ICAO 24-bit address
Also: hex code, ICAO hex, Mode S address, aircraft address
Unique 24-bit code, written as six hexadecimal characters, that electronically identifies an aircraft in the signals transmitted by its transponder.
What it is
The 24-bit address is assigned by the state of registry from blocks that ICAO allocates to each country under Annex 10. Twenty-four bits allow some 16.7 million combinations, usually written as six hexadecimal characters such as 3C1A2B. Aircraft registered in the United States sit in the block beginning with A, while German aircraft use a block running from 3C to 3F.
Mode S transponders and ADS-B include the address in every message, so radar, other aircraft fitted with TCAS and ground receivers can tell exactly which aircraft is transmitting. The address is tied to the register: an aircraft that moves to another country normally receives a new one. In the United States it is derived directly from the N-number by an algorithm.
On Vuelopedia
An aircraft's record shows its ‘Hex / ICAO 24-bit’ address where it is known, and that address is also what allows its live position to be shown when it is flying with ADS-B data.
Related terms
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This page was last updated on October 9, 2026
APA
Vuelopedia. (2026, October 9). ICAO 24-bit address. Retrieved October 16, 2026, from https://vuelopedia.org/en/glossary/icao-24-bit-address
MLA
“ICAO 24-bit address.” Vuelopedia, Fundación Poderia, 9 Oct. 2026, vuelopedia.org/en/glossary/icao-24-bit-address. Accessed 16 Oct. 2026.
Chicago
Vuelopedia. “ICAO 24-bit address.” Fundación Poderia. Last modified October 9, 2026. https://vuelopedia.org/en/glossary/icao-24-bit-address.
Harvard
Vuelopedia (2026) ICAO 24-bit address. Available at: https://vuelopedia.org/en/glossary/icao-24-bit-address (Accessed: 16 October 2026).
BibTeX
@misc{vuelopedia_en_glossary_icao_24_bit_address,
author = {{Vuelopedia}},
title = {{ICAO 24-bit address}},
publisher = {Fundación Poderia},
year = {2026},
date = {2026-10-09},
url = {https://vuelopedia.org/en/glossary/icao-24-bit-address},
howpublished = {\url{https://vuelopedia.org/en/glossary/icao-24-bit-address}},
urldate = {2026-10-16},
note = {Accessed 2026-10-16}
}Wikipedia
{{cite web |url=https://vuelopedia.org/en/glossary/icao-24-bit-address |title=ICAO 24-bit address |website=Vuelopedia |publisher=Fundación Poderia |date=2026-10-09 |access-date=2026-10-16 |language=en}}