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Stabilator & miscellaneous related stuff

Here's the latest Service Bulletin on the stabilator.

Much of the information presented here following this new development will now be obsolete. i will not remove anything for now; something may still be good reference.

Piper Service Bulletin SB-1189 Stabilator Horn Assembly Inspection.

Piper Service Bulletin SB-1189-88372 Kit, Torque Tube replacement.

FWIW DEPARTMENT - tube kits availability so-says-Piper, Feb to Apr 2011; but they've lied about other things too :). I've been waiting since Sept 2010 for tube kits.

So there you have it folks, why would anyone dare tackle the SB-1189 without parts?


To see photographs of the cracked torque tube horns mentioned below by Hans, open this link informative article by Denny Haskins.


This concerns all Comanche models; the torque tube horn forging.

[Now a not-so] RED HOT ISSUE - from Hans Neubert, read below.


Since many Comanche owners don't visit either site, we need to have volunteers at each airport that has Comanche aircraft to help them fill out spare questionnaires.

Let me give everyone the reasons for the questionnaire in the first place.

1. Collecting and maintaining the database on horn inspections and findings has been insufficient. Creating and mailing in the form is much more concise and current with the information needed.

2. In the draft phase, Piper/FAA were talking about repetitive inspections every 100 hours. My response was that 100 hours was unnecessary and potentially damaging to the airframe.

With enough data to justify, I'll be arguing to get 1000 hours or 10 years, whichever comes first.

3. I want to make sure that those that have made the inspection, that they get credit for it, retroactively.

4. If the data supports the conclusion, I would like to eliminate certain models, except for a one-time inspection, unless done already.

5. For those that have replaced their horns, that they get credit for that, and not be required to inspect again until the time/hour limit in #2 is reached.

How much data do I need? I estimate that there 4660 Comanches registered, world wide. I need to have at least 1000 inspection questionnaires in order to make a presentable case. Anything less, and we are at the will of the authorities.

So, do your part, and get the information on every Comanche at your airport, and send it in. There are more cracked horns out there.

Be assured, since a cracked horn is an airworthiness issue (not maintenance, like the corroded torque tube), an AD will come. I will do my part if Comanche owners unite and do their part.


The Comanche Stabilator has a few issues; here is a list and links. This may not be complete, it is from my research. If you are aware of something that should be here for the good of all, please Contact me.

Airworthiness Directive 74-13-03

Airworthiness Directive 76-19-07

Airworthiness Directive 94-13-10

Piper Service Bulletin 411A Stabilator Torque Tube Bearing Block Attachment Fitting Rivet Replacement.

Piper Service Bulletin 464A Inspection of Stabilator Torque Tube Bearing Block Attachment Fitting Rivets. This is remedied by installation of the Piper Kit 760-835 as pictured below.

Special Airworthiness Information Bulletin - CE-04-88

Piper Service Bulletin SB-1160 Stabilator Torque Tube Assembly Inspection.

Piper cover page - Torque Tube Replacement Kits.

Very informative article written by Denny Haskins of Redlands, CA. This really covers the horn issue well.

There is a "stabilator flutter" movie floating around on the internet. Scary!

I'm in the process of writing another methodology, this one for the stabilator: lots of color photos, do's and don'ts, replacing the bearings, horn forging treatment, trim drum clearance, setting the stops, and balancing. It will probably include the loan of the special tools to make life simple. Why? If you attempt this operational procedure using the Service Manuals as your reference you'll find that confusion sets in because of the need to jump around the SM to different sections. My writing will have it in one place. Stay tuned, pending the FAA action expected!


760-835 Hi-Shear Rivet Replacement

Per the photo above - $195 for one airframe including the NLA 28216-000 plates [owner produced].

Save a bunch; buy this kit.

The above photo shows the content of the Hi-Shear Rivet Kits; however this is not how Piper packages their kits. Their P/N 760-835 "HI-SHEAR RIVET REPLACEMENT" as described in their literature states materials required for one fitting; the kit I provide, pictured above, is for all four fittings including the cover plates; i.e. one kit for the entire airframe, not four kits @ $176.98 each [w/o cover plates] as you would from Piper. This is Piper's recommended method; not an AMOC. The prevailing wisdom is to do all four at one time, rather than as necessary. If you're tempted to repair only the loose one[s], would logic not suggest the others will follow?

Another small mention; at the February 2009 Laughlin, Nevada fly-in we discovered one 400 Comanche with loose rivets in the tail cone bulkhead. That condition was discovered during the inspection for loose stabilator bearings and/or loose rivets in the mounting blocks.


760-835 Hardware Only

760-835 hardware requirements
760-835 hardware requirements, bagged

Per the photos above; $125 adequate for one airframe


760-835 Cover Plates

View from inside
View from outside; stabilator removed

These photos show how to determine whether the Piper method of compliance has been accomplished. You're looking for the riveted cover plate as the above photos illustrate.


More stabilator trivia

Illegal Repair

According to the Piper Service Manuals the repair to this stabilator is illegal. Repairs are limited to replacement of complete skin sections, ribs, hinges, spars, etc. and paint. No filler materials are allowed on all movable tail surfaces. This photo shows a patch to the outboard aft area. See sections 4-47 and 4-48 [ref SCSM] Structural Repairs.


Click here for a compilation of information; some trim mechanism details and recommended torque values for the stabilator mounting bolts.


AS RECEIVED

Click on the photo above for a photo of the nearly-finished product.

Click here for one process for treatment of the torque tube and horn.


SL-667A - Stabilator attachment bolts. Here you’ll find an interesting note about the correct torque value for the twin on page 3.

 

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