Some owners want to change the registration "numbers" (which include letters) on an
aircraft, perhaps to display their initials, to have an alphanumeric sequence matching other aircraft they own or for other reasons. You may select any unused registration number, with a few provisos. For example, some numbers are reserved and others aren't legal (such as any number starting in "0"). Changes in registration numbers are made after the FAA approves permanent registration. A title company can reserve and file the necessary paperwork. The FAA fee for a change in registration number is $10. Once the documents have been filed, the agency grants approval within 30 days. (The aircraft's transponder must be restrapped to the new number.)