Click on the link below to view my github repository for converting a 6 character hexadecimal ICAO (mode-s) aircraft code to it's corresponding registration (tail) number. This is a php script and will only accept U.S. civilian aircraft ICAO numbers. These numbers range from A00001 to ADF7C7. Please note that this is just a calculation and the resulting registration is not necessarily assigned to an aircraft. Conversely, this script will also convert registrations to their corresponding ICAO address.