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Takeoff With Packs On/Off?  
User currently offlineAmericanF100 From United States of America, joined Aug 2001, 243 posts, RR: 0
Posted (4 years 9 months 3 weeks 6 days 8 hours ago) and read 12549 times:

Hi,

I was just wondering what conditions or reasons are taken into consideration when deciding whether or not to use packs during takeoff? Does it have to do with the weather? What about the weight of the aircraft? Is it aircraft specific or are there kind of general rules regarding the use of the AC packs? I seem to remember reading something that said using packs on takeoff reduces aircraft performance, but I can't exactly remember and was just looking for some clarification. Any information would be greatly appreciated!

Regards,

Matt

32 replies: All unread, showing first 25:
 
User currently offlineCosmicCruiser From United States of America, joined Feb 2005, 2255 posts, RR: 15
Reply 1, posted (4 years 9 months 3 weeks 6 days 8 hours ago) and read 12551 times:

Of course it's using bleed air off the engines hence less thrust.

User currently offlineFLY2HMO From , joined Dec 1969, posts, RR:
Reply 2, posted (4 years 9 months 3 weeks 6 days 7 hours ago) and read 12567 times:

This is me just being nitpicky, but technically its PACS (pressurization and Air conditioning system) of course the term may vary from manufacturer and what have you not.

Quoting AmericanF100 (Thread starter):
Does it have to do with the weather? What about the weight of the aircraft? Is it aircraft specific or are there kind of general rules regarding the use of the AC packs?

A combination of all that you mentioned.

A heavy airplane departing at a hot and high airport will most likely need to perform a PACS off takeoff.

How you do it though depends on the aircraft. Most airliners have at least 2 PACS, some heavies have 3 or more.

I'll try to recall the operation for the 73G, though it's been a while since my training and I'm too lazy to pull out the manuals  Wink

The 737 has two PACS. They can be powered by the APU or either one or both of the engines.

At my (ex) airline, SOP for hot and high situations was to either turn off both PACS, or leave one running off of the APU. Once in flight you could switch them back on or to the normal engine bleed source. You could also have 1 PACS running off of both engines to have a lesser impact on performance.

Current 737 drivers here might know better.


User currently offlineAmericanF100 From United States of America, joined Aug 2001, 243 posts, RR: 0
Reply 3, posted (4 years 9 months 3 weeks 6 days 7 hours ago) and read 12553 times:

Thanks for the nice explanation as well as the clarification on the acronym. I will refer to them properly from now on!

User currently offlineJarheadK5 From United States of America, joined Nov 2005, 216 posts, RR: 1
Reply 4, posted (4 years 9 months 3 weeks 6 days 7 hours ago) and read 12532 times:

In the KC-10 (which is basically a DC-10-30), the decision to takeoff with packs on/off is dependent on a lot of things, as determined by the flight engineer. I'll list several of them, in descending order:
- takeoff gross weight
- OAT
- runway length
- obstacle-clearance restrictions
- other climbout restrictions
- noise abatement restrictions



Cleared to Contact
User currently offlinePGNCS From United States of America, joined Apr 2007, 2828 posts, RR: 45
Reply 5, posted (4 years 9 months 3 weeks 6 days 7 hours ago) and read 12530 times:



Quoting FLY2HMO (Reply 2):
This is me just being nitpicky, but technically its PACS (pressurization and Air conditioning system) of course the term may vary from manufacturer and what have you not.

That may be where the term came from, I really don't know, but no manual for any aircraft I have ever flown refers to it that way; every manual I own spells it "Packs" and I have flown the A-320, DC-9, MD-80, MD-90, 727, 737, 747-400, 757, 767, and L-1011. There may be manuals out there that use your acronym, but they are in the minority.

Quoting AmericanF100 (Thread starter):
Any information would be greatly appreciated!

Sometimes performance dictates that thrust be maximized, and packs off will be required, the alternative being offloading weight from somewhere. It's hard to generalize as there are a huge variety of aircraft, route structures, and procedures out there. Packs off takeoffs range from almost never, to absolutely always. In one 767 variant I flew SOPs required every takeoff to be packs off due to the potential to overtemp engines quite easily. All things being equal I would rather not do packs off takeoffs for several reasons largely relating to passenger comfort; the cabin climbs with the plane until the packs come on. On some aircraft the delay between moving the pack switch out of off and the beginning of pack operation may be the better part of a minute during which time the cabin climbs with the airplane, possibly at a few thousand feet a minute, which is very uncomfortable on the ears.


