If you own an aircraft that was registered in the month of May of any year, your aircraft must be re-registered by September 30, 2011. You should submit your re-registration application as soon as possible since you won’t be able to operate your aircraft legally after September 30 until you receive your new registration certificate. Online re-registrations will be accepted until July 31, 2011. After that, you will need to submit your re-registration application to the FAA via mail.
For June-issued certificates, aircraft owners may submit re-registration applications starting August 1, 2011 through October 31, 2011. After October 31, those aircraft may not be operated legally until the owner receives the new registration certificate. Online re-registration applications may be submitted here by entering the aircraft’s N-number and re-registration code to begin the process, or you may submit a written re-registration application to the FAA via mail.
For a discussion of the FAA’s re-registration requirements, please read my article Understanding The FAA’s New Aircraft Re-Registration And Renewal Requirements.