Definition
The unique identifier assigned to an individual aircraft for use in air traffic control communications, flight plans, and surveillance systems. For most general aviation aircraft this is the registration number (such as N12345); for airline and commercial flights it is the company call sign and flight number (such as UAL238).
Plain English
The name or number that identifies a specific aircraft to controllers and computers. It is how the aircraft is labeled on a flight plan, on a radar screen, and in radio calls.
Context Anchor
Seen in FAA abbreviation lists, flight-plan information, air traffic control records, and aviation notices when a specific aircraft or flight must be identified.
Why Pilots Care
Accurate identification prevents confusion between aircraft and supports safe separation and routing decisions.
Intuition Check
ACID does not mean a chemical here. In this FAA context, ACID is an abbreviation for the identification of an aircraft or flight.
Example Sentence 1
The pilot entered the ACID into the transponder so the flight would be correctly tagged on the controller's radar display.
Example Sentence 2
The flight plan listed the correct ACID to ensure proper routing through controlled airspace.