What does the phrase "gear down" indicate in aviation?

The phrase "gear down" indicates that the landing gear of the aircraft has been lowered and is locked in place in preparation for landing. In aviation terminology, this call-out is a critical part of the landing checklist and is essential for ensuring the aircraft's safety during the landing phase.

When the landing gear is "down," it means that the pilots have completed the necessary procedures to deploy the landing gear, allowing the aircraft to make contact with the runway safely. This procedure is crucial because the landing gear needs to be in a locked position before touchdown to support the weight of the aircraft and withstand the forces involved in landing.

In the context of the other choices, "gear down" does not refer to the landing gear being in transit during takeoff, serviced and not operational, or raised after takeoff, as these actions involve scenarios that are not related to the specific meaning of "gear down" in the context of landing an aircraft.