What must a pilot of a retractable landing gear aircraft report before crossing the runway threshold during an approach?

In the operation of retractable landing gear aircraft, it is essential for pilots to ensure that their landing gear is in the correct position before landing. Reporting "Gear down" before crossing the runway threshold signifies to air traffic control and any other relevant parties that the landing gear has been successfully extended and is locked in place, ready for landing. This is a critical safety check that ensures the aircraft is configured correctly for landing.

Furthermore, confirming that the gear is down can prevent potential accidents or mishaps that could occur if the gear were inadvertently left in the retracted position. The practice of visually confirming and reporting the status of the landing gear is a standard procedure that enhances situational awareness for both the pilot and those monitoring flight operations.

In this context, reporting "Gear up" would indicate the gear is not extended and could lead to a dangerous situation, while "Final approach" and "Touchdown" pertain to different phases of the landing sequence rather than the specific requirement to confirm landing gear position. Hence, "Gear down" is the correct and necessary report a pilot should make before crossing the runway threshold.