12-21-2009, 07:04 AM
There are alot of ways to do that Roy. I've always prefered the simple ones as opposed to the higher math.
For the top of descent just estimate 3NM per 1000 feet of altitude to lose...from your example 33000-12000=21000. 21 x 3 = 63NM on a 3* descent. The easy way to determine a 3* descent is Groundspeed x 5 = Vertical speed..so at say 450Kts ( 450 x 5 = 2250 or ~2300FPM).
Obviously wind and speeds will change as you descend so this is not an exact science..but it is a reasonable estimate.
Hope that helps.
Randy
For the top of descent just estimate 3NM per 1000 feet of altitude to lose...from your example 33000-12000=21000. 21 x 3 = 63NM on a 3* descent. The easy way to determine a 3* descent is Groundspeed x 5 = Vertical speed..so at say 450Kts ( 450 x 5 = 2250 or ~2300FPM).
Obviously wind and speeds will change as you descend so this is not an exact science..but it is a reasonable estimate.
Hope that helps.
Randy