Given a desired descent angle of (say) 3º, and your speed in KTAS, what is the corresponding descent rate in feet per minute?
Rule of thumb: for descent angle of 3º, multiply your speed in KTAS by 10 and then divide by 2 to give descent rate in feet per minute. (Or just multiply by 5 if you find this easier in your head.) Example: if speed in KTAS is 150 knots, descent rate is 150 * 10 / 2 = 750 fpm (3º gradient). Add 50 to this value if you want to be a bit more accurate, so more accurate value = 800 fpm. Add a third of this value for every degree over 3º, so for a 4º angle the descent rate would be 800 * (4/3) or 1050 fpm approximately.
