# When do you know when to start descending?

This what I usually do I got it from a topic somewhere on here I forgot where it was or what I searched but you take your current altitude say your cruising at 34,000 and you wanna descend to 3,000 subtract 34,000-3,000 you get 31,000 divide that by 1,000 or 1 and you get 34 times that by 3 31+31+31 you get 93 So you should start descending That far from your destination or what I do I usually add 10 miles so I descend like 110 or 120 if I feel like I’m too fast I usually slow down for descend around like 130 miles then begin my descend at like 115 or 120 with a vs of 1800 make sure to descend at vs of 1500-2500 but yea that’s usuallly what I do hope it helps

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No need to calculate that much, just use http://aerotexas.com/desplan/desplan.php

Its pretty accurate and I never had any issues with it.

Some tips:

FL300-350: 130nm, -1800fpm
FL350-380: 140nm, -1800fpm
FL380+: 150-155nm, -1800fpm

This is also quite accurate, however you need to monitor your distance/height and change the V/S if needed. (Oh and don’t forget to distract the airport elevation from your initial climb)

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Rule of thumb take your Flight level (ie 35,000 ft =FL350) then devide by 3. Then add about 20nm for slowing down, especially in the B777!

Ie FL350 = 350/3 = 116nm + 20nm = 136nm DTG.

REMEMBER to make alterations for height of airport above sea level.

PS this is similar to what professional pilots do IRL

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o as an example would this be right

my altitude is 35000 and the airport is 2,000 ft height. It would be 3500-2000 which is 33,000 and add 100 to the first two numbers which would be 133. So I would be descending 133 nm away from the airport?

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Thank you for all the help

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Thank you :)

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Yep that’s correct!

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Thank you for helping me

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Of course!

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For me, I usually start descend based on my altitude.
example: if I am cruising at 35,000, I would start my descend about 120 nautical miles away from airport.

• IFS
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Thanks, I’ll be sure to try it! 😀

I see you’re new on this forum. Welcome!
It’s great you are here and you’re asking the right questions. This forum is a very important extension of the IF app. You’ll find loads of good info here.

Make sure you use the search button, as most questions you have, plus the ones you haven’t even thought of asking, have already been asked.

A great way to start your way on this forum is to check out the link below.

Have fun. Hope to see you around!

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Below 10000 feet it’s quite difficult to descend at a rate of -2000fpm without gaining speed. You should rethink your theory by making a slow down to maximum -1500fpm under 10000 feet.

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It depends, on the aircraft just alter the VS after 10,000 as you near the point where you want to enter the glide slope

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This works the best:

Your crusing alt. (Ex. 32,000)- perfect alt to go on ils (3,000) : V/S (-1800) you are decending = 16,1111 mins to your destenation you start decending with v/s - 1800

32000-3000: 1800 = 16,1111

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Wow that dosnt give you a lot of tine to descend and lose speed. No need to overcomplecate the operation. Professional pilots ( see the link in my post higher up) which is FL/3.

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That would probably work out fine if you sold roller coaster tickets to your passengers and descended between 2500 and 3000 fpm

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