ATIS (Automatic Terminal Information Service) is a continuous broadcast of recorded aeronautical information. The ATIS enables the controller to broadcast the current weather as well as remarks and NOTAMs for pilots to be aware of, so both the pilots and controllers are assured that they are operating under the same airfield information.
A letter of the Phonetic Alphabet is used to identify an ATIS transmission, this letter is then relayed between pilots and controllers to ensure everyone is operating under the same airfield information.
At minimum, the ATIS is updated at least once an hour. Each alphabet letter phonetic word must be used sequentially.
When the first controller opens the phonetic word used will be ‘Alpha’. While the controller is open they’ll update and publish new ATIS broadcasts, thus changing the ATIS information and phonetic letter. Then say for example, that first controller wants close and is currently using information Echo. They will then handoff to the next controller and that controller will then resume from where the last controller ended off as long as there is no change in the ATIS information.
In the real world, the same procedure is followed and the ATIS phonetic letter will continue to cycle through the entire phonetic alphabet until there is a broadcast interruption of
more then 12 hours. Once there is a broadcast interruption of more then 12 hours, the ATIS letter will then be ‘Alpha’, and then the cycle continues again.