A320 Packs on Eng Vs Apu On T/O

[kuwait340]

hello...

just wondering to know this :

is using Eng's to supply packs on T/o would save the Apu life duration as the Eng's will need 2-3 degrees more on the flex power for t/o (i think these 2-3 degrees will not affect the eng life...correct me if i am wrong) this is ofcourse when max avail eng's power is not required i.e flex t/o.

Or...using the apu for the packs would save the eng's life and maintenance cost on the long term ?

i am saying this because for the last year and a half we are using apu to supply the pack for t/o...and now the apu's are being useless and not as before when it comes to supply air cond on ground as some times we request external air cond unit in hot and humid days.

thanks

[Field In Sight]

It depends on who maintains your engines / apu's.

The effect of 2-3 degrees reduction in flex on the engines depends on how much flex is being used.

i.e. at close to TOGA a reduction in 2-3 degrees is very significant as regards to engine wear. Not so much at lower power settings.

At my company it probably costs just as much using the APU as we do all of our take-offs with the packs off anyway.

FIS.

[kuwait340]

that's true...

but in our region ..we can't do a packs off t/o...as it is totaly uncomfortable.

thanks for you kind reply.

[Jetset320]

In our company APUs are "pay by the hour", so that brings in whole new economies of scale. We try to use APU as little as possible.

[sergejv]

...At my company it probably costs just as much using the APU as we do all of our take-offs with the packs off anyway.

And what about in icing condition when we can't use APU bleed with Wing AI on ?