172's and 175's Defect Report

[wingnut]

I know this doesn't apply to the majority here, but thought it would be another good place to advise of problem I recently found on a 175 with tailwheel conversion.
Horizontal stab forward spar was almost completely broken at the center lightning hole; the flanged hole that the elevator trim cables pass thru, between the 2 attach bolts that attach the forward spar to the fuselage bulkhead. Movement, when grabbed at either end of stab and push up/down, was very notable. A quick removal of the horizontal to vertical stab fairing, and flashlight, and you can see the lightning hole. This particular example has 2 cracks, radiating diagonally (10 oclock and 5 oclock as viewed from aft). Each crack was over an inch long, extending to the upper and lower flanges of the spar. This was scary.

Edit to add this; this spar was also buckled severely, and I suspect the buckling occured first from improper ground handling, and this allowed subsequent flexing during handling and/or turbulence which cause work hardening and cracking

There is NOT an AD on this.

Cessna has a service bulletin they consider mandatory SEB94-8, which addresses this exact issue, and includes all 175's and 172's thru 1986, whether or not they have been modified. They also note that improper ground handling can cause this problem.

In my Malfunction/Defect Report I recommended an AD for visual inspection at annual. This is an area that should be looked at anyway, and therefore would not/should cost anything for a quick look. The purpose being to make people aware, so they will look closer for cracks.

NOTE: The above SB does NOT include any 170's. The forward spar on the 170 doesn't have the 2.5" diam lightning hole like the 172's/175's, and would likely never have this problem, but all the more reason to be mindful of who, and how, your aircraft is being handled.

[170C]

Thanks for the "heads up" information Del. I, for one, will be taking a look at mine shortly. Certainly makes the installation of the tail handle accessory more pressing. Plan to get mine installed at annual in April.
Frank

[GAHorn]

As Del mentions..the stabs are somewhat different.

Perhaps it might be helpful to have a better idea of exactly where the cables pass-thru?

Here's the two stab illlustrations. For the curious,..where does the cable pass, Del? The cable routing in both IPCs do not clearly show. (click on pic to enlarge...then click on it again to further enlarge)

172/175 Horiz Stab click to ENLARGE

170 Horiz Stab

EVERYONE:
From Day ONE of my C-170 ownership, Cleo Bickford enthusiastically condemned using the vertical and horizontal tailfeathers to manuever the airplane on the ground. Pushing/Pulling on the Vertical will lead to expensive damage, and one of the most common failures is a small attach-bracket which holds the leading edge of the dorsal-fairing on A/B models. (See that small screw on the fuselage, just ahead/below the "NO PUSH" placard below? That screw holds the small, dorsal inner-attach-bracket which is commonly broken.)

When moving the tail left-or-right...Cleo suggested using the TIP RIB (item 45 in Fig 14 above) of the fwd stab spar to push horizontally on the tail...OR...use your butt alongside the fuselage. DO NOT PUSH or pull on the vert. stab.

BEST SOLUTION for fwd/aft movement: B.A.S. TAil-Pull Handles (and use your butt alongside the fuselage.)

[wingnut]

For the curious,..where does the cable pass, Del?

On the 172's and 175's the trim cables pass thru a 2.5" diameter flanged lighting hole, which is both vertically and horizontally centered between the forward spar attach bolts.

On the 170's the trim cables pass thru a .75" diameter non-flanged hole, close to the left forward spar attach bolt. The 170 spar does not have the large lightning hole in the center, which makes it much less likely for it to buckle.

[GAHorn]

...On the 172's and 175's the trim cables pass thru a 2.5" diameter flanged lighting hole, which is both vertically and horizontally centered between the forward spar attach bolts....

You are referring to the area shown for items 6 ?? (No hole is depicted, but you mean to say one does exist, correct?)

[wingnut]

...On the 172's and 175's the trim cables pass thru a 2.5" diameter flanged lighting hole, which is both vertically and horizontally centered between the forward spar attach bolts....

You are referring to the area shown for items 6 ?? (No hole is depicted, but you mean to say one does exist, correct?)

Yes, there is a 2.5" hole, although the IPC doesn't show it. The Cessna SB shows this much better. If anybody wants a copy, I can email, or maybe George would like to add it to the library. I can't even post pictures , so I'm not even trying a file

[Bruce Fenstermacher]

Files are much easier to post than pictures Del.

[wingnut]

Files are much easier to post than pictures Del.

Bruce,
You don't know my level of patience (lack of) with my computer, and my computer skills . But I'll try in the morning, when I'm fresh . IF...........

If it okay to post 172/175 info on this site? Do ya'll want me to? I knew there were a few, some, one or two?? that may benefit from the info, but wasn't sure if it was appropriate for this site.

[Bruce Fenstermacher]

Del we have several members who own a 172 or 175. I say post away.

[c170b53]

Del you're on a distinguished path, enlighten as many as you can. I've found those confident in their work are most likely to share their experience and knowledge. Good on ya !

[GAHorn]

Cessna Single Engine (Service) Bulletin SEB 94-8 is copyrighted and therefore may not be posted here.

TIC170A Members may access pertinent info in the MX Library.

[Indopilot]

I posted on the MX spot but this seems to be where the action is. I have found a crack radiating upwards from the .75 hole in the 170 spar so they are not immune from this problem as well. This whole area including the fuselage attach bulkhead has alot of potential for cracks with all the motion of the elevator bellcracnks flexing things. Well worth taking the time to look around with a bright light and mirror, especially while someone goes stop to stop with the elevator. While you are there also take a close look at the areas where the tailwheel steering pulley mounts bolt to the lower fuselage bulkhead. Brian

[ptporebski]

I've got an early model straight tail 172 that I have been upgrading and definitely appreciate the information posted here. I joined the Association since the 170 & 172 straight tails share so much in common. This organization has been the best money I have spent on the plane. I am really glad that I stopped by the tent at Sun-N-Fun and spoke with Bob & Carol Coates. Looks as though I need to look at my horiz stab. Thanks again for the information.

Pete P.
1959 C-172
(Red Headed stepchild to C-170)

[tomrw]

Thanks for posting this alert. I'll check my '58 TD and my '56 trike model 172. I WILL send photos if I find a crack.