Electric trim INOP

[DonMuncy]

On my last flight, my electric trim quit working. It has its own switch on the panel and cycled that. No help. Has anyone had this happen or know of any common faults for that failure.

The most obvious way to start (from my perspective) would be to check the motor to see if it is getting power. Any better ideas?

[carusoam]

Check the cb to see if a mechanic has pulled it, or it popped out on its own...

Experience from my last annual... 

Best regards,

-a-

[PT20J]

Which autopilot? Does the autopilot work?

[Amelia]

Oof. Bad memories, except in my case, it was ALL the trim inop, (stuck full-nose-up) due to a totally jammed jack screw. Apparently a known issue with 231s, for which a fix actually existed.  Surprise! Thanks to a very knowledgeable CFI and friend, I learned how to manage it better than I did the last time.

[Oldguy]

Assuming you have a King A/P and electric trim, I would do the following:

1. Power up the avionics. (Start plane or not - you and your battery's choice).
2. Cycle trim switch on panel (as you have done).
3. Reset breaker on panel.
4. Run A/P test and note light flashes and beeps.

The KFC/KAP test cycle checks all components of the A/P including the electric trim. There actually is a method to the number of light flashes and beeps. If it is not what you normally see/hear, it can help lead to the failing component.

If it is a King A/P, there should also be a section in the Supplement for it discussing the test of the autopilot you are doing before you fly. In my supplement, it is Section IV - Normal Procedures, Pre-flight. It covers the A/P test and testing the manual electric trim.

If you have something other than a KFC/KAP, I am pretty sure none of this helps.

[DonMuncy]

Thanks. I knew if I asked, someone would be able to point me in the right direction. Excellent advice John.

[Oldguy]

4 minutes ago, DonMuncy said:

Thanks. I knew if I asked, someone would be able to point me in the right direction. Excellent advice John.

What I forgot to include is to take your findings and talk with someone who knows what the count of flashes and beeps means. Someone like Autopilots Central or Bevan (sp?) would be the names I have seen mentioned on here in the past.

[DonMuncy]

Even more good help.

[Parker_Woodruff]

Make sure you tested the autopilot and it had completed its self-test (on the ground is best) prior to running the electric trim.

[PT20J]

On the KAP/KFC 150 autopilot, the TRIM light will be on after avionics power up to remind you to press the TEST button below it. Manual Electric Trim (MET) will not work if the TRIM light is on. On mine, pressing TEST results in TRIM flashing four times and five beeps. The manual doesn’t specify the number of beeps and according to Steve at AP Central it varies. The important thing is that the TRIM light stays off after the beeping is done. If it doesn’t stay off, then the test failed and the MET is disabled. In that case, it could be the autopilot computer, or the TRIM rocker switch which is a circuit breaker, or a broken wire somewhere.

Skip

[Bob - S50]

And of course it could also be the trim servo.  If it turns out to be the servo I have a used one (KS272) I'm selling for $300.  Part number 065-0029-11

[ArtVandelay]

My AP has a relay, in my case, I pulled the relay from its socket, cleaned the contacts, after it worked like a charm.


Tom

[ohdub]

I've had mine stop working several times, every time it has been the wire/connection to the thumb switch on the yoke. Last time it happened my avionics shop replaced the wire with a longer one and have had no issues since.

[flyboy0681]

3 hours ago, Oldguy said:

The KFC/KAP test cycle checks all components of the A/P including the electric trim. There actually is a method to the number of light flashes and beeps.

My rule of thumb is that the cost of repair is commensurate with the number of beeps outside of five. For example, four beeps translates to 4AMU, three equals 3AMU, so on and so forth.

[Vno]

I had a similar problem with my trim and KAP 150 autopilot. It ended up being the trim switch itself. I consulted with Bob at http://www.webairconsulting.com

over the phone and walked through the troubleshooting to confirm it before I started replacing parts. Well worth the small fee I paid.

Brian

 

Slight fib on my part. It was the red DISC switch (button) that failed. Not the trim switch.

Edited January 25, 2020 by Vno
Pilot Error

[DonMuncy]

I went out to the hangar this  morning. After cycling the autopilot circuit breaker, everything seems to work fine. We may never know!

Thanks for all the help. If the gremlin returns we may have to revisit it.

[MooneyMitch]

As with electric intermittent issues, odds are your trim issue will return.

In my former profession , We’d rather have a complete failure, rather than an intermittent situation.  Much easier to diagnose.

 

[CaptRJM]

The yoke mounted trim switch is notorious. Three microswitches and small diameter spring wire is all that makes it work. Dirt, wear and number of cycles all add up to it not working. 
 

Just for grins I’d loosen it from the yoke and give it a good dousing of a good contact cleaner like DetoxIT 

[moosebreath]

Hmmm ... working after recycling the breaker the next day is not a good sign.  It sounds like the beginning of the self test failure due to bad computer power supply capacitors to me. Look at my posts about that problem in a thread from a couple of years ago.

The sure sign of the capacitors being at fault is if the problem reoccurs and can be cleared after the alternator has been running for a few minutes after start.

I hope this is not it ...  Your basic hanger elf can not replace those caps and it is $1000 or so to get it done if I recall correctly.

[Bob Weber]

On 1/24/2020 at 12:12 AM, DonMuncy said:

On my last flight, my electric trim quit working. It has its own switch on the panel and cycled that. No help. Has anyone had this happen or know of any common faults for that failure.

The most obvious way to start (from my perspective) would be to check the motor to see if it is getting power. Any better ideas?

 

 

When it fails again, if you can access a couple points in the system with a voltmeter, I can help you trace the problem rather quickly.

 

Bob Weber

webairconsulting.com

616 822 1999 eastern time

[MooneyMitch]

My experience with my former KFC150 system was similar to Don’s situation.  Intermittent test mode with TRIM test/system engagement.

Testing revealed faulty transistors, capacities in trim servo.

Economically repaired by Sacramento CA Executive Airport avionics facility.  

If this is the case for Don, hopefully an avionics facility with appropriate test equipment near Dallas.

[PT20J]

When mine did that, it turned out to be a cold solder joint on the interconnect between boards in the computer. Lot’s of things can cause this apparently. 
Skip

[MooneyMitch]

54 minutes ago, PT20J said:

When mine did that, it turned out to be a cold solder joint on the interconnect between boards in the computer. Lot’s of things can cause this apparently. 
Skip

Completely agree...... an avionics facility with correct test equipment is quite valuable for efficient economical diagnosis and repair.  My experince.

I was fortunate to take the aircraft to the facility, as opposed to sending individual parts separately.

[DonMuncy]

Thanks everyone.

[whiskytango]

On 1/24/2020 at 8:45 AM, Amelia said:

Oof. Bad memories, except in my case, it was ALL the trim inop, (stuck full-nose-up) due to a totally jammed jack screw. Apparently a known issue with 231s, for which a fix actually existed.  Surprise! Thanks to a very knowledgeable CFI and friend, I learned how to manage it better than I did the last time.

Amelia,

This happened to me on my first flight with my current 231.  It has been "fixed" several times, except that the problem remains - if using electric trim it goes to full nose up trim and stays there. I gave up and just use manual trim, which always works fine.  I would be interested in learning what the known issue and fix are, because apparently my A&P hasn't heard about it.