The aviation security system in U.S. airports has evolved over time, often in response to specific threats or incidents. Before major changes, travelers could bring full-sized bottles of shampoo or cans of shaving cream through security, and friends or family could meet passengers at the gate for a farewell hug. The current system, however, was built layer by layer as new vulnerabilities were identified, often following attacks or attempted attacks. These include incidents like bombs hidden in luggage and hijackers who used planes as weapons. The most dramatic shift in air travel occurred on September 11, 2001, when 19 al-Qaida hijackers took control of four commercial airplanes, crashing two into the World Trade Center in New York, one into the Pentagon, and another in Pennsylvania. Before the 9/11 Commission identified systemic failures, the Federal Aviation Administration (FAA) had already begun implementing new security measures, such as restricting access to airport gates and banning knives from carry-on bags. Congress later created the Transportation Security Administration (TSA) to oversee passenger and cargo screening. The 2001 law also mandated reinforced cockpit doors, more air marshals, and full screening of all checked luggage. Over time, the TSA introduced risk-based screening methods to speed up the process for some travelers, though civil liberties groups raised concerns about potential bias in the selection criteria. A major turning point in aviation security occurred nearly 13 years before 9/11, when a bomb destroyed Pan Am Flight 103 over Lockerbie, Scotland, killing 270 people. This attack led to significant changes in security protocols, including more rigorous baggage checks and intelligence-sharing agreements. The FAA also conducted covert tests to evaluate the effectiveness of security systems. By 2001, the agency had identified explosive devices as the most dangerous threat to commercial aviation, a view that shaped the response to the 9/11 attacks. In the years following 9/11, new threats continued to influence security measures. In 2001, Richard Reid attempted to detonate explosives in his shoes on an American Airlines flight, prompting a new rule requiring passengers to remove their shoes during screening. Later, a 2006 plot involving liquid explosives in beverage bottles led to the “3-1-1” rule, limiting liquids to 3.4 ounces in a single clear plastic bag. In 2025, the Trump administration ended the shoe screening requirement, but the threat of hidden explosives led to the introduction of full-body scanners, which use radio waves to detect prohibited items. Today, travelers are accustomed to stepping into these scanners with feet apart and hands raised. The TSA continues to refine security procedures. Facial recognition technology is now being used to verify passenger identities, and new aircraft must include a retractable security gate between the cabin and cockpit. Experts argue that no single security measure is foolproof, but combining multiple layers creates a more resilient system. As threats evolve, so too does the security landscape at U.S. airports, ensuring that air travel remains as safe as possible.