AmericanF100
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Takeoff With Packs On/Off?

Tue Dec 08, 2009 2:47 am

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
 
CosmicCruiser
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RE: Takeoff With Packs On/Off?

Tue Dec 08, 2009 3:28 am

Of course it's using bleed air off the engines hence less thrust.
 
Fly2HMO
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RE: Takeoff With Packs On/Off?

Tue Dec 08, 2009 3:40 am

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.
 
AmericanF100
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RE: Takeoff With Packs On/Off?

Tue Dec 08, 2009 3:43 am

Thanks for the nice explanation as well as the clarification on the acronym. I will refer to them properly from now on!
 
jarheadk5
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RE: Takeoff With Packs On/Off?

Tue Dec 08, 2009 4:14 am

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
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PGNCS
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RE: Takeoff With Packs On/Off?

Tue Dec 08, 2009 4:22 am



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.
 
Fly2HMO
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RE: Takeoff With Packs On/Off?

Tue Dec 08, 2009 4:29 am



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
 
Mir
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RE: Takeoff With Packs On/Off?

Tue Dec 08, 2009 5:11 am

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
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474218
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RE: Takeoff With Packs On/Off?

Tue Dec 08, 2009 5:23 am



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?
 
tdscanuck
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RE: Takeoff With Packs On/Off?

Tue Dec 08, 2009 5:56 am



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.
 
AAR90
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RE: Takeoff With Packs On/Off?

Tue Dec 08, 2009 6:53 am



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
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glen
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RE: Takeoff With Packs On/Off?

Tue Dec 08, 2009 9:38 am

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.
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DocLightning
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RE: Takeoff With Packs On/Off?

Tue Dec 08, 2009 8:40 pm

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.
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bri2k1
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RE: Takeoff With Packs On/Off?

Tue Dec 08, 2009 8:50 pm

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.
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PGNCS
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RE: Takeoff With Packs On/Off?

Tue Dec 08, 2009 9:05 pm



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).
 
Goldenshield
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RE: Takeoff With Packs On/Off?

Mon Dec 14, 2009 7:45 pm



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.
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bri2k1
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RE: Takeoff With Packs On/Off?

Tue Dec 15, 2009 3:50 pm



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?
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Goldenshield
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RE: Takeoff With Packs On/Off?

Tue Dec 15, 2009 7:56 pm



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.
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JETPILOT
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RE: Takeoff With Packs On/Off?

Thu Dec 17, 2009 9:32 pm

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.
 
PGNCS
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RE: Takeoff With Packs On/Off?

Thu Dec 17, 2009 11:54 pm



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.
 
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Francoflier
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RE: Takeoff With Packs On/Off?

Fri Dec 18, 2009 4:24 am



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.
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Mir
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RE: Takeoff With Packs On/Off?

Fri Dec 18, 2009 4:50 am



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
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HAWK21M
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RE: Takeoff With Packs On/Off?

Fri Dec 18, 2009 8:19 am

Out here its reffered to as bleeds off T/O.
regds
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Goldenshield
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RE: Takeoff With Packs On/Off?

Fri Dec 18, 2009 10:34 am

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]
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747classic
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RE: Takeoff With Packs On/Off?

Fri Dec 18, 2009 2:30 pm

"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.
 
PGNCS
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RE: Takeoff With Packs On/Off?

Fri Dec 18, 2009 6:56 pm



Quoting HAWK21M (Reply 22):
Out here its reffered to as bleeds off T/O.
regds
MEL.

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. Some aircraft can only turn off the packs (not the bleeds) and cannot use the APU for pneumatics in flight (or procedurally the packs have to be off per SOP), whereas some aircraft can use the APU for pneumatics in flight, and the engine bleeds can be closed allowing air from the APU to run the packs; that would be "bleeds off" though the packs are still on.

Have a great day!  Smile
 
WestJetForLife
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RE: Takeoff With Packs On/Off?

