Welcome Guest. Sign in or Signup

1 Answers

slant range error

Asked by: 8901 views General Aviation

please describe the slant range error

Ace Any FAA Written Test!
Actual FAA Questions / Free Lifetime Updates
The best explanations in the business
Fast, efficient study.
Pass Your Checkride With Confidence!
FAA Practical Test prep that reflects actual checkrides.
Any checkride: Airplane, Helicopter, Glider, etc.
Written and maintained by actual pilot examiners and master CFIs.
The World's Most Trusted eLogbook
Be Organized, Current, Professional, and Safe.
Highly customizable - for student pilots through pros.
Free Transition Service for users of other eLogs.
Our sincere thanks to pilots such as yourself who support AskACFI while helping themselves by using the awesome PC, Mac, iPhone/iPad, and Android aviation apps of our sponsors.

1 Answers



  1. Dan Chitty on Jul 28, 2015

    Below is a helpful explanation found from an internet article:

    DME displays distance in nautical miles, groundspeed in knots, and time-to-station in minutes. Beware, however, that DME groundspeed and time-to-station are only accurate when you are flying directly to or from the ground station. If you are flying in any other direction, you will see groundspeed that is erroneously low and time-to-station that is erroneously high.

    If you are flying away from the station, groundspeed will be accurate but “time-to-station” will actually show “time-from-station” and will increase as you get farther and farther from the station.

    Another thing to remember is the DME measures the straight-line distance from the aircraft to the ground station. This is called “slant range” and is slightly more than the actual horizontal distance because of the difference in elevation between the aircraft and the station. The most extreme case of “slant range error” occurs when the aircraft passes directly over the station; instead of reading zero, the DME shows the altitude of the airplane above the station (in nautical miles).

    For example, if the station is at sea level and you’re flying at 9000 feet, the DME will show 1.5 NM as you pass directly over the station. When you’re 2 NM away from the station horizontally, the DME will read 2.5 NM. At greater distances from the station, slant-range error is considered negligible.

    Slant range error also affects groundspeed and time-to-station displays when you’re close to the station. Displayed DME groundspeed drops below actual groundspeed as you approach the station and then climbs back to normal after you pass it. Displayed DME time-to-station may not count all the way down to zero as you fly over the station.

    +1 Votes Thumb up 2 Votes Thumb down 1 Votes


The following terms have been auto-detected the question above and any answers or discussion provided. Click on a term to see its definition from the Dauntless Aviation JargonBuster Glossary.

Answer Question

Our sincere thanks to all who contribute constructively to this forum in answering flight training questions. If you are a flight instructor or represent a flight school / FBO offering flight instruction, you are welcome to include links to your site and related contact information as it pertains to offering local flight instruction in a specific geographic area. Additionally, direct links to FAA and related official government sources of information are welcome. However we thank you for your understanding that links to other sites or text that may be construed as explicit or implicit advertising of other business, sites, or goods/services are not permitted even if such links nominally are relevant to the question asked.