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Cracking on steps

bruceh said:
I was under my RV-9A tonight cleaning the belly and lo and behold, the passenger side step has a small crack. This is at 183 hours. QUOTE]

Sorry to hear that.

bruceh said:
I haven't painted the airplane,
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So, I assume there's no primer on it then..

bruceh said:
Does anyone have a definitive protocol for getting this fixed.
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Step one.. Get a non-certified, non-primered, chocolate chip cookie... :D

P.S. This is a "thread bomb." See http://www.vansairforce.com/community/showthread.php?t=130389
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posterman said:
Perhaps this has been mentioned before but all the 6's & 7's I have seen with cracked passenger steps were on aircraft where passengers routinely faced towards the rear of the aircraft and stepped down when exiting instead of facing forward and backing out by placing their left foot on the step.

Has anyone else observed this correlation?
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It's a great idea to instruct passengers how to climb in and out of the airplane properly but I don't believe it's the reason most of them crack.

I think vibration has the most to do with it and the fact that they are under engineered. Notice that even Vans beefs up the steps on their own airplanes.

Why Vans chooses to do nothing about it year after year baffles me.
 
boom3 said:
It's a great idea to instruct passengers how to climb in and out of the airplane properly but I don't believe it's the reason most of them crack.

I think vibration has the most to do with it and the fact that they are under engineered. Notice that even Vans beefs up the steps on their own airplanes.

Why Vans chooses to do nothing about it year after year baffles me.
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How did they "beef up" their steps?
 
ppilotmike said:
How did they "beef up" their steps?
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From post #6 at the beginning of this thread. (From Russ the step manufacturer for Vans.)

I would recommend any one having problems with this, weld a strap on the bottom side that extends down about two inches, Vans actually does this on there demo planes because people of all sizes climb in and out of them all day long all the time.
 
I agree and seriously doubt that stepping on the passenger step either way has any effect on how our steps have been cracking. Per photos posted by others, my passenger step has cracked exactly the same way and I don't have too many passengers that fly with me on a regular basis. So the passenger step is not used often, yet my pilot step has no cracking so far and I have been using the pilot step almost weekly for about 9 years (about 700 hrs). Also, I always supervise each passenger while they step up onto the wing and enter the cockpit as well as fully supervise how they exit the plane and step down off of the wing, and no one has ever stepped down facing the rear of my RV, they all have faced forward per my instructions... My supervision is mostly related to passenger safety.

If the cause of the passenger side step cracking is related to propeller pulse vibration, etc. as many on this forum have suggested, because there really is no standard configuration of engine/propeller (engine horsepower, 2 blade vs 3 blade props, fixed vs CS props, metal vs whatever material) there may not be a way to zero in on the actual culprit. And some on this forum have reported both steps have cracked, some even have reported that steps have cracked on an RV that has not yet flown??

Welding a support onto each step (or at least the Passenger step) as Vans has done seems to be the favored solution, and this solution seems to have worked. Friends of mine who are engineers (structural and mechanical) have looked at the problem and suggested removing the step from the airplane and slicing open the step and the tube that goes inside the fuselage and inserting and welding in an I-Beam like support. They claim that this I-Beam type of support should eliminate the vibration and make the step much stronger. The mechanic who is currently doing my condition inspection agreed that the I-Beam would be a good fix. Some other RV owner on this forum posted photos of exactly this solution, and my mechanic did pretty much the same type of fix on my passenger step.

This work on my step was recently completed and the step is currently being painted... I hope and expect that this solution will solve the step crack problem, and if the pilot side step shows the same crack, we'll probably use the same solution.

Victor
 
sounds like an opportunity for one of the VAF vendors

I'd love to just take off the steps, ship them to someone who would weld up the reinforcements and ship them back.
 
Alan from AntiSplat has a theory that the cracking is caused by vibration. He has suggested drilling a hole in the step and adding some sand to damp out the vibration before a crack occurs. IIRC I think he's done it for several of his friends.

I went ahead and added sand to my steps. So far no cracks. I figured it couldn't hurt.
 
I added sand then welded up the hole. Guess we will see. I kinda wished I would have taken them off my taildragger, I really dont use the one on the left side cause every time I start to step on it I think of all the problems everybody has and just step across it.
 
