A320 Packs Off and Flex Temp

[ok45]

Hi, I'm new here. I was searching and reading some thread about usage of packs-off takeoff in this forum, seems like most agree that a packs-off takeoff will increase the performance capability so as to carry more weight, even in the Flex mode.

I was wondering if I could've been taking off underpowered in a case like this:

TOW: 65 t
RTOW Chart saying:
Flex 60 would lift 65,5 t
Flex 65 would lift 64.7 t
Then Packs Off Correction saying +800 kgs
With that data then I elected to use Flex 65 with packs off. In hope the plane will have enough performance to carry 64.700+800= 65.500kgs

Is that correct? As I recalled from the Normal OPS, Airbus stated a packs-off takeoff will increase performance in a TOGA takeoff, and for Flex, it will reduce EGT. Which as I get it, that there will be no weight correction for Flex+Packs off

Any idea guys?

[The African Dude]

My understanding is that you will have a lower EGT due to the lower N1 (higher flex) of the engines at 65 Flex. However, since no bleed air is lost from the compressor to the packs, for the same N1 you will generate more thrust, meaning your MTOW for the given conditions will increase.

[Cough]

You have to remember what the flex temp does - It simulates the max thrust the engine can produce, if the OAT is 65C. When you turn the packs off, the FADEC senses this and you can watch the target EPR/N1 (depending which engine you have) increase.

[Citation2]

Keep it simple, in your car when you switch on air conditioning , it increases fuel consumption. For the same speed lets say 50km/h , you will have a higher RPM than without AIr Conditioning.

If conditions permit, depending on the runway length, A packs off take off will generally increase the flex by 1 or 2 degrees , which means a lower thrust and N1 for take off , therefore a lower EGT consequently saving engine life.

[WildCatFromWildBush]

Flex corrections

You have both MTOW and Flex Temp corrections at the bottom of the chart. For MTOW determination, use weight correction, for flex temperature use flex corr.

[Bolubo]

stupid answer from me will be:

PACKS off in TOGA, more on to "performance reason"

PACKS off in flex mode for higher FLEX temp, will reduce required thrust and engine's EGT, which more on to economical reason (engine's life and or reduce fuel consumption)

see you in paradise

[Cough]

Surely the required thrust stays the same, it can just be achieved at a higher flex temp with the packs off?

[ok45]

Re:

Thanks for the answers guys, yeah I think I started to understand the "why" behind the EGT reduction and flex performance increase in packs-off. It just I couldn't find where to find the answer, not even in the RTOW manual

[ok45]

Re:

I've found the statement "Note: In case of deviation from the chart reference conditions (QNH, air conditioning…), corrections have to be applied to the flexible temperature" in Airbus Getting Grips With Aircraft Performance, under page 7.1.3. Flexible Temperature Determination.

Like Cough's said "required thrust stays the same, it can just be achieved at a higher flex temp with the packs off" is the reason for EGT Reduction. Cheers all, thanks for the insight.

Bolubo: Tell me we're in the same island!