The problem
This problem is not catastrophic and develops over time. It is noticed by checking the slack in the elevator trim at the elevator. It is something we all do during preflight; wiggle the trim portion by the elevator. Well, mine moved more than desired if a small amount of pressure was applied. It kind of clicked between two extremes. It was within tolerance last year, but this year it needed to be fixed. By the way, this problem is not noticed inside the plane at all. The problem in my case was with the actuator inside the horizontal stabilizer which a linkage attaches to. The actuator changes the direction of movement and translates a cable/chain movement to moving the linkage connected to the trim.
Here is a picture of how the cables make it back to the actuator. The actuator is labeled 6.
Here is a picture of the overhauled actuator which was eventually installed inside the horizontal stabilizer:
How to solve it?
- Start with A&P
- Read Service Manual and Parts Manual
- Check with Cessna Pilots Association or Mike Busch from Savvy Owner Seminars
- Check with A&P again
- Try to find parts or documentation myself
- Discuss and work with A&P to finish the repair (help where possible)
Start with A&P
First step was to talk with the A&P about it. He mentioned that it was probably the actuator and was going to be expensive to fix. Like $1500+... Ouch! But these large expenses seem to happen when you own a plane, and hopefully more than one problem does not happen in one year. I talk about some of my past operating expenses here and past thoughts on general plane maintenance here. This year during the annual it was time for this one. We looked up inside the elevator inspection port and confirmed the actuator was where the slack was occuring.
Read Service Manual and Parts Manual
I think it is valuable to look through and try to understand the repair myself. I am an engineer and also like mechanical things, so it is not too bad. I often do not understand it completely, but I get the general idea.
You can get some on-line parts and service manuals for free here. If your year is not available here, I would still suggest getting the manuals. When I got my manual pdfs, I did not know about the free manual website, so I purchased my parts manual from McCurtain Technology Group. The PDFs or CDROM of the PDFs are around $20 which seems reasonable. I also got my O-470R manual from Continental, but this is more expensive: $80. Maybe that one is not so necessary, but I like having them. I also found MA-4-5 Carburator overhaul instructions on-line and Marvel-Schebler/Facet/Precision Airmotive Carburator Handbook and Troubleshooting techniques PDF for looking at carburator questions.
So I found information on my problem in the parts manual on Page 201D, and my part number is 1260074-1. The area which talks about my problem in the service manual is Page 9-7. It talks about how to check the allowed free play in the system as well removal and installation procedures.
Check with Cessna Pilots Association or Mike Busch
The three main resources I like to use for figuring out complicated or expensive repairs are:
- Cessna Pilot's Association forums
- Cessna Pilot's Association member technical support requests
- Ask Mike Busch from Savvy Aviator Seminars (I took the course)
In this case, I started with the CPA member technical support request. If you don't own a Cessna, I am sure there are similar groups to ask for help from. Within a day, I had a good start to figuring out my problem. Evidently, CPA had done an article in the October 2006 issue of the CPA magazine on my problem and how to overhaul the actuator. The magazine is even available on-line to members. $183 in parts and some labor. Perfect!
Check with A&P again
So then I went back to the A&P to discuss what I found. I really like that my A&P appreciates my working with him this way. I think over time I am getting better at digging, and it is saving him time in the end. He can spend his time actually fixing the problem. If I don't get it quite right, I have some ownership in the fix so that makes me feel better too.
So this time, one of the A&Ps remembered doing the actuator overhaul repair in the past and said it was not easy. The key hard part was drilling a hole in a round bearing. It is like drilling a hole off center in a ring made of hardened bearing material. When I saw what was necessary, it did not look easy. Maybe with the right equipment it would be, but without it would be hard. They were willing to do it, but they warned it could be a fair amount of labor time.
Check for new parts
So how much would it be to get a new part, used part, or overhauled part, or repair a part??
Then I start with iWantCessnaParts.com for checking on new aircraft parts. They have a good method for showing if parts are superceded by another part number. They also have good prices as far as new parts go, but mine was $1500. Ouch! Maybe I could get one used, repaired, or have the A&P repair it.
Check for used parts
There is a long list of used parts places available in the Cessna Pilots Association member section.
It was also possible to find used parts on-line with these two methods:
I found it for $250, but getting a used one could have a similar problem as the one I am replacing, or it could be somewhere in between for tolerance. So there is some risk there. I think you check with them and send it back if it is not acceptable, but you do incur the shipping costs.
I also asked on the CPA forums for advice on the trim actuator, and people mentioned getting the actuator through eBay and possibly getting an overhauled or repaired part.
Checking on Repaired or Overhauled parts
The Aviation Group was mentioned for getting an overhauled elevator trim actuator. It appears that actuators are their specialty. I mentioned the part number and they could get me one for $450 plus shipping and return of my core including the 8130-3 approval form. Not bad... I also found Robair Repair and they could do the repair for $500. When I had to replace my spinner bulkhead at my last annual, a repaired part worked well.
So I decided to head this route. It was similar price to if my A&P did it, but it was by somebody very familiar with doing the work, and it was a guaranteed price.
Finish up with the A&P
Now it was time to finish up. A plan was in place. I had the A&P finish taking out the actuator, I ordered the part from The Aviation Group, and watched things come together. I didn't swing any of the wrenches for this repair since it wasn't an owner maintenance item, but I watched it at many steps. This is the way I like to work and my A&P is ok with this as well as owner obtained parts.
Summary
In the end, I saved quite a bit over a new part and ended up with what I think is the best solution. It did take a bit of time, but I understand my plane better and understand the expense better. I think it falls in line with the concepts I learned at the Savvy Aviators Seminar. If you don't have time for this kind of watchful eye, I think Savvy Aircraft Maintenance Management might be a good idea. I haven't tried it, but it sounds interesting for people without the time or interest in understanding maintenance.
/Brian
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