What process does Distance Measuring Equipment primarily rely on for calculating distance?

Distance Measuring Equipment (DME) primarily relies on measuring the time it takes for a radio signal to travel to an aircraft from a ground station and back. This process involves sending a pulse of radio energy to the ground station, which then immediately sends a reply back to the aircraft. By measuring the elapsed time between sending the signal and receiving the return signal, the DME can calculate the distance to the ground station.

The key concept here is that radio waves travel at a known speed, specifically the speed of light. Therefore, by knowing the time it takes for the signal to complete the round trip, one can calculate the distance using the formula distance = speed × time. Since the signal must travel to the ground station and then back, the time measured is halved to determine the one-way distance to the station.

The other options do not apply to the primary function of DME. For example, radio signal phase shift is relevant in other systems but not for direct distance measurement in this context. Measuring altitude does not directly relate to DME operations, which focus on horizontal distance rather than vertical height. Using barometric pressure is related to altitude but not distance, so it does not contribute to DME’s distance calculations. The correct answer highlights the essential