How far is the localizer effective?

How far is the localizer effective?

• A. 12 nm
• B. 18 nm
• C. 24 nm
• D. 30 nm

Answer: (B)

The localizer provides lateral guidance along the runway centerline, and its usable range is defined by its standard service volume. For a typical ILS, the localizer is effective out to about 18 nautical miles from the antenna. Within this range you can rely on the course indication to stay on the runway centerline; beyond roughly 18 NM the signal becomes unreliable for precise lateral guidance. The other options are outside this standard service volume, so they don’t reflect the typical effective distance of the localizer.

The localizer provides lateral guidance along the runway centerline, and its usable range is defined by its standard service volume. For a typical ILS, the localizer is effective out to about 18 nautical miles from the antenna. Within this range you can rely on the course indication to stay on the runway centerline; beyond roughly 18 NM the signal becomes unreliable for precise lateral guidance. The other options are outside this standard service volume, so they don’t reflect the typical effective distance of the localizer.