The problem with the step is the gusset. When you step down a lot of stress is placed at one small spot. That's where the crack starts.

step%20crack_zpsqmofpy9e.jpg


The stress needs to be spread over a larger area. A doubler installed in the area in the picture will solve the problem.
 
ArVeeNiner said:
Alan from AntiSplat has a theory that the cracking is caused by vibration. He has suggested drilling a hole in the step and adding some sand to damp out the vibration before a crack occurs. IIRC I think he's done it for several of his friends.

I went ahead and added sand to my steps. So far no cracks. I figured it couldn't hurt.
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Where is that thread that Alan posted, I remember he said that me mounted a transducer on the step before and after and confirmed that there was a lot of prop wash vibration on the passenger side step and the sand trick worked. mine are getting filled with sand!
 
Focus

This thread reminds me of a large engineering meeting (70+ engineers) where the overhead projector stopped working. 5 six sigma black belts jumped up to attack the projector and get it working. The room was focused on them. Meanwhile, an astute (and largely unnoticed) engineer quietly leaned over and plugged in the extension cord in the back of the room. The projector came to life and everybody cheered for the success of the black belt team, who promptly beamed, taking credit their save, high fives all around.
 
BillL said:
This thread reminds me of a large engineering meeting (70+ engineers) where the overhead projector stopped working. 5 six sigma black belts jumped up to attack the projector and get it working. The room was focused on them. Meanwhile, an astute (and largely unnoticed) engineer quietly leaned over and plugged in the extension cord in the back of the room. The projector came to life and everybody cheered for the success of the black belt team, who promptly beamed, taking credit their save, high fives all around.
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I've got one of those stories :)

Working as a student aide in college, at the university-run computer instruction center (courses for professionals, businesses, etc., to learn then-new technology like MS-DOS and such LOL!).

Dr. High and Mighty comes running in to the office yelling at all the students and staff, very upset that *A WHOLE ROW OF COMPUTERS ARE DEAD! WHAT DID YOU GUYS DO?!"

Two of us calmly walked in to the classroom and started checking power cords. "I'VE ALREADY PLUGGED ALL THOSE IN!!!! NOTHING IN THIS ROW IS WORKING!"

Uh, yeah...he'd plugged them in alright. He had plugged all the power strips into each other in a big circle. Guess he forgot to plug at least *one* of them into the actual wall outlet.

Did we get a thank you? Yeah, right...
 
Networks

RV7A Flyer said:
I've got one of those stories :)

Working as a student aide in college, at the university-run computer instruction center (courses for professionals, businesses, etc., to learn then-new technology like MS-DOS and such LOL!).

Dr. High and Mighty comes running in to the office yelling at all the students and staff, very upset that *A WHOLE ROW OF COMPUTERS ARE DEAD! WHAT DID YOU GUYS DO?!"

Two of us calmly walked in to the classroom and started checking power cords. "I'VE ALREADY PLUGGED ALL THOSE IN!!!! NOTHING IN THIS ROW IS WORKING!"

Uh, yeah...he'd plugged them in alright. He had plugged all the power strips into each other in a big circle. Guess he forgot to plug at least *one* of them into the actual wall outlet.

Did we get a thank you? Yeah, right...
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Can't count the number of computers and labs I've seen with switches plugged into each other instead of the network.:D

To keep this on topic, I plan to buy some 4130 square stock, cut it on the edge so the part is triangular and weld the length to the back side
 
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Nice Save Wirejock!

wirejock said:
Can't count the number of computers and labs I've seen with switches plugged into each other instead of the network.:D

To keep this on topic, I plan to buy some 4130 square stock, cut it on the edge so the part is triangular and weld the length to the back side
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Post picts when done so others can follow. Thanks!
 
8A Step Modification

This is just my attempted solution for the cracking step problem; for an 8A step in my case. I should note that I?m not a welder, so I used what I had. If I was a welder, I probably would have fashioned a similar, but probably better and lighter, fix. My fix added 6 oz. to the step.

Process: Removed most of Van?s supporting flange (stress concentrator). Cut-out a backplate from streamlined tubing (one-size-up) and straightened it lengthwise (the piece curls slightly when cut due to residual stress). Attached the backplate with set screws and 3M 2216 structural adhesive. Fashioned a compression block from 1? x 1.25? 6061T6 bar stock to spread the boarding load. Attached the block with set screws and 2216.