User currently offlineFLY2HMO From , joined Dec 1969, posts, RR:
Reply 6, posted (4 years 9 months 3 weeks 6 days 7 hours ago) and read 12527 times:



Quoting PGNCS (Reply 5):

That may be where the term came from, I really don't know, but no manual for any aircraft I have ever flown refers to it that way; every manual I own spells it "Packs"

True. The 737 manuals indeed say packs. But I've seen the PACS acronym used in training CBTs and in my airline ops classes in college. I guess I'm just used to using the term that way. Same difference, really  Smile


User currently offlineMir From United States of America, joined Jan 2004, 21654 posts, RR: 55
Reply 7, posted (4 years 9 months 3 weeks 6 days 6 hours ago) and read 12504 times:

Very, very rarely will an airplane take off without the packs on (and yes, the manual for the airplane I'm working with at the moment calls it a pack, so I'm going to call it a pack). The more important question is what is running the packs. They can be run off of either engine bleed air or APU bleed air. Engine bleed air is preferable, since it means that you don't need to run the APU, so you can save some fuel. But it does sap your performance, so in the event that you really need the extra power (normally in hot/high conditions or short runways), you can leave the APU running for takeoff and have the APU bleed air powering the packs. If the APU is inoperative for some reason, then you're talking about an unpressurized takeoff (packs off until at a safe altitude, then turn the engine bleeds on and the packs on). This isn't that comfortable for the passengers, so it's something you really want to avoid unless you have no other options.

Most jets will have pneumatic ice protection for the wings and engines, and this air comes from the engine bleeds as well. So it too saps performance, and if you get into a situation where you need the anti-ice, you may have to use the APU on takeoff to run the packs, since running both the anti-ice and the packs off the engines would be too much of a hit. Interestingly (and somewhat frustratingly), the airplane I'm working with at the moment can't use the APU if the aircraft has been sprayed with anti-ice fluid, due to the possibility of the fluid getting into the APU inlet and smoking up the cabin. So at the time when you really would like to have the APU running the pack (because you're going to have the anti-ice on in those situations), you can't - you either have to run everything off the engines and take the performance hit, or go take off unpressurized.

-Mir



7 billion, one nation, imagination...it's a beautiful day
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 8, posted (4 years 9 months 3 weeks 6 days 6 hours ago) and read 12491 times:



Quoting FLY2HMO (Reply 6):
True. The 737 manuals indeed say packs. But I've seen the PACS acronym used in training CBTs and in my airline ops classes in college. I guess I'm just used to using the term that way. Same difference, really

The ATA title for Chapter 21 is "Air Conditioning and Pressurization" so maybe the acronym should be ACAP?


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 9, posted (4 years 9 months 3 weeks 6 days 5 hours ago) and read 12465 times:



Quoting FLY2HMO (Reply 2):
This is me just being nitpicky, but technically its PACS (pressurization and Air conditioning system) of course the term may vary from manufacturer and what have you not.

All aircraft have a PACS (although they may not use that name). One PACS may contain multiple air conditioning *packs*, which refers to a specific component of the PACS; specifically, the air cycle machine and related plumbing and heat exchangers.

Quoting FLY2HMO (Reply 2):
The 737 has two PACS.

To be technical, the 737 has one PACS (one system). That PACS contains two air conditioning packs, one mix manifold, two risers, an outflow valve, pressure relief valves, a pressure controller, etc., etc.

Tom.


User currently offlineAAR90 From United States of America, joined Jan 2000, 3474 posts, RR: 47
Reply 10, posted (4 years 9 months 3 weeks 6 days 4 hours ago) and read 12445 times:



Quoting FLY2HMO (Reply 2):
Current 737 drivers here might know better.

Even though it is easy and a pretty regular operation out of KSNA, I still utilize the checklist...

