Cabin Flood Indicator INOP

2 weeks 1 day ago - 2 weeks 1 day ago #1487 by OG GarlicSalt
Working on a Hawker 900XP pilot reported cabin flood valve indication always full.

After doing some initial trouble shooting I find that the valve is operating and that the potentiometer that is responsible for the indication is turning with the valve (located behind the aft monuments behind lav sink/closet). After checking this I went into the flight deck to get some readings at the indicator.

Indication on the left non responsive

Once inside i did a few checks

First thing I wanted to check the potentiometer 10k resistor and see what the readings were. I checked both from GND-REF and got about 10K ohms on both.

Next I checked from GND-SNG to see what was the OHMs output as the valve is moving.

I found that the on the working Floor indicator the OHM reading ranged from about 300ohms at valve closed to 5.5k ohms at valve open. I then found on the broken flood indicator that that when the valve was physically in the full closed position im getting a reading of 5k ohms and physically full closed 8k ohms. So seems that we have found our culprit.

Even though at this point im 95% of the potentiometer being bad i wanted to fully check the indication downstream. So i made a jumper to jump the signal input to both sides of the indicator.

So I hooked up with full jumper set but with the floor valve signal wire going to both sides of the indicator. As i suspected in this setup the indicator was moving on both sides with the floor valve operations. Telling me 100% the potentiometer is the culprit. Also if i didn't have the other floor valve so easily accessible an indicator like this could also be checked with a decade box.


After changing the potentiometer out the indication was good as new.

Last edit: 2 weeks 1 day ago by Mark.

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2 weeks 1 day ago #1488 by Mark
Replied by Mark on topic Cabin Flood Indicator INOP
I created a ATA 21 under Hawker and moved your post there.

Great find. I forgot Hawkers use different nomenclature for some systems. "Flood" is normally associated with lights, but I'm guessing these would be the overhead vents in the cabin??? 

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