Three Degree Glideslope [Aviation Rules of Thumb]

#1 - Divide groundspeed by 2, then add a zero.

example: 120kts / 2 = 60, add '0': 600 fpm

#2 - To maintain a 3 degree glideslope (eg. ILS) multiply your groundspeed by 5. The resulting number is the rate of descent to fly.

example: Groundspeed = 110 kts x 5 = 550 fpm rate of descent to maintain a 3 degree glideslope

#3 - With glideslope out on an ILS approach with DME, multiply the distance to go by 300. That should give you the height in feet you should be above the threshold.

example: 4 nm to the threshold. Multiply by 300 = 1200ft

#4 - Add a zero to your indicated speed, divide by two. This should keep you stabilized on the approach.

example: 150 knots on the GS. 150(0) / 2 = 750fpm descent. 120(0) / 2 =600fpm descent, etc.

#5 - Take your AGL height and divide it by three hundred. This is the distance from the threshold you need to start your three degree glidepath.

example: 600ft AGL / 300 = 2 nm