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Runaway trim!


marky_24

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Just a reminder to keep an eye on your electric trim. 

As I was taxiing to the runway I was setting the trim for take off with the wheel, which I always do to check for binding or what not. I could not move the wheel very easily.  After a second I noticed that the left half of the split electric trim switch was stuck down,  I centered the switch and could freely move the trim wheel now.  I ran the trim full up and full down on the electric trim, everything performed nominal.  

 

I took off and did some local flying. When I returned I decided to a touch and go, not to start a debate about touch and goes, but on the roll out I set the trim for take off then set the flaps for take off, and applied full power. As I was watching the airspeed come up to 65 MPH I was launched into air by a big  "irregular SFC" aka heave in the runway, "SGU RWY 01/19 BTN 2000FT S APCH END RWY 19 AND 3000FT N APCH END RWY 01 IRREGULAR SFC". 

I figured I would just accelerate in ground affect and climb out, only to my astonishment the plane tried to nose drive into the ground! 

I had to apply a good deal of back pressure to stay level,  as I accelerated and began to climb out the airplane just wanted to nose dive. I glanced down and saw that the trim had run full nose down!  The switch had stuck after I trimmed on the roll out. I got it back into trim, went around the pattern and decided to call it a day.

I sprayed the switch with contact cleaner and that took away the stickiness.

Edited by marky_24
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A pal of mine had that happen in flight, full nose up trim.  Took her and her husband everything they had on the yoke to keep the nose down.  Landed safety, but hit the edge fo the runway with the gear, sheared it off and totaled the aircraft.  She bought herself another Mooney.

I've read that a sudden pitch up maneuver can relieve the situation.  All that said, three cheers for my little trim wheel.

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I learned, as demonstrated by my guardian angel Mooney-owner CFI friend,, that with full nose-up jammed trim, if the pilot selects full flaps and reduces power, the pressure is quite manageable. Wish I’d known that then! In the much lamented 231’s case, it was a purely mechanical jammed stab-trim issue, and as it turned out, a malfunction Mooney was well aware of, but had not widely disseminated a cure for. No electrical issue, trim wheel was jammed, too.Something to do with the clutch plate.  Mooney subsequently issued a Service Letter, so that every mechanic who touches a Mooney of that model should know the fix for it.

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Been there done that. After my nose down runaway trim a few years ago I always place my hand on the wheel when using the electric trim just to make sure it stops when commanded. The issue back then was the King trim switch, which under certain circumstances, stuck in the down position.

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Just now, N201MKTurbo said:

Don't forget your trim disconnect switch.

If I has a sticky switch, I would turn off the electric trim and just use the wheel until I got it fixed.

Only good advice if you are aware as it's happening and in transit.

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12 hours ago, marky_24 said:

Just a reminder to keep an eye on your electric trim. 

As I was taxiing to the runway I was setting the trim for take off with the wheel, which I always do to check for binding or what not. I could not move the wheel very easily.  After a second I noticed that the left half of the split electric trim switch was stuck down,  I centered the switch and could freely move the trim wheel now.  I ran the trim full up and full down on the electric trim, everything performed nominal.  

 

I took off and did some local flying. When I returned I decided to a touch and go, not to start a debate about touch and goes, but on the roll out I set the trim for take off then set the flaps for take off, and applied full power. As I was watching the airspeed come up to 65 MPH I was launched into air by a big  "irregular SFC" aka heave in the runway, "SGU RWY 01/19 BTN 2000FT S APCH END RWY 19 AND 3000FT N APCH END RWY 01 IRREGULAR SFC". 

I figured I would just accelerate in ground affect and climb out, only to my astonishment the plane tried to nose drive into the ground! 

I had to apply a good deal of back pressure to stay level,  as I accelerated and began to climb out the airplane just wanted to nose dive. I glanced down and saw that the trim had run full nose down!  The switch had stuck after I trimmed on the roll out. I got it back into trim, went around the pattern and decided to call it a day.

I sprayed the switch with contact cleaner and that took away the stickiness.

I would replace the switch because it wears. Not very expensive.

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1 hour ago, Amelia said:

I learned, as demonstrated by my guardian angel Mooney-owner CFI friend,, that with full nose-up jammed trim, if the pilot selects full flaps and reduces power, the pressure is quite manageable. Wish I’d known that then! In the much lamented 231’s case, it was a purely mechanical jammed stab-trim issue, and as it turned out, a malfunction Mooney was well aware of, but had not widely disseminated a cure for. No electrical issue, trim wheel was jammed, too.Something to do with the clutch plate.  Mooney subsequently issued a Service Letter, so that every mechanic who touches a Mooney of that model should know the fix for it.

The mighty Mimi was my aforementioned pal. Perhaps using the word "pal" was presumptuous, but I thought it sounded better than "casual acquaintance".

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20 hours ago, carusoam said:

Great report, Marky.

How are your arms after that? Was the full down trim a work-out?

Under low power, the weight of the nose with full down trim can be stronger than many pilots...

Seeing if @Amelia is around... she may have some insight...

Best regards,

-a-

It definitely took both arms to overcome it,  but it wasn't too hard to keep it level or slightly climbing. 

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On 7/11/2018 at 9:25 AM, jetdriven said:

i have three colored, collared circuit breakers on my C/B panel for this reason.  A/P... ALT HOLD..   and ELEC TRIM

So I go the colored rings too the other day to mark C/Bs with.  There's no electric trim C/B on my 85' 231.  Or am I being blind/stupid? 

Edited by pwnel
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3 minutes ago, pwnel said:

So I go the colored rings too the other day to mark C/Bs with.  There's no electric trim C/B on my 85' 231.  Or am I being blind/stupid? 

If it's a King AP, you'll need to pull the autopilot circuit breaker. Keep in mind that there is also a trim switch just in front of the throttle marked "ELEV TRIM".

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Also, in almost all(maybe all?) King autopilot planes the yoke disconnect button also removes power from the trim servo, so the process is press and hold the red button, retrim manually, then turn off the trim switch on the panel and/or pull the AP breaker.

 

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48 minutes ago, flyboy0681 said:

If it's a King AP, you'll need to pull the autopilot circuit breaker. Keep in mind that there is also a trim switch just in front of the throttle marked "ELEV TRIM".

Century 2000, but I would imagine it's the same thing.  And yes, of course the "ELEV TRIM" button. I simply leave this on all the time so tend to forget about it.  (only 3 months into Mooney ownership). 

So I have the gear C/B,  Autopilot C/B and Alternator C/B marked for easy recognition for emergency procedures.

Edited by pwnel
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