How is the DME slant range calculated?

The correct approach to calculating the DME (Distance Measuring Equipment) slant range is by measuring the distance directly between the DME station and the aircraft. DME measures the time it takes for a radio signal to travel to the aircraft from the station and back, allowing it to calculate the straight-line distance from the aircraft to the DME facility.

This measurement is essential for navigation, especially in approaches and departures, as it provides pilots with accurate distance information. The DME slant range reflects not only the horizontal distance but also incorporates the altitude of the aircraft, resulting in the true slant range.

The other options, although related to navigation, do not accurately represent how the DME slant range is calculated. For instance, while aircraft altitude and GPS coordinates provide valuable context for navigation, they are not the basis for the DME calculation itself. Finally, estimating distances based on previous waypoints lacks the precision offered by the direct measurement method used in DME operations.