B737NG “PACK” NNC

[B738HT]

Question on the PACK NNC:
After pushing the TRIP RESET, if both the PACK lights keep illustrated, why we set R RECIRC FAN AUTO & L RECIRC FAN OFF?

We know that RECIRC FAN could reduce the packs' working load, I guess turn off the fan would reduce the warm air from E&E bay to cabin, but why not turn both L&R fans off?

[cosmo kramer]

We know that RECIRC FAN could reduce the packs' working load

Recirculation fans have no effect on pack workload. It's myth and poorly written in the FCOM.

With recirculation fans OFF, the airflow in the cabin is below what is required for certification, but it doesn't change the workload on the pack.

Had Boeing build the aircraft without recirculation fans, they would have had to make the pack deliver more airflow in order to make certification requirements.

Hence, the recirculation fans saves fuel (as written in the FCOM), compared to if the aircraft was built without recirculation fans.

In any case, recirculation fans off, doesn't increase pack load and subsequent fuel consumption (you won't find anything about increased fuel consumption in the MEL either). But if the aircraft is full, your cabin crew will most likely complain that they can't breathe in the cabin and ask you to turn the temperature down, even by normal temps (as they can't find any other reasonable explanation for the sticky air).

P.s.
My QRH have no mention of the recirculation fans in the pack trip off NNC. What 737 do you fly?

[de facto]

Each recirc fan recirculate half of the required amount of air in the cabin.
If the recirc fans were off,or non existent,the bleed demand would be higher since all air source to the mix manifold would come from the packs alone.

The right fan recirculates air from the cabin and the Equipment cooling exhaust.
By keeping the fan in auto,you maintain a minimum of air circulation therefore a cooler temperature...i understand it as a need of a light breeze in a hot summer day
The left is selected OFF as recirculating air from a closed pressurized air conditionning bay wouldnt seem to help cooling the cabin.

Kramer,i guess you dont fly the NG.

[cosmo kramer]

If the recirc fans were off,or non existent,the bleed demand would be higher since all air source to the mix manifold would come from the packs alone.

Nonsense... That is the myth I mentioned. It is exactly like I wrote in my previous post. Look in your mel for recirculation fans, and show me the extra fuel you need to carry (none, as there is no higher demand on the pack).

I do fly NG. The pack are fixed and always deliver the same output, no matter what the condition of the cabin is (recalculations fans on or off). Those flows are either normal flow or high flow.

[Skyjob]

Multiple versions of air conditioning systems in the NG gents...

6/7 and 8/9 are different from each other.

The reason for turning the left recirculation fan off is similar to closing shades, turning off galleys and IFE, opening flight deck door and opening the outflow valve: reduce any heat created inside the airframe and maximise all remaining available ventilation!

[cosmo kramer]

What I wrote applies to 600-900. Recirculation's fans are/fan is there, because without them/it (or off), the cabin airflow doesn't meet certification requirement.

If they are/it is on or off, doesn't change a thing about the output of the pack (which is always the same for the selected flow rate).

[de facto]

Kramer

Come on,you really think it would show a few kilos ,if that,of fuel needed int he MEL,really?...from the AMM:

The purpose of the right recirculation fan is to recirculate the conditioned air from the collector shroud. This will reduce the requirement for bleed air taken from the engines for air conditioning to the passenger cabin.

Less bleed required,less? Think what you want of it.....
AMM:

S AUTO
With both packs operating in AUTO, each pack regulates to normal flow rate approximately 55 Ibs/min. This is the normal in-flight schedule. It provides optimum airplane performance, but requires a recirculation fan to meet de- sired cabin ventilation rate. As cabin altitude increases, the pack valve is biased to supply a lower airflow rate.

Now if you fly the Ng..i suggest you read your QRH slowly again....until you get to the recirc fan part.

[B738HT]

I think the PACK TRIP OFF NNC is for B737-700, and I am talking about the 737-800.

[galdian]

Where I am on 73-8 the NNC is only headlined PACK and the recirc fan switching are items 9 and 10 of 17 steps.

[cosmo kramer]

Come on,you really think it would show a few kilos ,if that,of fuel needed int he MEL,really?...from the AMM:

DeFacto, you are always such a wise ass... Do you really think they would have built in a heavy recirculation fan system, that requires maintenance and cost fuel every leg to carry, if the penalty was only a few kg of fuel of omitting it?

Thrust me, the packs have no clue what is going on in the mix manifold. Your AMM quote doesn't say otherwise.

Her is help to decipher your AMM, as it say EXACTLY what I wrote initially:

This will reduce the requirement for bleed air taken from the engines for air conditioning to the passenger cabin...

...as compared to if the aircraft had NOT been equipped with recirculation fans, as the higher amount of bleed air would have been necessary to meet cabin flow certification requirement.

This is the normal in-flight schedule. It provides optimum airplane performance, but requires a recirculation fan to meet de- sired cabin ventilation rate

...but requires a recirculation fan to meet desired cabin ventilation rate...