2yl6734.jpg


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Results: TBD (no warranty implied.)

Note: Because I added a relatively long, asymmetric backplate and thus considerably changed the step?s resonant frequency characteristics, I decided not to go with Allan?s sand-damping solution; at least for now. Also, it is my personal opinion that boarding loads are, by far, the main initiators of the cracking. That being said, Allan has shown that in-flight loads are also an issue. I would venture that boarding loads start the cracking and then in-flight loads contribute from there.
 
Calling all structural analysis folks...

So,...structure is not "my area",.. But have seen and been in enough discussions to be dangerous,.. .

So,.. Seems to me the root is at the root of this problem,.. The lack of transition in load carried from streamline tubing (with thin wall) to "large thick plate" relatively speaking. There is a "discontinuity" at that point which acts as a stress riser. There have been several attempts at easing it,... And i kinda like the one above, but believe a better and less draggy solution is available,..even if it means more intricate work.

FAA has recommendations for repairing streamline tubing,.. And you can find others on web. So,.. Borrowing this approach to help ease the transition. Essentially,..take another section of tubing, Cut trailing edge of tubing and insert into existing design tubing. Wild guess,.. Two inserts would do it,.. One 3 inches in length and one half that, with shortest on inside. At the top of the step as it attaches to the plate. Weld would be most elegant/correct,..

Will need to look at thickness of plate and "built up section" to decide if need for post weld heat soak. (Don't recall limits). Will need to be careful on fitup of streamline tube to plate to get good weld and joint performance with total thickness

Ok,.. That is enough stirring of the pot for me,....would the guys that know, please weigh in and get us straight
 
thinkn9a said:
So,...structure is not "my area",.. But have seen and been in enough discussions to be dangerous,.. .

So,.. Seems to me the root is at the root of this problem,.. The lack of transition in load carried from streamline tubing (with thin wall) to "large thick plate" relatively speaking. There is a "discontinuity" at that point which acts as a stress riser. There have been several attempts at easing it,... And i kinda like the one above, but believe a better and less draggy solution is available,..even if it means more intricate work.

FAA has recommendations for repairing streamline tubing,.. And you can find others on web. So,.. Borrowing this approach to help ease the transition. Essentially,..take another section of tubing, Cut trailing edge of tubing and insert into existing design tubing. Wild guess,.. Two inserts would do it,.. One 3 inches in length and one half that, with shortest on inside. At the top of the step as it attaches to the plate. Weld would be most elegant/correct,..

Will need to look at thickness of plate and "built up section" to decide if need for post weld heat soak. (Don't recall limits). Will need to be careful on fitup of streamline tube to plate to get good weld and joint performance with total thickness

Ok,.. That is enough stirring of the pot for me,....would the guys that know, please weigh in and get us straight
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Wallace,

As an example of an I-beam type solution that we did to my airplane (my post #156 on this thread)... see post #17 (from March, 2011) and this link of his repair photos: https://www.facebook.com/media/set/?set=a.1151935778595.19363.1833677196&l=e4471f22ae

My step repair is rock solid, looks good, and should never need any further repair.

Good luck.

Victor
 
I-beam solution

Victor,..
I like the carry through of the design,..
But have not yet noodled through how it really works long term.

Generally speaking, i beams have meat on top and bottom and relative thin on middle,.. Your design is opposite.

If load seen is tensile probably ok,.. If bending,.. What I am wondering is,..How well does it distribute the load,.. Or is the "point load" / concentration just moved from the plate,... To the end of the insert. (Yes it is better than current)

Certainly it is stiffer and better and will last longer,..

How long has it operated since fix?
 
Victor's repair ought to solve the problem permanently. It adds shear stiffness where needed and prevents the local bending that I think leads to the cracks.

It lets the tube wall act as caps on a beam.

Nice solution - elegant.

Dave
 
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Russ McCutcheon said:
Very nice solution Victor! How was the slot cut in your step?
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Russ,

My mechanic used a small (about 1" in diameter) pneumatic cut-off wheel to create the slots. I'm not sure what material the cut-off wheel was, probably reinforced fiberglass... He told me that cutting through the tubes wasn't much of a problem, but he said that it was tough cutting through the plate.

The work was completed about 6 weeks ago during my condition inspection.

