What distance measurement is provided by GPS DMEs?

• A. Vertical distance
• B. Horizontal measurement from waypoint to aircraft
• C. Slant range
• D. Ground distance

Answer: (B)

GPS DME shows the horizontal separation between the aircraft and a waypoint, i.e., the distance along the Earth's surface projected between the two positions. It uses the aircraft’s GPS position and the waypoint’s position to compute a straight-line distance over the surface (a great-circle distance), ignoring altitude. That’s why the distance readout is horizontal distance from the waypoint to the aircraft.

Vertical distance would require altitude difference and isn’t what GPS DME provides. Slant range is the distance to a physical DME station, not to a GPS-defined waypoint. Ground distance might imply following terrain or a path on the ground, which isn’t how GPS DME distances are reported.