Gradient to Rate Table
This is the scientific version :
Sine of the angle X 6076 = Gradient (feet up or down per N.M.)
The sin of the angle is also the % gradient.
With the gradient in hand :
Altitude divided by Gradient = Distance
Altitude divided by Distance = Gradient
Gradient X Distance = Altitude.
Note: Altitude is above runway threshold elevation, (not sea level).
In the front of the Jepp approach chart book is a chart "Gradient to Rate Table".
E.g. Take the popular 3 degree angle for the ILS,
The Grad is 318 ft per NM. 5.2 % Grad. (The sin of 3 deg is 0.052335)
Sine is used as it represents slant range DME distances. (Hypotenuse).
This formula can be used to set the FPA on Airbus for constant descent angles on approach.
Here is a very helpful exercise. If you want to capture the Glide Slope from above, you need to double the GS angle of 3 degrees. So 6 degrees is needed to capture the slope from above. The quick way to determine the rate of descent to set up is to determine the Ground Speed, add 10 then add a zero.
EG: GS 170 + 10 = 180 + a zero = 1800. This is the rate of descent for
6 degrees at 170 kts GS. (1800 FPM).
So 140 = 1500 fpm, 150 = 1600 fpm etc, etc.
CAUTION : never exceed 2,000 fpm rate of descent.
Have fun flying.