What are the CDIs scaling changes for an Approach?

The correct answer indicates that for an approach, the CDI (Course Deviation Indicator) scaling changes to ±0.3 nautical miles (NM). This specific scaling is utilized during the final approach phase of an instrument approach procedure, allowing for greater precision in lateral navigation.

Using a ±0.3 NM scaling provides pilots with enhanced situational awareness and more accurate guidance as they approach the runway, which is crucial for maintaining the correct flight path especially in conditions where visibility may be limited. This narrower scaling allows pilots to react more effectively to any deviations from the intended course, thereby improving safety and increasing the chances of a successful approach and landing.

In contrast, broader scale options such as ±1 NM, ±2 NM, or ±5 NM, while useful in other phases of flight, do not offer the same level of granularity required when close to the runway. Wider scale indications can lead to slower reactions and less precision in maintaining the desired flight path during critical landing phases. The choice of ±0.3 NM thus ensures that the pilot is operating with the most responsive and accurate instrument guidance during this vital phase of flight.