Packs OFF for take off?
 

In my company in the US the standard procedure is to use engine bleed ON, and packs ON for T/O. At higher weight/altitude/temperature on shorter runways the performance can come back with Packs OFF for T/O. In that case we can T/O with the packs OFF from start of the T/O till climb power set, but we also are allowed to leave the APU Bleed ON, and Packs ON for T/O, because as far as engine performance is concerned the packs are not taking any engine bleed air.
As I have sat in the jump-seat of every large operator in the US I know that using the Packs during T/O is definitely the standard in the US. In a different thread someone said that "the vast majority of operators use Packs OFF takeoffs" and "Packs Off takeoffs is an option which is quite routinely adopted as standard in Europe" when not limited by performance. I worked in the EU until 2005, and I know back then that wasn't SOP, but things could have changed since then. Any airline pilots care to join in and tell me what your SOP is for a none performance limited T/O?

What would be the benefit of an no packs? Unless it's a ferry flight with a pressurization issue or a flight with an APU inop, why not use the packs?

I sometimes hear pilots mistakenly call a BLEEDS OFF takeoff PACKS OFF but they clearly mean the former.

It's been a while since I did a packs off takeoff in the Airbus, but we literally turned the packs off. In the 737, I remember doing bleeds off...

ed to add - Doing it for better flex temp hence engine life

It removes much of the bleed load from the engine. Engine and performance-wise, the effects of switching the packs off are the same as running the packs off the APU. Some other implications exist depending on type: on the A320, the APU bleed would start to feed the wing anti-ice after departure if it is switched on, which is not approved.

Usually, on the CFM 320, a packs-off takeoff will use a flex temperature of 3-4 degrees higher than a takeoff with the packs fed by engine bleed. So while fuel burn is likely similar, the engine will be run a few degrees cooler, bringing some maintenance cost benefits. In case of a performance-limited takeoff, a packless takeoff (with APU or not) will result in a few 100kg more MTOW for field length or 2nd segment limited departures.

Here, a packs-off takeoff is encouraged but not at all mandatory. Crews may freely select to run the packs off the engines or the APU, whichever they deem most appropriate overall.

A320 carrier. Packs OFF as SOP, but not it's not a requirement. Performance is rarely an issue so I guess it's more to do with maintenance / lease costs. Days to leave the Packs ON could be e.g. really hot and sunny days.

We do a No Engine Bleed Off Takeoff so infrequently that we reference a supplementary normal checklist when we do. 737: Packs left in auto, Isolation valve switch to close, Engine bleed switches to off, APU bleed on.The gotchya is to avoid the DUAL BLEED light when reconfiguring the panel during the climb, so again rather than teaching "remember the reverse C" we just tell pilots to reference the sup normal checklist.

Understand that everyone on here wants to remain anonymous, but what kind of carrier/size of fleet/location?

FCOM recommends Packs off take off to reduce the maintenance cost. My outfit does not push pilots to do it. We are never performance limited. I do it sometimes to demonstrate to new pilots or sometimes in winter for the sake of good airmanship. I’m surprised to read most airlines do not perform packs off take off.

What FCOM is that? You’re surprised to read most airlines do not perform packs off take off? There are reasons.

It’s a terrible idea because;
1. The increase of cabin altitude warnings when pilots invariably forget to reconfigure. (During a busy phase of flight)
2. The discomfort passengers feel going from an unpressurized to a pressurized cabin.

US, pax, 700 ac fleet

It’s official Airbus FCOM. And this is not a 737-300 like in the case of Helios flight 522. You can not forget the packs on Airbus. I mean you can temporarily but you will get an ECAM and oral alert after passing 1500 feet. There is no discomfort if procedure is done properly. At least I never heard of it personally.

Hi
FCOM Packs Off for take-off for the Airbus A320 is done either by :

#1 PACKS OFF

Or

#2 Apu left running after start with APU Bleed left on

We find for various technical and maintenance reasons that it’s better to use APU running with APU Bleed On .

In the summer here 40C + and density altitude approaching 5000’(ft) with 2000m runways we regularly perform packs off (APU On and APU Bleed On) with Flap 3.

This enables us to pull a full pax load out of Mining FIFO Ports for a 1hour 35min flight back to Perth Wa (Australia).

cheers
buddy

Those threats have been thoroughly analyzed by Airbus when they decided to remove the after takeoff checklist. You will instead perform an acceleration flow and in case you forget to then
The ECAM will pop up if you forget the packs off.
The discomfort is easily mitigated by selecting packs on with a 10 seconds interval.

Yes, should have mentioned 737 in my case. The bus is of course ahead in tech, even though the Max will now let you know if you need to reconfigure the packs after takeoff.

I sent you a PM.

My place (737NG and Max) per SOP is packs auto, bleeds on for take-off. If performance limited (rarely), we do an engine bleeds off take-off with the APU left running as per +TSRAs procedure above, referencing a checklist.

I’d say a big issue with Packs OFF take-offs is the passenger discomfort. The temperature rises pretty quickly in a full aircraft. Maybe when the loads are 50-80% full, the heat in the cabin isn’t too bad, but nowadays with high load factors it gets stuffy and claustrophobic pretty quickly. And as for not starting the APU during pax boarding……..

For the past 3 airlines I've flown at - always packs off (A320)

@Hunterboy, this is a different issue.

Airbus says that whenever passengers are on board for more than 20 minutes, air conditioning should be provided. As an APU cycle is needed for engine start on most types anyways, there is no point in letting cabin crew and passengers stew in their own sweat on the ground, and even less in possibly causing medical issues in frailer persons on board. After startup, ample bleed is available. Airbus Green Operations advises to run only one pack, but both are available if more flow is desired.

For a packless takeoff, the packs are switched off during lineup and back on when climb power is set, sually in case of NADP 1 or 2 at 1000´AAL. This normally causes no major heating of the cabin or discomfort in the ears. With NAP B (1500/3000), pressure differences may be a little more noticeable but definitely not painful. As has been mentioned, the Bus will complain above 1500´AAL by writing AIR PACK x OFF whenever an otherwise serviceable pack is not switched on - it is really hard to forget the packs and run into the CAB ALT warning.

But still - whenever the crew deems a packs-on takeoff more appropriate, there is nothing in the books disallowing this.

Depends also on the engines. Usually with V2500, pack on take off, on CFM, packs off.

Never flown the A320, we had a procedure in the 757 to use APU bleed for the packs on the rare occasions we needed more power out of limiting airports

If there’s no option to supply air for the packs from the APU I understand why they are turned off when necessary for increased power on take off


What I don’t understand is leaving the APU and it’s bleed on with the packs off. What benefit is that ?