FAA Description of Airworthiness Concern: Main Landing gear tie strut

[tcraft]

Extracted from cover letter from FAA:

"You are probably aware of this recent incident
involving a failure of a BC-12D MLG tie strut due to corrosion. An old
1978 Taylorcraft Aviation Corporation Service Bulletin attempted to
address this problem, but the FAA has decided to issue an ACS to remind owners and operators of the importance to check their structure for potential
corrosion related problems. I know with on your involvement in the
Taylorcraft community you of all people appreciate the need to keep on top
of aging aircraft issues. If you will, please share this ACS as
appropriate with your club members.

At this time, the FAA has not made a determination on what type of
corrective action (if any) should be taken. The resolution of this
airworthiness concern could involve an Airworthiness Directive action, a
Special Airworthiness Information Bulletin, or the FAA could determine
that no action is needed at this time. The FAA’s final determination will
depend in part on the information received in response to this ACS. As
described in the ACS, we consider this airworthiness concern as “Information”. We are also sending this ACS to AOPA, the TC holder and
other Taylorcraft type clubs.


ACS Document attached (We converted to .pdf format)

[steve canyon]

We just discovered a crack all the way across the bottom of the left main tie strut on our BC- 12D in around same place as the FAA ACS. Took the right side off and after sanding off paint found holes rusted through in the same area . I just became an owner of this airplane so someone dropped the ball on this because there were not drain holes . Our A&P repaired it by sleeve on inside and out . kind of a dumb design . bolted on the bottom and welded in solid at the top. If anyone knows why it was done that way I'd like to know.

[3Dreaming]

I have heard stories from someone who spoke with the engineer that designed the gear, and he supposedly gave a very long and detailed explanation of why the tie strut is done that way.

[waltermrich]

Would you mind posting photos, if you have any , it is a concern for most of us.

[steve canyon]

Hope this Helps

[steve canyon]

Here's a couple more

[PA1195]

Nice catch on the corrosion and repair. It's a credit to the A&P for actually repairing and not just demand a replacement gear. I have a similar repair from a dent on mine. In addition to internal and external corrosion that tubing can be subject to impact from gravel and excessive side loads. Any exposed metal should be promptly cleaned and primed/painted.

My suggestion is to blow through the drain hole and confirm air without debris exiting the tubing cluster under the bungees. I DON'T know if all three gear tubes are open at the upper cluster. I'd then spray preservative oil into the diagonal drain hole and upper cluster and position the gear to let it coat the interiors. There's likely another hole under the brake stuff above the axle where the two outside clusters meet. If there coat the tubing with preservative.

Edit: I believe the bottom bolt arrangement is for adding a support plate for wheel pants. The outboard end of the axle is threaded to accept a fastener for the pants.

Gary

[waltermrich]

That looks like and excellent splice, would you know where your A&P got the tubing for the splice and what size it is ? Thanks for posting

[3Dreaming]

I have repaired some by replacing the lower end with the next size larger streamlined tubing using 1/2 of the splice and locating it near the top cluster.

[steve canyon]

My A&P got 2 pcs. of streamline 4130 tubing 2 ' long each , 1 slightly smaller than original tube ID and 1 slightly larger than out side from Aircraft Spruce for $85. it was enough to repair both sides . I spent quite a bit of time trying to find some streamline tube same size as original with out any luck. We replaced bungees with winter ones since we had it apart and they needed replaced . I uploaded a tool I made for installing bungees. It worked real well.

[bluerooster]

The one on my right gear was repaired by welding in a replacement strut. I was wondering why it was larger than the left side until I found the write up in the logs.

[waltermrich]

Has any one heard of making a cable to tie the landing gear strut on each end incase of failure, the landing gear struts are definitely a concern on our 77- 78 tear old aircraft , I recently found rust on the lower few inches of the landing gear strut on mine , A repair will be in order with a sleeve over the lower end of the strut, but would that be considered a major repair, Any feed back, have to discuss this with my A&P and any examples of repairs would certainly help.

[Hank Jarrett]

The reason for making a welded attach at one end and a bolted attach at the other is if welded at both ends the tube can be loaded in bending as well as tension/compression. With a bolt at at least one end the bolt acts as a pin and allows rotation eliminating any bending loads. If the tube doesn't get loaded in bending it can carry much more load for the same size tubes. It is the same reason most bridge sections are attached both pinned joints instead of being solid. On bridges they also add in links to allow for expansion and contraction of long sections but our gear isn't long enough for that to be as much of a problem. You would NOT want the support tube welded at both ends!

Hank

This problem is another reason we REALLY need a gear fixture. Minor axle misalignment can cause lots of problems on landing. Toe and castor of the axle can be critical.

[waltermrich]

Thanks for chiming in did not know that.

[Robert Lees]

The other reason for a bolt at the bottom of the tie strut is somewhere to attach the wheel spat bracket.