In a DME system, what type of distance is calculated in nautical miles from the aircraft to the ground station?

• A. Lateral
• B. Slant range
• C. Horizontal
• D. Vertical

Answer: (B)

Slant range is the straight-line distance from the aircraft to the ground station along the line of sight. DME measures the time delay of radio signals between the aircraft and the ground station and converts that to distance, which is reported in nautical miles. This distance accounts for altitude, so it’s the actual path the signal travels, not just horizontal separation. The horizontal distance would ignore the altitude, and the vertical distance is only the altitude difference, not the full line-of-sight path. In other words, slant range is the hypotenuse of the triangle formed by horizontal distance and altitude.