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My trim system failed yesterday!

pierre smith

Well Known Member
As I levelled off at 2500' yesterday, I needed some down trim so I pushed the button...WHOA!!...it pitched UP!

The trim indicator bars worked but not the real trim, so I immediately landed. On the ground, I looked over my shoulder at the trim tabs and heard the trim motor running, both up and down, but no motion of the two tabs, so I got out and walked back there.

Grabbing a trim tab, I moved it up and down, the other one accompanying it!

After I removed the tail fairing, the two cables were still attached to the bellcrank but when I reached in there, it moved up and down, when it shouldn't, since it's a pivot point for the trim servo.

Crawling in the tailcone, we saw the AN-4 bolt, castellated nut and a couple of washers lying close to each other! We searched and searched for a cotter key back there but never found one! We put the bellcrank (F-1095B, page 11-9) back in place and this time, cotter-keyed the bolt, since it's a pivot point, and tried the trim and it worked normally.

My gut instinct tells me that there never was a cotter key installed and this airplane has 5+ years and over 500 hours on it and that the nut, then a washer, then the bolt, all progressively fell out over the years and had never been checked during condition inspections!

For all of you -10 guys, remember, it's a rather difficult area to inspect because it's underneath the supporting structure and you probably have to crawl back there to really check it over well.

The airplane, nevertheless, stayed quite controllable, although with considerable forward pressure to hold the nose down, since the tabs had moved downward when I first pushed the "down" button, instead of up, because the whole assembly moved toward the front of the airplane, pulling the tabs down, and the pitch up.

Whew! Yes, I did say a "Thank You" prayer:)

Best,
 
My Goodness Pierre!! NOT FUN!! Glad you are OK and thanks for reporting this. I'm going to check my -4 for all attachments. I'm in middle of inspection time. This gives me added incentive to be cautious & focus on what I'm looking at. You've done us all a great service.

Thank you & happy flying,
 
Whew!

Glad you're safe! Sobering lesson, thanks for sharing.

+1

Congrats Pierre! You dodged a large caliber OOPS. Much easier hearing from you how it happened than reconstructing the pile of aluminum without your help! At least, the fellas at the NTSB use that phrase...

Carry on!
Mark
 
I've added this particular item to my "checklist" just to be sure its not missed during an annual. I think if I were you, I'd probably be looking at the rest of the control attachements just to be sure there wasn't a similar condition somewhere else.

As for the "Waddington Effect", I agree a post maintenance flight test is never a bad idea. It was required in my old job when any task was performed that could effect flight characteristics where ground testing could not ensure proper operation (flight control rigging for example).

However, some folks may interpret this to mean (and take literally), "if it ain't broke don't fix it". The whole premise of aircraft maintenance and inspections is not to wait till something breaks to fix it. Things wear out over time and most failures show evidence of pending failure, preventave maintenance is a critical part of aircraft safety and reliability!
 
I just did my annual. In that area I use a mirror and a flashlight. I then take pictures with my iPhone at all the angles needed to see everything by just reaching in from the back. I can then review on the spot or at home for confirmation that all is well. Pictures work great in many areas. Reaching in to confirm jamb nuts are tight is a must to.

It is nice to know that the tabs did not flutter. :eek: thanks for testing:D

Glad it worked out well, bet the heart was sure racing.
 
USB camera

I bought my wings in the QB stage from another builder. I wanted to check everything out so I bought a USB camera with a 7m cord on the auction site. It has LED lights and works great. It takes photos and video that can be recorded on my laptop. It was from a US seller and got here is 5 days. Total delivered cost $26.

I was able to check everything I felt I needed to. I used a piece of pex tubing in a couple places to run the camera through so I could extend it to areas I couldn't just push the cable to. I even ran it into my engine to inspect. It started giving me a yellow picture and blurry and I realized it was in the oil.

I am very satisfied and believe it will be a great way to inspect and keep record of the inspections. For $26, one of the best tools I have and potentially the most important.
 
