An airport slot is a small opening in a fence or wall that allows an aircraft to take off or land. Air traffic controllers assign aircraft slots according to their priority.
Most airports have two types of slots: general aviation slots and military slots. .
Aircraft flying in general aviation slots have the Lowest priority and are given first priority when there are delays. Aircraft flying in military slots have the highest priority and are given only when there are no other aircraft available.
When an aircraft is assigned to a slot, the controller assigns it a clearance code, which is a unique identifier for the aircraft.
An airplane’s clearance code is displayed on the windshield and on a panel near the cockpit. The controller will give the clearance code to the pilot before issuing the takeoff or landing clearance.
Airport slots work like locks on a door. When an airplane is assigned to a slot, it can only leave or enter that slot.
If another airplane is already in that slot, the first airplane can’t enter and the second airplane can’t leave. If there’s no other aircraft in that slot, the controller can issue a takeoff or landing clearance for either airplane.