C-172 Airframe Questions

[RFlyer]

I went to look at a C-172 for sale over the weekend. I basically did a walkaround and found a couple of things and was wondering how costly they are to put right, but even more, whether they are signs of a plane that may not have been maintained well.

- Elevator Outboard Hinges

If you hold the elevator on either side of the outboard hinges and try to move them up and down they should have no play in them. On this model, both sides had some play so some work is needed to put them back.

- Aileron Actuator Arms

I'm referring to the little arms that are visible when you stand under the aileron and look upwards with the aileron pushed fully up. I've always tried rotating the little arm to check the play in it and usually get a crisp 'clack' sound as it reaches the points of maximum rotation. Over the years I've come to consider this a normal response. On this plane I had to actually look at the arm to see that it was moving and there was no sharp clack sound - just a kludgy halt - which makes me think it's gummed up or something.

Overall the airframe only has 2200 hours on it and the engine was overhauled 200 hours ago (in '06). The plane has been maintained by getting its annual inspection and kept in a hangar for the decades he has owned it. The owner claims the AME is picky so I'm wondering how things like that hinge and actuator arm could have been missed - I'd be surprised if they could get that way between annual inspections. Or am I just being picky?

[qa guy]

The aileron rod ends should not have any play, but they should rotate freely.(sometimes you will get some lateral, but should be no raidal play) The elevator bearings and bushings should only take a few hours.
I would highly recommend getting a proper pre-purchase done by an AME who knows small pistons. So many owners make the same mistake. look carefully for cracked cylinders. especially if they were replaced from 04-07.

Also, just because an annual was done recently it doesnt mean that the airplane is airworthy. The owner can defer just about anything he wants. So the guy who inspected it did not necessarily miss anything. Thats one thing that sucks about putting your name in an owners log who defers everything.....it makes you look bad!
What is very important is who did the engine o/h? How are the log entries? Is it just "annual inspection c/o" year after year?

[RFlyer]

The aileron rod ends should not have any play, but they should rotate freely.(sometimes you will get some lateral, but should be no raidal play)

Right - that's what I meant to say - relatively easy to rotate with a firm metallic click at the stopping point.

I would highly recommend getting a proper pre-purchase done by an AME who knows small pistons

I'm trying to decide if it's even worth proceeding to that step and definitely plan on getting an AME to have a close look at the final candidate.

Question re: your comment on checking for cracked cylinders - is there something about products in the year range you specify?

Thanks for your reply!

[crazy_aviator]

The owner can defer just about anything he wants. So the guy who inspected it did not necessarily miss anything. Thats one thing that sucks about putting your name in an owners log who defers everything.....it makes you look bad!

WHATS WRONG is that very few AME s will write down every pilot deferred discernable snag or deficiency after the maintenance release as the CARS implicitely state.

[iflyforpie]

Yes. Here in Canada we don't say 'aircraft airworthy' anymore when we sign a release. Heck, you can sign a release for just about anything, as long as anything outstanding is referenced in the release or the limits of the release are self-evident (an extensive sheet metal repair on a removed wing or the overhaul of a hydraulic pump for example). I don't have any problem writing 'blah blah problem, owner advised, no action taken'

WRT the problems that Cessna has, yes, play in elevator hinges is a no no. In fact, I don't think I've ever come across a bad elevator bearing on a 172 without removing the elevator first (lots on Cherokees owing to the centralized and highly stressed location of the bearings).

Elevator re and re should only be a couple hours and the same for the bearings. They are oilite bearings IIRC so replacement shouldn't be too much. The needle bearings I just put on the rudders for our Skymaster were over $40 each.

With aileron push-pull rods, it is tough to deduce anything by rotating it. About all it tells you is that the bearings are free (good thing), but it doesn't really give an indication of wear.

I grab the trailing edge and gently move it up and down while I have my finger on the rod or bearing, listening and feeling for play. This is what we are most concerned about.

Cessna only gives free-play figures for the trim-tab in the maintenance manual, but IIRC AC43.13 gives you a formula where you divide the chord of the control by a figure and you arrive at the allowable free-play. Don't quote me on this but I believe it winds up being about 1/4" total for a 172 aileron (which translates into a very small amount of play in the bearings).

Aileron control-rod bearings are around $40-$50 each (should do all four at the same time to get the desired fix..... at least it isn't a Mooney where there are zillions! ) and shouldn't take very long to re and re and rig, because you aren't disturbing the system (just set the ailerons to the flaps like they were before or count turns).