To calculate
Top Of Descent point (the point at which you need to begin your descent to reach the desired altitude at the desired time): Use 6.5 miles per minute (at Mach .65 in descent) as the basis. If you are cruising at 33,000 ft. and wish to descend to 5,000 ft. at the next waypoint, at a descent rate of 1,800 ft./min., you need to
figure the time to descend 28,000 ft. (33,000 - 5,000). Divide 28,000 ft. by 1,800 ft./min. and you will get 15.56 minutes. At 6.5 miles per minute, you need to begin your descent at 101 miles from the next waypoint (15.56
minutes multiplied by 6.5 miles per minute). This is a “No Wind” calculation. If you have a tailwind, the miles per minute will be greater; if you have a headwind, the miles per minute will be lower.

Descend with throttles at idle at initial descent. Set auto throttle to hold descent airspeed of Mach .65 to 16,000 ft. and 250 KIAS below 16,000 ft