N1 Vibes

Does anybody know if Boeing built in a delay to the Fire indication system on the 744 for the RR application?

I.e. for a full fire indication (whistles and bells) can there be a delay of X seconds between the Loop A discrete and the Loop B discrete setting the Fire indication before annunciation?

And also for a fault indication is there a buffer of X seconds that a fault has to be present before a Fault message is set?

Many thanks,

N1 Vibes

spannersatKL

To my knowledge no buffer would need to look at the diagrams before being certain. In Dual loop mode both loop detect then signal to MAWEA and bells/red lights.

Also in this case it isnt a 'fault' its a fire....its real.

In case of a failed loop there is a Status mesage set for example
ENG 1 LOOP B.

In my experience these only set when you test the system (this is done on a daily check using the overhead buttons) and find a failed loop.

It should also be noted that the RB211 has a Turbine overheat system linked to the Fire Warning system.

N1 Vibes

cheers spanners,

finally got the answer from Boeing:

A fire detected on one loop is annunciated as a 'full fire', as soon as a fire OR fault is detected on 2nd loop

There is a 20 second buffer in Loop Fault indications.

Many thanks,

N1 Vibes

SMOC

N1 Vibes,

So have I got this right,

If you get a fault in one loop and within 20 sec get a fault in the second, this will result in a FIRE ENG _

Also

If you get a Fault in one loop and and 30 sec later get a fault in the other, you will get >DET FIRE/OHT _

Cheers

banana head

No - You need an actually FIRE sensed in the first loop, then either a FIRE or a LOOP FAIL sensed in the second loop within 20sec. This is to guard against a LOOP FAIL due damage at the point of Engine Failure.

N1 Vibes

smoc/bh,

we initially thought it was 2 loop faults within 20 seconds. But then with some experimenting on a good engine proved bananaheads correct knowledge. It seems though that we had a very interesting defect, to get a full ENG FIRE (red) we needed a chafe through both loops at the same place going to ground.

Interestingly we actually had the softwire of one loop chafing on the connector screw of the other loop - so we thought this was our defect. Utnil we realised the softwire was 'unshieled' at the point of chafing, and we actually had a 2nd chafe in a completely different part of the system that then took both loops to ground.

A precautionary tale - never assume you've nailed an avionics defect when you find ony ONE chafe!

Regards,

N1 VIbes