OVATION ELECTRIC TRIM SWITCH

[Alan Maurer]

DEAR MOONEY PEOPLE, On downwind today the electric trim switch quit just when I wanted to trim up for landing. I am not sure where to start checking for what is broken. Used the trim wheel easily but not sure if the switch is bad or to look elsewhere. Glad to have some advise....

Thanks

Alan N913ND Ovation 2 DX

[PT20J]

Trim is usually part of the autopilot. Which autopilot do you have? Does the trim work with the autopilot but just not when you use the switches, or does it not work at all? Did you check for a tripped breaker?

[Alan Maurer]

Hi...no popped breaker. AP was off downwind turning base....AP is Garmin GFC700. Never have autopilot turned on in immediate airport area.I could take off tomorrow and see if electric trim works with autopilot turned on but for now not sure

[Schllc]

1 hour ago, Alan Maurer said:

Hi...no popped breaker. AP was off downwind turning base....AP is Garmin GFC700. Never have autopilot turned on in immediate airport area.I could take off tomorrow and see if electric trim works with autopilot turned on but for now not sure

Electric trim will not work with the autopilot off. 
why do you turn it off?  
 

[StevenL757]

11 hours ago, Alan Maurer said:

DEAR MOONEY PEOPLE, On downwind today the electric trim switch quit just when I wanted to trim up for landing. I am not sure where to start checking for what is broken. Used the trim wheel easily but not sure if the switch is bad or to look elsewhere. Glad to have some advise....

Thanks

 

7 hours ago, Schllc said:

Electric trim will not work with the autopilot off. 
why do you turn it off?  

Alan @Alan Maurer, Schllc’s comment is correct.  With the AP Power rocker switch off, the manual electric trim switch on your control column will not drive your pitch trim, since the AP Power switch powers your servos.  You can engage the Flight Director, but you’ll have to reach down and trim manually using the wheel.

Other than trying to prevent what you may perceive (I’m guessing here) as a runaway trim condition, I’m also not sure why you’d shut the AP Power rocker switch off (curious to understand the reasoning) in the “immediate airport area”..  Engaging the autopilot is one thing.  Shutting the system power off is another.  Leave that switch on; and, in the unlikely event of a problem, pull the autopilot CB to combat any abnormal condition with the AP.

Steve

Edited April 16, 2023 by StevenL757

[Guest]

Look for broken wires at the forward end of the pilots control column where the wires exit the tube.  There should be an Adel clamp to secure the wire harness, often wires break in this area from constant flexing.

[Alan Maurer]

Steve, The panel AP rocker switch was on. I turn the AP off with the big red button on the yoke. Electric trim on yoke would not trim airplane. I just used the manual trim wheel between the seats. I know if I turn off the rocker switch on the panel that the electric trim will not work...

I am going to try it again today

[StevenL757]

46 minutes ago, Alan Maurer said:

Steve, The panel AP rocker switch was on. I turn the AP off with the big red button on the yoke. Electric trim on yoke would not trim airplane. I just used the manual trim wheel between the seats. I know if I turn off the rocker switch on the panel that the electric trim will not work...

I am going to try it again today

Gotcha…thanks for the clarity.  The way I read your initial post was that you turned the power off to the AP, hence my earlier comments, so this clears it up.  In this case, I tend to agree with Clarence about a likely broken wire producing an intermittent connection, but as you say, test again (and again), and see what happens.  For your sake, I sincerely hope it’s an easy fix and not a servo or switch problem, as I know both are big $$.

[flyboy0681]

2 hours ago, Alan Maurer said:

Steve, The panel AP rocker switch was on. I turn the AP off with the big red button on the yoke. Electric trim on yoke would not trim airplane. I just used the manual trim wheel between the seats. I know if I turn off the rocker switch on the panel that the electric trim will not work...

I am going to try it again today

Ah, you meant that you "disengage" the A/P.

[LANCECASPER]

6 hours ago, Alan Maurer said:

Steve, The panel AP rocker switch was on. I turn the AP off with the big red button on the yoke. Electric trim on yoke would not trim airplane. I just used the manual trim wheel between the seats. I know if I turn off the rocker switch on the panel that the electric trim will not work...

I am going to try it again today

Not sure if yours is a King or STec or Garmin, but there are threads on Mooneyspace that advise against using the red A/P disconnect button to regularly shut off your autopilot (on the King I believe). Too much power going through that switch and the switch when disassembled shows arcing in many cases.

Here's a recent thread, which if you read all the way through, shows that it was a bad disconnect switch.

 

 

[Alan Maurer]

Hi Everyone, I always use the big red button on the yoke to disengage the autopilot. As observed, if AP is disengaged or turned off using the rocker switch, it also turns off the electric trim on my Ovation. I do not know of any other way to disengage the AP although it is maybe possible to press the AP button on the GFC700 

and it would disengage...never tried that! But...everyone stay tuned...I am heading for the airport to fool with it

[Alan Maurer]

So....Problem could be intermittent. in hangar, turned power on and AP rocker switch...I then pushed the electric trim button on the yoke......no trim movement....I them moved the manual trim wheel a few turns and then tried the electric trim switch again....and it worked perfectly!!!  Could this be a lubrication problem??

