KitSmith
Topic Author
Posts: 1
Joined: Mon May 28, 2018 6:23 pm

Flying with air conditioning packs off?

Mon May 28, 2018 6:49 pm

Hello Everybody!

I am a long time flight simulation enthusiast, a beginning student pilot in real life, and a big fan of historic aircraft. It is a pleasure for me to be on this forum.

I was recently looking through the preview of this book, containing stories of a veteran Pan Am flight attendant, and a couple of things there just caught my attention, as they did not make much sense to me.

One such thing is this. On page 274 she talks about how pilots were always so cheap and then says the following

"They were even cheap with the oxygen that we had to consume on the flights, especially on those trips to Tokyo over the North Pole were we flew so high up that it was always difficult to breath properly, and that was because they would switch off the air-packs which provided constant new air..."

Apparently some further explanation follows on the next page, but by coincidence the preview does not show page 275. I tried to get the complete book but, sadly enough, was unable to find it anywhere for a reasonable price.

So, my main question about this is, what is she referring to? Why would you ever want to switch the air conditioning packs off in flight at high altitude? Would it not completely depressurize the aircraft gradually? Are you even allowed to try that on a passenger service?

I understand that if they were flying extremely high on those routes for greater range or something like that, cabin altitude could have been higher than usual, because of the differential pressure limit. But when it is difficult to breathe to the point of having to consume oxygen bottles, is that not a serious problem already?

While I have no concrete reason to doubt her story, I have no idea about how accurate she is on technical details. On the other hand, if she remembers having to use oxygen, that is hardly a tiny technical detail I think.

If anyone has the rest of her explanation, or knows what she is talking about, I would love to know that!

Thank you!
 
GalaxyFlyer
Posts: 862
Joined: Fri Jan 01, 2016 4:44 am

Re: Flying with air conditioning packs off?

Tue May 29, 2018 2:37 am

40+ years of professional flying and her comment is rubbish. You don’t normally fly with the packs off.

GF
 
battlegroup62
Posts: 23
Joined: Mon Jul 03, 2017 5:05 am

Re: Flying with air conditioning packs off?

Tue May 29, 2018 4:28 am

If its Pan Am and flying over the north pole it is probably a 747. There are 3 packs on a 747s and all can be shut down in flight but to preserve cabin pressure 1 must remain running. When one or more of the packs are shut down the air circulation is reduced in this case 1/3 per pack and temp control would be very sluggish. It would get stuffy and warm in the cabin and with less air coming into the cabin and in theory I suppose the oxygen level could go down since people are using it and it isn't being replaced as quickly with only one pack pumping in air. Almost all pressurized aircraft that have multiple packs can maintain pressure with only one, but it depends on the operator whether they can MEL the inop and do revenue service with only 1 running.
We have to keep planes airworthy. That doesn't mean they have to fly.
 
pikachu
Posts: 132
Joined: Thu Feb 07, 2002 5:58 pm

Re: Flying with air conditioning packs off?

Tue May 29, 2018 4:28 am

You can always tell a flight attendant. Just not very much...
 
mmo
Posts: 1526
Joined: Thu Apr 18, 2013 3:04 pm

Re: Flying with air conditioning packs off?

Tue May 29, 2018 4:51 am

On the 747 classic family, it was recommended on flights which were lightly loaded to shut down one pack. That would offer some fuel savings at no cost to cabin air quality. The poster who talked about one pack operation was OTL. The problem with one pack operation is if that pack fails you now have bigger problems to deal with. That is why the Boeing procedure was to turn one pack off.
If we weren't all crazy we'd all go insane!
 
Lpbri
Posts: 92
Joined: Tue Sep 27, 2016 7:18 pm

Re: Flying with air conditioning packs off?

Tue May 29, 2018 11:17 am

Problem is, when you shut down one pack, the remaining pack has to work harder. Nothing saved.
 
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Francoflier
Posts: 4460
Joined: Wed Oct 31, 2001 12:27 pm

Re: Flying with air conditioning packs off?

