Fire detection, loop breakage...

[PRNAV1]

I'm confused with how the loop system works when a loop breaks giving a fault indication but yet once you select said loop off or both loops off the detection system still works..what am i missing. if it's a closed circuit how does the sytem operate. i'm refering to the sytem onboard airbus.

any help plz.

[bfisk]

Originally Posted by PRNAV1

what am i missing

Probably the comma and period keys? Say what, now?

[PRNAV1]

Abit rushed i know, sorry. Think it's still s clear question. Just want a brief explination...

[IFixPlanes]

Originally Posted by PRNAV1

...
once you select said loop off or both loops off
...
i'm refering to the sytem onboard airbus.
...

Select loop off on Airbus?
Maybe "I" miss something?

[Luftwaffle]

If it's like the DHC6, this may help.

[TURIN]

Short answer is that the system is a dual loop type.

If one loop breaks you still have a servicable second loop.

The logic of the circuit detects a break when the gas pressure in the loop drops. The 'loop' is a sealed tube containing a gas and a gas impregnated metal core. When there is a temp rise then the impregnated metal core releases it's gas and consequently increases the loop gas pressure. This triggers the pressure switch, indicating a fire.

If the second loop gas pressure also fails within 20secs? Then the logic assumes a catastrophic engine burst and detects a fire.

There is a lot more to this but I'm busy. Hope this helps.

[IFixPlanes]

So here is the Fireloop for Airbus A320Fam. (Without possibility of switching)

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...and the Fire Detection Unit FAULT-Logic:

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...and the Fire Detection Unit FIRE-Logic:

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and here the Logic of the 737NG (With possibility of switching)