Is the GPWS test function available when weight is on wheels?

The GPWS (Ground Proximity Warning System) test function being available when weight is on wheels is accurate because the system is designed to provide critical alerts and warnings about the aircraft's altitude and proximity to the ground. When the aircraft is on the ground, it is essential for pilots to be able to conduct tests on safety systems, including GPWS, to ensure they are functioning correctly before flight. The GPWS provides valuable warnings during any phase of operation, including the ground phase, so having the ability to test it while the aircraft is on the ground enhances safety by verifying that the system is operational prior to takeoff.

The other contexts regarding the GPWS test function do not align with how the system is designed to operate; it is not limited to just airborne scenarios or exclusive phases like takeoff, as its reliability is crucial during all stages of flight.