Tue May 29, 2018 12:20 pm

KitSmith wrote:
One such thing is this. On page 274 she talks about how pilots were always so cheap and then says the following

"They were even cheap with the oxygen that we had to consume on the flights, especially on those trips to Tokyo over the North Pole were we flew so high up that it was always difficult to breath properly, and that was because they would switch off the air-packs which provided constant new air..."


This right there is all you need to know about this F/A's knowledge of what goes one behind the cockpit door and about her preconceived ideas about pilots.

Absolutely every part of this sentence is, at best, wrong and at worst an offence on common sense. I wouldn't even know where to start...
I'll do my own airline. With Blackjack. And hookers. In fact, forget the airline.
 
mmo
Posts: 1526
Joined: Thu Apr 18, 2013 3:04 pm

Re: Flying with air conditioning packs off?

Tue May 29, 2018 1:40 pm

Lpbri wrote:
Problem is, when you shut down one pack, the remaining pack has to work harder. Nothing saved.

Not true at all. Boeing and McD proved on a lightly loaded aircraft IIRC on the 747 Classic it was less than 240 you could get a 2% fuel savings by running with one pack off because of the reduced bleed air demand.
If we weren't all crazy we'd all go insane!
 
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747classic
Posts: 2363
Joined: Sat Aug 15, 2009 9:13 am

Re: Flying with air conditioning packs off?

Tue May 29, 2018 2:49 pm

Lpbri wrote:
Problem is, when you shut down one pack, the remaining pack has to work harder. Nothing saved.

On the 747 classic series three packs are normally installed (on some freighters only 2 packs for weight saving).
After the fuel price escalation in the late seventies one pack was switched off below a certain passenger load (company policy, stated in the aircraft operation manual.)
This adapted operating procedure is saving fuel, because the remaining two packs are not able to operated more than 100% open.
Later the pack valve control was changed from on/off to a three position switch : on, 1/2, off. In the 1/2 position the pack valve was partly opened, reducing the pack flow.

After this modification optimal adustment of the airconditioning flow was possible in line with the actual number of passengers on board.

Note : On the 744 the pack switch positions are renamed in off, normal and high. The packs are standard operated in the normal mode ( in fact this is the reduced mode of the 747 classic) and can be switched to the high position.(100% open position) when needed.
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
e38
Posts: 513
Joined: Sun May 04, 2008 10:09 pm

Re: Flying with air conditioning packs off?

Tue May 29, 2018 5:37 pm

KitSmith, as other A.Net members have pointed out, this would not have happened--"switch the air conditioning packs off in flight at high altitude . . " as stated by the Pan American flight attendant.

As you correctly stated, to do so would cause the cabin to slowly depressurize, resulting in hypoxia and eventual unconsciousness for everyone aboard the aircraft, unless everybody was using supplemental oxygen.

Not under any circumstance would a pilot do this, unless it was a result of an abnormal or emergency situation, in which the crew would promptly descend to an alititude not requiring oxygen (if possible).

From working with flight attendants, I have made two observations: (1) most flight attendants, while very good at their jobs, have very little knowledge of aircraft systems/technical operations, and (2) flight attendants enjoy making jokes about how cheap pilots are, even if they don't completely understand the joke--i.e., somebody else told them the joke and they think it is funny to re-tell it to others.

As other posters have commented, many aircraft have "low flow" or "reduced output" settings on the packs which helps fuel economy (on the aircraft I fly it is based upon number of passengers and crew aboard the aircraft), but of the aircraft I have flown, not ever was there a procedure to completely shut down the packs. Yes, there are some pilots who are cheap, but they would not do this--they would probably ask for separate checks at the bar instead.

Also, note that in your narrative about the flight attendant, she didn't say she actually used oxygen, just that the pilots were cheap with the oxygen (her comment really doesn't make much sense).

Just as an aside, for the aircraft I fly, when established at normal cruise altitudes (35,000 - 40,000 feet), the cabin is usually pressurized to about 7,500 feet.


e38

P.S. you stated, "I am . . . a beginning student pilot in real life, . . ."
Congratulations, and I wish you well with your flying goals and aviation endeavors!
 
