B737NG CARGO FIRE NNC
 

I'm wondering why the CARGO FIRE NNC instructs you to switch one pack off (the later models turn one pack off and the other to high).

With the flaps up the other pack changes to high flow, but I am not sure why you want this.

Maybe the answer is obvious but I can't see it. Can anyone shed any light for me?

It must be done to force the Smoke Removal Mode !!!
The smoke removal mode opens the overboard exhaust valve to remove smoke from the EE compartments and flight compartment.

Thanks Ifixplanes I didn't pick that up. It leads me to more questions though.

On later NGs the smoke removal mode is activated if fwd cargo fire is sensed without a pack regulating to high. Is turning one pack off just to retain compatibility with earlier models?

When i read quickly over the schematic there must be one pack in HIGH to energize the smoke control relay.
http://img146.imageshack.us/img146/7...alvetv8.th.jpg

Errr....Ifixplanes...does that mean manually selected to HIGH, or auto selection to HIGH as a result of turning off the other pack?
Also, when the pressurization system has the cabin in excess of 2.5 psi (when the overboard exhaust valve is normally closed), the NG will partially open that valve, regardless of the capability of the system to maintain proper pressurization.
My understanding is that the classic will only open that valve if pressure can be maintained.

Cheers, FD :bored:

Cargo fire warning Does not necessary mean smoke remover procedure required.Try think of it as reduce total air exchange with outside thus the extinguishing agent can stay longer in the cargo hold to dampen the fire and less fresh oxygen go in there.Just What I reckon.

Thanks for taking time and effort to answer Ifixplanes. Are the diagrams you have in the public domain?

In the smoke removal configuration air from the electronics bay is dumped instead of being diffused to the lining of the forward cargo hold. This allows an increased ventilation rate through the cabin whilst stopping air from circulating to the forward cargo hold.

The two bottles should give three and a quarter hours of fire suppression in a hold to cover 180min ETOPS (in NG).

This is my interpretation of Boeing Vol 2 (the only info I have).

The drawing said "PACK SWITCH" and "BLLED AIR CONTROL PANEL (P5)":
So it must be switched manually.
No, it is out of the AMM (Aircraft Maintenance Manual)