Definition
A single letter of the phonetic alphabet (Alpha, Bravo, Charlie, and so on) attached to each new ATIS broadcast at a tower-controlled airport. The letter identifies which version of the recorded airport information the pilot has listened to. When conditions or information change, the airport issues a new ATIS recording with the next letter in sequence.
Plain English
A code letter at the start of the recorded airport information that tells controllers which version of the recording you heard. Each time the recording is updated, the letter advances to the next one (Alpha, then Bravo, then Charlie, and so on).
Context Anchor
You encounter an ATIS code before contacting ground, tower, approach, or departure control at an airport that has an ATIS broadcast.
Derivation
The code uses the ICAO phonetic alphabet, the same letter system pilots use over the radio. Cycling through letters is a simple way to version the recording so everyone knows which update they're working from.
Why Pilots Care
Confirming the ATIS code verifies that the pilot has the latest weather, runway, and operational data before taxi, takeoff, or approach.
Intuition Check
Do not think of “code” here as a password or secret code. It is simply the letter identifier for the current ATIS broadcast.
Example Sentence 1
On first contact, the pilot reported, 'Tower, Cessna 172 Sierra Mike, ten miles north, inbound with information Charlie.'
Example Sentence 2
After the ATIS code changed to Delta, the new winds and runway in use were included in the broadcast.