If an aircraft was not approved for return to service after an annual inspection, what must the owner obtain to fly it to another maintenance base?

To fly an aircraft that has not been approved for return to service after an annual inspection, the owner must obtain a Special Flight Permit. This type of permit is specifically designed to allow an aircraft that may not currently meet all regulatory requirements for a standard operation to be flown under certain conditions for a limited purpose, such as to a maintenance facility where it can receive necessary repairs or inspections.

The Special Flight Permit is crucial in situations where aspects of the aircraft's airworthiness have been found lacking, but it may still be safe to operate under restricted conditions. This ensures that the aircraft can be transported without violating aviation regulations or compromising safety.

In contrast, the other options do not provide the necessary legal framework or authority for flying an unapproved aircraft. Routine Flight Approval does not exist in this context; Maintenance Authorization is more related to allowing maintenance providers to work on the aircraft, not flying it; and a Temporary Flight License is not a recognized term or permit under aviation regulations. Therefore, the only correct course of action in this scenario is to secure a Special Flight Permit.