Instrument Rating Checkride Practice Test

What type of distance does DME measure?

1. Horizontal Distance

2. Vertical Distance

3. Slant Range Distance

4. Ground Distance

The correct answer is: Slant Range Distance

Distance Measuring Equipment (DME) measures slant range distance, which is the actual straight-line distance from the aircraft to the DME ground station. This measurement reflects the hypotenuse of a right triangle formed by the vertical and horizontal distances between the aircraft and the station. Understanding slant range distance is crucial for pilots because it provides a direct measure that can be affected by altitude. When an aircraft is flying at a high altitude, the distance indicated by the DME will be greater than just the horizontal distance to the station, as it takes into account both the horizontal and vertical components. This distinction is important for navigation and approach procedures since pilots need to be aware that DME readings change with altitude, which affects their positioning relative to the navigation aid. Understanding DME's function helps ensure accurate navigation and positioning during instrumental flight.