federal security checks, strict carry-on rules, and a boarding pass just to reach the gate. That was not always the case. For decades, private contractors hired by airlines ran security, and passengers could be seen off by friends and family at the gate.

Today's system was built piece by piece, often in response to attacks or attempted attacks that exposed new weaknesses — from bombs in luggage to hijackers using planes as weapons.

"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," said Mary Schiavo, an aviation disaster attorney.

9/11: A turning point

No event changed air travel more than September 11, 2001, when 19 al-Qaida hijackers seized four planes, crashing two into the World Trade Center, one into the Pentagon, and another in Pennsylvania.

Before that day, authorities assumed hijackers wanted to negotiate, not deliberately crash planes, according to Schiavo, who served as the US Department of Transportation's inspector general from 1990 to 1996. "The focus at the time, generally, was not on suicide attackers," she said.

The Federal Aviation Administration (FAA) quickly restricted gate access to ticketed passengers and banned knives and box cutters from carry-ons. Congress then created the Transportation Security Administration (TSA), shifting screening to a federal workforce. The same law required reinforced cockpit doors, more air marshals, and screening of all checked luggage for explosives.

As lines grew, TSA introduced PreCheck for pre-vetted travelers and began using watchlists and background checks to sort passengers by risk. Civil liberties advocates warned that opaque criteria and inaccurate lists could lead to discriminatory profiling.

Earlier lessons: Lockerbie

Nearly 13 years before 9/11, a bomb destroyed Pan Am Flight 103 over Lockerbie, Scotland, killing 259 people aboard and 11 on the ground. Investigators found the explosive was hidden in a radio-cassette player inside a suitcase checked without an accompanying passenger.

The December 1988 attack "stimulated the most significant changes in aviation security since the early 1970s," former FAA Administrator Jane Garvey told the 9/11 Commission in 2003. The FAA ordered X-ray or physical checks of all checked bags on US carriers at European and Middle Eastern airports, and required that bags belong to flying passengers.

The agency also assigned security personnel at major airports, set up intelligence-sharing, tightened cargo controls, and researched explosives-detection technology. It even ran covert tests simulating terrorist tactics.

Post-9/11 plots

On December 22, 2001, Richard Reid tried to ignite explosives hidden in his shoes on a Paris-to-Miami flight. Passengers subdued him. TSA soon asked travelers to remove shoes voluntarily; the rule became mandatory in 2006 after British authorities disrupted a plot to use liquid explosives to destroy transatlantic airliners. TSA banned nearly all liquids, then replaced that with the "3-1-1" rule limiting containers to 3.4 ounces in a single quart-sized bag. In July 2025, the shoe screening requirement was ended.

On Christmas Day 2009, Umar Farouk Abdulmutallab tried to detonate explosives hidden in his underwear on a flight to Detroit. The device failed, but the attempt pushed TSA to fast-track full-body scanners, which use radio waves to detect a wide range of prohibited items.

Still evolving

Security continues to change. TSA is expanding facial recognition for identity checks, and new passenger planes must now have retractable secondary barriers to protect cockpits when main doors are open.

"Any one layer of security can be breached," said Sheldon Jacobson, a University of Illinois professor whose research contributed to TSA PreCheck's design. "But collectively, when you put them on top of each other, what you end up with is a very resilient system."