737NG - ENGINE & WING CONTROL CB

[DeltaHotel]

Hi,
I've had this recurring problem on the 738 lately and would like a mechanic's input.

The circuit breaker labeled Engine & Wing Control at position P18-3 A6 has tripped a couple of times over the last few weeks.

Initial symptom is a failed light test on the anti ice panel. Both Wing Anti Ice valve lights and the #1 engine anti ice valve fail to illuminate on the test.

Also, the wing anti ice that is supposed to trip off on takeoff fails to do so leaving wing thermal anti ice on for the initial climb out.

When snagged maintenance closed it saying cb was reset and test serviceable.
Was hoping to get some insight on this issue if anybody has seen it before.

Thanks.

[Troubleshot]

What are the blue lights doing after the CB is reset? dim-to-bright-to dim seem right? next time you taxi, bright up the throttles till you hit the take-off warning horn (not sure if you could do that without scaring pax lol) Valves should transition for the WAI. The light test thing seems odd though, could be the control panel itself causing all the grief since you bring up the #1 Eng AI too. Also, I am not a 100% sure but if memory serves me I believe there is Air/Ground logic that disables the WAI once weight off wheels is sensed.....I could be mixing up different 737 models but I think that is the case for the NG.

Hard to troubleshoot without touching the plane, surprised there has been this many CB resets without more investigation. Next log book entry should state that there have been many CB resets prior to draw more attention to it. Sometimes during a crew change snags like this bounce around for a bit till someone catches it.

[NeverBlue]

I believe it's most likely the control box.

The test function is initiated in the control box I believe and if the CB for the box is popping and you have no test lights it's probably the place to start.

[ourkid2000]

It's interesting how different AC can be. I don't know the NG too well but I'm assuming it does not want bleed air on the wings when you want take off thrust or on climb out? Our aircraft, you turn that wing anti ice on and you're getting it.

[Troubleshot]

It's interesting how different AC can be. I don't know the NG too well but I'm assuming it does not want bleed air on the wings when you want take off thrust or on climb out? Our aircraft, you turn that wing anti ice on and you're getting it.

I think it is 53 degrees of throttle advancement on the NG and the WAI valves should close. If the WAI is selected "on" and throttles go back below 53 degrees the WAI should be in operation again. I think the PSEU also has a say in its operation if memory serves me.

[NeverBlue]

...and a low enough temp in the wing ducts

[ourkid2000]

Again, I don't know the NG at all but I have a couple questions for the op.....

With that particular CB out, I can almost 99% assure you that the system will never test. Does it test properly with the CB back in? Same goes for the Wing Anti-Ice switch........when you lift off, the switch is supposed to trip off and you state that it is not doing this. Did you happen to notice if the CB was popped when the switch failed to trip off?

[dashx]

Did maintenance write down the ATA reference when they released the plane? Out of curiosity I went to the 737 FIM Chap 30 Ice and Rain Protection 30-11 task 810 just to see what is involved.

Not that I am an expert on the 737.......

And definitely not an expert on copy and paste of pdf documents to Avcanada

[NeverBlue]

I think ourkid is correct. CB popped and the control is out of the loop and no test functions will operate correctly on the control. The WOW discrete is fed to the control box I think.

I can't see the CB popping for any other reason than a short in the control box or some sort of intermittent short on the power wire that the CB is feeding to the control box.
...but anything is possible.

[conehead]

Did maintenance write down the ATA reference when they released the plane?

Probably went like this; "C/B re-set. Wing anti-ice checked "servicable" as per AMM 30-11-00."

Was I close?

[DeltaHotel]

Did maintenance write down the ATA reference when they released the plane?

Probably went like this; "C/B re-set. Wing anti-ice checked "servicable" as per AMM 30-11-00."

Was I close?

That's exacly it !

I havent flown in a while now so I don't know if they narrowed down the source of the problem.
Initially, the way we noticed the problem was '' ah would you look at that, wing anti ice didnt trip off on takeoff '' . Then we would just manually set the switch to off.

It's only on the next light test (ground) that we noticed the 3 blue lights wouldnt come on.
I suspect the Cb trips off before sending the signal to the switch to close. Most likly on taxi out, before takeoff...

I'll post here when I find out more ...

[NeverBlue]

True Dat!

CB's are actually one of the simplest things to troubleshoot...they have but 1 function.