744 RB211 Fire Loops - Time Delay?
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 |
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. |
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 |
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 |
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 _ |
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 |
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