...aka if a recirculation fan(s) is/are not there, the desired (regulatory required rate for certification) will NOT be met.

Checkmate. You should ask the questions on this board and not answer them as you are usually wrong. But Keep backtracking, you never had a history of being able to admit fault. I don't expect you to do otherwise in this thread.

[cosmo kramer]

Yes, you are right that the recirculation fans are indeed in the checklist. I was looking at a an older version (800) QRH of my own computer. The points are indeed in my current company QRH as point 9 and 10, so it must be a added recently to the checklist.

Point 9/10 are AFTER it has been establish that BOTH pack have tripped and cannot be restored. So the purpose of the switching would be to remove a source of heating of the cabin.

[B738HT]

Would you like to tell me the exact difference between L&R RECIRC FAN, or which compartment the fans recircle?

[de facto]

Kramer,
I love to steer with you its hilarious,you seem to know my history..its not reciprocal and i hope you dont mind.
Please read my post slowly....and digest...then type.

Now if my posts are generally wrong,please excuse me..as still waiting for proof of it and I am not considering your inputs as facts and correct either.
If you prove me wrong with facts/docs rather than pure say then yes ill mea culpa anytime...even with you...

Yes, you are right that the recirculation fans are indeed in the checklist. I was looking at a an older version (800) QRH of my own computer

Glad we cleared that one early enough in the discussion.

Now back to the subject,

You write:

Do you really think they would have built in a heavy recirculation fan system, that requires maintenance and cost fuel every leg to carry, if the penalty was only a few kg of fuel of omitting it?

I never said so...but as usual you put words in my mouth...they built it to meet the recirculation output of the packs up to the published service ceiling.
I said MEL may not reflect a fuel penalty as it may be really minimal..
Hence my reference of the AMM:

It provides optimum airplane performance, but requires a recirculation fan to meet de- sired cabin ventilation rate. As cabin altitude increases, the pack valve is biased to supply a lower airflow rate.

You write:

If they are/it is on or off, doesn't change a thing about the output of the pack (which is always the same for the selected flow rate).

I never said the opposit, i said if the fans were off,more bleed output will be required for the packs to give their scheduled volume of air....this uses extra fuel,as minimal as it may be.

After i wrote:

Quote:
If the recirc fans were off,or non existent,the bleed demand would be higher since all air source to the mix manifold would come from the packs alone.

You wrote:

Nonsense... That is the myth I mentioned.

So Here form the AMM:

Recirculation System
The recirculation system uses a fan to move air from the passenger compart- ment to the main distribution manifold. This reduces the amount of air that the packs need to supply.

You understand that sentence?

...aka if a recirculation fan(s) is/are not there, the desired (regulatory required rate for certification) will NOT be met.

I never said otherwise.

But if the aircraft is full, your cabin crew will most likely complain that they can't breathe in the cabin and ask you to turn the temperature down, even by normal temps (as they can't find any other reasonable explanation for the sticky air).

Well here im baffled....when the fans are off the air becomes sticky?
So you are saying that the recirculation fans remove humidity?
My ears are wide open.

[de facto]

B738HT Would you like to tell me the exact difference between L&R RECIRC FAN, or which compartment the fans recircle?

Recirculated air is drawn from the space in the air conditioning distribution bay by the left recirculation fan, the air is drawn through filters and is discharged into the mix manifold. It mixes with air from the packs or external conditioned air for distribution into the passenger compartment.

Conditioned air in a collector shroud is recirculated by the Right recirculation fan.
The shroud collects air from the passenger compartment exhaust grilles in the carpet risers and the equipment cooling exhaust.

[cosmo kramer]

Defacto, there is probably a reason that you can only find a job in China, A your technical knowledge, B your ability to read and C your attitude. Look at the thread history and who started to get personal. Thank you I do know how to read my manuals, which you obviously need help doing.

Glad we cleared that one early enough in the discussion

Actually that post was for Galdian, but I am glad to hear you can read a step-by-step 18 point checklist too. Well done!

I never said so...but as usual you put words in my mouth...they built it to meet the recirculation output of the packs(???) up to the published service ceiling.

As usual you are writing BS. The packs doesn't recirculate anything. And it has nothing to do with service ceiling. You are so full of crap, it unbelievable that you are truly a pilot. They are there to ensure sufficient airflow through the cabin at all levels. It has nothing to do with pressurization, the aircraft pressurizes fine without Recirculation Fans!! They are simply there to move the air around in the cabin, because otherwise the air is not moving fast enough to meet certification requirements.

I never said the opposit, i said if the fans were off,more bleed output will be required for the packs to give their scheduled volume of air....this uses extra fuel,as minimal as it may be.

Ahh backtracking started. "You never said that" Except, get it into your head that the packs deliver more than enough from the get go to pressurize the aircraft. Their scheduled volume of air is sufficient, only with RFs off the air won't move around in the aircraft at the required (for certification) flow rate.


