Question

When in approach arm mode, what changes in the course deviation indicator scale?

1) The scale remains the same
2) The scale becomes larger
3) The scale becomes smaller
4) The scale disappears

Answer 1

In approach arm mode, the course deviation indicator (CDI) scale becomes smaller, meaning it shows larger deflections for smaller deviations, which allows for more precise course alignment during an instrument approach.

Step-by-step explanation:

When an aircraft's navigation system is in approach arm mode, the course deviation indicator (CDI) scale typically becomes more sensitive. This implies that, compared to en-route navigation modes, the CDI will show larger deflections for a given amount of deviation from the course centerline. Therefore, when the approach arm mode is active, it can be said that the scale effectively becomes smaller, making it easier for the pilot to fly more precisely on the approach course. This change in the CDI scale sensitivity ensures that the pilot receives more accurate guidance when aligning with a runway during an instrument approach, which is crucial for safety, especially in poor visibility conditions.