Final answer:
Pilots must have their pilot and medical certificates on hand whenever they are acting as pilot in command or as a required crewmember. This ensures confirmation of their qualifications and medical fitness for operating an aircraft.
Step-by-step explanation:
The question pertains to the regulatory requirements for pilots concerning when to have their pilot and medical certificates while flying. According to aviation regulations, pilots must have their current and appropriate certificates in their personal possession or readily accessible in the aircraft any time they are acting as pilot in command or as a required crewmember. This is not only a matter of following procedure but also a critical safety measure to ensure that the individual operating or helping to operate the aircraft is qualified and medically able to do so. Similarly, just as pilots use checklists to ensure safety before takeoff, other industries such as medical facilities use the World Health Organization's surgical safety checklist as a measure to reduce accidents and ensure a safe environment.