If you want to descend from FL370 down to FL220, how far out do you start your descent?

To determine when to begin a descent from FL370 to FL220, it is essential to consider the general rule of thumb for altitude changes, which is around 3 nautical miles for every 1,000 feet of descent. In this case, the altitude difference is 150 nautical feet (from FL370 to FL220).

To calculate the descent distance:

1. Calculate the altitude difference: 370 - 220 = 150.

2. Apply the rule of thumb: 150 feet / 1,000 feet per 3 nautical miles = (150 / 1,000) * 3 = 4.5 nautical miles.

However, when calculating the appropriate descent point for a passenger aircraft and factoring in a safe and comfortable descent rate and typical procedures, pilots often plan for a more extended descent distance to allow for any additional variables such as airspace congestion, weather conditions, or speed adjustments.

Based on common practice, starting a descent from around 45 miles out provides ample time for the aircraft to gradually descend while accounting for the entire descent profile and ensuring compliance with air traffic control guidelines and other considerations. Therefore, starting the descent from 45 miles out helps to ensure a smooth and efficient transition to the lower altitude of FL