How are aircraft inoperability issues often marked?

Marking aircraft inoperability issues is crucial for ensuring safety and maintaining clear communication among flight crews and maintenance personnel. The approach of tagging controls—such as the mixture control—as 'Aircraft Inoperable' provides a direct visual indication that particular systems or functions are not operational. This method is effective because it prevents the pilot from inadvertently attempting to use a control that may pose safety risks due to malfunction.

Tagging helps to convey important information quickly and directly to anyone interacting with the aircraft, ensuring that regardless of who is operating or inspecting the aircraft, they are aware of existing issues. This method is part of a broader safety protocol in aviation, which emphasizes clear and visible indications of aircraft status.

The other options might involve aspects of communication or record-keeping, but they do not provide the immediate visual cue required to alert a pilot during operation. Thus, tagging the control is the most reliable and recognized method of indicating inoperability issues.