B737NG “PACK” NNC
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? |
We know that RECIRC FAN could reduce the packs' working load 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? |
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:O 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. |
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. 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. |
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! |
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). |
Kramer
Come on,you really think it would show a few kilos ,if that,of fuel needed int he MEL,really?:ugh:...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. 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. |
I think the PACK TRIP OFF NNC is for B737-700, and I am talking about the 737-800.
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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.
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Come on,you really think it would show a few kilos ,if that,of fuel needed int he MEL,really?...from the AMM: 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... This is the normal in-flight schedule. It provides optimum airplane performance, but requires a recirculation fan to meet de- sired 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. :ok: |
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. |
Would you like to tell me the exact difference between L&R RECIRC FAN, or which compartment the fans recircle?
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Kramer,
I love to steer :mad: 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 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 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). 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. Nonsense... That is the myth I mentioned. 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. ...aka if a recirculation fan(s) is/are not there, the desired (regulatory required rate for certification) will NOT be met. 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). So you are saying that the recirculation fans remove humidity? My ears are wide open. |
B738HT Would you like to tell me the exact difference between L&R RECIRC FAN, or which compartment the fans recircle? 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. |
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 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 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. 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. Well here im baffled....when the fans are off the air becomes sticky? |
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. The packs doesn't recirculate anything 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. 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 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 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:D:ugh: |
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.
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Already done my china tour but thanks! The packs doesn't recirculate anything they built it to meet the recirculation output of the packs The air that is recirculated come from the packs,no??? 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. |
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. |
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. 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 They are there to ensure sufficient airflow through the cabin at all levels. AIRFLOW(packs and or recirc fans) RATE IS DIRECTLY LINKED TO RECIRCULATION RATE!!!!!! |
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