Possible Rudder Airworthiness Directive

[Steve Pierce]

There has been a lot of talk about a possible Airworthiness Directive being released following the January10, 2022 NTSB Aviation Investigation Report on the Structural failure of part # 40622 rudders which are used on most all of our rag and tube Piper aircraft. This report highlights five case of failed rudders, all five had an aftermarket beacon or strobe installed on top. The details are here:


NTSB AIR-22-02
https://drive.google.com/file/d/18yK...ew?usp=sharing


I had a chance at Oshkosh to speak with a friend of mine who happens to be the Director of Aviation Safety at the NTSB and is a Piper owner himself. He showed me the rudder post from one of the failed rudders and I could see pits and the crack emanating from it.




Then in December Piper issued Service Bulletin 1379 addressing the cracking rudders which brought up discussions of an Airworthiness Directive. My opinion at the time and my friend at the NTSB agreed that given the amount of time that had taken place between the incidences and the present and the lack of a Notice of Proposed Rulemaking it was very unlikely.


Piper Service Bulletin 1379
https://drive.google.com/file/d/16Kq...ew?usp=sharing


Fast forward to last weekend when Airframes Alaska posted a video via email and on Facebook stating that there is an Airworthiness Directive coming out and they discussed that the early rudders made from 1025 mild steel were the effected rudders, not the rudders made from 4130 chrome-moly steel that Piper changed to according to drawing 40622 on June 3, 1974.They went on to say that their rudders are made of 4130 and would eliminate the AD. This stirred up a lot of questions about where this information about an emanate AD had come from. I asked that question on Facebook on Saturday evening.





Sunday afternoon I was informed that the FAA had contacted Airframes Alaska inquiring about their stock of rudders because this AD was coming out. I immediately reached out to my contact at the NTSB who was not aware. Then I called Dakota Cub and they had been contacted some time ago asking if there was a way to identify their rudders from Piper rudders. Pieces were starting to click.


Monday morning I called my contact at AOPA who is a Super Cub owner and he had not heard any talk of a forth coming AD and when he started digging around found out no one at AOPA could find anything either.


I did a Google search and came across an FAA Aviation Concern Sheet dated 9/4/2020 and made a phone call to a contact I have in the FAA that works on these types of things. He could not tell me if there was an AD coming out but he could tell me how they do a risk analysis on these types of things and flight controls are high up on the list. It doesn't seem there will be an Emergency AD but I am betting money the Notice of Proposed Rule-making is coming soon. These usually have a 60-80 day comment period, after which the FAA has to read and respond to. This can take a month or more and given backlog on Ads I wouldn't be surprised if it took longer.


FAA Airworthiness Concern Sheet
https://www.faasafety.gov/files/noti...A-18_REV_D.pdf


So my thought process went to an Alternate Method of Compliance. Members of ShortWingPipers.org had discussed the use of inserting a piece of 3/4” 4130 tubing inside the 7/8” rudder post. This takes a little cleaning out of the weld burn through of the rudder steering arm and would also require some rosette welds to make the two tubes one and eliminate the two tubes working inside of each other. I also spoke to Clyde Smith (the Cub Doctor) who's idea is to cut a hole in the top of the rudder post and run a short piece of tubing past the top hinge where the cracking has occurred and rosette welding that in, capping the hole in the rudderpost and recovering the top of the rudder.


Over the weekend I started getting texts, phone calls etc. in response to the Airframes Alaska video. In two of those cases it seems two of the owners have dodged the bullet so to speak. One owns a 1976 model Super Cub so he would have had a4130 rudder from the factory and the other one had a new FAA/PMA'd rudder installed at rebuild about 10 years ago. All FAA/PMA'd rudders are4130 chrome-moly. There has been no PMA granted for a mild steel rudder. I contacted Airframes Alaska, F. Atlee Dodge, Dakota Cub and Univair about identifying their rudders in the field if logbook entries were not available. The only one that is identifiable is Dakota Cub, they have a square hole in one side of the steering arm.




From discussions with the FAA I was told when they looked back into the history of this issue they found12 cases of cracked rudders and several involved major damage to the aircraft. Piper built 45,000 airplanes with this rudder of which about 20,000 are still on the US registry. It is my intent to relay here everything I have learned on this subject and I hope that those commenting to both this thread and the Notice of Proposed Rule-making will be educated with these facts. I feel we need to respond and hopefully avoid this Airworthiness Directive but be aware of the issue at hand and be diligent in the inspection of this area.

Thanks for taking the time to read all of this and educate yourself.

[JWE]

Thanks for posting this, Steve.

[fishhook]

Who would have known corroded parts could have cracks start and break eventually? Not like there is frequent inspections done on aircraft or anything.
In all honesty, lets take the 12 that failed, and triple or quadruple it for unreported or ones taken out of service during annuals, that is still a very very small percentage against 20k+ of these out there. Its age catching up to these birds, the older they are the higher the chance of corrosion or fatigue, and people will immediately start jumping on the bandwagon of "bad design" or "flaw".
Anyways thanks for the insight, sounds like an AD is coming out possibly in the next 6 months or so.