With APU:
Right Pack............................................................................................AUTO
Isolation Valve....................................................................................CLOSE
Left Pack ..............................................................................................AUTO
Engine 1 Bleed........................................................................................OFF
APU Bleed................................................................................................ ON
Engine 2 Bleed........................................................................................OFF
Trim Air Switch ......................................................................................... ON
Wing Anti-Ice Switch ...............................................................................OFF

After Takeoff (After airplane clean up when workload permits)
Engine 2 Bleed......................................................................................... ON
APU Bleed...............................................................................................OFF
After pressurization stabilizes:
Engine 1 Bleed......................................................................................... ON
Isolation Valve......................................................................................AUTO
APU ...................................................................................... AS REQUIRED

Without APU:
Engine 2 Bleed .......................................................................................OFF
APU Bleed ..............................................................................................OFF
Engine 1 Bleed .......................................................................................OFF
Left Pack.............................................................................................. AUTO
Isolation Valve ................................................................................... CLOSE
Right Pack ........................................................................................... AUTO
After Takeoff (After airplane clean up when workload permits)
Engine 2 Bleed .........................................................................................ON
When Cabin Rate of Climb indicator stabilizes:
Engine 1 Bleed .........................................................................................ON
Isolation Valve ..................................................................................... AUTO



*NO CARRIER* -- A Naval Aviator's worst nightmare!
User currently offlineGLEN From Switzerland, joined Jun 2005, 224 posts, RR: 2
Reply 11, posted (4 years 9 months 3 weeks 6 days 1 hour ago) and read 12403 times:

On the MD11 the automatic system controller switched packs off automatically when setting T/O-Thrust.

On the A330/340 we originally switched off packs for take-off only when necessary due to performance problems.
Then there was quite a discussion to switch them off for every take-off in order to save fuel - on the other hand the additional cycling of the packs produces more maintenance costs. With high fuel prices the benefit of switching them off for every departure is bigger then the additional costs. So we have them off for every take-off by now.



"The horizon of many people is a circle with zero radius which they call their point of view." - Albert Einstein
User currently offlineDocLightning From United States of America, joined Nov 2005, 19785 posts, RR: 59
Reply 12, posted (4 years 9 months 3 weeks 5 days 14 hours ago) and read 12236 times:

Will the passengers notice it when you turn off the packs (assuming it's just for a few minutes and doesn't result in significant cabin temperature change)? I know that when they do engine starts, you can hear the circulation fans stop in the cabin, but I've not noticed the fans turn off before takeoff on any flight.

User currently offlineBri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 13, posted (4 years 9 months 3 weeks 5 days 14 hours ago) and read 12231 times:

I've noticed it. Most RJs seem to, at least in the mountain states where I do a lot of flying on them. I think it's especially noticeable on them because the quieter engines are mounted further back.


Position and hold
User currently offlinePGNCS From United States of America, joined Apr 2007, 2828 posts, RR: 45
Reply 14, posted (4 years 9 months 3 weeks 5 days 14 hours ago) and read 12222 times:



Quoting Mir (Reply 7):
Very, very rarely will an airplane take off without the packs on

No. It is totally dependent on the aircraft, operator, and performance situation. Some aircraft I have flown never take off with packs on, ever.

Quoting Mir (Reply 7):
They can be run off of either engine bleed air or APU bleed air. Engine bleed air is preferable, since it means that you don't need to run the APU, so you can save some fuel. But it does sap your performance, so in the event that you really need the extra power (normally in hot/high conditions or short runways), you can leave the APU running for takeoff and have the APU bleed air powering the packs

Not always true. Some planes are not allowed or physically can't use the APU for bleed air except during ground operations (DC-9, MD-80, 727, 747, etc.) while many other operators elect to shut down the APU after all engines are running for fuel savings. There are other complications with using the APU for bleed air in this situation on some aircraft when thermal anti ice systems are in use.

Quoting DocLightning (Reply 12):
Will the passengers notice it when you turn off the packs (assuming it's just for a few minutes and doesn't result in significant cabin temperature change)?

Depends on the aircraft and passenger. The vast majority of passengers are not as clued in to aircraft operations as the readership here is, but they likely would notice the cabin climb being at a higher rate than normal in their ears after departure, and might note the temperature moving toward the ambient outside the aircraft for a bit. On some aircraft you may notice essentially nil airflow until the packs are reinstated after departure (think DC-9 or MD-80, for instance).


User currently offlineGoldenshield From United States of America, joined Jan 2001, 6047 posts, RR: 14
Reply 15, posted (4 years 9 months 2 weeks 6 days 15 hours ago) and read 11828 times:



Quoting Bri2k1 (Reply 13):
I've noticed it. Most RJs seem to, at least in the mountain states where I do a lot of flying on them.

