Final answer:
A pilot must have their pilot certificate with them or readily accessible in the flight compartment whenever they are operating an aircraft.
Step-by-step explanation:
According to aviation regulations, a pilot certificate must always be in the pilot's personal possession or readily accessible in the flight compartment while the pilot is operating an aircraft.
This is a legal requirement and ensures that a pilot is recognized as qualified to operate the aircraft in question. Not carrying a pilot certificate during flight operations can result in regulatory penalties or fines.