What is the formula to calculate Initial Descent Rate?

The formula to calculate the Initial Descent Rate is derived from the concept of gradient and how it relates to ground speed or true airspeed. When calculating the descent rate, one needs to consider the angle of descent, which is often expressed as a gradient. The gradient provides the relationship between altitude change and horizontal distance.

In this context, the correct approach is to take the gradient and multiply it by the true airspeed (TAS) or ground speed (GS). This formula effectively converts the gradient into a vertical descent rate over time, as it calculates how much altitude is lost during horizontal travel.

Using either TAS or GS in the formula provides a clear representation of how quickly an aircraft is moving forward while descending. The division by 60 is necessary to adjust for the units involved, ensuring that the descent rate is expressed in feet per minute instead of feet per second given that the speed is typically measured in knots (nautical miles per hour).

This understanding is crucial for pilots when planning descent profiles and ensuring safe and efficient descents, especially when approaching an airport or navigating through controlled airspace.