LOU wrote on Jun 30^th, 2011 at 6:32pm:

Mark & BrianG, the 3X the altitude is at idle power. This 3X altitude, is a good place to start your descent plan. You apply the wind and adjust the distance.  Your example using the ground speed is fine, but the old planes did not have ground speed readout, so you had to do a time vs distance on the DME and calculate GS. None of that sissy information in these old birds. Which ever system you use, you need to keep updating the calculations in your head as you descend so as not to bust an altitude or get too low or too high since winds change etc. In the Boeing manual it states that the most efficient flight path is a power off descent. In the real world there are many factors that constantly change during either climb or descent. Temperature also effects what the plane will do in climb or descent. A/I on or off makes a difference. Remember, these are just guides, but they worked pretty well. When I got to the fancy planes with all the computers and glass it was apparent that the atmosphere would change a lot as you climbed or descended. One of the greatest tools is the wind vector arrow in the HSI. Keeping track of changes in the local wind was a great help in flying the profile. I don't remember the exact numbers from the flight handbook, but I seem to recall a descent at cruise mach to around FL290 or so and then around 290 to 300 KTS down to 10,000 feet and then 250 KTS. If you descend slower you will be high and of course too fast, lower. Hint: if you see you are too high or too low on the descent profile...adjust speed to get back on the profile.  :P You can always add some thrust if you are getting too low. We hardly ever needed spoilers unless ATC changed some altitude restriction at the last minute. You could adjust the FPM/IVSI over a wide range with speed changes. To slow from 300 KTS to the 250 KTS restriction at 10,000' would take several miles, so you had to factor that as well.

Thanks again for your invaluable information Lou. I have been cheating and using the default GPS 500. :-[ From now on I will go by the 3X the altitude is at idle power rule. I will ignore the GS that appears in the GPS. That's going to an interesting challenge, I'm 1350 miles from Honolulu (as I type) and so I will get to test that rule in about 3 hours or so. ;) If I mess this up it's back to approach and landing practice I will go. :(

Mark