September 11 attacks permanently transformed airport security

The terrorist attacks of September 11, 2001, fundamentally and permanently altered airport security protocols across North America and Canada. Prior to the attacks, security measures were significantly less rigorous; domestic passengers could often pass through minimal checks and proceed to gates without presenting identification or boarding passes.

On that day, nineteen hijackers affiliated with Al-Qaeda bypassed metal detectors using knives and tear gas to hijack four commercial aircraft. The attacks resulted in the deaths of nearly 3,000 people when two planes struck the World Trade Center towers, a third hit the Pentagon, and a fourth crashed in a Pennsylvania field. In the aftermath, the previously fluid travel experience was replaced by a complex succession of checkpoints and strict security protocols.