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Thread: Well now I know why my Mode C died inflight

  1. #1
    Member Float Pilot's Avatar
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    Default Well now I know why my Mode C died inflight

    When I flew up for the dreadful seaplane seminar, the lady with ATC started flipping me &### over the radio because she said my mod C was giving out weird altitudes all of the sudden.

    Yesterday it stopped sending out altitude info all-together. Well it turns out that an old cable-tie broke and the wire bundle to the encoder eventually shifted close enough to the yoke bicycle chain that it could fray some encoder wires. I was very lucky not to have a wire fire. Yikes.
    Floatplane,Tailwheel and Firearms Instructor- Dragonfly Aero
    Experimental Hand-Loader, NRA Life Member
    http://site.dragonflyaero.com

  2. #2
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    ​Lucky indeed!

  3. #3
    Member Float Pilot's Avatar
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    Apparently it was doing it when I was full back on the yoke only... So full stall landings. Which is how I do them... It took awhile to find. It has been cable tied up in there for many years... Kinda gives a guy the willies.
    Floatplane,Tailwheel and Firearms Instructor- Dragonfly Aero
    Experimental Hand-Loader, NRA Life Member
    http://site.dragonflyaero.com

  4. #4
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    Probably should make you wonder what else your mechanic has been missing during those 100 hour inspections.

  5. #5
    Member theultrarider's Avatar
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    Good catch Float Pilot and way to follow up on being told what was happening on radar.

    Don't be too quick to toss a mechanic under the bus here. There are SO MANY things a mechanic, even a VERY GOOD mechanic will not catch on an inspection. The top of that list is intermittent electrical shorts. ESPECIALLY if the driver/pilot does not inform them of the issue. And describe it to the mechanic to the best of their abilties. It is tough to find issues when you don't know that there is one. I have turned alot of wrenches in my life and often defend mechanics. I drive trucks and not planes for a living. And it pisses me off to no end when a driver will turn in his truck for preventive maintainance and ***** when they get their truck back and "the **** mechanic didn't fix "xxx". Well did you write it up??? Of course not. They should just fix it! Arrrrg. Talk with your mechanics guys.

    Once again, good catch and way to follow up on knowing something wasn't right and figuring out why.

  6. #6
    Member Float Pilot's Avatar
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    It was found by Doug at Peninsula Aero Tech in Kenai. I went to him a few days after the lady at Anch app control ( the same one who lectured me for using the real pronunciations of REPORTING POINTS) read me the riot act when I started transmitting the wrong Alt on Mode C last weekend. Originally it was just a wrong altitude from the encoder, BUT it was close enough to make it seem like maybe the encoder altimeter was just a little off. So I turned it off and stayed outside of class C on the way home.

    But it seemed weird to me, since it worked just fine three days before that... So I made an appointment at Pen Aero tech.

    Two landings later, it was only sending out Mode A info and no mode C info. ( when I came to Kenai to have it looked at)
    His magic box told us that the mode A was working ok and sending out the dialed-in code, by nothing was coming from the encoder for Altitude info.

    So Doug went Olympic gymnast and started digging around. Eventually he found the offending wires by feel due to the weird installation location of my encoder box.

    His theory is that the old flex tie from years ago finally gave up and I probably frayed one wire on the way to Anchorage. There are multiple wires sending data for different altitude blocks. In Anchorage Airspace it just so happened that I was close enough to the squawking Alt that it was almost believable.
    Later after a landing back at Homer and another at Kenai I had managed to whack a couple more wires. So by the time he pinged it with his machine, it was dead in mode C.

    We later pulled out another item from the panel and gave ourselves a good look much closer to the top end of things.

    I am not going to point fingers at my IA down here. I shoved a camera up under my panel and took photos during every annual and 100 hour. ( Because it is the only way you can see some of those places ) and those wires & zip ties looked OK back in February when we installed the new 406 remote switch.

    If I keep this plane I will probably gut the entire panel next winter and try to loose some extra weight with some newer gear. Although I am seriously thinking about going to a C-180.
    Floatplane,Tailwheel and Firearms Instructor- Dragonfly Aero
    Experimental Hand-Loader, NRA Life Member
    http://site.dragonflyaero.com

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