B737NG Extinguisher Test

[Cirrus22]

Hi all,

This is a (fairly pedantic) issue that's been bugging me for a while regarding the extinguisher (squib) test on the 737. (Specifically NG, but I don't believe there's much of a difference between them here).

The EXT TEST switch on the Overheat/Fire Protection Panel is spring loaded to centre and has 2 positions for testing the squib circuit continuity: 1 and 2.

I'm trying to find a definitive answer on what specifically each position tests. Bill Bulfer's 737NG Cockpit Companion says:

- Position 1 tests the #1 and #2 squib on LEFT bottle and APU squib
- Position 2 tests the #1 and #2 squib on RIGHT bottle and APU squib

This page however says otherwise:

B737NG - ATA26 - FIRE PROTECTION

It says that:

- Position 1 tests the #1 squib on LEFT and RIGHT bottles and APU squib.
- Position 2 tests the #2 squib on LEFT and RIGHT bottles and APU squib.

Can anyone confirm which is correct? Cheers!

[ImbracableCrunk]

If you look at the panel and switch itself, the answer seems to be printed there. You select either (bottle) 1 or 2. That then will test squib L, R, and APU.

1 means L.H. bottle and 2 means. R.H. bottle and L and R refer to squibs.

That's my take, anyway.

[aveng]

- Position 1 tests the #1 squib on LEFT and RIGHT bottles and APU squib.
- Position 2 tests the #2 squib on LEFT and RIGHT bottles and APU squib.

Correct - position of the s/w shows the squib number your testing.

[IFixPlanes]

Maybe this explain it:

[Cirrus22]

Perfect, thanks chaps.

While we're on the subject of fire protection - according to the FCOM the cargo compartment fire protection system is a 'dual loop' system.

Does 'dual loop' mean that the forward and aft cargo compartments EACH have two detector loops, or that there are two detector loops spanning BOTH compartments?

I'd guess by the layout of the cargo fire panel that each compartment has two loops, but the FCOM schematic isn't particularly clear.

[aveng]

yes -dual loops in both cargo compartments

[Avenger]

Cırrus note some NG have dual cargo fıre bottles, some only one bottle. The second bottle ıs dıscharged automatıcally a fıxed perıod after the fırst bottle and contınues to dıscharge to maıntaın approx 2% haylon ın the cargo hold. Whenever the cargo fıre system dıscharges a sıgnal ıs sent to the cabın pressure controller and the cabın starts to de pressure at about 750fpm hence LAND AT NEAREST SUITABLE AIRPORT ın QRH.
If the aırcraft lands and the system logıc ıs not reset, the second bottle wıll start to dıscharge agaın after take off. Just for ınfo