Subelement K: K – Aircraft— Topic 68: Distance Measuring Equipment
Question 3-68K4
Element 3 (GROL)What is the main underlying operating principle of an aircraft’s Distance Measuring Equipment (DME)?
Explanation
Distance Measuring Equipment (DME) operates on the fundamental principle that radio signals travel at a known, finite speed. An aircraft transmits an interrogation pulse to a ground-based transponder. Upon receiving this pulse, the ground station waits a precise, fixed delay and then transmits a reply pulse back to the aircraft.
The aircraft's DME system measures the total elapsed time between sending its interrogation and receiving the reply. By subtracting the known fixed delay of the ground station and dividing the remaining round-trip time by two (for one-way travel), the system can accurately calculate the distance (slant range) to the ground station using the speed of light.
Answer B is incorrect because DME relies on radio signal propagation time, not differences in DC voltages. Answer C is incorrect; while frequency shifts (Doppler effect) relate to speed, they are not the primary mechanism for distance measurement in DME, nor does DME measure altitude directly. Answer D is incorrect as phase inversion is not the underlying principle for distance determination in DME.
Related Questions
3-68K2 The Distance Measuring Equipment (DME) measures the distance from the aircraft to the DME ground station. This is referred to as:3-68K3 The Distance Measuring Equipment (DME) ground station has a built-in delay between reception of an interrogation and transmission of the reply to allow:3-68K5 What radio navigation aid determines the distance from an aircraft to a selected VORTAC station by measuring the length of time the radio signal takes to travel to and from the station?3-68K6 The majority of airborne Distance Measuring Equipment systems automatically tune their transmitter and receiver frequencies to the paired __ / __ channel.3-69K1 All directions associated with a VOR station are related to: