PACKS OFF TAKE OFF

[CHAPARRAL]

Packs off take off is standard operating procedure in my company.
The objective is to prolong engine life as much as possible, and we do it
always despite the fact the manufacture (airbus) pointing out the real save
of a reduced T/O thrust is produced at high OAT/pressure altitude.
I always believe this practice to be a nonsense because of an increase in
cycles/degradation in pack life, with little gain in engine life, and to
corroborate this i just had an air cycling machine failure after a packs off
T/O.
Any comments/suggestions?

____________________________________________________________ _____
Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp

[411A]

Would agree, unless max PERFORMANCE for the takeoff is needed, packs off is a complete waste of time.
Old ideas die hard....

[BAE employee]

Leaving the packs on means one less thing to forget later. Who needs a cabin altitude alert in the climb?

[GlueBall]

No harm done departing with at least 1 pack, especially when operating in the tropics. Actually, one way to keep all packs running during takeoff is to run them exclusively off APU bleed air and keep the engine bleeds off if max T/O thrust and max air conditioning are desired. Been there. Done all that. :cool:

[DontSink]

Hi Chaparral

No sugestions, since I`m not enough qualiflyed, but a good topic for the engineers!
I had already realised that the airline in question always performed a bleeds off TO, that wishling sound before TO... as a pax... Where I fly, it makes no sense to use bleeds off for a Reduced TO, only for a Full TO. "All systems should be used in their normal config, unless necessary for performance (air cond. case)... all checklists assume systems in their normal config" - from 737 QRH!
É complicar a aviação :mad:

Cheers
:)

[mutt]

Glueball,

You might be interested in knowing that neither of your suggestions will work in an FAA certified B777. Single Pack operation reduces takeoff weight even more than having two packs working. You aren’t allowed to use the APU for takeoff.

Chaparral,

The majority of the engine life savings come from the initial thrust reduction, I believe that RR quote a 12% increase in blade life for a .01 EPR reduction (RB211-524D4). This saving isn’t constant and at a certain point you will have achieved your maximum savings regardless of further thrust reductions. Therefore turning the packs off to increase the engine savings isn’t really offering you a lot of benefit.

Obviously you should keep a system where you can increase you takeoff weight with Packs Off when required.

Mutt.

[ 06 November 2001: Message edited by: mutt ]

[QAVION]

Leaving the packs off for takeoff won't allow you to prepressurize your aircraft.. and your passengers' ears may suffer from the uncomfortable pressure "bump" at rotation/takeoff. Modern jetliner cabins are normally prepressurized to a pressure altitude slightly below that of the airfield during the early stages of the takeoff roll (to reduce the bump effect).

Rgds.
Q.

[ 08 November 2001: Message edited by: QAVION ]

[dusk2dawn]

mutt, could you please expand that 777-no-APU-t/o statement ? From my 737 days I seem to remember that the APU was mighty handy when it came to no-bleed t/o or one gen inop for a couple of days.

[EGGW]

My company operates the A321 with V2500, and we always operate with packs off for take-off. The benefit for engine wear has been enourmous, and engine life has been increased by about 30%. We currently have an AD on the A320 regarding Braking performance, and the problem amongst many things is the reduction in Flex temperature. I know on short runways i now mostly operate packs-off, the increase in the Flex temp can be up to 8 degrees, reducing the EGT on take-off by quite a margin.
Packs-off is not an issue with good SOPA's, and anyhow the Airbus FBW reminds you if the packs are off when the Flaps are set to 0, with an ECAM caution.
The pressure bump does not occur on modern aircraft in my experience...

[schit.furbraen]

About pressurisation on take/bumps etc,packs don't have much input on take off, The out flow valves controls this. as the aircraft depressurises with the rate set. Bumps after take off, on selecting packs can be ironed out by selecting each pack in turn with a pause. I know you have to get it all ready for coffee!!
Another thing it is cheaper to fix cold air units than to change engines early. As well should consider the extra fuel burn on take off etc.....

[ 10 November 2001: Message edited by: schit.furbraen ]