The aviation security system that travelers encounter at U.S. airports was built layer by layer, often after attacks or attempted attacks exposed new vulnerabilities

The aviation security system that travelers encounter at U.S. airports was built layer by layer, often after attacks or attempted attacks exposed new vulnerabilities

As the 25th anniversary of 9/11 nears, here’s how those attacks, the earlier bombing of Pan Am Flight 103 and subsequent plots shaped airline and airport security