Full scale RNAV deflection enroute equals how many miles?

• A. 1 mile
• B. 2 miles
• C. 5 miles
• D. 10 miles

Answer: (B)

The main idea here is how far off you can be from the planned RNAV track before the display saturates. On enroute RNAV, the lateral deviation indicator has a full-scale deflection of 2 miles. That means when you’re about 2 miles to either side of the desired course, the CDI hits its edge, signaling you’re at the limit of what the display can show for off-course deviation. This 2-mile scale is chosen to balance readability and the typical accuracy of GPS in enroute flight, giving you a clear sense of being on or off course without chasing tiny deviations on long legs. If you’re on course, the deflection is zero; as you drift away, the indicator moves toward the edge, and at 2 miles you reach full-scale.