Rudder Failure - NTSB Notice 2252

[Penguin]

I did a search, and it doesn't seem like this has been mentioned yet. AD in the works? I received this email this morning, as I am sure a bunch of us did. Any thoughts from the experts?



NTSB-Structural Failure of Piper Rudder Posts
Notice Number: NOTC2252
[FONT=&quot][FONT=&quot]NTSB recently issued an Aviation Investigation Report AIR-22-02 highlighting an urgent safety issue involving Piper part number 40622 rudder posts made of American Iron and Steel Institute (AISI) 1025 carbon steel, which our investigations have found to fracture due to fatigue.

Select this link to view Aviation Investigation Report AIR-22-02:
https://www.faasafety.gov/files/notices/2022/Feb/AIR2202.pdf[/FONT]
[FONT=&quot]In this AIR, we called on the Federal Aviation Administration to issue an airworthiness directive that describes the safety risk associated with the continued use of this part and require owners and operators to address the unsafe condition, such as by replacing them with rudders equipped with a post made of AISI 4130 low-alloy steel or its equivalent.[/FONT]
[FONT=&quot]What You Should Know
We developed this report and recommendation as a result of investigations into two accidents both occurring in Anchorage, Alaska--ANC20LA059 on June 8, 2020, and ANC21LA064, on July 23, 2021--involving airplanes, designed and built by Piper Aircraft Inc., that sustained substantial damage when their rudders structurally failed in flight. In both cases, the airplanes were being operated as Title 14 Code of Federal Regulations Part 91 flights. The NTSB also examined three additional similarly fractured rudders.[/FONT]
[FONT=&quot]What You Can Do
We encourage all owners, mechanics, and operators to read our Aviation Investigation Report and be aware that posts made of AISI 1025 carbon steel in Piper Aircraft Inc. part number 40622 rudders are susceptible to fatigue cracking under normal service conditions. Recently documented structural failures of these rudders indicate a serious hazard to flight safety that warrants action.

Recent publications are available in their entirety on the NTSB website. Other information about available publications also may be obtained from the website or by contacting—[/FONT]
[FONT=&quot]National Transportation Safety Board
Records Management Division, CIO-40
490 L’Enfant Plaza, SW
Washington, DC 20594
(800) 877-6799 or (202) 314-6551[/FONT]
[/FONT]

 

[55-PA18A]

I wonder how many of the planes that might be included in a potential AD still have the original rudder, or one made by Piper prior to 1974?

 

[bob turner]

All of mine do.
So, two failures in over 80 years? All three of my ancient Cubs are full of 1025 steel.

 

[BC12D-4-85]

Someone with concerns might contact the Anchorage AK FSDO and see if the NTSB's recommendation is being considered

Edit: More about the AD process: https://www.faa.gov/aircraft/air_cert/continued_operation/ad/issue_pub/

Gary

 

[salex]

There are also three other very informative threads here on this topic. One thread is titled "PA-18 Rudder Steel Identification," another is titled "Cub Rudder Failure," and there is another older Sept. 2020 series on the same topic over in the "Oops, darn it . ." thread.

 

[skywagon8a]

From the report:
"Although the five rudder posts that we examined had beacons or strobes installed that increased the posts’ susceptibility of failure, our analysis shows that, even without the additional stress of these components, in-service stresses likely exceed the endurance limit for AISI 1025 carbon steel rudder posts that have corrosion, scratches, or surface roughness features."

All of the damaged rudders had beacons mounted on the top where the added mass would have the most leverage against the failure location! But the added mass only LIKELY exceeded the limits. In other words it's only a guess on their part that the addition of the beacons made no difference.

My question is: How many of these rudders have bent WITHOUT the beacons being installed?

Based upon this report, the only potential AD I see is one to remove any beacons from the top of the rudder.

It's also interesting to notice the only two shown in pictures are on float planes. Is there a different natural frequency when floats are installed which concentrates these loads on the top rudder hinge area? I'd wager there has never been a vibration analysis done on this combination. As one who has witnessed this type of test being done, I know that the most obscure mass of weight in an innocuous location can effect the natural frequency of an airplane. What engines did these planes have? That would change the natural frequency. So many unanswered questions.

My opinion based upon what I've read here is that any chances of an AD on the rudders is just a nothing burger. Don't get worked up about one.

 

[CharlieN]

Since the top of the rudder post is an open tube, this has two components involved here.
One, moisture entering the tube.
Two, this electronic world where so many people/mechanics now have decent bore scopes, look down inside the tube every year.
The planes with 1020 tubes are how old now, how many times have those tubes been recoated? Probably does not matter since the design was broken from the start.

