Elevator trim wire snaps mid-flight

dwalt

dwalt

Pre-takeoff checklist
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DWalt
This morning I did a short XC from KPDK to KGVL and back in an Archer II.

Shortly after takeoff, the EGT quit on me, but no biggie. Continued on to Gainesville without a hitch, did a touch and go, made a crosswind departure, and headed back towards PDK.

As I reached altitude and started reducing power, I began to adjust the trim accordingly. Well, the trim wheel felt a little tight and then suddenly spun freely and the cable snapped and became all wrapped up on the side of the wheel.

Had to keep some serious back pressure for the whole trip back. Then decided to slow the plane down and let the flaps help out. This helped level things out and required a lot less back pressure to keep the thing from sinking.

The approach/landing was certainly a knucklebuster since the last trim adjustment was made for climb, but I made it back fine.

This was my first real "situation" while flying, and just figured I'd share.
 
An out-of-trim Archer is definitely a handful!
 
That trim cable has likely been fraying for some time, and no mechanic has caught it. Not good at all. I wonder what the rest of the control system looks like?

Dan
 
Good job dealing with the issue.

On a related note, how many of us run the trim from full-up to full-down (or vice versa) during the preflight?

I ask because I didn't normally make this check, until one time a smarter CFI than my original was checking me out on a Mooney I was going to ferry. The trim felt normal except for the last couple of turns in the up direction. Closer inspection found a significant problem with the cable that connects the trimwheel to the jackscrew on the tail (moonies move the whole tail, not a trim surface). The weird feeling was the frayed section passing over a surface (roller or pulley I guess).
 
TMetzinger said:
On a related note, how many of us run the trim from full-up to full-down (or vice versa) during the preflight?
Click to expand...
Good point. I'm going to remember to add that to my list.
 
That is a progressive inspection failure. Cables don't just snap. They fray for years and months before, and get detected on annual inspection. Unless it was a Parker 51 inspection.....

Good job. Fire your maintenence provider. If it's a club plane, bring it up at the meetings.....and if they don't do something, find another club.....
 
Bruce, it is possible if a cable is kinked for it to appear ok under "general" inspection if it's wrapped around a capstan, and then fail catastrophically when it's under direct tension. I saw a film of that happening on a towing cable when I was in CG boot camp. Cost four deck hands their legs and two their lives.
 
TMetzinger said:
Bruce, it is possible if a cable is kinked for it to appear ok under "general" inspection if it's wrapped around a capstan, and then fail catastrophically when it's under direct tension. I saw a film of that happening on a towing cable when I was in CG boot camp. Cost four deck hands their legs and two their lives.
Click to expand...

Trim cables are little 1/16" things that seldom suffer any kinking. In any case, a proper inspection involves a look at the whole length of cable, for fraying, wear, corrosion, or other defects, and that will require running the trim though its travel to see it all. If one can't get a good look, one can still use his fingers to feel it. Broken wires within the cable will snag fingers long before the cable becomes dangerous. The load on the cable is far from it's breaking strength if it's not frayed or corroded.

It's just sloppy maintenance. I twice found elevator trip cables chafed halfway through, both times in Citabrias, where the installer had run the cables improperly and they had been chafing on the upper elevator cable. The first time was in a low-time, young airplane and the defect was created at the factory. The second time was in a much older, rebuilt Citabria. Both had undergone numerous 100-hour inspections (like 20 times in the first one!) in the time the cables were chafing and not once were they caught, which means that nobody was paying attention. No flashlight through the bottom inspection hole or anything.

And when a trim cable breaks in a Champ or Citabria, that trim tab will run away and flutter. The cables control it directly via a control horn. Surely it's worth doing the inspections right. The owner is paying for proper maintenance, after all.

Dan
 
Another reason to periodically run the trim all the way in both directions, to lubricate the jack screws. (Cessna 180/5, early 182, Mooney, etc.)