As I started out, the cause of this myth, is the poor wording of Boeing. Or rather the wording is ok, but they don't complete the sentence.

The recirculation system uses a fan to move air from the passenger compart- ment to the main distribution manifold. This reduces the amount of air that the packs need to supply.

...compared to an aircraft built without RFs, as such an aircraft would have been required to have the packs supply a higher output to keep the air moving fast enough to meet cabin flow rate certification requirements. A.k.a. to pump in more air and open the outflow valve more.

Well here im baffled....when the fans are off the air becomes sticky?

That's because you are less fortunately gifted, that this baffles you. When the air doesn't move (or moves too slowly), and you have close to 200 people breathing in and out, yes the air does become sticky. And the O2 level will go down. Kind of like classroom training and everyone looks sleepy (Defacto probably fast asleep), it usually helps to open the window 5 mins. Alas we don't have that option in a 737, so we have to have either packs in high flow (costs a lot of fuel) or have recirculation fans on.

[de facto]

Defacto, there is probably a reason that you can only find a job in China, A your technical knowledge, B your ability to read and C your attitude. Look at the thread history and who started to get personal. Thank you I do know how to read my manuals, which you obviously need help doing.

Already done my china tour but thanks!

The packs doesn't recirculate anything

Where did i write that they do??do you read english??

I wrote the FANS help the required recirculation output of the packs to meet the packs cabin scheduled flow rate to the optimum of 55 lbs/min in AUTO and that obviously to its max ceiling.

The air that is recirculated come from the packs,no???

Here again what i wrote earlier from the AMM:

With both packs operating in AUTO, each pack regulates to normal flow rate approximately 55 Ibs/min. This is the normal in-flight schedule. It provides optimum airplane performance, but requires a recirculation fan to meet de- sired cabin ventilation rate. As cabin altitude increases, the pack valve is biased to supply a lower airflow rate.

They are there to ensure sufficient airflow through the cabin at all levels.

Correct except when the air recirculated from the fans is missing,the packs need to provide more air to to the mix manifold?right?you understand that?

Again i never wrote recirc fans are for pressurization!!!you are an idiot.
I wrote fans air input to the mix manifold help packs in providing airflow to the cabin,packs are there for the pressurization.

When the air doesn't move (or moves too slowly), and you have close to 200 people breathing in and out, yes the air does become sticky

If they are all full of like you for sure..
Cold sticky air ,awesome!
Listen to your CA,turn down the temp next time and your ACM will do the work of your lack of knowledge!

Alas we don't have that option in a 737, so we have to have either packs in high flow (costs a lot of fuel) or have recirculation fans on

Oh now you tell me.....
So I see,your aircraft are junk,you cant use packs in high,and you dont want to cool the cabin,then you wonder why its sticky indeed.....marvelous

[aveng]

Correct me if I'm wrong, but isn't there a correlation with one pack off and the recirc switch position to putting the remaining pack in 'high flow' mode.

[cosmo kramer]

Already done my china tour but thanks!

Ahh, back at home in India?

The packs doesn't recirculate anything

Where did i write that they do??do you read english??

here... (I do, apparently you have a problem remembering what you write):

they built it to meet the recirculation output of the packs

The air that is recirculated come from the packs,no???

No, it comes from the cabin and the E&E compartment.... Back to the manuals son.

I wrote the FANS help the required recirculation output of the packs to meet the packs cabin scheduled flow rate to the optimum of 55 lbs/min in AUTO and that obviously to its max ceiling.

I can't believe it. Ha ha, it's almost sad there you say it again, get it into your head. The Packs don't recirculate anything. And there is no such thing as a required recirculation output. Listen, you obviously have no grasp of these things. There is a required flow rate in the cabin, for cooling, odor control and maintaining reasonable O2/CO2 levels.

[cosmo kramer]

Correct me if I'm wrong, but isn't there a correlation with one pack off and the recirc switch position to putting the remaining pack in 'high flow' mode.

No, with one pack off, the other pack will always operate in high flow mode regardless of RFs switch position (with flaps up).

[de facto]

Their scheduled volume of air is sufficient, only with RFs off the air won't move around in the aircraft at the required (for certification) flow rate.

Correct,,what you dont seem to understand is that packs Air and recirc fans air are used to move this air around in the cabin...
Air from packs and recirfan meet in the mix manifold and then out into the cabin...wall risers for the packs to get cool dry ACM non sticky in.

We agree or not?

With fans off.....its fine/optimum until high cabin altitude when as the AMM states and posted here zillions time:

As cabin altitude increases, the pack valve is biased to supply a lower airflow rate

You write that the packs..

They are there to ensure sufficient airflow through the cabin at all levels.

What in the sentence above from the AMM are you not able to grasp???

AIRFLOW(packs and or recirc fans) RATE IS DIRECTLY LINKED TO RECIRCULATION RATE!!!!!!