What is the difference between localizer and glide slope?

• A. They are identical in function; both provide vertical guidance.
• B. Localizer provides horizontal guidance; glide slope provides vertical guidance.
• C. Localizer provides vertical guidance; glide slope provides horizontal guidance.
• D. Localizer guides to the threshold; glide slope controls flare.

Answer: (B)

The key distinction is that one subsystem handles horizontal guidance while the other provides vertical guidance. The localizer is the horizontal guidance component of the Instrument Landing System; it centers the aircraft on the runway centerline by feeding left-right deviation information, guiding you to fly along the runway’s extended centerline. It does not give any vertical descent information.

The glide slope, on the other hand, is the vertical guidance component. It provides the intended descent path toward the runway (typically about a 3-degree glide angle) and tells you whether you are above or below that path, allowing you to descent along the proper vertical profile. When used together, they give a precise approach path—lateral alignment from the localizer and vertical descent from the glide slope.

Statements claiming they are identical, that the localizer provides vertical guidance, or that the glide slope handles flare are incorrect. Flare is a pilot-controlled maneuver near the runway, not commanded by these guidance signals, and the localizer does not supply vertical information while the glide slope does not control horizontal alignment.