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Post subject: Posted: Sun Sep 11, 2005 4:19 pm 

Yup, the easiest rule of thumb (and the one I use) is to simply triple the altitude you have to lose.
But then you have to know how fast to decend....
Try taking your groundspeed, divide by 2, then add a zero.
e.g. 250kts/2 = 125, add a zero = 1250fpm descent rate.
This way, you won't be leveled off while still 30 miles from the airport and trying to figure out what went wrong
Darryl: That's exactly what's done in the "real world" ... Take your groundspeed and convert that to nm/min. Then figure out a time to descend based on a known rate of descent. Multiply your G/S (in nm/min) by the time to descend and the product is your TOD.
e.g. Flying 240kts G/S = 4 miles/min. We want to descend at 1500fpm and we have to lose, say, 10,000 feet. So.... 10,000 feet at 1500fpm = 6.6666666666666666666 minutes. At 4 miles/min, that's approx 26.7 nm (6.67*4). Pull the power back at 27nm, keep the VSI pinned at 1500fpm and you'll look like a star!
To add a level of preciseness, calculate your TOD from the point at which you will be commencing the approach: Remember that it could be 20 miles on "this" side of the airport, or 20 on the "other" side.
Oops: I'm getting a little offtopic from "rules of thumb" ... Doh!
Cheers!
Gary
Edited By Gary Madore on 1126456932











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