How the conversion works

The FAA holds the US block of addresses from A00001 (N1) to ADF7C7 (N99999). Registrations are numbered in order (N1, N1A, N1AA … N1AZ, N1B … N10 …), and an aircraft's address is its position in that list. Valid N-numbers have up to five characters after the N, start with a digit from 1 to 9, and end with at most two letters (never I or O).

When you need it

  • Programming a new transponder or ADS-B unit, which asks for the code in hex or octal.
  • Finding an aircraft on ADS-B tracking sites that search by hex code.
  • Checking a reserved or changed N-number: the code changes with the registration, so the transponder must be reprogrammed.

The FAA registry lists the official code for each registered aircraft ("Mode S Code" on the registration record). If the two ever differ, use the registry's value.