Page "Airport security repercussions due to the September 11 attacks" Paragraph 2

Cockpit doors on many aircraft are now strengthened and bulletproof to prevent unauthorized access.

Unlike in previous years, passengers are generally prohibited from entering the cockpit during flight.

Some aircraft are equipped with CCTV cameras, so the pilots can monitor the cabin activity.

Pilots also have an option to carry a gun, but must be trained to use and operate it.

In the U. S., more air marshals have been placed onto flights to improve security.