With the CRJ-200, if the APU is inop, then bleeds closed is used so that 1) in the summer you want max performance, and 2) in the winter, you can have anti-ice operating. The main thing here is that the 10th stage bleed air (A/C), and the 14th stage bleed (Anti-ice) cannot be operated at the same time.

With the CRJ-700/900, if the APU is inop, then it's slight different: 1) In the summer, packs will be off for takeoff, and 2) In winter, packs will be on, as the bleed air will mix depending on demand of the system.

I can't speak for the ERJs.



Two all beef patties, special sauce, lettuce, cheese, pickles, onions on a sesame seed bun.
User currently offlineBri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 16, posted (4 years 9 months 2 weeks 5 days 19 hours ago) and read 11732 times:



Quoting Goldenshield (Reply 15):
The main thing here is that the 10th stage bleed air (A/C), and the 14th stage bleed (Anti-ice) cannot be operated at the same time.

Interesting. What happens in cruise climb, cruise, or descent, when you don't need maximum thrust, but want to operate full anti-ice and A/C? I assume you want to cruise with the APU off to save the fuel since you have both engines running. Can one engine operate A/C and the other anti-ice?



Position and hold
User currently offlineGoldenshield From United States of America, joined Jan 2001, 6047 posts, RR: 14
Reply 17, posted (4 years 9 months 2 weeks 5 days 15 hours ago) and read 11708 times:



Quoting Bri2k1 (Reply 16):
Interesting. What happens in cruise climb, cruise, or descent, when you don't need maximum thrust, but want to operate full anti-ice and A/C? I assume you want to cruise with the APU off to save the fuel since you have both engines running. Can one engine operate A/C and the other anti-ice?

Below 12,500 (or whatever a given company mandates) with the APU inop, you would be running anti-ice. Above that, you'll be running pressurization. There's then an intricate dance that goes on with the upper panel as the crew switches bleed sources between anti-ice and pressurization.

Normally, though, with the APU operating, you'd have it handle the anti-ice until mid 20's, or until the PIC no longer deems it appropriate.

As for your other questions, I'd have to let a pilot answer that, as it's too technical, and beyond the systems knowledge required to do my job.



Two all beef patties, special sauce, lettuce, cheese, pickles, onions on a sesame seed bun.
User currently offlineJETPILOT From United States of America, joined May 1999, 3130 posts, RR: 29
Reply 18, posted (4 years 9 months 2 weeks 3 days 14 hours ago) and read 11565 times:

The 727 always took off with both packs on. The 727-200 had an auto pack trip system. If the EPR dropped below a certain value on takeoff one pack would automatically trip offline.

User currently offlinePGNCS From United States of America, joined Apr 2007, 2828 posts, RR: 45
Reply 19, posted (4 years 9 months 2 weeks 3 days 11 hours ago) and read 11543 times:



Quoting JETPILOT (Reply 18):
The 727 always took off with both packs on. The 727-200 had an auto pack trip system. If the EPR dropped below a certain value on takeoff one pack would automatically trip offline.

We didn't. Normal operations took off with one pack on for fuel savings, though we did have packs off numbers if performance required them. I never flew the 727-100, but spent several years on the -200 and did my share of time on the panel. I can't remember much about the corrections, but recall all the EPRs being slightly different values due to the bleed corrections. I think 0.02 EPR increase was right for a pack off on the respective side, but am not positive.


User currently offlineFrancoflier From France, joined Oct 2001, 3775 posts, RR: 11
Reply 20, posted (4 years 9 months 2 weeks 3 days 7 hours ago) and read 11506 times:



Quoting DocLightning (Reply 12):
Will the passengers notice it when you turn off the packs (assuming it's just for a few minutes and doesn't result in significant cabin temperature change)? I know that when they do engine starts, you can hear the circulation fans stop in the cabin, but I've not noticed the fans turn off before takeoff on any flight.

It depends on the aircraft.

Temperature wise, the pax might feel it, especially on a stuffy day in a full cabin.

Sound wise, it depends on the system architecture. Bigger aircrafts have recirc fans that stay on when the packs are off, and which you will hear much more than the packs themselves.
Recirc fans are there to recycle the cabin air. That way less 'fresh' air from the packs is needed and you save fuel. But if for whatever reason the packs are set to deliver a higher flow, then some of those recirc fans might turn off.