I personally can not blame a strobe light when the known side forces on the structure far exceed the loads the light imposes.

Many structure utilize doublers as stress points, on my build I have addressed this as well as using doublers in many other places in the structure. It is simply sound engineering.

 

[cubpilot2]

I’ve not seen a rudder with an open rudder post. The stubs on top are welded to a closed off structure.

 

[CharlieN]

I’ve not seen a rudder with an open rudder post. The stubs on top are welded to a closed off structure.

Ahh, thank you for the reminder, I am in error, and that stub is not lined up with the post as well if I recall. It is another plane that had a continuous post, not that I can recall it at this time.

 

[skywagon8a]

I personally can not blame a strobe light when the known side forces on the structure far exceed the loads the light imposes.

Many structure utilize doublers as stress points, on my build I have addressed this as well as using doublers in many other places in the structure. It is simply sound engineering.

My question is: How many of these rudders have bent WITHOUT the beacons being installed?
Is there a different natural frequency when floats are installed which concentrates these loads on the top rudder hinge area? I'd wager there has never been a vibration analysis done on this combination. As one who has witnessed this type of test being done, I know that the most obscure mass of weight in an innocuous location can effect the natural frequency of an airplane. What engines did these planes have? That would change the natural frequency. So many unanswered questions.

Charlie, I'm not suggesting the mass weight of the beacon has the leverage to bend the rudder post. I'm suggesting that it's presence at that location effects the natural frequency of the component parts. When that frequency is altered, sometimes things happen which are not expected. I can elaborate on this, it's just not appropriate on this forum.

 

[stewartb]

4 of the five airplanes are 75 years old. All are Alaskan so likely have spent much of their lives parked outside. The only surprising thing here is that anyone’s surprised.

 

[Penguin]

I wonder how many SC folks are running rudders with beacons. I have one on mine and never really questioned it.

 

[BC12D-4-85]

I came away from the analysis Dockets feeling their focus was on changes from original in the external tubing surface near the breaks. Possibly weakened material that was marginal even when new and unblemished. They did note a potential rudder harmonic between 600-700 engine rpm.

Gary

 

[wireweinie]

Sorry but I'm not buying a connection with a beacon mount. Too many out there that have them or had them installed and not a lot of troubles noted. Also, the beacon is installed on the same axis as the rudder post itself. That means that the air pressure on the beacon is the same no matter which way the rudder is pointed NOT just when the rudder is moved side to side.

If you're worried about yours, go out and push on it. If it breaks or bends with hand pressure, you should be happy you caught it then and not in flight.

Web

 

[BC12D-4-85]

Ok, how about a 2 piece external clamp over the affected area? Too much AM coffee.

Gary

 

[wireweinie]

Not being a smart a$$ here. If you have a primary flight control with evidence of corrosion which weakens it's structure, just replace the part affected. In this case, if I found a customers aircraft with corrosion on the main rudder post, I'd check to see if the corrosion impacted it's strength. If not, clean the corrosion off and repaint. If it did cause the post to weaken, then replace the rudder. I suppose that you could just cut out the post and weld in a new one, but at shop rate, that doesn't seem cost effective.

Web

 

[skywagon8a]

How about 4’ of 3/4”. 4130 and a few rosette welds you have a reinforced tubeView attachment 59903

That's about as simple as it gets.

 

[dgapilot]

How about 4’ of 3/4”. 4130 and a few rosette welds you have a reinforced tubeView attachment 59903

Don't need 4', how about only a foot inserted 6" above and below the top of the hinge and rosette weld in place. Pull the tailwheel steering bellcrank off and slide it up from the bottom.

 

[Phil Kite]

If the inside of the tube was cleaned out with a wire wheel and drill, then a tube could be slid inside and glued with structural adhesive epoxy and the reinforcement could be done with fabric still on. Could run a borescope up tube to check for corrosion pitting first.

 

[dgapilot]

If the inside of the tube was cleaned out with a wire wheel and drill, then a tube could be slid inside and glued with structural adhesive epoxy and the reinforcement could be done with fabric still on. Could run a borescope up tube to check for corrosion pitting first.

Not really a fan of epoxy for something like that, and not an approved method so you would likely need an STC for approval. Inner sleeve with rosette welds is already approved via AC 43.13-1B


Sent from my iPad using Tapatalk

 

[supercrow]

"IF" this becomes an AD, and repair is a part of it, they may specify a specific way to make that repair. If you have done yours differently you will be starting over.

