What does it mean for an aircraft to be "Grounded"?

An aircraft being "grounded" specifically means that it is unable to take off due to various reasons, which can include adverse weather conditions or mechanical issues that prevent it from being airworthy. This status implies that the aircraft is temporarily kept on the ground instead of being allowed to operate flights. It’s important for safety and operational reliability; grounding ensures that any potential risks are addressed before the aircraft is cleared for flight.

The other options suggest states of operation that do not align with the definition of being grounded. For example, readiness for takeoff implies that the aircraft is prepared and able to fly, which opposes the notion of being unable to take off. Similarly, scheduling for maintenance indicates a planned check-up without necessarily preventing takeoff; the aircraft may continue flying until the maintenance is performed. Finally, being in the air for a prolonged period describes an operational status rather than that of an aircraft being grounded, which focuses solely on its inability to take off.