Slant Range to Ground Distance Calculator

Why DME doesn't show ground distance directly

DME (Distance Measuring Equipment) reports slant range - the direct line-of-sight distance to the station - not the actual horizontal ground distance, a difference that becomes significant at high altitude and close range.

Worked example

For a 10 nm slant range reading at 30,000 feet altitude:

Altitude = 30000 / 6076.12 = 4.94 nm

Ground Distance = sqrt(10² - 4.94²) = 8.696 nautical miles

This is exactly why a DME reading can show a surprisingly large distance even when an aircraft at high altitude is nearly directly overhead a station - the reading reflects the diagonal line-of-sight path, not the true distance across the ground.