FADEC Caution light

Discussion off all the ADs.
KD8COO
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Re: FADEC Caution light

Post by KD8COO »

In all our various FADEC problems, we always just had the yellow light. Never got the red one. Sounds more serious than whatever we had going on for awhile.
N645XL
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Re: FADEC Caution light

Post by N645XL »

Based on my experience with two faulty WOT switch circuit incidents exhibiting the same symptoms, I'd recommend you check it first before you invest a lot of effort in other areas. My symptoms started with a flickering WOT LED. It's hard to detect in daylight because of the short duration. I didn't notice mine flickering (the first time I received a FADEC Caution in-flight) until I was flying into the dark hours. Once I noticed the flickering LED I understood the FADEC Caution. The WOT switch circuit opens when you push the throttle full forward. A circuit break (wire or a bad solder joint on the switch terminal) mimics a full-throttle request regardless of throttle position. Your FADEC caution light may likely illuminate in flight at cruise RPM as mine did if you have an intermittent WOT circuit. At low RPMs (post landing taxi) my red FADEC Warning light also illuminated along with the FADEC Caution light.

You can check the wire harness or solder joint integrity by removing the upper cowling, turning on the two FADEC switches, grabbing the harness where it meets the switch and wiggling it around gently. You'll need someone watching the WOT LED or a cockpit mirror to see if the WOT LED illuminates as you wiggle the wires. Of course, you want the throttle around idle and all proper safety precautions. If the WOT LED illuminates or flickers with the wiggling you likely have a broken WOT circuit. It's a pretty easy and fast test and, if defective, it'll provide you the symptoms you describe.

There have been issues with the soldering on these switches so it's likely poor quality from the supplier to Continental and fairly easy to fix with the right tools and materials. It seems a supplier liked to cover up poor quality soldering (or no soldering) with the potting compound. The switches themselves are Mil Spec and should last a long time. If you have to buy a replacement switch with a new harness from Continental they're about $1,400 so it's worth it to repair the faulty solder joint (if that's what it is).

Of course this is my experience (times 2); however, others on this site have run into the same issue. It could be systemic. My personal option would be to present the evidence to Continental and ask them to do right by you. I'd consider it a latent defect that should be covered under warranty but I'm no lawyer. I posted the photo earlier in this thread to show the bracket my A&P fashioned to keep the harness from moving in the wind under the cowling. I will also add, the FAA inspector that approved the bracket also requested a defect report on the two switches.

If your WOT circuit is good your next step may be to run a diagnostic and send any files necessary to Continental for analysis. Anything more than this basic trouble-shooting would be unfamiliar territory to me. This is also no substitute for your A&P's expertise. Hope this helps. Bob
NylonStringNinja
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Re: FADEC Caution light

Post by NylonStringNinja »

Hey dkirby

Make sure you note the times you had these problems and have TCM decode your data card. When I have worked with the FADEC folks there I found them very helpful. You should have no trouble identifying the cause of the warning lights by looking at what kind of readings the sensors recorded at those times. Not only is this nice, and helpful, but it is also necessary on our airplanes for intermittent issues like this. Unless a mechanic has a very good understanding of the FADEC system they may not make use of this capability and could spend $80/hr grasping at straws; or worse think they found the cause but be wrong and send you on your way.

I would also suggest that this warning light behavior could also likely be caused by the engine speed sensor (SSA) giving erratic readings.

Good luck
KD8COO
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Re: FADEC Caution light

Post by KD8COO »

NylonStringNinja wrote: I would also suggest that this warning light behavior could also likely be caused by the engine speed sensor (SSA) giving erratic readings.
Yes, I believe that one of our investigations showed as high as 13,000 rpms in the log. Engine speed sensors are known to fail in some curious ways. :-)
DavidFortlage
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Re: FADEC Caution light

Post by DavidFortlage »

I'm the new kid on the block having purchased N572XL a week ago. My purchase was contingent upon correcting the FADEC problem for which I received a monitary addendum to the contract. In my case, the problem was "solved" by cleaning the wiring harness connection that go through the firewall.. From what I've read on the forum, there is no one solution to the problem. Will keep you posted.
thordehr
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Re: FADEC Caution light

Post by thordehr »

I love the bracket idea so much that I had our mechanic look at what it would take to replicate it and get it signed off. He reminded me of a standard practices zip tie technique. Two zip ties over and between the harness and the nearby tele-flex cable, and it's secure! No sign off required, took 20 seconds and may prevent a lot of heartbreak later. I've seen this technique used with more than one horizontal zip ties to make a support spanning larger distances.

Image
stever
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Re: FADEC Caution light

Post by stever »

Looks like i have managed to get myself a dodgy throttle switch.
Before we attempt the repair, has anyone who has already done this have details of how they successfully removed the potting compound with out damaging the internals? And what they re-potted it with?
tafisama
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Re: FADEC Caution light

Post by tafisama »

The switch is perfectly fine but one of the wires has broken.It is most likely the bottom one connected to the NC terminal.Mine played up last year when I was flying to William Creek.I had to do what I had to so that I could get home.It had happened before and had been soldered so I knew what to do.[attachment=0]IMGThe Avionics guy put a piece of clear pvc hose and sqeezed in the sealant,cant remember the name.We then added a clamp as suggested by N645 Bob.Since then,no problem at all.The switches dont break at all,its the wire that breaks at solder join.
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tafisama
Posts: 110
Joined: Wed Dec 18, 2019 9:09 pm
Based: Adelaide,SA
Tail Number: XLY
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Re: FADEC Caution light

Post by tafisama »

This is how we finally clamped down the wire lead.
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