Which action is classified as preventive maintenance for pilots?

Changing tires is classified as preventive maintenance because it involves routine upkeep that helps ensure the aircraft remains airworthy and functions correctly. Preventive maintenance encompasses tasks that are generally simple, do not require specialized knowledge or extensive training, and are typically aimed at preventing larger issues from developing.

While replacing tires can be a straightforward process, it directly contributes to the aircraft's safety and performance by maintaining proper handling and ground operation capabilities. This task is necessary to inspect and maintain the condition of the aircraft, reducing the risk of tire-related failures during flight.

The other options involve more complex procedures that might require specialized skills, certifications, or could be considered major repairs rather than routine preventive upkeep. For instance, repairing avionics systems and replacing engine components often necessitate comprehensive knowledge and training specific to those fields, positioning them outside the realm of what pilots can perform as preventive maintenance. Painting the aircraft, while visually important for protection against corrosion, does not directly affect the immediate operational aspects and is not considered preventive maintenance in the same context.