Woodreau
Posts: 1606
Joined: Mon Sep 24, 2001 6:44 am

Re: Flying with air conditioning packs off?

Tue May 29, 2018 7:24 pm

KitSmith wrote:
I tried to get the complete book but, sadly enough, was unable to find it anywhere for a reasonable price.!


Why don't you go to your local library and see if they can get a copy through the interlibrary loan for you to borrow?
Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.
 
DualQual
Posts: 679
Joined: Sun Mar 05, 2006 6:10 pm

Re: Flying with air conditioning packs off?

Tue May 29, 2018 11:42 pm

Woodreau wrote:
KitSmith wrote:
I tried to get the complete book but, sadly enough, was unable to find it anywhere for a reasonable price.!


Why don't you go to your local library and see if they can get a copy through the interlibrary loan for you to borrow?


Why waste valuable time reading a book that, based off this discussion, is useless, incorrect drivel.
There's no known cure for stupid
 
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PowerliftDrsTX
Posts: 16
Joined: Tue Jan 02, 2018 2:51 pm

Re: Flying with air conditioning packs off?

Thu Jun 07, 2018 1:22 pm

GalaxyFlyer wrote:
40+ years of professional flying and her comment is rubbish. You don’t normally fly with the packs off.

GF



agreed. you read something that was written by someone who has no idea what they are talking about. most have 2 packs and can operate on only one but are often altitude/icing restricted at that point.

rubbish.
 
Ryanair01
Posts: 227
Joined: Fri Dec 27, 2013 9:27 pm

Re: Flying with air conditioning packs off?

Thu Jul 12, 2018 12:13 pm

747classic wrote:
Lpbri wrote:
Problem is, when you shut down one pack, the remaining pack has to work harder. Nothing saved.

On the 747 classic series three packs are normally installed (on some freighters only 2 packs for weight saving).
After the fuel price escalation in the late seventies one pack was switched off below a certain passenger load (company policy, stated in the aircraft operation manual.)
This adapted operating procedure is saving fuel, because the remaining two packs are not able to operated more than 100% open.
Later the pack valve control was changed from on/off to a three position switch : on, 1/2, off. In the 1/2 position the pack valve was partly opened, reducing the pack flow.

After this modification optimal adustment of the airconditioning flow was possible in line with the actual number of passengers on board.


Bingo! From what I understand Pan Am had the same policy of turning packs off below a certain load. This worked on the 747-100, but there was a problem with the 747-SP because it flew at a higher altitude. This caused breathing and light headedness problems for cabin crew, although not passengers because they were just sat there and not working, shifting trolleys, lifting in the galley etc etc.

The only reason I've heard about this is that early 777-200s had a similar problem, as it was underestimated what the optimal levels required for different passenger loads at different altitudes are.

I think a lot of the posters above owe the nice lady an apology.......
 
Ryanair01
Posts: 227
Joined: Fri Dec 27, 2013 9:27 pm

Re: Flying with air conditioning packs off?

Thu Jul 12, 2018 12:19 pm

747classic wrote:
Lpbri wrote:
Problem is, when you shut down one pack, the remaining pack has to work harder. Nothing saved.

On the 747 classic series three packs are normally installed (on some freighters only 2 packs for weight saving).
After the fuel price escalation in the late seventies one pack was switched off below a certain passenger load (company policy, stated in the aircraft operation manual.)
This adapted operating procedure is saving fuel, because the remaining two packs are not able to operated more than 100% open.
Later the pack valve control was changed from on/off to a three position switch : on, 1/2, off. In the 1/2 position the pack valve was partly opened, reducing the pack flow.

After this modification optimal adustment of the airconditioning flow was possible in line with the actual number of passengers on board.


Bingo! From what I understand Pan Am had the same policy of reducing the number of packs that were switched on below a certain load. This worked on the 747-100, but when first introduced there was a problem with the 747-SP because it flew at a higher altitude. This caused breathing and light headedness problems for cabin crew, although not passengers because they were just sat there and not working, shifting trolleys, lifting in the galley etc etc. The sectors described by the book's author were operated by the 747-SP.

