SESK: Stuff Everyone Should Know · sesk.info/aero-dme-signal-time
How does distance-measuring equipment determine distance?
DME measures the round-trip travel time of a radio signal.
- By timing a radio signal ✔
- By reading tire rotation
- By measuring cabin pressure
Why: The airplane sends a signal to compatible ground equipment and receives a reply. Travel time lets the equipment calculate distance.
Huh, didn't know that: DME measures slant range, the straight-line distance to the station, so the airplane's height is part of the reading.
Why did the radio signal come back? It had a round-trip ticket!
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References
Answer: By timing a radio signal. The airplane sends a signal to compatible ground equipment and receives a reply. Travel time lets the equipment calculate distance.
- Civil Air Patrol, Journey of Flight Teacher's Guide www.gocivilairpatrol.com/media/cms/2nd_edition_Teachers_Guide_5D3166D76F9B1.pdf
The DME sends a signal and measures the time it takes to go from the aircraft to the VORTAC and return.
Checked 2026-10-10.
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