What is the main requirement for pilots concerning their medical certification under FAR?

The requirement for pilots concerning their medical certification under FAR is primarily that they must hold a valid medical certificate that is appropriate to the level of operation they are conducting. This means that the type of medical certificate required can vary depending on whether a pilot is flying as a private pilot, a commercial pilot, or an airline transport pilot. Each level of operation has its own set of standards and conditions for medical certification that ensure the pilot’s safety and that of others in the aviation environment.

For instance, a first-class medical certificate is required for airline transport pilots, which has stricter standards compared to a second-class or third-class medical certificate, which might be sufficient for private or commercial pilots. The validity of this certification is crucial as it assesses the pilot's physical and mental fitness to operate an aircraft safely.

This rigorous approach ensures that all pilots are capable of performing their duties without any medical impairments that could pose risks during flight operations. Other options do not accurately reflect the comprehensive requirements set by the FARs regarding medical certifications for pilots.