What is the typical effective range of a localizer signal?

• A. 6 NM
• B. 15 NM
• C. 18 NM
• D. 35 NM

Answer: (C)

The signal from a localizer is designed to give accurate lateral guidance only within a certain distance from the runway end, where its beam shape and strength meet the accuracy requirements for instrument approaches. The nominal usable range for a localizer is about 18 nautical miles. Within this zone, the course deviation indicator reliably shows how far you are from the runway centerline and how to steer back toward it. Beyond roughly 18 NM, the signal weakens and the angular differences used to determine left-right deviation become less reliable, so the localizer’s guidance cannot be trusted as effectively. While actual installations can vary with equipment and terrain, 18 NM is the standard figure pilots learn for the typical localizer range.