Mode S Transponder

[Danial9874]

Hello guys, I know that the Mode S is a secondary surveillance and communication system which supports Air Traffic Control (ATC). Each Mode S transponder equipped aircraft is assigned a unique address code. Using this unique code, interrogations can be directed to a particular aircraft and replies can be unambiguously identified. But, who provide/ allocate the Mode S codes to aircraft ? ICAO ? National Airworthiness Authority ?

[EXDAC]

https://www.icao.int/WACAF/Documents...Assignment.pdf

[DaveReidUK]

Originally Posted by Danial9874

But, who provide/ allocate the Mode S codes to aircraft ? ICAO ? National Airworthiness Authority ?

Both.

ICAO allocates a range of addresses to each country. The country's NCAA (or equivalent) assigns addresses to individual aircraft.