Not quite related to this post but equally important

Some of you may recall a move called "Doc Hollywood". It stands out in my memory because of the a few scenes. The plot goes like this. Micheal J Fox, a young doctor driving across the country to a new job in California gets distracted while driving through a small town and hits a fence. He is cited and the judge learning he is a doctor sentences him to community service in the down. His fancy Porche roadster damaged in the accident is taken to the only auto repair shop in the hillbilly town (no offence to those hillbillies on this site). The auto repair will take a few weeks. A few weeks later the roadster is fixed and the auto repair guy hands the keys over. He also hands a box of parts as well and says "We don't know where these go, but here they are anyway".

What sticks in my mind about this is that when doing your inspection and you are removing screws and nuts and washers. Keep track of everything (including tools). If you end up with an extra item or a missing tool it is a very unnerving feeling.

It is truly amazing what can be left behind or omitted during a build or inspection.

Food for thought.
 
Flutter ?

Is it unreasonable to assume that a trim tab coming completely loose on the elevator would induce catastrophic flutter failure?
 
Is it unreasonable to assume that a trim tab coming completely loose on the elevator would induce catastrophic flutter failure?

I think it depends on circumstance. If you are decending from altitude, near or at Vne, and it happens, probably not an unreasonable assumption at all. However, many have "tested" these machines well beyond Vne on purpose or accident, but probably not with a disconnected trim tab.

PS - glad to here things worked out Pierre. A credit to your experience and knowlegde of your machine.
 
WOW Pierre! And you and Jenny just got back from Key West. My friend, someone is looking after you. And congrats on knowing your plane, and knowing what to do. Thousands of flight hours certainly helped in this case.
Tom
 
Ditto!

WOW Pierre! And you and Jenny just got back from Key West. My friend, someone is looking after you. And congrats on knowing your plane, and knowing what to do. Thousands of flight hours certainly helped in this case.
Tom

Tom expressed my thoughts precisely. And I appreciate you sharing it with us, Pierre.
 
Thanks for the reminder, Pierre. Very glad to hear that you're okay. We can apply this to anything we're flying.
 
Great lessons

Thanks Pierre - this is one of the best reasons for having this site.

I got my Cherokee out of annual one time, did my preflight which included manually moving the stabilator and it didn't seem to move through its full range. After much searching, I found that the large vacuum hose under the panel has been displaced by the mechanics, and was blocking the control column. Lesson - every time someone works on your airplane A LOT of extra caution is needed. Inspect thoroughly then circle the field at altitude until you're sure everything is working properly.
 
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Great story, Pierre. An issue like you had is one reason I do stop-and-go's instead of touch-and-go's in the -10.

-Rob
 
Nightmares?

I keep thinking about the return trip from Key West, in IMC, the last flight before the one where the trim system failed. Perhaps the trim system failed DURING that flight and we simply didn't know it!

It was on the next flight that I discovered the failed system, with a more forward CG since I was solo.

All of you guys need to check every single control system from a point of origin to the final attach point, during every condition inspection. Look at one rudder cable from the pedal to the rudder and all points in between. Do the same for the elevator pushrods...inspect every attach point and jamb nuts at each point all the way from the stick to the elevator.... remember the -10 that recently lost elevator control during his flare?

Do the same for all the controls and especially the engine controls.

Best,
 
I normally move all the control surfaces on my preflight, but from now on my walkaroung will include checking the trim tabs for movement, instead of just moving the elevators.

Thanks for posting, glad you are OK.
 
This is one reason I do my conditional inspections as a progressive rather than all at one time. I usually take at least two months to complete the inspection. this way it makes it easier on my back and joints and I am able to be more thorough while inspecting each section. I do the inspections during the week so that I can fly on the weekends. I believe that most experimental guys tinker with thier planes all of the time anyway so why not inspect smaller areas when there is tinkering downtime?
 
I like the idea of a progressive inspection plan. Keeps the plane available without a longer down time. Does anyone have "a plan" that seems to work well?
 
Glad you're O.K. Pierre! Am I remembering correctly that there are now castellated nuts that have the nylon stopnut material in them? Belt and suspenders for those critical fasteners...I'm doing my condition inspection now and might have to find a few of those...

