What type of distance does DME provide?

DME, or Distance Measuring Equipment, provides a measurement commonly referred to as "slant range." This is the direct line-of-sight distance from the aircraft to the DME ground station, which takes into account the elevation difference between the aircraft and the station. Because DME measures the hypotenuse of a right triangle formed by the horizontal ground distance and the vertical distance (altitude), it reflects the total distance inclined from the plane to the station, rather than just the horizontal or vertical components.

In aviation navigation, understanding that DME gives slant range is crucial because pilots must account for their altitude when interpreting the DME readings, particularly when they're navigating at different elevations in relation to the ground station. This contrasts with a simple horizontal ground distance or vertical distance, which would not accurately reflect the total distance when considering the aircraft's altitude above the terrain.