What is the additional coverage angle of a localizer from 10 NM to 18 NM?

To understand why the additional coverage angle from 10 nautical miles (NM) to 18 NM is 10°, we can use the concept of coverage angles in aviation navigation.

When considering a localizer, which operates as a type of radio-based navigation aid, it provides lateral guidance to the runway centerline. The coverage area can be visualized as a cone, where the tip is at the localizer and the base expands as you move farther away.

The coverage angle can be understood as the angular spread that the localizer signal covers as the distance increases. If we look at the distances involved:

• The initial coverage at 10 NM typically corresponds to a certain width at that distance.

• At 18 NM, the coverage is wider.

To find the additional angle of coverage, you can calculate the difference in angles at 10 NM and 18 NM. Generally, the localizer has a standard angular coverage, typically around 5° to each side of the centerline to provide adequate lateral guidance.

The change in coverage from 10 to 18 NM usually results in an increase of a predefined angular range, and this increase can be calculated based on the specific characteristics of the localizer's beam width and how it expands over distance.

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