How does DME ensure accurate distance measurement?

Distance Measurement Equipment (DME) ensures accurate distance measurement primarily by calculating the time delay of received signals. DME operates using a system of radio signals. When the DME unit broadcasts a signal towards an aircraft, the aircraft's DME transponder receives this signal and simultaneously replies with its own signal back to the ground station. The system measures the time it takes for the signal to travel to the aircraft and back to calculate the distance. Given that radio signals travel at the speed of light, the DME can accurately determine the distance based on this time delay. This method is reliable and precise, making it the cornerstone of DME functionality for distance measurement in aviation.

Other methods, such as broadcasting constant signals, adjusting for atmospheric conditions, or utilizing navigational satellites, do not directly measure distance in the way that calculating time delay does and are not the primary operations of DME.