Where does the DME indicator show the greatest error between ground distance and displayed distance to the VORTAC?

The DME (Distance Measuring Equipment) indicator shows the greatest error in the distance calculation when the aircraft is at high altitudes close to the VORTAC (VHF Omnidirectional Range/Tactical Air Navigation). This occurs because DME measures slant range distance, which is the straight-line distance from the aircraft to the ground station, rather than the horizontal distance. At high altitudes, especially when near the station, the slant distance can differ significantly from the actual ground distance due to the steep angle of the radio signal.

As the aircraft approaches the VORTAC at higher altitudes, the difference between the direct line of sight distance (the slant distance) and the actual horizontal ground distance increases, leading to this notable error in the DME reading. Understanding this is crucial for accurate navigation, as pilots must be aware of these discrepancies, especially during maneuvers near navigational aids. The other scenarios involving low altitudes, whether close or far from the VORTAC, yield less error due to the more level flight path and the reduced angle impact on distance measurement.