How do we renew an expired aircraft registration? It needs repair and is not airworthy. The loan on the aircraft was paid off. We may need to sell the aircraft and transfer the title. How is the registration related to the title?
The FAA's registration site says (emphasis in the original):
If aircraft registration has expired and a renewal certificate has not been issued, received, and placed in the aircraft, then the aircraft is without authority to operate.
If a renewal application was first received by the Registry after the expiration date, the renewal process no longer applies. An aircraft owner may apply for registration of an unregistered aircraft under 14 C.F.R. §4731(a), by filing an Aircraft Registration Application, AC Form 8050-1, the $5.00 registration fee, and evidence of ownership (if it is not already on file at the Registry).
In other words, it's effectively a new registration. The title could be used as the evidence of ownership.
You can find form 8050-1 here.