What does slant range refer to?

• A. Vertical distance from the aircraft to the ground station
• B. Horizontal distance to the ground station along line of sight
• C. The horizontal distance from the aircraft antenna to the ground station, due to line-of-sight transmission of the DME signal
• D. Distance along the flight path to the ground station

Answer: (C)

Slant range is the straight-line distance between the aircraft and the ground station along the signal’s line of sight. In DME, the radio pulse travels directly from the aircraft to the ground station, and the time delay is converted to distance using the speed of light. Because the aircraft is above the surface, this distance is not purely horizontal; it’s the diagonal distance (the hypotenuse) between the two points. So, slant range reflects the actual LOS distance, not just horizontal separation.

The vertical distance is altitude, not slant range. The distance described as horizontal along line of sight is misleading because slant range isn’t purely horizontal. The distance along the flight path to the ground station isn’t what DME measures—the readout is the LOS distance between the aircraft and the station.