FDIO field 02 corresponds to what data?

• A. Message Type
• B. Aircraft ID / AID
• C. Beacon Code / BCN
• D. Flight ID / FID

Answer: (B)

In FDIO transmissions, information is laid out in numbered fields, with each field carrying a specific data element. The second field is designated for the Aircraft Identification, called the AID. This identifier is the unique label used to recognize which airplane the data refers to—often the flight number or callsign used by ATC.

Why this is the right fit: knowing the Aircraft Identification in field 02 lets controllers and the system clearly link all subsequent data to the correct aircraft, ensuring accurate tracking and communication. The other items don’t fit here: the Message Type is typically indicated elsewhere to tell you what kind of message you’re receiving, the Beacon Code is the transponder squawk code, and Flight ID is not the standard identifier used in this particular FDIO field layout.