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Airbus A320 - Performance Caclulation

Stefan Nirschl

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Stefan Nirschl

Dear folks,

bought the following video: https://shop.justplanes.com/at/Aer-Lingus-A320/p/108650

May someone of you has watched this as well. I have a question to the first leg of the video, Dublin to Lisbon.

The plane is pretty heavy at this leg but they want to avoid starting with toga performance. So they adjusted a little bit the figures of outside temp and QNH to get performance data with Flex Temperature. So it seems that they calculated with other figures than what were the actual ones at this specific day. So i understand that they want to avoid TOGA to reduce wearing of the engines as much as possible. But on the other hand i ask myself, can they calculate with other data (temp, QNH) than the actual ones?

Thanks for any opinion on that,

happy flying,

Stefan Nirschl



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Robin Locher

Hi, you can not calculate with different data.
So you can not decrease the OAT or increase the QNH.  You can just do it the other way round to have MORE margin.

At the end it has to be save, and if they have to use TOGA then they must use it. 

I did not watch the video. 

So what did they chance?

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Stefan Nirschl

Hi Robin,

thxs for the response.

The current weather at this clip was QNH 996 and Temperature 15.

They planned to start at rwy 28 at Dublin.

For the takeoff calculation they planned to take full lengh of the rwy and calculated with reduced OAT by 5 degree celsius to 10 and reduced QNH by one 1 to 995.

Together with an actual slight tailwind they than become FLEX performance figures.

But i dont understand why they calculated with a lower OAT. From my understanding they should plan at least with the actual OAT of 15, like the way you mentioned above. Calculating with higher temperature lead to some extra margin but will cause an affect the other way round when you calculate with lower temperature than the current actual one.

But for sure they are doing right, but i would like to understand why they do so.


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John Price

That’s interesting Stefan. I’m obviously missing a trick here because I too would have thought that increasing the temperature would provide greater margin, not reducing it.

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Robin Locher

Sorry but I don’t think that’s correct. Because lower temperatures will Increase performance. 
I never heard one airline which do this. 

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