In an ILS approach, what is the rate of descent for a 3° glide slope calculated as?

In an ILS (Instrument Landing System) approach, the rate of descent required to maintain a 3° glide slope can be calculated effectively using the ground speed of the aircraft. This descent rate is important for pilots to know in order to achieve a smooth and safe approach to the runway.

To derive this calculation, the formula generally used is to take the ground speed in knots, multiply it by 10, and then divide by the tangent of the glide slope angle. For a 3° glide slope, the tangent is approximately 0.0524. When working with simpler numbers for practical application, a conversion is often made referring to the glide slope in terms of altitude lost per distance traveled.

At a 3° angle, for every nautical mile you travel horizontally (which is approximately 1,852 meters), you will descend about 318 feet. When this is adjusted based on ground speed—accounting for the conversion scale—the correct computation aligns with multiplying the ground speed by 10 and dividing it by 3 to convert the ratio of height lost to distance traveled into the rate of descent in feet per minute.

This calculation gives a quick way to determine the vertical speed required to maintain a 3° glide slope, which is vital