1. Take your altitude and multiply it by 3. That equals your distance in miles
to begin your descent.
2. Now take half your ground speed. This is your rate of descent in hundreds
example: If you are flying at 12,000 ft at a ground speed of
150 kts and you need to descend to 2,000 ft, the difference is 10,000 ft. Multiply
10*3 = 30 miles out you must begin your descent. Half your ground speed is 75,
add a zero, and 750 ft per minute is your rate of descent.