Runaway Trim

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pelmet
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Runaway Trim

Post by pelmet »

"C-GGWG, a Piper PA-44-180 Seminole aircraft operated by the Sault College Of Applied Arts And Technology, departed Sault Ste. Marie, ON (CYAM) on a local training flight. While the aircraft was in level flight at 5000 feet, the pilots used the electric elevator trim and experienced a trim runaway to full nose up. The pilots were unable to overpower the aerodynamic force load and had to reduce
power to regain control of the aircraft. As the aircraft slowed down, the pilots were able to manually trim the aircraft and pulled the circuit breaker for the electric trim. An emergency was declared, the aircraft was given priority and landed without further incident.
The aircraft had an issue with the trim the day before which was deferred with a note to not use the autopilot. The autopilot has been deactivated along with the electric trim servo and the aircraft will be flown to a maintenance facility for further troubleshooting."

Reducing power is a good idea. Steep bank may help as well.
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PilotDAR
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Re: Runaway Trim

Post by PilotDAR »

Yes, pull it into a tight turn, and balance out the control forces until you get get it resolved. I've had a similar experience in a C206, and its scary!
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oldtimer
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Re: Runaway Trim

Post by oldtimer »

What ever happened to the big red button on the steering wheel that is there to shut off power to both the electric trim and the autopilot. Every airplane I have ever flown with electric trim or an autopilot with attitude control has one.
Even the little Seminole should have an emergency checklist that covers a runway trim.
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pelmet
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Re: Runaway Trim

Post by pelmet »

oldtimer wrote:What ever happened to the big red button on the steering wheel that is there to shut off power to both the electric trim and the autopilot. Every airplane I have ever flown with electric trim or an autopilot with attitude control has one.
Even the little Seminole should have an emergency checklist that covers a runway trim.
How many seconds to full nose up trim. How many seconds to reach over(while fighting the aircraft to maintain control) and grab the checklist. You might just want to know what to do prior to the trim runaway.

I remember the Beech 99 having an extremely difficult to pull CB for the trim. My plan with a runaway that could not be stopped by normal means was...Gang Bar Down. Then worry about the other stuff.

Maybe it was the wrong plan but the checklist item of pulling the CB would have full nose-up trim by the time you figured it out.
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Illya Kuryakin
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Re: Runaway Trim

Post by Illya Kuryakin »

pelmet wrote:
oldtimer wrote:What ever happened to the big red button on the steering wheel that is there to shut off power to both the electric trim and the autopilot. Every airplane I have ever flown with electric trim or an autopilot with attitude control has one.
Even the little Seminole should have an emergency checklist that covers a runway trim.
How many seconds to full nose up trim. How many seconds to reach over(while fighting the aircraft to maintain control) and grab the checklist. You might just want to know what to do prior to the trim runaway.

I remember the Beech 99 having an extremely difficult to pull CB for the trim. My plan with a runaway that could not be stopped by normal means was...Gang Bar Down. Then worry about the other stuff.

Maybe it was the wrong plan but the checklist item of pulling the CB would have full nose-up trim by the time you figured it out.
Still....
The question remains....what about the wheel mounted "big red button"?
Illya
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pelmet
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Re: Runaway Trim

Post by pelmet »

Illya Kuryakin wrote:
pelmet wrote:
oldtimer wrote:What ever happened to the big red button on the steering wheel that is there to shut off power to both the electric trim and the autopilot. Every airplane I have ever flown with electric trim or an autopilot with attitude control has one.
Even the little Seminole should have an emergency checklist that covers a runway trim.
How many seconds to full nose up trim. How many seconds to reach over(while fighting the aircraft to maintain control) and grab the checklist. You might just want to know what to do prior to the trim runaway.

I remember the Beech 99 having an extremely difficult to pull CB for the trim. My plan with a runaway that could not be stopped by normal means was...Gang Bar Down. Then worry about the other stuff.

Maybe it was the wrong plan but the checklist item of pulling the CB would have full nose-up trim by the time you figured it out.
Still....
The question remains....what about the wheel mounted "big red button"?
Illya
It has been a long time.....what does the big red button do? We had no autopilot
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confusedalot
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Re: Runaway Trim

Post by confusedalot »

Suspect the big red button is an anachronism for split switch systems found in certain transport category certified systems? One part of the switch is the actuator, the other the trim brake? I would think that pipers are not required to go through that sort of certification process.
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Chuck Finley
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Re: Runaway Trim

Post by Chuck Finley »

The plane that I fly has a "reverse" circuit breaker collar installed on the trim CB for easier disconnect.

