Airport security after September 11 attacks

Improved security on aircraft
Cockpit doors on many aircraft are now reinforced and bulletproof to prevent unauthorised access. Passengers are prohibited from entering the cockpit during the flight, for United Airlines and American Airlines since 2001 and major changes have been made since 2006.

Identification checks
On September 11, some hijackers lacked proper identification, yet they were allowed to board. After 9/11, passengers who are 18 years old and above must have identification cards in order to fly.