Sat Dec 19, 2009 12:58 am

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 about 3,500 feet up, and during the summer (when it isn't snowing), the temperature can exceed 30°C/86°F. This makes for a pretty interesting situation when you're flying a 737-800 full of passengers and fuel from YYC to say...YYZ or YUL (trans-country).

WS, according to what I've heard, utilize a 'bleeds-off' approach, by turning the engine bleeds off before entering the takeoff runway, set throttle, climb to about 400-600 feet AGL and then turn the engine bleeds on to provide pressurization.

Then again, I could be wrong, as I don't have the 737 operations manual or WS checklists with me...I just heard word of mouth.

Nik
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HAWK21M
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RE: Takeoff With Packs On/Off?

Sat Dec 19, 2009 10:23 am



Quoting PGNCS (Reply 25):
Some aircraft can only turn off the packs (not the bleeds) and cannot use the APU for pneumatics in flight (or procedurally the packs have to be off per SOP),

Interesting......
On the B737 out here Bleeds off & Pack off T/O is common.More so the Former.
regds
MEL.
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cobra27
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RE: Takeoff With Packs On/Off?

Sat Dec 19, 2009 1:15 pm

PACS: I think first they call it pacs, and then make something like pressurization and air conditioning system. Some are usefuel, others are just plain stupid
Military and aviation guys just love acronyms: I heard once check you MD (then the guy asked what was that: it was memory device on yoke.
 
brons2
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RE: Takeoff With Packs On/Off?

Fri Dec 25, 2009 8:55 am



Quoting PGNCS (Reply 14):
On some aircraft you may notice essentially nil airflow until the packs are reinstated after departure (think DC-9 or MD-80, for instance).

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. It's pretty noticeable in the summertime when they shut off the air-conditioning for takeoff on the MD-80!!
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HAWK21M
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RE: Takeoff With Packs On/Off?

Sat Dec 26, 2009 7:53 am



Quoting Brons2 (Reply 29):
It's pretty noticeable in the summertime when they shut off the air-conditioning for takeoff on the MD-80!!

Does the MD-80 have a gasper fan installed?
regds
MEL.
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PGNCS
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RE: Takeoff With Packs On/Off?

Tue Dec 29, 2009 9:04 pm



Quoting Brons2 (Reply 29):
Quoting PGNCS (Reply 14):
On some aircraft you may notice essentially nil airflow until the packs are reinstated after departure (think DC-9 or MD-80, for instance).

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. It's pretty noticeable in the summertime when they shut off the air-conditioning for takeoff on the MD-80!!

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 need packs off numbers going to DFW in an MD-80 routinely; I would be less surprised to see it going to ORD. I have flown plenty of three hour legs in an MD-80 out of AUS, and can't ever recall requiring packs off numbers; the runways are long, the field elevation is reasonable, and there's no terrain considerations; of course near MGTOW on a hot day would be when you would see it, so I believe you. I don't know if AA has the JT8D-217's or -219's, which could also be a factor. Of course the airflow WILL stop during engine start, which can seem like a very long time, and that's every flight.

Quoting HAWK21M (Reply 30):
Quoting Brons2 (Reply 29):
It's pretty noticeable in the summertime when they shut off the air-conditioning for takeoff on the MD-80!!


Does the MD-80 have a gasper fan installed?

No, but I wish it did. It does have a recirculation fan, but it only works in flight. Incidentally, HAWK, the MD-80 is one of the aircraft that cannot run packs from the APU in flight (neither can the DC-9; MD-90 is a different story). In the MD-80 only a packs off takeoff is possible. Hope that helps!
 
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HAWK21M
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RE: Takeoff With Packs On/Off?

Wed Dec 30, 2009 6:37 am



Quoting PGNCS (Reply 31):
the MD-80 is one of the aircraft that cannot run packs from the APU in flight

Any reason,even below 8000ft,Is it not practically possible or an SOP.
regds
MEL.
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