Also has the yoke switch that should de-energize
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Re: Runaway Trim

Post by gwagen »

Usually the big red button is the a/p disconnect, which if the trim is being run by the a/p that will stop the issue.

If the plane doesn't have an autopilot but does have electric trim, you generally won't have this red switch.

Though in my limited experience, in pipers the standalone electric trim rarely works and if it does, usually gets hung up halfway through the travel.

Probably just the old cans I had to fly......

Whenever I climb into something old and unfamiliar, I do not use the autopilot. I don't trust autopilots older than me, I'd much rather hand fly.

That said, I've witnessed more issues with newer units than older ones.
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pelmet
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Re: Runaway Trim

Post by pelmet »

if opposite trim switch is not working.....Gang Bar down for the Beech 99/King Air(turns all electrics off). No trim wheel on board.

For the Piper Seminole(the subject aircraft).....master switch off. Then manually trim.

As can be seen on the thread, by the time the discussion is over on what to do, you have full trim deflection.
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Re: Runaway Trim

Post by PilotDAR »

During my time flying the Siai Marchetti 1019 (which had some weird control forces) I noted with some interest that the electric trim seemed to be the only pilot pitch trim control. The "procedures" sections of the flight manual made no mention of manual trim, so I simply planned the "pull the breaker" approach to a trim runaway. To my surprise, after I left the plane, I was told, and late shown, that if you pulled away one of the velcro'd military styled fabric inside panels, there was a trim wheel hidden in there! Funny they would not placard on that fabric: "Remove for trim wheel access"!

In my days flying the 310, I enjoyed a very reliable auto pilot, though my later experience showed me to always suspect auto pilots. In fairness, the failings could probably be attributed to less than ideal maintenance, but I was the pilot, not the maintainer. I was sent to fly a maintenance check flight in a Bellanca Viking, a charming, and very agile plane. Later in the flight, I switched on the auto pilot for a check (CAVU weather). Heading bug set on course, heading select selected, auto pilot on, and wow, what a sharp right roll! That's not right! More methodical, do it again - same outcome. Okay, it's not right, how wrong is it? Left engaged, it would roll through at least 120 degrees angle of bank (where I stopped things, it would have kept rolling). That's enough of that = snag. So the boss sends me back up with the avionics tech, and his box of special screwdrivers. Now the Viking, just like a Piper Aztec, has a steel tube structure, so the tube goes from the windshield ceiling to the glareshield (to the firewall engine mount, I suppose). The avionics tech seems less than interested in being there, and perhaps not convinced my snag is real. So, I brief what I'm going to do, including my selections, what will happen when I turn it on, and a count down of sorts. Well, as the plane crisply rolled right through 90 degrees, I remember seeing the tech's white knuckled hand firmly grasping that tube, and his painfully saying "Okay, I believe you, I believe you!". Then the screwdriver turning of potentiometers started in earnest with my promise not to let it roll that far again. 'Could not tune it in, the whole controller went back to the factory.

I prefer hand flying....
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pelmet
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Re: Runaway Trim

Post by pelmet »

PilotDAR wrote: The "procedures" sections of the flight manual made no mention of manual trim, so I simply planned the "pull the breaker" approach to a trim runaway.
How easy is it to find an individual CB to pull when almost all your strength is being used to push or pull and it is poor viz requiring an instrument scan. CB's in some aircraft are in difficult to get to locations. Master off(at least in the daytime) is probably easier in most small aircraft as the artificial horizon is still working and the procedure works quickly...because you know where the switch is and is easy to turn off. It may not be the best idea for all situations though.
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goingnowherefast
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Re: Runaway Trim

Post by goingnowherefast »

The aircraft in question was likely flown by a student and instructor. One can man handle the controls while the other looks for the CB.

