737NG cargo fire question
 

hello gentlemen.

i have question re: GARGO FIRE on the NG. why is it that one pack must be turn off in this check list?. And in the event that you my be already running on one pack, what do you think the best cause of action might be.

thanks inadvance

1 pack operation would reduce the airflow through the cargo bay. This action helps retain the inerting gas (halon) in the bay from the discharge bottle(s) for maximum effectiveness.

No packs operation could allow the smoke to enter the passenger cabin. If you are already on 1 pack - no need to change config. Recirc Fans off however.

Thanks VAPilot2004. This makes sense and your reply is appreciated. Cheers

???
The cargo bay is pressurized but NOT ventilated, and that's what still keeps me wondering... :confused:

worries in the mornin'
 

once again i'm coming to the conclusion, that my B738 manuals are just poor in terms of beyond-basic-layout info.
i mean I DO KNOW those cargo holds are cat C, supposed to be absolutely fire proof untill the crew reaches the next hotel bar. and they are not ventilated. 'used' cabin air and 'used ' eq. cooling air (inflite overboard ehaust valve closed) flows "around the linings" so those dogs etc don't freeze solid.
and the holds DO HAVE some very small pressure exchange mechanism to the outside.
and if u turn one pack off in flight the left recirc quits.
and on the newer B738 in the event of a fwd cargo smoke detection (by the way those cargo 'fire' detectors are only smoke detectors) the eq cooling exhaust fan will stop running while the off-light will be inhibited.

BUT WHY?

air flowing AROUND the cargo hold won't influence some fire on the inside?!?

But ... what about the integrity of the lining? If this were breached by fire/explosion, then prohibiting air flow would be best course. Belt 'n braces I know!