 

[Scott 2020]

Basically handcuffed until some sort of directive materializes yes, but doesn't prevent discussion on the issue that could develope a recommendation in responce to the proposed rule making, whever that happens.

To achieve reinforcement of the area (assuming no visable damage is detecte), drive rivets or cherrymax would work in lieu of rosette welds so no fabric work required.

The problem I see is getting a snug fitting tube past the hinge points. The hinges were of course gas welded so internal deformation of the rudder tube is likely. I've looked at mine and the weld point is visable on the inside of the tube. Possibly could be polished with an abrasive bit on the end of a long extension.

AC43.13 allows clearance og .063" for an internal sleave but it antisapates welding the sleave to the tube at the joint.

The ID of the tu e is actually larger than 3/4". 7/8 OD with .035 wall is .805" or so so a 3/4" OD tube is within the clearance limit in AC43.13.

It appears the real concern here is the potential loss of rudder control due to the failed rudder getting tangled with the stab wires. I'd certainly like to see more work done on whether or not this could actually happen. Its clear the top of the rudder ends up close to or in contact with the stab wire. The key question is can it actually prevent movement of the rudder to the extent that cannot be overcome by the pilot's foot.

A more comprehensive analysis of the potential failure scenarios will indicate how urgent the issue is. So far the failures have left the bulk of the rudder intack and functional with positive outcomes in terms of injuries or deaths. This suggests time is available to find a practical, balanced solution.
S

 

[akwing]

for those who are talking about repairing an old ass rudder...are you being serious?

you do realize you can get a new rudder for less than $1500? $750 for the rudder and another $750 (at most) for the cover job.

barely a drop in the bucket compared to the cost of owning an airplane

its not like they're trying to AD your 1025 steel fuselage.

 

[BC12D-4-85]

Given today's supply chain challenges (just being nice) replacement rudders may become a hot market item prone to surcharges and delays. Hope there's a better fix.

Gary

 

[wireweinie]

for those who are talking about repairing an old ass rudder...are you being serious?

you do realize you can get a new rudder for less than $1500? $750 for the rudder and another $750 (at most) for the cover job.

barely a drop in the bucket compared to the cost of owning an airplane

its not like they're trying to AD your 1025 steel fuselage.

That's my thought also. And as I've said above, if you're worried about your rudder go out and push on it. That post is made of steel tubing. If hand pressure bends or breaks it, it's time for a new one. If you're scared to push on it, are you telling me you're ok with flying it?!

Web

 

[supercrow]

for those who are talking about repairing an old ass rudder...are you being serious?

you do realize you can get a new rudder for less than $1500? $750 for the rudder and another $750 (at most) for the cover job.

barely a drop in the bucket compared to the cost of owning an airplane

its not like they're trying to AD your 1025 steel fuselage.

Agreed. My life and aircraft are worth more that the risk. Already ordered a new one for mine. Done deal for me.

 

[frequent_flyer]

you do realize you can get a new rudder for less than $1500? $750 for the rudder and another $750 (at most) for the cover job.

I would expect a very sharp increase in the cost, and a very sharp drop in availability, if an AD required rudder replacement and did not allow any alternate means of compliance. The price of Piper PA-28 wing inspection panels kits more than doubled when a spar inspection AD specified additional inspection holes as one means of compliance. There was no stock anywhere and an enterprising producer of equivalent parts was shut down.

It's not difficult to make an input at the NPRM stage and, if many inputs suggested the same repair technique, I would expect that input to be considered.

 

[bob turner]

I dunno - if the fix is an interior tube with rosettes, I assure you I will do that. Seems like it might take three hours including fabric patch, not counting drying time.

Speaking of drying time, did I tell you about how I won't spray anything with Cyanoacrylates in it? We had a local painter spray some landing gear and a rudder I had prepared through Polytone white - even gave them the paint and thinner.

The fee was really outlandish - $1600, I think. Wasn't my money, but I asked. Six hours for drying time!

Most of you know how long it takes to hang, spray, and clean the gun for three pieces of Cub.

 

[skywagon8a]

There is something called AMOC Alternate Method Of Compliance on most ADs. This is a situation where there already have been several ideas mentioned. Also five bent rudders, don't automatically make an AD. Also many many times the NTSB has recommended an AD and the FAA does nothing. We all are aware, I'm sure we can handle it without government intervention. Don't loose any sleep over this.

 

[akwing]

There is something called AMOC Alternate Method Of Compliance on most ADs.

know of any existing AD's with an AMOC that requires inspection of steel tubing that is covered by fabric?

curious what the AMOC is for similar issues..