B737CL Air System

[AlwaysReady]

Hi guys,

This question has been lingering around my head for quite sometime and hope you guys can share a light.

(A) we all know the recirculation fan will inhibit when the packs go into high flow. So does that means with:

high flow = cold air, hence recirculation fans not needed as recirculation fans introduce cold air into the mix manifold?

but isnt the recirculation fan purpose is to reduce workload and such?

(B) correct me if i'm wrong, Left Pack supplies to the flight deck but the left pack controller controls the temperature to the aft cabin. Why is there a contradicting flow.


Hope you guys understands my question and can give a glimmer of light to my tunnelling vision.

Cheers mate

[BOAC]

We are talking 300/500 CL, as the 400 is different.

A) High Flow has nothing to do with temperature, just air volume. Recirc fan likewise just 'recircs' what is there independent of temperature.

B) L Pack controller controls Cockpit temp. There is an excess of supply (think relative volumes) so the excess goes off into the cabin. Thus any changes in temp selection on the left pack WILL have an effect on the cabin temp but a small one, over-ridden by the R Pack setting.

Do you have access to any 737 tech info?

[AlwaysReady]

Yup, specific on the 400 series, Not on the other series


So if the high flow is about the volume, why does the recirculation fan inhibits itself during high flow operations?
L fan inhibits when either pack is high
R fan inhibits when both pack is high

Ya i do have the tech info. But doesnt specific enough, more like a walk in a park which confuses me more then telling me.. lolx.

[BOAC]

I think you are quite confused! Initially you talked about THE recirc fan (3/500)- the 400 has 2. Now you mention both!

I guess the recirc switches off because the flow is sufficient in high flow?
.
The 'left pack controller' does NOT control the cabin..There are 2 Pack controls but 3 zone controls, none of which you mention.

Where do you get this thing about the 'left pack controller' controlling the cabin?

[Cough]

The left controller (primarily) controls the left pack of course, its also the backup for the right pack and vice versa. The left controller primarily controls the trim air modulating valves for the zone temp which supplies the aft cabin air, the right controller controls flight deck and fwd cabin....

Re the recirc fans (Guess mode on..) . Mostly, you will enter high flow following pack failure of the opposite pack. Regulations require a certain volume of FRESH air per pax, so if on a single pack the recirc fans are on, maybe Boeing worked out that the volume wasn't guaranteed. Hence, they get inhibited? Maybe? (Guess mode off...)

[BOAC]

Folk often get confused by the 400 - there is no Right or Left 'PACKCONTROL'. Whereas on the 3/5 the left and right knobs control the respective packs output temperatures, on the 4/8 they do not.

[Cough]

The -3/-5 have a control cabin and passenger cabin temp selector, which were closely related to pack output (unless selected to manual of course), but they weren't quite left and right pack...

Agree the point on the -4 temp selectors - There is still the left and right electronic controller though...

References.. (http://www.smartcockpit.com/data/pdfs/plane/boeing/B737-classic/systems/B737CL-Air_Systems.pdf)

[Yeelep]

Re the recirc fans (Guess mode on..) . Mostly, you will enter high flow following pack failure of the opposite pack. Regulations require a certain volume of FRESH air per pax, so if on a single pack the recirc fans are on, maybe Boeing worked out that the volume wasn't guaranteed. Hence, they get inhibited? Maybe? (Guess mode off...)
I'm not sure having the recirc. on/off will make a difference to the fresh air volume. My guess would be preventing recirc. air from getting to the flight deck in the case of the left pack failing.

[AlwaysReady]

Thanks for your all the view, appreciate it
Ya my question is more towards the 400series..(maybe my question isnt clear enough so i try to rephrase my quesion)

(A)So like wut ive said, the 400 has 2 recirc fan. and it inhibits itself during highflow

Auto-
inflight - Left recirc : it inhibits when either pack in high
Right recirc : inhibits when both pack in high
on grd Left recirc : inhibits when both pack in high
right recirc : will work regardless

(left recirc collects from aft of fwd cargo compartment )
(right recirc collects from pax cabin and equipment cooling)

so why does it inhibits is the question..

(B) Since left pack provides air to the cockpit and right to the cabin as per say, I've learn that there is also something called electronic pack/zone controller located in the E&E compartment which provide inputs for pack and zone temperature control and each controls the ram air door

Left pack/zone controller - primary control for the left pack and standby for the right
Right pack/zone controller - the opposite

the question is, in my CBT it also states that

left pack/zone controller : provide temperature control for the aft cabin and standby for the flight deck
right pack/zone controller: provide temperature control for the fwd cabin and the flight deck

which explains 2 pack controller and 3 zone contorller

So since Left pack/zone controller control left pack which is suppling air to the flightdeck, why its also providing temperature control for the aft cabin and only standby for the flight deck??

[BOAC]

Re Recircs - we have told you a few times - ask Boeing. We do not know the exact flow requirements.

Re Pack controls: You need to forget left and right pack control in the 3/500 sense for the 4/800. Think of these ELECTRONIC controllers as mysterious black boxes that get info from both packs and all three zones. They will set the pack delivery to satisfy the zone with the most cooling need. Obviously if that is the cockpit they will adjust the left pack (Right Controller): if the aft zone, they may well control just the right pack (Left Controller) or both (Left and Right) etc etc

STANDBY is a mode which takes over the other controller task when it fails. Left and right are effectively meaningless in this context and should be forgotten. This should all be in your 'CBT' - which one are you using?

[AlwaysReady]

Yup, noted the answer on the recirc fan.. thanks!! =))

[aveng]

Scratching my memory a bit - but isn't the recirc fan turned off when high flow selected some sort of smoke clearance mode. The reason being that smoke in the Aircon would likely be caused by a f**king big fan than by bleed air.:\