The only reason I've heard about this is that early 777-200s had a similar problem, as it was underestimated what the optimal levels required for different passenger loads at different altitudes are.

I think a lot of the posters above owe the nice lady an apology.......
 
stratclub
Posts: 222
Joined: Fri Jan 05, 2018 10:38 pm

Re: Flying with air conditioning packs off?

Thu Jul 12, 2018 6:58 pm

O.K., O.K., O.K. Miz Flight Attendant, We are sorry you don't have a coherent understanding about how aircraft systems function...........

She did say "they turned the packs off" which is not the same as turning one pack off.
 
BravoOne
Posts: 2739
Joined: Fri Apr 12, 2013 2:27 pm

Re: Flying with air conditioning packs off?

Thu Jul 12, 2018 9:37 pm

It was not uncommon in the 707 to turn the turbo compressors off and just run on bleed air. Can't recall if we left one TC running or not but bleeds produced better fuel specs.
 
stratclub
Posts: 222
Joined: Fri Jan 05, 2018 10:38 pm

Re: Flying with air conditioning packs off?

Fri Jul 13, 2018 8:08 am

BravoOne wrote:
It was not uncommon in the 707 to turn the turbo compressors off and just run on bleed air. Can't recall if we left one TC running or not but bleeds produced better fuel specs.

Sounds like a good plan. We had the seals on a T/C fail in flight and it filled the cabin with an oily mist.
 
N766UA
Posts: 8012
Joined: Thu Jul 29, 1999 3:50 am

Re: Flying with air conditioning packs off?

Sat Jul 14, 2018 3:43 am

I’ve never met a flight attendant, veteran or otherwise, who knew what they were talking about vis-a-vis aircraft systems.
 
stratosphere
Posts: 1472
Joined: Sat Sep 22, 2007 12:45 pm

Re: Flying with air conditioning packs off?

Sat Jul 14, 2018 5:48 am

N766UA wrote:
I’ve never met a flight attendant, veteran or otherwise, who knew what they were talking about vis-a-vis aircraft systems.


Seen a pilot or two that are pretty ignorant of aircraft systems too. I have been in this biz 30+ years I found the old timers the 727/DC-9 steam gauge guys had far more system knowledge than today's pilots. I have sat in class with new hire pilots they do not even touch things they did years ago systems wise. Pilots today are system managers nothing more.
 
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longhauler
Posts: 5737
Joined: Sat Mar 06, 2004 12:00 am

Re: Flying with air conditioning packs off?

Sat Jul 14, 2018 1:37 pm

stratosphere wrote:
N766UA wrote:
I’ve never met a flight attendant, veteran or otherwise, who knew what they were talking about vis-a-vis aircraft systems.


Seen a pilot or two that are pretty ignorant of aircraft systems too. I have been in this biz 30+ years I found the old timers the 727/DC-9 steam gauge guys had far more system knowledge than today's pilots. I have sat in class with new hire pilots they do not even touch things they did years ago systems wise. Pilots today are system managers nothing more.

That is true, but it is also by design.

For example, when my Dad was flying a Super Connie from YYZ to LHR, there were 5 flight crew members. Captain, First Officer, Flight Engineer, Navigator and Radio Officer. When I fly a Triple from YYZ-LHR we have 2 flight crew members. In the "old days" flight crew members had to know everything because nothing was automatic ... now we watch and marvel.

Today, I don't care how the GPS/IRS works any more than my Dad knew how the Navigator ran the Loran, the output was the same. Same thing with the Radio Officer vs the CPDLC/ADS, or deep into any of the systems of Boeing's finest, vs how much a Flight Engineer would have to know the Connie. As we fly with less and less pilots in the cockpit, we have to rely more and more on automatic systems with less actual systems knowledge.

30+ years ago when I flew the A300, I had to know that one light illuminated at 900C and extinguished at 840C. Today I just have to know that if the light is illuminated the system is hot. Honestly, does it really matter the specifics?
Just because I stopped arguing, doesn't mean I think you are right. It just means I gave up!

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