Which statement about the aircraft radio navigation system is true?

• A. The system includes VOR, ILS, and DME.
• B. The system includes TACAN.
• C. The system includes GPS.
• D. The system includes ADF.

Answer: (A)

Air navigation in civil aviation relies on a set of ground-based radio aids that provide direction, distance, and approach guidance. VOR gives azimuth information so you can determine your bearing from a station. ILS supplies precision approach signals with a localizer for horizontal alignment and a glide slope for vertical descent. DME works with those stations to tell you how far away you are, giving you range to the VOR or ILS facility. Put together, VOR, ILS, and DME cover the essential navigation and approach guidance used en route and for instrument landings.

TACAN is a military system (civil use is often via VORTAC, which combines VOR with TACAN). GPS is satellite-based navigation, not a ground-based radio navigation aid, and ADF/NDB is an older radio beacon system not part of this standard navigation trio. So the statement that the system includes VOR, ILS, and DME accurately describes the common civil radio navigation setup.