Runaway trim

[Alan Fox]

We lost an experienced pilot at Beechtalk and the consensus is that was a trim issue......Just curious about those with electric trim if you have your trim breaker identified and have gone over procedures for this.......It sounds like pretty scary stuff , as for now , I am going to leave the trim off and manually trim for now.....

[wiguy]

The mention of a trim problem or 'runaway trim' is just one possibility mentioned. The partial reason is a wreckage picture with the trim tab deflected a fair amount. I really don't buy it was a trim issue, especially runaway trim. Yes, early yet in the investigation.

It was a shorter grass runway, 2000'. It rained a good amount just days or less prior, they were at least fairly heavily loaded, 5 onboard. The grass was likely wet, ground may of been 'spongy'. Yes, three were kids of various ages. It was a family trip, heading back to UT. They may of had the fuel light loaded.

Don't know the exact airframe, most performance charts close to it show about a 2000'(+) length to clear a 50' obstacle, off pavement. The witnesses said they never got above the trees.

Yes, truly a very tragic accident, heartbreaking. I'll say this partially with the help of hindsight(BTDT), but if it's tight and there the plane sits, fly solo and light to a nearby paved field to pick up the passengers. The cause of these accidents often end up rather simple, not so much a rare mechanical failure at the worst time. Yes, two years from now the most likely cause will be reported.

The pilot was well liked and known, with a great family.

[Marauder]

We lost an experienced pilot at Beechtalk and the consensus is that was a trim issue......Just curious about those with electric trim if you have your trim breaker identified and have gone over procedures for this.......It sounds like pretty scary stuff , as for now , I am going to leave the trim off and manually trim for now.....

Alan - I don't have the trim breaker identified but do have a switch on the panel to turn it off. Anyone who has done an aborted landing in a Mooney with full flaps and trimmed for landing knows the initial pressure to overcome the nose up situation. That is a known situation.

A runaway trim could be more difficult to initially diagnose because how many of us look at the trim indicator or the trim light on the autopilot on a take-off roll to see if the trim is moving?

Hopefully they will determine the cause for the crash and help us better understand what we can do to prevent it from happening to us.

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[Danb]

Early in my flying career I had runaway trim in instrument conditions transitioning to approach into Myrtle Beach, I had no idea where my breaker was but in a dire state I reached over and my mind knew where it was and I pulled it I was very close to a stall,,I can see how it could happen after it occurred again the repair shop fixed it the first time they could not figure what was wrong..

[201er]

Early in my flying career I had runaway trim in instrument conditions transitioning to approach into Myrtle Beach, I had no idea where my breaker was but in a dire state I reached over and my mind knew where it was and I pulled it I was very close to a stall,,I can see how it could happen after it occurred again the repair shop fixed it the first time they could not figure what was wrong..

With a runaway trim or autopilot situation where it is imperative to regain control, I would start with shutting the master switch, stabilizing the plane, and only then go digging for the breaker.

[Alan Fox]

Mike , this was mentioned in the other site ,the problem being in actual on approach or lift off , you don't want to shutoff all the nav equipment ..Also it was mentioned when you hold the A/P disconnect , it will disable the trim (until you release it)  ..

[flyboy0681]

I've posted my harrowing experience here several times. Two years ago after takeoff the controls were getting real heavy and I was starting to descend (with all seats filled) and I had to pull back on the yoke by clutching it at the bend in my elbows. I then noticed the trim indicator was all the way nose down and I got on the wheel as if my life depended on it - because it did. Scared the living daylights out of me but the situation couldn't be explained at the time. Several weeks later the same thing happened and it turned out to be the trim switch, which stuck on occasion when applying nose down trim. The switch was replaced but now I always - always - check with my right hand that the wheel has stopped moving. 

 

After that episode I added a yellow marker to the breaker.

[Marauder]

Mike , this was mentioned in the other site ,the problem being in actual on approach or lift off , you don't want to shutoff all the nav equipment ..Also it was mentioned when you hold the A/P disconnect , it will disable the trim (until you release it) ..

Alan -- even if they were departing into IFR conditions, if my immediate disengagement technique didn't work (pull the breaker, hold the AP disconnect), I would certainly shut off the master to ensure the electric trim was off. I don't know the electrical failures of an electric trim, but I could see a situation where the typical shutoff mechanisms may be involved in the runaway.

The primary instrument for IMC is the vacuum powered attitude indicator. Any proficient IFR rated pilot certainly could maintain directional control of the plane solely by the AI without electrical power. Even in a glass cockpit situation, the vacuum powered AI or a battery backup AI is required.

I hope they do find the root cause of this accident.

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[PaulB]

I have a separate toggle switch on my panel for the electric trim. That accident really made me think about that switch but it does sound like there were other factors at plays as well

[PaulB]

Here's my switch. Above the prop.

[Alan Fox]

Chris I don't argue that the master will work , but it is not what I would consider the first on the list ...

[flyboy0681]

Chris I don't argue that the master will work , but it is not what I would consider the first on the list ...

