Pressurization Systems

[dsee8driver]

Yes, you must be on a twin-engine wide body. That would make sense. I probably should have been more clear when I said that; I was referring to 3 and 4 engine wide bodied jets. They are the ones who have 3 packs.

Any twin engine airliner is going to have only 2 air conditioning packs because one engine cannot feed more than one pack.

I'm on a 4 engine jet and we only have 2 packs...

 

[Gulfstream 200]

Relax, dude. I just curious what aircraft he's describing. I didn't mean any offense to anyone. I just wondered what airplane he's describing. I am familiar with several different types of environmental systems, and I like to compare and learn.

Dont worry about Hawker F/O....he's just a bit "on edge"......

today, after landing, he used the brakes and his boss nearly fired him.

 

[rfresh]

rfresh, your systems description is very good, but not all of your information is applicable to all jet aircraft, not even all widebody transports. In addition, the nomenclature used to describe various valves and other parts varies considerably between the manufacturers. Can you share with us please which type aircraft environmental system you're describing for us?

That is correct, I'm not trying to say this is the way the systems are on all jet aircraft.

Also, as you point out, the names to describe these parts can differ from manufacturer to manufactuer.

The jets I'm describing these systems which operate in the same manner and have the same component names or close to the same component names are the B-727, B-737, B-747, L-1011, DC-10, MD-80 and MD-90 aircraft.

There will always be exceptions as someone pointed out he flys a twin wide body with only 2 packs and recently someone pointed out they fly a 4 engine jet with only 2 packs.

That's what is great about a place like this, even I learn something everyday when others can share about what equipment they are flying on. I find it all very interesting; 4 motors 2 packs, 2 motors on a wide body 2 packs - interesting indeed!!

 

[rfresh]

I'm on a 4 engine jet and we only have 2 packs...

Very cool - that is a DC-8 yes? I imagine because that jet is so old that the engines combined don't have enough bleed air capacity to feed 3 packs?

Does that change if the -8 has had the engine mods to the larger CFM engines I see a lot of freighters using? I'm just wondering if they modified the FE panel and A/C system to handle a 3rd pack or not? Thanks.

 

[dsee8driver]

Very cool - that is a DC-8 yes? I imagine because that jet is so old that the engines combined don't have enough bleed air capacity to feed 3 packs?

Does that change if the -8 has had the engine mods to the larger CFM engines I see a lot of freighters using? I'm just wondering if they modified the FE panel and A/C system to handle a 3rd pack or not? Thanks.

Well the 70 series with the cfms put out plenty of air. I can't answer about the 3rd pack or not since I don't know how much demand a third pack would require. It is better then the NASI system with the 60 series birds.

 

[HawkerF/O]

Dont worry about Hawker F/O....he's just a bit "on edge"......

today, after landing, he used the brakes and his boss nearly fired him.

Of course I am on the edge. Wouldn't you be if your boss came up front everytime you turned final with a cattle prod to make sure those brakes do so much as get tapped? And now you know the rest of the story.

Now Mr. G200, how about that shine box I've been telling you to go home and get???????

 

[sky37d]

While you could question his antics, many people don't know this stuff.

And, some, actually, could care less. Well, that's not the case, it's not that I don't care, it's just intellectual trivia, and quite frankly Charlotte, I don't give a darn. I have enough intellectual trivia to occupy me today, thank you.

I would care, if it was worthwhile to do so, but since it isn't, I don't.
uke: :beer:

 

[Amish RakeFight]

Here's some trivia for ya

And, some, actually, could care less. Well, that's not the case, it's not that I don't care, it's just intellectual trivia, and quite frankly Charlotte, I don't give a darn. I have enough intellectual trivia to occupy me today, thank you.

I would care, if it was worthwhile to do so, but since it isn't, I don't.
uke: :beer:

It's Scarlett

 

[Dangerkitty]

Any twin engine airliner is going to have only 2 air conditioning packs because one engine cannot feed more than one pack.

Actually, I dont think your above statement is true. If I remember correctly the B-757, B-767, and the B-777 all have three packs.

 

[-Xavier-]

Actually, I dont think your above statement is true. If I remember correctly the B-757, B-767, and the B-777 all have three packs.

...and like he said, every aircraft is different and each is tailored to their own specs.

Thanks for the thread Ralph. I've learned some new things.

 

[sky37d]

It's Scarlett

Thanks
My wife would know, but I tend to tune out the old movies she watches.

 

[Cardinal]

Thanks rfresh, this is indeed a good and worthy thread. Many of the new guys I fly with don't have a clue about this stuff, ask the airplane to do something it can't and then cuss at the poor machine because it didn't.

During recurrent preflight training I have actually witnessed a person say that a little 5 inch, 4 bladed electric fan underneath the right wing is what pressurises the airplane. In fact, it is the blower that pulls air across the heat exchanger for our freon vapor cycle machine.

During a discussion about deferred maintenance, the topic of MEL'ing our one and only pack (ACM) came up, somehting that happens with some frequency. The response? "Wow, that would get really hot!" It's frightening out there - Save me.

 

[sky37d]

And I take back everything I said.
It is a worthwhile discussion, and has been very informative.

 

[AV80R]

rfresh - thanks for the post, I enjoyed it! av80r

 

[FL420]

Very informative thread. A good review.

I do believe the following statement implies that bleed air is turning the compressor and/or turbine of the ACM:

By the time you reach cruise, the ACM's are receiving the minimum amount of air through them to keep them turnng.

I thought this was the case for the longest time, probably because the systems descriptions and operations in the Aircraft Flight Manuals have been "dumbed down" for pilots and therefore gloss over the subject. If I'm not mistaken, each ACM compressor and turbine are driven by a powerful AC electric motor. I have never seen it in print but I have deduced this from the high amperage(forget how high) circuit breakers for the pressurization system on the overhead panel on the B757 and the high pitched whine from the packs I can silence by pulling said CB's(on the ground only of course.)

I have never been a plumber and I could be mistaken so if I am I fully expect for someone to set me straight.