Thanks for the heads up in general and glad you shared this with us.
 
All of you guys need to check every single control system from a point of origin to the final attach point, during every condition inspection. Look at one rudder cable from the pedal to the rudder and all points in between. Do the same for the elevator pushrods...inspect every attach point and jamb nuts at each point all the way from the stick to the elevator.... remember the -10 that recently lost elevator control during his flare?

Do the same for all the controls and especially the engine controls.

Best,

I make the control systems a major inspection item at every condition inspection also. I grab the pushrods and twist and verify that they hit a hard stop both ways as the rod ends hit the edge of the bell crank. This will verify good jam nut installation and no loose bearings. I once saw a DAR catch an aileron pushrods wing root bolt missing a nut on an aw inspection. That's scary (although not as scary as if it had been an elevator pushrod). I also have found an auto pilot pushrod with loose jam nuts that could have twisted itself off either end, which could have ended in a very bad day with jammed ailerons. Control connections and the big fan in front are my biggest concerns. Got to keep the pilot from sweating too bad.
 
Thanks for sharing Pierre and we are glad that you are OK.
Annual coming up this week so I will surely check those as well.
 
+1 for VAF and Pierre

I must confess that I missed this pivot bolt on my just-finished first annual inspection. It is hard to see without either crawling WAY back in the tail cone, removing the entire elevator trim assembly, or (what I did last night) using a borescope to check it. Mine was correctly installed and in place but I must once again give kudos to this site and its honest and open contributors (only $25/year, are you kidding me?!!).

My thoughts on this event and the other recent (and more serious) control-system disconnect incident: I am going to make a list of every single control system linkage, bolt, rod-end bearing, jam nut, pivot bolt, etc. in the entire plane - according to where it is accessed (there really aren't that many). At every single oil change, I will open one or more of these access panels and look things over - such that I put an eyeball on the entire list in a year. This might be overkill but for a new plane it seems like an easy and simple way to effect a PM schedule. Since I wouldn't be touching anything unless something is amiss, I hope not to be susceptible to the Waddington effect.

I would be happy to post/share my list of control linkages for anyone else to use/comment on/improve.
 
Made my day!

Bryan, you just made my day. I told my wife, Jenny, the other day, that if only one guy checks his airplane's trim system and all the other controls, it would make the few minutes it took to make the post worthwhile.

I'm reminded of the approach Kahuna and the team take to inspect each other's airplanes...a great way to go about it.

We're family here and these kinda findings really ought to be shared.

Best,
 
I would be happy to post/share my list of control linkages for anyone else to use/comment on/improve.

It would be great to have a single drawing (maybe with a few supporting detail drawings) of all the control system connections on each model of Van's aircraft.

PS: maybe Van's could produce this for us ;)
 
True

It would be great to have a single drawing (maybe with a few supporting detail drawings) of all the control system connections on each model of Van's aircraft.

PS: maybe Van's could produce this for us ;)

True, but it would only take an hour or so with the plans to make an exhaustive list, with part numbers, access points, etc.
 
We're even

Bryan, you just made my day. I told my wife, Jenny, the other day, that if only one guy checks his airplane's trim system and all the other controls, it would make the few minutes it took to make the post worthwhile.

I'm reminded of the approach Kahuna and the team take to inspect each other's airplanes...a great way to go about it.

We're family here and these kinda findings really ought to be shared.

Best,

Well, we're even then, because what you posted woke me up to a connection that I neglected to look at partly because it is out of sight and partly I guess because I didn't (duh) figure that a failure in that mechanism would be all that critical. I guess a person would have to be awfully darn sure that his linkage was perfect to not at least wonder about it when reading about an experience like yours. I'm a new enough plane owner that I'm not cocky in the least, so I go check it - especially when it's so easy to look at that one. I certainly have confidence in my plane, and have never found an oops (yet) but I know some better builders than I am who have - as a famous guy once said: Trust but verify (myself).
 
Me too. A recent post about ingesting an airbox bolt made me wonder, did I safety wire them? Fortunately I took lots of photos during the build, and was able to find one showing the safety wire in place.
 
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