[i‚lek′trän·ik ′dis·təns ‚mezh·ə·riŋ i‚kwip·mənt] (navigation) A navigation system consisting of airborne devices that transmit microsecond pulses to special ground beacons, which retransmit the signals to the aircraft; the length of expired time between transmission and reception is measured, converted to kilometers or miles, and presented to the pilot.