What is the main operating principle of Distance Measuring Equipment (DME)?

The main operating principle of Distance Measuring Equipment (DME) is based on measuring the time it takes for radio signals to travel to a ground station and back to the aircraft. When an aircraft transmits a signal to the DME station, the station responds, and the DME onboard the aircraft calculates the distance by measuring the time interval between the transmission and the reception of the signal. Since radio signals travel at the speed of light, this time measurement can be converted to a distance, providing pilots with precise information about how far they are from the DME station.

The other options do not correctly describe how DME operates. For example, GPS signals are not the basis for DME functioning, as DME relies on traditional radar principles rather than satellite navigation. Similarly, while signal strength measurement and magnetism are principles in other contexts, DME does not utilize these methods for calculating distance. Understanding this principle is essential for pilots and navigators to ensure accurate navigation and safety in flight operations.