BA have a SOP that all takeoffs above 300 tons are packs off. It is not often a performance issue, more as has been alluded to, fuel and engine conservation. But they do operate hot and high where, on some days, packs off are required for performance.

eg. Jo'burg, Nairobi, Mexico.

And to muddy the waters, they also in addition load the aircraft with an aft C of G to squeeze the last kilo out of the performance.

Packs off take offs will give a lower EGT for the same EPR or N1 setting - good for engine life.

And since it's good for engine life, that equates to long-term fuel savings. :ok:

And to add grist to the mill even an individual airline's SOP can change with time...in BA's case with the 744 from always having the packs on if performance allowed, then to APU to Ctr pack and then finally (perhaps) to all packs off above 300 tonnes...seems to depend on the latest enviromental priority /engineering demand / New Training Manager's previous fleet:bored:.....

Actually, at some carriers it has more to do with pax comfort rather than rabid fuel conservation, sir. :ooh:

When selecting the packs back on after t/o we nearly always get a brief ">Trim Air Off" Eicas. It clears after about 5 secs.

Does anyone have a tip to stop this happening? ie. select Pack x on first?

Wow, I thought passenger comfort was an Idea abandoned back in the late 1980's. :ugh:

On an individual basis, flex / reduced power take off's do not save fuel.


Whilst not the most cost efficient profile when taking into account all other factors a full power take off followed by a max continuous thrust climb to altitude will save the most fuel.


This will allow the Aircraft to get to cruise Altitude as soon as possible where it burns the least fuel.


This is my technique when operating at the very limits of my Aircraft's performance on long range operations and has made a noticable difference.

What is the big deal - packs off or packs on? Just remember the three B's at 10K, bleeds (packs), babes and bulbs and all will be fine and dandy - especially with the bean counters.

stilton:
You have stated this quite correctly, given your condition of min fuel for max range. I believe this is true for most turbofan aircraft.

Just don't overlook the " taking into account all other factors " for more mundane ops. Those "all other factors" are far from trivial.

Considering that this has bounced up again.... I would say that PACKS ON are for passenger comfort, PACKS OFF are for "rabid fuel conservation :)

Mutt

Hot-high-heavy = more payload.