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Old 12-16-2020, 10:42 AM
pilot2512 pilot2512 is offline
Join Date: Aug 2007
Location: Spring, TX
Posts: 478


The common thing to all the switches in the stick would be the ground as there is only 1. You may lost your ground all together or it is shorted to another wire in the stick. There are several places under the stick for wires to get pinched. That is at least a starting point.

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Old 12-16-2020, 10:44 AM
Steve Melton's Avatar
Steve Melton Steve Melton is offline
Join Date: Apr 2011
Location: Cincinnati, OH
Posts: 3,034

Originally Posted by blaplante View Post
I see lots of people with electric trim using the all in one "hat" switch. That's a single point of failure. What happens if it sticks or shorts internally?

I followed the Cessna 182T trim design - two rocker switches. BOTH have to be pressed up or down to make the trim move. If either one sticks on the trim doesn't move. Oh and there's a preflight checklist item to confirm no trim movement if you only actuate one switch.
yep, the hat switch is the highest potential trim failure point for me. especially when climbing in and out the tight cockpit it could become damaged. at least I try to protect it with a hard cover.

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RV-9A, Tip-up, Superior O-320, roller lifters, 160HP, WW 200RV, dual impulse slick mags, oil pressure = 65 psi, EGT = 1300F, flight hours = 800+ for all

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Old 12-16-2020, 10:51 AM
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ClayR_9A ClayR_9A is offline
Join Date: Jan 2005
Location: Dallas, TX
Posts: 173
Default Practice runaway trim!

Flying one day in my 9A it suddenly and unexpectedly pointed to the ground.
My electric trim switch is near my throttle so I can use my index finger to reach up and touch it when needed.
After slowing down go get the back pressure manageable, I applied a bunch of up trim to get things back in trim... but it took a lot longer than I would have liked before I realized that's what the issue was.

The only thing I can figure is that my hand was on the throttle and finger was next to the trim switch, and without realizing it, my finger hit and held the switch. I can imagine this would be even easier to do with a hat switch on the stick.

I encourage everyone to practice what it feels like to have a runaway electric trim so you know in advance what it feels like, and what to do about it.

I also asked GRT to add a pop-up warning on the screen if the trim goes out of normal range - that would have helped identify the problem faster. I haven't seen them add the feature yet though.
Clay R- RV9A - Flying since 2004 - 425 hours
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Old 12-16-2020, 10:51 AM
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rvanstory rvanstory is offline
Join Date: Dec 2016
Location: New Braunfels
Posts: 352

Curious to know from OP.... Was your G3X set up for reduced trim motor speeds at cruise and/or maximum trim time before shutoff? I have my G3X set up for 25% trim motor speed at cruise and max of 2 seconds before “timing out”. I had hoped these settings get me some margin of safety in event of a runaway trim. Curious to know if I have a false sense of security?
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Old 12-16-2020, 10:58 AM
andrewtac andrewtac is offline
Join Date: May 2014
Location: Friendswood TX
Posts: 315

Long ways away from flying my 10, but planning on using advanced panel with their vpx type cbs. In my 8 I have electric trim, with a trutrak in the middle for autotrim. Every prestart check when I check circuit breakers in I put my fingers on the trim circuit breaker. I might add an switch on my 10 to be able to interrupt up after seeing this. Need to do some research. Thanks for sharing, got me thinking.
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RV10 in progress
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Old 12-16-2020, 11:05 AM
DRMA DRMA is offline
Join Date: Jan 2016
Location: Sugar Land, TX
Posts: 450

Originally Posted by dweyant View Post
I was able to unstick the trim, and run it to full stops numerous times with no issues, however I had to do it from the soft keys on the G3X touch.

Dan - Where are the G3X Touch soft keys for trim located? I wasn't aware of these.

Also, as described by another poster, I have my trim controlled by my G3X system and set up with a maximum 2 second run time for the elevator trim, which should prevent a runaway due to a stuck trim switch. (My max run time for the roll trim is longer, as that trim isn't as effective and a longer run doesn't introduce as much out-of-trim.) Perhaps if you have your trim through a VPX system this isn't an option? I also have my trim breaker marked with a yellow breaker cap so I can find it quickly if needed.

Glad you were able to maintain control and get safely down.

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Old 12-16-2020, 11:07 AM
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Mike S Mike S is offline
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Location: Dayton Airpark, NV A34
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Originally Posted by ClayR_9A View Post

I encourage everyone to practice what it feels like to have a runaway electric trim so you know in advance what it feels like, and what to do about it.
Originally Posted by andrewtac View Post
Need to do some research. Thanks for sharing, got me thinking.
Best responses of the entire thread.

Doesnt solve the OP question, but still invaluable to anyone reading this thread.
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Old 12-16-2020, 11:15 AM
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g3xpert g3xpert is offline
Join Date: Sep 2010
Location: Olathe, KS
Posts: 2,952
Default Trim Switch Wiring

Originally Posted by dweyant View Post
Had a really scary experience yesterday.

Was flying from central Texas to Tennessee. putting along with a nice 30 knot tail wind when all of a sudden my Autopilot kicked off.

I was having just a little bit of turbulence, so my first thought was it was more than the AP could handle. However by the time I grabbed the stick and started to mess with reengaging the AP I realized something was very wrong.

My elevator trim had gone crazy on me, going full down deflection.

As you can imagine it is really hard to control an airplane in such a situation. I did (obviously) manage to get the plane under control, but I was unable to get the trim to move back to the proper position.

I wound up declaring an emergency (amazing how easy that is to do when you really need one). The controller was great and found me an airport close by so that I could shoot the RNAV approach, by hand, down to almost minimums.

Fortunately (very) I got the plane on the ground in one piece. Once on the ground I went about troubleshooting the problem.

I was able to unstick the trim, and run it to full stops numerous times with no issues, however I had to do it from the soft keys on the G3X touch. The buttons on my stick not only aren't working properly, but are performing the wrong function. the trim down button now works as right alieron....

Beyond that, and sending Garmin the logs they requested I haven't tried much troubleshooting yet.

Any ideas?

The trim switch wiring is probably a good place to start. If you put the G3X Touch into configuration mode, you can activate the physical trim switches and see which servo input is active. This should assist in identifying any wiring problems.

The maximum trim run time setting was implemented to limit the affect of a trim switch wiring issue. It is worth reviewing this setting and double-checking that it is programmed to a value that will protect against a potential switch wiring problem.

We will keep an eye of the datalogs from the G3X Touch to see what information can be gleaned from them as well.


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Old 12-16-2020, 11:53 AM
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longranger longranger is offline
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Since this doesn’t actually seem to be a model-specific problem, I suggest that this thread be moved to another forum such as Safety, General Discussion, or Ongoing Maintenance to better catch the attention of the general membership.
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Old 12-16-2020, 12:37 PM
JDeanda JDeanda is offline
Join Date: Apr 2013
Location: Ventura, CA
Posts: 207
Default I Love Our Manual Trim

There sure seems to be a lot of discussion around electric trim systems. Yeah, manual trim can fail, too. It could have a push-pull bit come adrift, and it can get stuck. But it cannot run away.
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