Thanks

Alan

[PT20J]

2 hours ago, Alan Maurer said:

So....Problem could be intermittent. in hangar, turned power on and AP rocker switch...I then pushed the electric trim button on the yoke......no trim movement....I them moved the manual trim wheel a few turns and then tried the electric trim switch again....and it worked perfectly!!!  Could this be a lubrication problem??

Thanks

Alan

Should be no problem using the yoke disconnect on a GFC 700.

I doubt it's a lubrication issue unless the trim wheel is very stiff when you turn it manually.

There are a couple of possibilities from your last test:

1) The switch in intermittent and moving the trim wheel was just a coincidence. 

2) There is something wrong with the servo and moving it manually freed it up.

I would try repeating you test multiple times on the ground to see if you get to a point where something is reproducible. A King autopilot will run the trim servo on the ground if you engage the autopilot and push or pull on the yoke, and this is a way to test that the autopilot can control the trim. The GFC 500 won't do this. I'm not sure about the GFC 700. However, you can do the test airborne -- just engage the autopilot and push or pull on the yoke and see if the autopilot runs the trim. If it does, it indicates that the problem is in the manual electric trim (most likely the yoke switch or wiring) and not the servo.

Skip

[Alan Maurer]

Skip, 

Moving the trim wheel between the seats seemed to loosen things up and then (on the ground) the electric trim switch on the yoke started working so it seems intermittent. I hate intermittent problems. Either way I can always trim the elevator. I will keep an eye on it. Thanks for advice!

Alan

[Schllc]

You can absolutely disengage the AP with the g1000 screen as well as the red disconnect button. 
I will tell you I have had this happen to me a few times over the years and the first time it freaked me out and I didn’t realize until I landed that I had actually flipped the AP rocker switch. 
I don’t know if I inadvertently hit it, or maybe a passenger, it just didn’t occur to me to check it, because I didn’t intentionally turn it off.

It’s happened a few times since then, and I always check the rocker switch first and it’s been flipped every time. 
if everything is working as normal now and you can’t recall if you checked the rocker switch in flight, I’m betting that’s what it was. 

[Alan Maurer]

Schlic

In  hangar yesterday , I turned power on and panel AP switch on. Then tried yoke electric trim switch with my hand resting on between seats wheel to see if it turned....at first nothing happened and it would not rotate (trim) so I then moved the wheel between the seats a few turns AND ...then repeated the whole thing and the yoke electric switch started working. To add to this saga, Sarasota Avionics looked into this after the January Lakeland Mooney course  as in a dual instruction flight, everything got stuck. They looked at the servo and mechanism in the back and lubricated whatever drives that device and said all was fine. I will ask them to have another look.

 

[Schllc]

9 hours ago, Alan Maurer said:

Schlic

In  hangar yesterday , I turned power on and panel AP switch on. Then tried yoke electric trim switch with my hand resting on between seats wheel to see if it turned....at first nothing happened and it would not rotate (trim) so I then moved the wheel between the seats a few turns AND ...then repeated the whole thing and the yoke electric switch started working. To add to this saga, Sarasota Avionics looked into this after the January Lakeland Mooney course  as in a dual instruction flight, everything got stuck. They looked at the servo and mechanism in the back and lubricated whatever drives that device and said all was fine. I will ask them to have another look.

 

When I turn on my g1000 it easily takes 2-3 minutes after I turn on AP switch. Before it starts engaging. 
fwiw, I’m just trying to be optimistic.  
I would like to know what the problem is when you find out. 

[Alan Maurer]

Well, the electric yoke switch has started working again. Problem is not solved. Annual in three months and for now will just watch it. Thanks everyone for advice,

Alan

N913ND

[Frank]

On 4/16/2023 at 10:58 PM, Schllc said:

You can absolutely disengage the AP with the g1000 screen as well as the red disconnect button. 
I will tell you I have had this happen to me a few times over the years and the first time it freaked me out and I didn’t realize until I landed that I had actually flipped the AP rocker switch. 
I don’t know if I inadvertently hit it, or maybe a passenger, it just didn’t occur to me to check it, because I didn’t intentionally turn it off.

It’s happened a few times since then, and I always check the rocker switch first and it’s been flipped every time. 
if everything is working as normal now and you can’t recall if you checked the rocker switch in flight, I’m betting that’s what it was. 

Isn't that a circuit breaker switch? It's possible the circuit breaker is tripping.

[thinwing]

something not mentioned but I have observed various pilots mashing that trim switch...it is vary robust design but i thinks its internal contacts can be damaged by excessive force that later causes intermittant contacts

 

[carusoam]

The trim switch itself sees a lot of force… especially during go-arounds…

there are a couple of micro switches that support the mechanical aspect of the switch…

The BK version has seen a ton of discussion around here…. It is a common procedure to swap in new micro switches for maintenance…

PP thoughts only, not a mechanic…

Best regards,

-a-