[Hardtailjohn]

" I feel we needto respond and hopefully avoid this Airworthiness Directive but beaware of the issue at hand and be diligent in the inspection of thisarea."

This line says it all. Thanks, Steve!
JH

[OLDCROWE]

If you had a rudder replaced, say during a rebuild, how do you confirm if it's constructed of 4130 or mild?

[Steve Pierce]

If you had a rudder replaced, say during a rebuild, how do you confirm if it's constructed of 4130 or mild?

If it was a used rudder you don't. All new PMA'd rudders are 4130.

[cubdrvr]

It would be interesting to know the age of the rudders that broke. Did they all have a top mounted beacon.....and was it the beacon that caused the breakage. Could a beacon produce similar damage to 4130?
Top sleeve seems like an appropriate compliance.
Thanks Pierce ! Mine is old steel.

[SJ]

Pierce, thanks for taking the time to do this. A lot of folks wouldn’t bother. I appreciate that about you.

sj

[dgapilot]

All we can do is monitor the Federal Register to see if an NPRM is ever issued. If one comes out we need to get EVERY owner and mechanic that works on fabric Pipers to send in comments. The internal sleeve is likely the best fix for this issue short of buying a new rudder.

Even if an AD is never issued, anytime your rudder is uncovered, do a detailed inspection of it. You can buy an endoscope from Amazon for about $50 or less so you can get inside and look around. Just pushing on the top of the rudder with about 10 lbs of force will give you an idea of the integrity of your rudder.


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[Steve Pierce]

So I experimented with two rudders this morning. One was an old Univair 4130 rudder which was TIG welded when manufactured and the other was an original mid 50s rudder of a Pacer which would have been oxy/acetylene welded . I used a piece of 3/4" OD x .049" wall 4130 tubing as a sleeve. It slid right into the 4130 TIG welded rudder. On the old Pacer rudder I shot some Corrosion X inside the rudder tube and some grease on the 4130 liner tub and lightly taped the tube in all the way to the top of the rudder as my daughter held the rudder. Nice and tight and I can remove it if I needed to. I don't see the two tubes working inside one another and wearing like I was told by an engineer that wanted to see rosette welds to make the two tubes one.

Per my conversation with folks at AOPA today I am seeking ideas for an AMOC (alternate means of compliance) if and when the NPRM (notice of proposed rulemaking) comes out for an AD on this.

I have also requested the accident/incident reports on the 12 rudder cracks that the FAA has identified to see if these were all 1025 steel rudders and if all had rotating beacons installed.

[BC12D-4-85]

To save weight what about driving in a liner just long enough to sleeve the weak area? Retain it with external rivets that would mark the rudder as being reinforced?

Gary

Edit: P/N 40622 rudder print of dimensions and location of some fractures.

Edit: Or rosette spot welds as noted earlier.

[bob turner]

Either way, this would save big bucks. If Steve can get the AMOC in a final AD so we can all use it, we would owe him big time! Weight considerations aside, this would be at least as good as a new 4130 rudder.

[dgapilot]

So I experimented with two rudders this morning. One was an old Univair 4130 rudder which was TIG welded when manufactured and the other was an original mid 50s rudder of a Pacer which would have been oxy/acetylene welded . I used a piece of 3/4" OD x .049" wall 4130 tubing as a sleeve. It slid right into the 4130 TIG welded rudder. On the old Pacer rudder I shot some Corrosion X inside the rudder tube and some grease on the 4130 liner tub and lightly taped the tube in all the way to the top of the rudder as my daughter held the rudder. Nice and tight and I can remove it if I needed to. I don't see the two tubes working inside one another and wearing like I was told by an engineer that wanted to see rosette welds to make the two tubes one.

Per my conversation with folks at AOPA today I am seeking ideas for an AMOC (alternate means of compliance) if and when the NPRM (notice of proposed rulemaking) comes out for an AD on this.

I have also requested the accident/incident reports on the 12 rudder cracks that the FAA has identified to see if these were all 1025 steel rudders and if all had rotating beacons installed.

Sliding a tube in and bolting or otherwise not welding would save the cover. Personally I would prefer to run a sleeve 3 to 6” either side of the upper hinge and rosette welds. Less weight and permanently fixed.


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[Steve Pierce]

A short section of tubing could be used. 3/4" x .035" wall weighs .2673 lbs per foot and the rudder is a tad over 4 feet long so your gain is 1 lb. which won't hurt the W&B on my Super Cub at all.

[bob turner]

Any of those for the AMOC, if indeed they do an AD. Whatever they will approve. Even the rosettes will not require much fabric work if you TIG them.