Basically, the fans and airflow you hear and feel aren't always dependant on whether the packs are on or off, especially in bigger aircrafts.



Looks like I picked the wrong week to quit posting...
User currently offlineMir From United States of America, joined Jan 2004, 21654 posts, RR: 55
Reply 21, posted (4 years 9 months 2 weeks 3 days 6 hours ago) and read 11502 times:



Quoting Bri2k1 (Reply 16):
What happens in cruise climb, cruise, or descent, when you don't need maximum thrust, but want to operate full anti-ice and A/C?

Bombardier publishes performance numbers for running them both off the engines, so I'd say do that, unless you need the extra power for climb performance.

Quoting Bri2k1 (Reply 16):
Can one engine operate A/C and the other anti-ice?

It's physically possible, yes. But I can't really think of a reason that you'd want to.

Quoting Goldenshield (Reply 17):
Normally, though, with the APU operating, you'd have it handle the anti-ice until mid 20's, or until the PIC no longer deems it appropriate.

From what I recall, in the CRJ the APU can't do anti-ice - only the 14th stage engine bleed air can do that.

-Mir



7 billion, one nation, imagination...it's a beautiful day
User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 22, posted (4 years 9 months 2 weeks 3 days 3 hours ago) and read 11481 times:

Out here its reffered to as bleeds off T/O.
regds
MEL.



Think of the brighter side!
User currently offlineGoldenshield From United States of America, joined Jan 2001, 6047 posts, RR: 14
Reply 23, posted (4 years 9 months 2 weeks 3 days 1 hour ago) and read 11467 times:

Quoting Mir (Reply 21):
From what I recall, in the CRJ the APU can't do anti-ice - only the 14th stage engine bleed air can do that.

Good catch. I guess I wrote something down wrong. Either way, the pnuematic dance on climb-out is very popular in winter among CRJ pilots. Hence why the pilots LOVE to fly the -700/900; it does the config change for them.

[Edited 2009-12-18 02:52:18]


Two all beef patties, special sauce, lettuce, cheese, pickles, onions on a sesame seed bun.
User currently online747classic From Netherlands, joined Aug 2009, 2153 posts, RR: 14
Reply 24, posted (4 years 9 months 2 weeks 2 days 21 hours ago) and read 11439 times:

"Packs off" T/O was standard on the MP 747-200 freighter fleet, only with livestock or smelling cargo on board the air conditioning packs were operated during T/O.

Crew Coordination Procedure :

a) Use normal air conditioning during taxi.

b) Prior to entering runway ;
(1) Pack valve switches to close.

c) After Take off :
Restore normal air conditioning ;
(1) Place one pack valve switch to the open position at approximately 1000ft HAA (prior to reaching 2000 ft HAA);
(2) When cabin rate of climb stabilizes, place second pack valve switch to open position;
(3) Use same procedure for third pack if required: and
(4) Thrust setting adjust.
Adjust thrust as required for existing bleed air conditions.

Note : If operating with an engine failure, do not open pack valve until reaching the specified engine out acceleration altitude.

Ref : 747 OM-B 6.2.1.



Operating a twin over the ocean, you're always one engine failure from a total emergency.
25 PGNCS : Hi HAWK! Not to split hairs too finely but there is a difference (unless I misunderstand you), though not all aircraft are capable of both options. S
26 WestJetForLife : I asked my aircraft systems instructor at SAIT about a month ago regarding bleeds/packs operation during takeoff from hot and high situations. YYC is
27 HAWK21M : Interesting...... On the B737 out here Bleeds off & Pack off T/O is common.More so the Former. regds MEL.
28 Cobra27 : PACS: I think first they call it pacs, and then make something like pressurization and air conditioning system. Some are usefuel, others are just plai
29 Brons2 : I don't know anything about PACS or Packs, other than what I read here on Tech/Ops. As a passenger though, I do fly mostly on AA, and I live in AUS.
30 HAWK21M : Does the MD-80 have a gasper fan installed? regds MEL.
31 PGNCS : The MD-80 sometimes requires packs off performance data, though it's not extremely common. Where are you going out of AUS? I would be surprised to ne
32 HAWK21M : Any reason,even below 8000ft,Is it not practically possible or an SOP. regds MEL.
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