What does the “3-2-1” rule help pilots determine?

The "3-2-1" rule is a guideline that assists pilots in determining the appropriate time to begin their descent as they approach the airport for landing. Specifically, it suggests that for every 3 nautical miles from the airport, the pilot should start descending for every 1,000 feet of altitude to ensure a stable descent profile. This rule provides a practical and straightforward approach to managing descent, allowing pilots to calculate their descent point based on the altitude they are currently flying at, which is typically expressed in thousands of feet.

For instance, if a pilot is at 10,000 feet, they would ideally start their descent approximately 30 nautical miles from the destination. This rule aids in maintaining safe altitude and ensures pilots can manage their approach effectively, thereby improving the landing process and reducing the risk of being too high or low at the time of arrival.

Understanding the "3-2-1" rule is fundamental for pilots in achieving a smooth landing and helps in situational awareness as they prepare to enter the airport's traffic pattern.