What is the main underlying operating principle of a Distance Measuring Equipment (DME) system used on aircraft?

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Multiple Choice

What is the main underlying operating principle of a Distance Measuring Equipment (DME) system used on aircraft?

The essential idea is time-of-flight. DME determines distance by measuring how long it takes for a radio signal to travel from the aircraft to a ground station and back. The interrogation is sent, the ground station replies after a known, fixed delay, and the aircraft’s DME receiver measures the total elapsed time. Because radio waves travel at roughly the speed of light, that round-trip time is directly related to distance. After subtracting the known processing delay, the system converts the remaining time into a distance (the slant range) shown to the pilot. This is not about measuring voltages, phase shifts, or frequency changes—those methods correspond to other concepts and systems, not DME.

The essential idea is time-of-flight. DME determines distance by measuring how long it takes for a radio signal to travel from the aircraft to a ground station and back. The interrogation is sent, the ground station replies after a known, fixed delay, and the aircraft’s DME receiver measures the total elapsed time. Because radio waves travel at roughly the speed of light, that round-trip time is directly related to distance. After subtracting the known processing delay, the system converts the remaining time into a distance (the slant range) shown to the pilot. This is not about measuring voltages, phase shifts, or frequency changes—those methods correspond to other concepts and systems, not DME.

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