What must be displayed on an aircraft during operations under FAR regulations?

The requirement to display the aircraft registration numbers and markings during operations is a fundamental aspect of compliance with Federal Aviation Regulations. Specifically, under FAR Part 45, it is mandated that all civil aircraft in the United States must have their unique registration numbers displayed on the fuselage or on the tail. These registration numbers serve several important purposes: they identify the aircraft, provide a means for tracking ownership, and facilitate communication between the aircraft and air traffic control.

The registration must be of a size and visibility that meets regulatory standards, ensuring it can be easily seen and read from a reasonable distance. This requirement is crucial for enforcing airspace regulations and ensuring safety within the aviation system. Displaying the registration numbers and markings also helps in identifying the aircraft during various operations, including maintenance and inspection activities.

The other choices, while relevant in different contexts, do not meet the essential regulatory requirements for aircraft operations, emphasizing the importance of maintaining visible identification through the proper display of registration numbers and markings.