If ive got this right, spin737 is suggesting that a packs on takeoff is normal for a ng, and that if extra thrust was needed you might turn the engine bleeds off and use the apu to power the packs.I always fly with checklists, which may or may not be right I guess. Most seem to advise a packs off tackoff. Is this wrong formthe ng? My best guess is that it is correct for some airlines' sop, but far from essential so other airlines don't do it?Second thing that's still unclear is if packs on actually does increase engine thrust on the ng, or if the same amount of air is leaving the engines via the bleeds whether the packs are on or off.

If ive got this right, spin737 is suggesting that a packs on takeoff is normal for a ng, and that if extra thrust was needed you might turn the engine bleeds off and use the apu to power the packs.

He wins my vote !Fred.

@ryr738, you posted while i was typing, thx for the useful information. It answers some but not all of what I thought the grey areas were.As an additional question based on your info, the after takeoff flow includes packs to auto. I note they were in auto at the before takeoff flow stage. Is this correct - for bleeds off takeoff, are the packs on auto or off before takeoff?

On auto in both cases !Fred.

Ok, bleeds off procedure is now clear.I just checked my fs2crew flows for the 737, the default is for a packs on takeoff (pack are just turned off for engine start). There's an option at the briefing stage for a bleeds off takeoff procedure.Im obviously not flying the ngx with this program, im currently using fdc livecockpit with various checklists downloaded. The one i started using yesterday was apparently based on virgin blue procedures, so im going to have to refresh my memory as to whether that's packs on or off for takeoff (i just do whatever the fo tells me!).

@Peter !Yes, it is a bit different.Instead of me trying to explain it I will use some pics.You use a letter " C " type scan to set the switches for a No Engines Bleed takeoff or landing.( A no engines bleed landing could be used if extra go-around thrust is needed )After takeoff you do the same switch scan but in reverse order.It is recommended by Boeing that before you turn back on the No 1 engine bleed, that the Cabin Rate of Climb is stable !This makes sure the APU bleed valve is fully closed before you open the engine bleed valve.I hope the Pics are clear and easy to follow.Fred.

Thanks for posting those pics, Fred.

Let's see if we can sum this up:Takeoffs are normally with Packs on.You can take off without the PACKs on. You will not be pressurized until you reconfigure.You can take off with the engine bleeds off. You (your airline) may or may not have you use the APU for pressurization/air conditioning.A "Bleeds Off Takeoff" is generally understood to mean Engine Bleeds Off.Typically, if you're just a bit too heavy, then you might use the Engine Bleeds Off for added performance. For the -800, you can get 800lbs more off the runway and 2600lbs more for climb performance.Don't drop the rubber jungle.

Edited January 13, 201214 yr by Spin737

The standard procedure on the 737 is Packs on for take off. I haven't had to do a packs off T/O for performance yet.

Let's see if we can sum this up:

Spot on! Well done Matt.If we could only have a similar summary at the end of every topic without having to read through all the usual yapyap :(

Thx for the summary.What seems to be missing is expansion on point 2. Under what circumstance will you takeoff with packs off? Is this only when you're doing a bleeds off takeoff without the apu running?

Thx for the summary.What seems to be missing is expansion on point 2. Under what circumstance will you takeoff with packs off? Is this only when you're doing a bleeds off takeoff without the apu running?

It was already answered in 2 pages.Bleeds off, no packs avaiable, more thrust.You will take off wit bleeds off or packs off only if you need more thrust and you won't/can use the APU.When do you need more thrust?When some of the following exixt:-Short runways-heavy plane-hot day-high elevation runwayI think you must read the FCOM part 2 about pneumatic and air conditioning system.I think you have a little confusion with them.

You can take off without the PACKs on. You will not be pressurized until you reconfigure.

Thx for the summary.What seems to be missing is expansion on point 2. Under what circumstance will you takeoff with packs off? Is this only when you're doing a bleeds off takeoff without the apu running?

This is typically done when you need the performance boost for the bleeds off but do not have an operating APU.

British Airways B744Over 300tonnes the packs are off for takeoff

What seems to be missing is expansion on point 2. Under what circumstance will you takeoff with packs off? Is this only when you're doing a bleeds off takeoff without the apu running?

Pack switch position when all bleeds are off makes as much difference as the light switch position in your house during a blackout - ain't gonna work anyway :( Anyone with deeper understanding of NG pneumatic workings please correct me if I'm wrong.

It was already answered in 2 pages.Bleeds off, no packs avaiable, more thrust.You will take off wit bleeds off or packs off only if you need more thrust and you won't/can use the APU.When do you need more thrust?When some of the following exixt:-Short runways-heavy plane-hot day-high elevation runwayI think you must read the FCOM part 2 about pneumatic and air conditioning system.I think you have a little confusion with them.

Hi davierosoft,I've actually got no confusion about this at all and have read the FCOM part 2 and looked at the schematics for pressurisation. In the past two pages there's quite a number of incorrect statements.Spin737 stated right back at the start that packs were for pressurisiation and that it's the engine bleeds that you need off if you need to increase thrust. The only thing that hadn't been spelt out in his summary was why you would ever do a packs off takeoff in an NG (as opposed to other aircraft like the 747). Based on my non-professional knowledge of the NG it seemed that you would only do this in a bleeds-off takeoff when you're not planning to use the APU - as stated in my post above. I can't think of any other reason you'd do this i the NG, and spin737's reply seems to have comfirmed this.I've found this a useful thread for clarifying an area I thought I fully understood but which I am now much more confident in.Your reply showed a lack of understanding of my question/clarification - perhaps read posts more carefully before telling people they're confused and need to rtfm.