Victor
 
Changing cracked step on RV-9A

PerfTech said:
.....I suspected that prop wash was the culprit so I mounted a transducer on them to measure the vibration. Wow! It turns out it is prop wash and a harmonic from the engine.
.... Drill a small hole into the lower part of the step on one end, (the part you step on). Measure out some sand, approximately enough to fill the lower step portion about 2/3 up. Then reseal the hole.
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Hangar mate and I are in the process of replacing a cracked step on the passenger side of his RV-9A. My compliments to Allan Nimmo for his investigations revealing the most likely cause of the cracking problem to be the step resonating in the prop wash. I would like to ask any suitably credentialed harmonics experts on VAF to share their thoughts about a possible fix that does not entail drilling a hole in the step, partially filling it with sand, then re-welding the hole.

Late model cars and trucks that still have ?stick? radio antennas often have a wire molded in a spiral around the outside of it specifically for the purpose of disrupting its natural frequency, thereby preventing it from oscillating in the relative wind. This caused me to wonder if the same effect could be realized for the step by applying a bead of JB Weld in a wavy line pattern on the inside surface of the step leg. Is there anyone out there with a slide rule who can tell me if it?s worth a shot ? or should I go back to cleaning bugs off the wing?
 
Take 2

Prop wash is likely the culprit in most cases, but some have failed prior to first engine run...

curtis said:
Both of my steps have cracks that were discovered before the first engine run. There is another plane in my area where the R/H step is also cracked before the first engine run! What is weird that the cracks develop on the compression side of the strut. I don't believe the lead shot or sand will prevent this issue since I have seen the cracks BEFORE the engine was ran.
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This is a complex problem with likely several issues at play...

CanadianAce said:
... This is a fatigue failure. Compression fatigue cracks like these breed in residual tension zones, with high compressive stresses (amplified by notches), and oscillating motions. The brittle (non-ductile) material makes things worst by not yielding, increasing the crack propagation rate (the material strength is higher, but does not exceed the stresses). ...
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And that is why Van's own fix is to add the stiffener plate. It solves the vibration and the overload (heavy/jumping passenger) issues.

BillL said:
New Picture from OSH - Now - -you guys order some 4130 strip from Spruce for a few bucks, take your step, 4130 strip, and these pictures to a local welder and get those steps fixed! Or do it yourself.

****update: it was reported that Vans made the reinforcement piece from 4130 channel. This would be easier if it was available.****

Vans%2520Step%2520Repair%25202.JPG


vans%2520step%2520repair.JPG
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Shane:

Could it be that the steps that cracked before engine start were anomalous? In a production environment, it is possible that some steps could be overlooked and not get normalized after welding. With 4130 and the way the steps are loaded, that scenario would practically guarantee exactly the sort of failure in evidence. The failure in my partner's step is right along the edge of the weld, all the way across the chord.
 
Trick or treat!

XOverZero said:
Shane:

Could it be that the steps that cracked before engine start were anomalous? In a production environment, it is possible that some steps could be overlooked and not get normalized after welding. With 4130 and the way the steps are loaded, that scenario would practically guarantee exactly the sort of failure in evidence. The failure in my partner's step is right along the edge of the weld, all the way across the chord.
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It could be an anomaly; however, it would be unusual to see a failure in the compression zone unless it was caused by fatigue. (I am assuming the reporting of these pre-startup failures are accurate, and the QAQC process by Vans precludes a cracked part from being sent from the factory.)

Kyle Boatright said:
Have we established that the steps are supposed to be normalized after welding? I'd bet against it.
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Typically, it is not necessary to normalize (or better yet anneal) thin wall 4130. If the part is properly prepared (near perfect fit and at least 16'C before welding) and welded correctly (not at an excessively high temperature) then it should be sufficient to allow it to cool in air at room temperature.

It would be interesting to see if this failure would repeat if several owners who experienced early (<500 hr) failures replaced their steps with sand filled ones (ingenious solution to the harmonic prop wash issue btw). If these new steps made it well beyond the initial failure age of the originals, I think it would be safe to say the solution was found for most cases.

As for the others that failed before startup... be gentle when using your steps. Or strengthen the steps to allow for an increase in loading. This is where I like the Van's solution, since it corrects for both the prop wash and heavy foot issues.