After you do that, take off the inspection cover and squeeze the grease bag that surrounds the jack screw.

This would have been good advice for Alaska Flt #261, where their jack screw lubrication schedule was once every 2500 hours.
http://www.youtube.com/watch?v=ODsGGLZeisM
 
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Dan Thomas said:
Trim cables are little 1/16" things that seldom suffer any kinking. In any case, a proper inspection involves a look at the whole length of cable, for fraying, wear, corrosion, or other defects, and that will require running the trim though its travel to see it all. If one can't get a good look, one can still use his fingers to feel it. Broken wires within the cable will snag fingers long before the cable becomes dangerous. The load on the cable is far from it's breaking strength if it's not frayed or corroded.

It's just sloppy maintenance. I twice found elevator trip cables chafed halfway through, both times in Citabrias, where the installer had run the cables improperly and they had been chafing on the upper elevator cable. The first time was in a low-time, young airplane and the defect was created at the factory. The second time was in a much older, rebuilt Citabria. Both had undergone numerous 100-hour inspections (like 20 times in the first one!) in the time the cables were chafing and not once were they caught, which means that nobody was paying attention. No flashlight through the bottom inspection hole or anything.

And when a trim cable breaks in a Champ or Citabria, that trim tab will run away and flutter. The cables control it directly via a control horn. Surely it's worth doing the inspections right. The owner is paying for proper maintenance, after all.

Dan
Click to expand...

Somewhere I saw a picture of a control cable being misrun and sawing it's way through a piece of structural tubing.
 
It's also a good idea to check the flight controls before starting the engine. I was once feeling out the yoke on friend's Mooney while he was doing someone else. The sound of his left aileron chafing caught both our attention and we looked at each other. I swear you could not feel it in the controls but could definitely hear it. I'm sure he's had his mechanic look at it by now (you reading this RR).
 
In that case, Jay, I think the Mooney (like the Socatas) uses pushrods for aileron and elevators. And you can still have lubrication issues with pushrods (and corrosion too). I think the only cable driven things in Mooney flight controls are the trim system.
 
TMetzinger said:
Somewhere I saw a picture of a control cable being misrun and sawing it's way through a piece of structural tubing.
Click to expand...

Something like this:

HangarNoise1.gif


Note the notch in the channel above the pulley, cut by the cable after 84 hours in this state of misassembly.

A more classic case of fraying:

FB_04_11-9.jpg


Dan
 
I've only had one come up broken, a flap cable in a 172. It had corroded under the follow up cable attachment.
 
TMetzinger said:
Somewhere I saw a picture of a control cable being misrun and sawing it's way through a piece of structural tubing.
Click to expand...

True, I think you're thinking of the bonanza that made the rounds. That one ****ed me off due to the fact that someone had wrapped tape around the tube to protect it:mad2:
 
How many of you PA 28 owners actually require the A&P to remove the tail cone to clean and lube the cable drum and jack screw in the elevator trim?

It needs to be done at least once a year, really clean the actuator, and re-lube it.
 
TMetzinger said:
In that case, Jay, I think the Mooney (like the Socatas) uses pushrods for aileron and elevators. And you can still have lubrication issues with pushrods (and corrosion too). I think the only cable driven things in Mooney flight controls are the trim system.
Click to expand...

No cables on Money trim, tubes to the jack screw. Only cables I recall are with the auto pilot.
 
I've found many of the PA28 and PA 32 series ships with frayed stab. trim cables at the electric trim servo. We have been finding more of the older PA46 series ships with the same problem too. There was a Meridian not long back that broke a rudder cable because it was improperly routed in the belly during a wing replacement.

Someone hasn't been inspecting there aircraft very well if the cable ends up failing.
 
TMetzinger said:
Thanks... I thought there was a cable there. Must be mistaken. Is there a chain or something for the jack screw?
Click to expand...

