Originally Posted by JetB
What's a good formula for figuring out how far away from a fix to start down?
Say you're at 410 and need to get to "X" at 11,000/250knts, how far out should you start down?
j...
36 rule
3 times the altitude to loose, 6 times your groundspeed
using your example
30,000 feet to loose = (3*30)=90 miles
250 knots (assuming groundspeed) (250*6)=1500 feet per minute (FPM)
So I would start down around 100 milse from X and maintain 1500 FPM, now as you go down and your ground speed changes, you can adjust your rate, if the groundspeed increases, go down faster decreases, go down slower.
Another way to keep track of your progress is divide your distance from the fix by 3 and see if that equals your altitude.
So you are 30 miles from X (30/3)=10. so at 30 miles, to be on a 3 degree slope, you should be at 10,000 feet.
Remember to take into account your actual height above the ground. So if Im going into denver, 30 miles at 10000 feet only puts me 5000 feet above the ground, maybe a bit low, so I would shoot for 13 to 15,000 on the altimeter. Also keep distance to slow in mind, dont plan your descents so that you arrive over the field at 1500 feet AGL at 300 knots, prolly not gonna work out to well.