Airbus Packs Logic
 

Hello,
I was wondering the reason why Airbus prefers "packs" off take off while Boeing performs "bleeds" off for take off. Considering, restarting the packs have a negative affect on pack's service life by increasing the cycles it goes through in daily ops, why is Airbus so insistent on performing take off with packs off where bleeds off would give the same result while protecting the hardware.

If performance is limiting, the A320/21, A330 and A350 all give pilots the option of either packs off or packs on/APU bleed on (ie APU to Pack) for take-off. Neither the FCOM nor the FCTM express a preference for one over the other.

Similarly, the B744, B748 and B777 manuals all have procedures for Packs Off and APU to Pack take-off, with no preference expressed one way or the other.

If you shut off the bleeds, don't the packs go off as well? Much like turning a light off by flipping the switch, or unplugging it right?

FWIW, at my company, we never turn the packs off. If we need extra performance, the APU bleed is left on.

Restarting the packs does not have an appreciable effect on the service life. In engineering we measure the packs in flying hours and send the major parts for cleaning / refurbishment every ~12,000.

On the A320 family, you turn the bleed off you lose the wing anti-ice on that side.

https://www.avsoft.com/wp-content/up...SSD-A320-3.jpg

Depending on the runway length/obstacles, taking bleed off reduces assumed temperature. This has impact on engine life/EGT margin which increases fuel consumption in the longer term.

On the later model Bleed Monitoring Computers, the bleed will shut off if there no demand.

Reference pack life, it’s not normally measured in start cycles and have not seen any evidence (Airbus TFU/ISI) that a pack start cycle has a larger impact than hours of use.

Would it make a difference whether a pack was turned off by turning it off directly, or by turning off the bleeds supplying air to it? I doubt it.