The trim jack screw is connected directly to a torque tube that goes into the cockpit. The trim wheel drives the torque tube via a small enclosed chain. All the control surfaces in a Mooney are controlled via push-pull tubes. There is no cables or pulleys. Other than lubricating the rod ends there is no maintenance required. All the tubes are made of aluminum so corrosion is minimum or none.
A very safe and reliable system

José
 
kmead said:
I've found many of the PA28 and PA 32 series ships with frayed stab. trim cables at the electric trim servo. We have been finding more of the older PA46 series ships with the same problem too. There was a Meridian not long back that broke a rudder cable because it was improperly routed in the belly during a wing replacement.

Someone hasn't been inspecting there aircraft very well if the cable ends up failing.
Click to expand...

Probably because the trim drum likes to slip and no one wants to ever fix it:mad2:
 
This would have been good advice for Alaska Flt #261, where their jack screw lubrication schedule was once every 2500 hours.
Click to expand...

The lubrication schedule wasn't the issue with Alaska; it was mechanics using the wrong lubricant, and falsifying the work cards. It was also the pilots spending too much time testing and troubleshooting the trim when they should have got on the ground.
 
DouglasBader said:
The lubrication schedule wasn't the issue with Alaska; it was mechanics using the wrong lubricant, and falsifying the work cards. It was also the pilots spending too much time testing and troubleshooting the trim when they should have got on the ground.
Click to expand...


This.

As pilots, if you find yourself with what you think is any control issues DO NOT 'test' it in flight. You don't need to go to the stops or check full travel to confirm there's something abnormal. Just fly it slow and get it on the ground. Once on the ground now you can check and troubleshoot to your hearts content.
 
> Somewhere I saw a picture of a control cable being misrun and sawing it's
> way through a piece of structural tubing.

Cessna mfg'd a CJ2; and maintained it for years, without discovering a mfg defect
that misrouted a brake cable. Slowly, trip after trip, it finally sawed thru the primary
electrical bus.
 
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DouglasBader said:
The lubrication schedule wasn't the issue with Alaska; it was mechanics using the wrong lubricant, and falsifying the work cards. It was also the pilots spending too much time testing and troubleshooting the trim when they should have got on the ground.
Click to expand...

The lubrication schedule was part of the original problem. And yes, as in Swissair 111, they should have gotten it on the ground.

Swissair 111 was on fire. Instead of putting it on the ground they started dumping fuel because they were over landing weight.
 
Piloto said:
The trim jack screw is connected directly to a torque tube that goes into the cockpit. The trim wheel drives the torque tube via a small enclosed chain. All the control surfaces in a Mooney are controlled via push-pull tubes. There is no cables or pulleys. Other than lubricating the rod ends there is no maintenance required. All the tubes are made of aluminum so corrosion is minimum or none.
A very safe and reliable system

José
Click to expand...

Thanks! I must be misremembering the aircraft type... I'll have to go dig out the logbook because I remember writing the issue into the log entry explaining the .2 hours of time with no landings.
 
And an "oh god yes" to the discovery of a flight control issue while in the air. To me that's a get-it-on-the-ground-right-now situation, second only to a fire or structural issue.
 
TMetzinger said:
Thanks... I thought there was a cable there. Must be mistaken. Is there a chain or something for the jack screw?
Click to expand...
IIRC, the trim wheel is connected to a gear box with chain and sprockets . Gearbox truns type tubes. Tube attaches directly to the screw box that moves the whole tail.
 
TMetzinger said:
And an "oh god yes" to the discovery of a flight control issue while in the air. To me that's a get-it-on-the-ground-right-now situation, second only to a fire or structural issue.
Click to expand...

It's funny...obviously, my first priority was getting back on the ground safely, but for my first real "situation" while flying (alone, in particular), I didn't feel the least bit nervous.

I was focused and considering all possible scenarios, but didn't feel fearful at all - which is much different than I would have ever expected. Maybe it's because I knew it was not any kind of catastrophic failure, but it was weird looking back on how calm I was nonetheless.

