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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:
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.
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.
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.
Last edited by Steve Pierce; 03-08-2023 at 07:39 AM.
Thanks for the update on this. I am in the middle of a full restoration, and am considering just buying a new rudder to solve any issues down the road.
I may be all wet but it seems to me the rudder cracking at the or slightly above the post hinge seems to be linked to the beacon being on the top of the rudder and the aerodynamic stresses put on the rudder from it. Remove the beacon, inspect the post for cracks , pitting and corrosion and call it a day. I could be wrong but I would be willing to bet not just the 5 you mentioned, Steve, but all the cracked rudder posts had beacons on them when they cracked. AD should be pretty simple in my opinion.
If installed, remove beacon. Inspect rudder post for cracks and corrosion. Determine if it is original mild steel or aftermarket 4130 (or after 1974, 4130). If 4130 reinstallation of beacon is permitted, if mild steel, beacons or other items are not allowed to be placed on top of rudder post. If it is desired to place a beacon on the rudder post they might include a reinforcing procedure or something as suggested by Clyde, where you rosette weld a 4130 piece of reinforcing steel into the post for the top foot or so or even the whole length. Probably have to keep it as thin as possible to not affect weight and balance too much. I suggest IF/WHEN there is a comment period for an AD we flood them with something similar to make it as simple as possible or they will do something stupid like require all rudders to be replaced (exaggerating, I don't really think they would do that) or something equally stupid and expensive.
Could you repeat, or provide a link to, the discussion of which planes have "early rudders made from 1025 mild steel"? Is it all short-wings?
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.
seems to be linked to the beacon being on the top of the rudder
The beacon sure doesn't help, but the rudder balance forward of the hinge does concentrate the load in the area where the failures occured. Thankfully no tombstones yet and hopefully there'll be a solution that doesn't involve re-covering the rudder. Thanks for the continued investigation Steve...
Looking at the NTSB information and the horsepower listed for all the planes whose rudders failed only the PA-18 could come from the factory with the horsepower listed. It is likely all of them were modified by STC to much higher horsepower than they were originally built with. This would have obviously increased the aerodynamic loads on the rudder, especially at higher speeds with the drag of a beacon on top. You are correct that there is a concentration of loads where the failures occurred with the wires, rudder hinge ang the leverage force from the wind on the beacon all concentrating right there just above the hinge. Any small pit or corrosion in that area could easily lead to a crack and failure.
How difficult is it going to be to replace that rudder post?
I really do appreciate the effort you put into keeping us informed. How would I go about determining if this affects me, either by paperwork, serial number or visual inspection of my rudder?
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Possible Rudder Airworthiness Directive
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Originally Posted by walt.buskey