 

My first course of action will be to disable the A/P through the CB since there will be little time to start futzing around trying to figure out which component is responsible for the looming disaster.

[AndyFromCB]

You all need to lift some weights or something. I've played around with full up and full down trim on my Bravo. Nothing that cannot be easily overcome with one hand at lift off and approach speeds. Seriously, go hit the gym.

[flyboy0681]

You all need to lift some weights or something. I've played around with full up and full down trim on my Bravo. Nothing that cannot be easily overcome with one hand at lift off and approach speeds. Seriously, go hit the gym.

 

I weigh all of 130 pounds. No amount of time in a gym is going to allow me to lift more than six pounds at a time.

[AndyFromCB]

I weigh all of 130 pounds. No amount of time in a gym is going to allow me to lift more than six pounds at a time.

 

130lb? You can fit two of you in me and still have enough weight for a gallon and half of avgas ;-) At my skinniest, 34inch waist and no fat at all, I weight in at 220lb. Eastern European tree trunk built. I wish I was lighter for certain sports I enjoy.

[Amelia]

This happened to me on liftoff one night long ago... I hit a ridge in a crossing runway pretty hard right at 65-70, may have blown the right tire then, and suddenly the controls behaved very strangely, reluctant to climb at all, despite full power. Identifying the problem was the scary part, while attempting to fly the airplane at night at an unfamiliar controlled field.With not knowing if I had a serious engine issue, or something structural very wrong, I aborted the landing very awkwardly. Later it was obvious that the takeoff trim that was right when I started the roll was now all the way down. No wonder it suddenly didn't want to climb. Oof. Embarrassing, to say the least. So, strength to manhandle the elevator control was one thing, but deciding what had happened and exactly what to do about it was an unexpected complication. Now I have a much higher index of suspicion.

[PTK]

I wouldn't kill the master switch either. That's...well...overkill!

The goal is to arrest the ap from controlling the airplane and revert it back to manual flying. This can be done via several ways or layers of things to shut off. The master switch is not one of them.

First, just pressing the manual/electric trim (split) switch on thr yoke will disengage the ap. Can also turn off the elevator trim switch to turn servo motor off. Finally can always pull the cb.

Also don't forget that in a misbehaving trim condition just grabbing control of the trim wheel will overpower the clutch. This is, or should be, in the preflight checklist.

Edit: it is my understanding that a runaway trim (servo motor running) is extremely rare. Even rarer than that is to have a runaway trim servo that's engaged to the control surfaces.

Along the same lines I had a recurring but random issue with the ap failing the self test. Ended up being an ailing manual/electric trim switch (split switch.) It was driving me nuts because it was random depending on the position of the contacts in the switch. After I discovered it playing with it would fix the problem. Tried contact cleaner but didn't really work. This told me it was more than just gummed up contacts. I replaced the switch when I had the yokes off for the leatherwork. Works like a charm! I took the old switch apart and it appears that the springs had indeed weakened causing it to be "lazy."

[aviatoreb]

After that episode I added a yellow marker to the breaker.

 

I have the same breaker cover - in red.  The most important of all breakers to cover.

[Piloto]

Easiest way to disable a runaway trim and A/P is to just press on the yoke trim switch. Pressing on the switch will disengage the A/P from the trim and control surfaces. If the trim servo still acting turn the trim switch off. The split trim switches on the yoke are wired so both have to agree on the same command. This prevents having a stuck switch on a runaway trim down or trim up condition.

On some instances during an ILS coupled approach an apparent trim up condition may happen when the power setting is too low and the A/P is trimming up to catch the GS. This may cause to trim the plane to be behind the power curve. So no matter how much power you add it will not arrest the descent. To overcome this press on the yoke trim switch and push on the yoke to avoid a stall and regain control.

An apparent runaway trim down may also happen if the A/P approach mode is engaged with the G/S pointer way down.

Runaway trim events by itself are rare but can happens. If the yoke trim paddle is dirty or gummed it can get stuck. I had this problem and fixed by cleaning it with contact cleaner.

José

[Marauder]

Chris I don't argue that the master will work , but it is not what I would consider the first on the list ...

I wouldn't hit the master first either, but if I tried the AP disconnect, trim & AP power switches without success, I wouldn't be continuing to try things. Kill the juice.

Reminds me of the story my friend told me about his prop breakage in an E. He told me that the vibration was so bad that he couldn't reach the mixture. He needed to run his left arm down his left leg to reach the mags. Sometimes you need to do whatever stops the problem.

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[flyboy0681]

One theme that is constantly running through this thread deals with the interruption of the trim as it's moving. In my case I didn't seriously start noticing anything wrong until it was at full nose down. So what I'm trying to say is that by the time you may notice it, it has more than likely stopped travelling and pulling this breaker and turning off that switch will be pointless. Being aware of the warning signs is much more important.

[wiguy]

The prelim is out, with a handful of pertinent details sprinkled in.

http://www.ntsb.gov/_layouts/ntsb.aviation/GeneratePDF.aspx?id=CEN15FA267&rpt=p