Anyone else notice the same thing when anything has gone wrong with their flights? I assume it's just adrenaline or tunnel vision or something lol.
 
Tom-D said:
How many of you PA 28 owners actually require the A&P to remove the tail cone to clean and lube the cable drum and jack screw in the elevator trim?

It needs to be done at least once a year, really clean the actuator, and re-lube it.
Click to expand...


I removed the tail cone and watched the A&P service everything on my plane
 
rainsux said:
> Somewhere I saw a picture of a control cable being misrun and sawing it's
> way through a piece of structural tubing.

Cessna mfg'd a CJ2; and maintained it for years, without discovering a mfg defect
that misrouted a brake cable. Slowly, trip after trip, it finally sawed thru the primary
electrical bus.
Click to expand...

Something wrong with that. The cable is a part of the grounded aircraft structure, being attached to flight controls and the like. The primary bus is positive, and any contact with it by any grounded part instantly causes a short that cannot be overlooked by anyone. In fact, the 180/185 series have their battery boxes right next to the elevator cables, and if a mechanic replaces a positive battery cable with one just a little longer, it can contact the cable. One the insulation wears through, which doesn't take long, there's a massive current flow through that cable that will either burn it right off or weld the elevator hinges solid. Again, not ignorable.

Dan
 
rainsux said:
> Somewhere I saw a picture of a control cable being misrun and sawing it's
> way through a piece of structural tubing.

Cessna mfg'd a CJ2; and maintained it for years, without discovering a mfg defect
that misrouted a brake cable. Slowly, trip after trip, it finally sawed thru the primary
electrical bus.
Click to expand...

After five years of cirrus maintenance I was the first mechanic to open up the pannels and do the required inspections and servicing inside of several wing pannels...
 
TMetzinger said:
Good job dealing with the issue.

On a related note, how many of us run the trim from full-up to full-down (or vice versa) during the preflight?

I ask because I didn't normally make this check, until one time a smarter CFI than my original was checking me out on a Mooney I was going to ferry. The trim felt normal except for the last couple of turns in the up direction. Closer inspection found a significant problem with the cable that connects the trimwheel to the jackscrew on the tail (moonies move the whole tail, not a trim surface). The weird feeling was the frayed section passing over a surface (roller or pulley I guess).
Click to expand...

I do and I never see anyone else do that. I guess I just go the extra mile, I want to be sure all of it is OK and moving, not just look at it and think OK it is trimmed for takeoff, let's go..... you know?
 
Hey, that was you, huh? I heard it on the radio. Glad it worked out ok.
- Russ
 
write-stuff said:
Hey, that was you, huh? I heard it on the radio. Glad it worked out ok.
- Russ
Click to expand...

Yessir it was - and would you believe this: the tower declared emergency for me - never once declared it myself - and now the FAA is asking for lots of nice paperwork and info.

Makes you not want to give them heads up on stuff like this - all I told them was "just a heads up - we're planning on landing but may need to go-around" because of the issue.
 
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dwalt said:
Yessir it was - and would you believe this: the tower declare emergency for me - never once declared it myself - and now the FAA is asking for lots of nice paperwork and info.

Makes you not want to give them heads up on stuff like this - all I told them was "just a heads up - we're planning on landing but may need to go-around" because of the issue.
Click to expand...

Do you understand why control system failures are required to be reported?
 
dwalt said:
Yessir it was - and would you believe this: the tower declared emergency for me - never once declared it myself - and now the FAA is asking for lots of nice paperwork and info.

Makes you not want to give them heads up on stuff like this - all I told them was "just a heads up - we're planning on landing but may need to go-around" because of the issue.
Click to expand...

Well a flight control system malfunction is a required NTSB report.

If you'd had an emergency that didn't require a report (rough running engine) I'd doubt there would be any paperwork at all.
 
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