ICAO 24-bit address
All modern aircraft are assigned a unique
ICAO 24-bit address or (informally) Mode-S
"hex code" upon national registration and this address becomes a part of the aircraft's
Certificate of Registration. Normally, the address is never changed, however, the transponders are reprogrammable and, occasionally, are moved from one aircraft to another (presumably for operational or cost purposes), either by maintenance or by changing the appropriate entry in the aircraft's FMS system.
There are 16,777,214 unique ICAO 24-bit addresses (hex codes) available. The ICAO 24-bit address can be represented in three digital formats:
hexadecimal,
octal, and
binary. These addresses can be decoded and converted amongst each other online using tools such as those at
Airframes.org and
Kloth.net to obtain the aircraft's
tail number. Whichever format is used, the same information is carried through the signal.
Example of an ICAO 24-bit address:
§ Hexadecimal: AC82EC
§ Decimal: 11305708
(Note: rarely used format)
§ Octal: 53101354
§ Binary: 101011001000001011101100
(Note: occasionally, spaces are added for visual clarity, thus 10101100 10000010 11101100)
(These all correlate to the same
aircraft registration,
N905NA.)
FlightAware
