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FLEX Temp Calculation


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2 hours ago, Matty260191 said:

I see the data in the tables but doesn't show anything for flex. Like how can i work out best FLEX for a runway and current conditions from that. I get the SAT and Vspeeds are there. But what to do with that info.

Read the highist TEMP that you can take off under your runway and weight, that's your FLEX

FLEX is just assuming you takeoff at that temperature

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It's complicated, I'll try make an simple example.

Say you are tring to take off at an airport with 8000feet runway 500feet elevation, 20C, takeoff weight is 46000k,

So You first find the table for 500ft altitude, check it's the right airframe and engine, right condition and flaps.

On the table column, find 8000' long runway. if you have slope or wind, the runway lenth could be adjust longer or shorter, we just keep it simple here, so just 8000,

   >if it's 8100' I'll just use 8000 too, but you can find the value between 8000 and 8500.

now follow the column, first make sure at 20C, your MTOW is 49607, you are under it so it's a go. Then move down the line, find the weight close but higher than your actual TOW, here I got 46504 under the 40C line, and for 45C line it's 45110, so you can FLEX to 40C (or something like 41~42C if you try to be more accurate.)

You can also check the table for Flaps4 (or1\3, if you have)  to see if it could provide you higher FLEX, if it dose, that's better.


If I was too light, then all the way up to 50C as that's all data I have here.

PS: If your weight at 50C still makes you can take off at shorter runway, you should use the Vspd for your weight , if you decide not to use FLEX, you should also use the Vspd under the one fit your actual weight. BUT, it's also safe to use the Vspd under your actual Condition.

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