My time in old king airs is limited, but I can still remember where the switches were to turn off the main trim motor. It was engrained in my muscle memory, primary for this reason. I can't figure out why they never made an actual trim wheel for those old planes.
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pelmet
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Re: Runaway Trim

Post by pelmet »

goingnowherefast wrote:The aircraft in question was likely flown by a student and instructor. One can man handle the controls while the other looks for the CB.
Still takes time to find it, controls may have to be switched, etc. wasting critical seconds....and doesn't cover the single pilot scenario.

Notice this statement from the report using the plural word for pilot...

"The pilots were unable to overpower the aerodynamic force load and had to reduce power to regain control of the aircraft."

Not a good time to say....You have control.

Master off early on a nice day.
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Re: Runaway Trim

Post by 3genav »

oldtimer wrote:What ever happened to the big red button on the steering wheel that is there to shut off power to both the electric trim and the autopilot. Every airplane I have ever flown with electric trim or an autopilot with attitude control has one.
Even the little Seminole should have an emergency checklist that covers a runway trim.
The seminole (at least both Sault College ones do) does have the big red button, and has the checklist.

Something along the lines of holding the AP disconnect, or holding the wheel if need be, then pulling the CB.

I remember there was a check we did before we taxied to ensure the autopilot disconnect would stop the trim if we had a trim runaway. Granted, GGWG had issues with its autopilot for the past year or so, so maybe that had something to do with it?
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Re: Runaway Trim

Post by oldtimer »

It has been my experience that, except for some weird airplane systems, there are only two types of pitch trim systems. One is a mechanical trim tab on either one or both elevators and adjustment is made with a trim wheel in the cockpit. This system may also use the trim tabs as a servo tab, as in the Navajo. Electric trim is a servo attached to the elevator pitch trim cables that require electrical power to stay engaged and this is how the autopilot trims the airplane. Emergency procedures are to eliminate power by overpowering trim and then selecting pitch trim off. Retrim with the cockpit trim wheel, which should have been rotating. The second system is the trimable horizontal stab which usually requires electric trim unless it is a fabric Piper Cub or Cessna 180. If the airplane has the trimable stab and electric trim, it has to have a quick disconnect system such as the big red button on the control column to remove power and allow the selection of the standby trim system. Failing that, if the control column trim switches are selected opposite to the undesirable trim motion, the trimming should stop. That total electric system also requires a trim-in-motion wooler to warn the pilot. In the Metro series airplanes, it takes an average of 24 seconds to accomplish full trim motion of the trimmable stab from full up to full down or vice versa. IMHO, if electric trim is optional in the Seminole and is deferrable, then it has to be a trim tab system with a cockpit trim wheel. Normally, the trim wheel will not move when the electric trim/autopilot are engaged and it should have, not a circuit breaker, but a cockpit switch of some sort that will stop trim motion until the pilot can do one of two things. Either manually retrim as in the trim tab system/older Piper/Cessna 180 or have a second electrical trimmable stab system. Any one remember the clicking sound made when manually trimming a Cessna 180. That was a system to put a restriction in the system to prevent unwanted movement and to alert the pilot if that did not work.
Solution to the problem is to know the airplanes systems, how they work and what to do if they do not work as advertised.
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Re: Runaway Trim

Post by co-joe »

We had a really fat medic at one company that all the pilots referred to as "runaway trim". He'd get out of his seat to go get something out of the back and you'd see that trim wheel rolling like it was trying to leave...
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Re: Runaway Trim

Post by GyvAir »

co-joe wrote:"runaway trim"
OK.. so we're not supposed to laugh at fat jokes and all that, but that's a great nickname!
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Re: Runaway Trim

Post by Broken Slinky »

. Finley wrote:The plane that I fly has a "reverse" circuit breaker collar installed on the trim CB for easier disconnect.

Also has the yoke switch that should de-energize
I also installed the breaker caps on essentials like trim. I'm in the habit of running my hand across them as I do my checklist so I remember what row and position they're in.
They're colour coded caps with the same colour marked in my emergency checklist. In the even I have a complete brain fart or need assistance from a non-pilot, I can figure out the one to pull relatively easy.
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Re: Runaway Trim

Post by digits_ »

Broken Slinky wrote: I'm in the habit of running my hand across them as I do my checklist so I remember what row and position they're in.
So YOU are the one that makes all those labels fade :mrgreen:
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