In an ILS, which components provide the primary guidance for landing?

• A. Localizer and Glideslope.
• B. VOR and ADF.
• C. DME and TACAN.
• D. Antenna and transponder.

Answer: (A)

The key idea is that landing with precision relies on two simultaneous guidance signals: one for horizontal alignment and one for vertical descent. The localizer provides the lateral guidance, steering the aircraft to stay on the runway centerline by sending a signal that the cockpit NAV/LOC receiver translates into left-right guidance on the display. The glideslope supplies the vertical guidance, defining the intended descent path to the runway, so the pilot can descend on a steady 3-degree-ish slope and reach the correct height at the threshold. Together, these two components give the precise approach path needed for a safe landing.

VOR and ADF are general navigation aids that help you know where you are and what direction you’re headed, not the precise two-dimensional path for the final approach. DME and TACAN provide distance information, not the primary two-way guidance for alignment and descent. Antenna and transponder are parts of the aircraft’s communication and surveillance systems, not the landing guidance themselves.