What is the function of DME in the ILS?

The function of Distance Measuring Equipment (DME) in the Instrument Landing System (ILS) is to measure the distance between the aircraft and the runway. DME works by sending a signal from the aircraft to a ground station, which then replies to the aircraft. The system calculates the distance based on the time it takes for the signals to travel to the ground station and back. This provides the pilot with critical information about how far they are from the runway, allowing for more accurate approaches and landings.

In an ILS setup, this distance information is essential for pilots to make decisions regarding their descent and alignment with the runway. Having accurate distance measurements improves situational awareness, especially during low visibility conditions often associated with instrument approaches. This is why the correct answer highlights the role of DME in determining the aircraft's distance to the runway, a function integral to safe landing procedures.