B737 Cargo Fire Checklist

[Denti]

We have in some of our B737-300s a Cargo Fire Protection Sytem installed. In the checklist for a cargo fire the last two items left me a bit puzzled. According to the checklist you have to switch of the recirculation fan, which i can understand (no recirculation of fumes), and "One pack switch......Off" (plan to land at the nearest suitable airport).

Why do i have to switch one pack off? Why is it not specified which pack is to be switched off?

Any answers?

Denti

[TR4A]

This is from my QRH:

1. Cargo Fire Arm Switch (Fwd/Aft as appropriate)...Push
2. Cargo Fire Discharge Switch...Push & Hold 1 Sec
3. Recirculation Fan Switch...Off
4. Right Pack Switch...Off
5. Land Immediately At The Nearest Suitable Aiport.

Notes for items 3 & 4:
This action helps prevent smoke from entering the cabin through the air conditioning system from air that is circulated around and collected in the vicinity of the cargo bays. If the left pack is inop, the right pack should be left on.

[Denti]

Okay, here is it from our QRH (nearly the same):

Condition: Fire is detected in the related cargo compartment.

1. Cargo fire arm switch (FWD/AFT)....armed
2. Cargo fire discharge switch.....push
Push and hold for 1 second
Note: DISCH light may require upt to 30 seconds to illuminate.
3. Recirculation fan switch.......off
4. One pack switch........off
5. Plan to land at nearest suitable airport.

If i have to switch one pack off, why don't state which one? I would switch off the left one, to prevent any smoke delivered to the cockpit.

[Canuck_AV8R]

My checklist for Cargo Smoke/Fire states to turn off the RIGHT pack switch and land ASAP.

[rr892igw]

DENTI,

MY QRH IS THE SAME AS YOURS,I DO AGREE THAT HAVING LEFT PACK ON WILL HELP TO REDUCE POSSIBILITY OF SMOKE GOING INTO THE COCKPIT
BUT WITH REC FANS OFF THAT SHOULD MINIMIZE THE WORRY.FURTHER MORE THE SMOKE SOURCE IS IN THE CARGO HOLD NOT AS CRITICAL AS SMOKE IN THE CABIN.IN MY OPINION,HAVING ONE PACK INSTEAD OF TWO WILL REDUCE AIR EXCHANGE FROM
OUTSIDE,THUS HELP TO PROLONG THE EXTINGUISING
AGENT'S STAY IN THE CARGO HOLD FOR OBVIOUS
REASON.
SOME 737 CARGO PLANES PROCEDURES CALL FOR
BOTH PACKS OFF WITH A CAUTION NOTES SAYS:
DO NOT REPRESSURIZE SINCE FIRE RELATED STRUCTURAL DAMAGE MAY HAVE OCCURRED.THEN WHY
PAX PLANES LEAVE ONE PACK ON? I DON'T KNOW! :confused:

[CaptainSandL]

I think rr892igw has given us the answer, the procedure is essentially reducing the amount of air you are giving the fire. On a cargo aircraft you can safely switch the fan(s) and packs off, but with pax on board you need to give them one pack to breath and it doesn’t matter which pack is used.

S & L

[scanscanscan]

S&L.. I hope the crew are O2 masked and the masks are working, with sufficient supply available.
That is, if all the packs are to be turned off, and the aircraft to be depressurised, at an O2 required altitude.
I recall.. Pilot O2 masks are mentioned at the start of the QRH, and omitted on other pilot O2 masks required checklists.