Airport security repercussions due to the September 11 attacks

After the September 11 attacks, questions were raised regarding the effectiveness of airport security at the time, as all 19 hijackers involved in 9/11 managed to pass existing checkpoints and board the airplanes without incident. In the months and years following September 11, 2001, security at many airports worldwide was escalated to deter similar terrorist plots.

Prior to September 11, 2001, airport screening was provided in the U.S. by private companies contracted by the airline or airport. In November 2001, the Transportation Security Administration (TSA) was introduced to take over all of the security functions of the FAA, the airlines, and the airports. Among other changes introduced by TSA, bulletproof and locked cockpit doors became standard on commercial passenger aircraft.

In some countries, for example Sweden, Norway and Finland, there were no or only random security checks for domestic flights in 2001 and before that. On or quickly after September 11, decisions were made to introduce full security checks there. It was immediately implemented where possible, but took one to two years to implement everywhere since terminals were often not prepared with room for it.

Cockpit doors on many aircraft are now reinforced and bulletproof to prevent unauthorized access. Passengers are now prohibited from entering the cockpit during flight. Some aircraft are also equipped with CCTV cameras, so the pilots can monitor cabin activity. Pilots are now allowed to carry firearms, but they must be trained and licensed. In the U.S., more air marshals have been placed on flights to improve security.

On September 11, hijackers Khalid al-Mihdhar, Majed Moqed, Nawaf al-Hazmi and Salem al-Hazmi all set off the metal detector. Despite being scanned with a hand-held detector, the hijackers were passed through. Security camera footage later showed some hijackers had what appeared to be box cutters clipped to their back pockets. Box cutters and similar small knives were allowed on board aircraft at the time.

...
Wikipedia