The best solution is perhaps Guilherne's... just don't install them. This is my plan... now I only need to make up my mind on having a vertical or horizontal induction. ;)
 
CanadianAce said:
The best solution is perhaps Guilherne's... just don't install them.
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I didn't, and I'm glad of it. I carry a small, lightweight plastic stepstool for passengers. Yeah, it's a big step up to the wing on the -A model, but I can do it pretty easily. And if the day comes when I can't, maybe I'll install a step then (perhaps by then they'll have the cracking problem sorted out :) ).

Also, less weight, less drag...so I can go faster :)
 
Fred Stucklin

Those breaks are caused by nitrogen embrittlement. It has nothing to do with how you step on it or whether you are a few lbs. heavy. There is a very easy fix. It has to be done during the welding process. If they would use stainless steel welding rod (tig) this will end the problem. There is no need for additional trussing.
 
If it were hydrogen embrittlement, we'd be seeing these effects:

* The cracks would occur anywhere on the weld,
* Other stressed parts, like the engine mount and landing gear mounts, would crack.

If you're concerned about hydrogen embrittlement, you can bake the parts - you'll have to look up the baking process and follow it carefully.

Welding with a rod of the wrong material, and perhaps an incompatible material, might prove to be more problematic than the current design. It would certainly be harder to correct. Again, best to follow an established process here to get reliable results.

Dave
 
CanadianAce said:
Prop wash is likely the culprit in most cases, but some have failed prior to first engine run...



This is a complex problem with likely several issues at play...



And that is why Van's own fix is to add the stiffener plate. It solves the vibration and the overload (heavy/jumping passenger) issues.
Click to expand...

Keep in mind that Van's airplanes do not experience a typical step usage.....
Some of them get climbed in and out of more times in a day, than a lot of builders planes do in a year... by 100's of people in all shapes and sizes....

The repairs that have been made previously to Van's planes are all for damage that was clearly from load cycles. I am not yet convinced of cracking being cause by in flight vibration. I am not saying it isn't possible.... since there is likely a broad range in the level of vibration based on prop balance, etc., within the fleet. I just haven't seen any indications (so far) of any data to support it.
 
Install both steps!

On a 7A install both steps!

That's my advice after 1200+ hours.
I can't imagine having to look after a folding step stool.

As many rides as I've given the stool would have been a royal PITA.

I'm 5-11" and I want that step on my side also!
It's a real stretch not to use it.

My .02

Mark
 
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David Paule

Nitrogen embrittlement always occurs in the base material where the heat line pushed the carbon back away from the weld. 308 stainless is an acceptable filler for 4130. Been doing this process for over 50 yrs. whoever is concerned would do well to listen.
 
rvbuilder2002 said:
The repairs that have been made previously to Van's planes are all for damage that was clearly from load cycles. I am not yet convinced of cracking being cause by in flight vibration.
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I think your statement leads new builders to believe that it won't happen to them. Then one day down the road when it does they'll be back on this thread.

Whatever the reason the current design could be improved or an optional upgrade could be offered. Yes this may take a little effort on Van's part but double the price or something. It's just no fun drilling out rivets, sandblasting off your paint, paying a welder to add a support, then repainting.

I just don't buy that hundreds of people who otherwise baby their airplane somehow show no regard for their passenger step. (Constantly letting overweight passengers just jump on it backwards.)

Pretty please???
 
On the mark.

boom3 said:
Whatever the reason the current design could be improved or an optional upgrade could be offered. Yes this may take a little effort on Van's part but double the price or something. It's just no fun drilling out rivets, sandblasting off your paint, paying a welder to add a support, then repainting.
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This statement is bang on. There is a recognized issue that is ongoing. If the current part design is problematic it only makes sense for the manufacturer to change to design. The fact the manufacturer has upgraded this part on thier own demo unit says a great deal. The best way for this issue to progress forward is a new part design from Vans. Once implemented it will be clear soon enough if it resolves the issue.
 
Russ McCutcheon said:
I have seen the result of fractures along a “heat affected zone” many times and I have to disagree with you this time as the break does not follow the heat affected zone or the weld but rather is simply in a straight line perpendicular to the load. In my 20+ years of working with 4130 I have seen that it never breaks on the tension side, rather it will break on the compression side if the load is sufficient to buckle or compress the tubing repeatedly, it becomes work hardened along the compression line and eventually breaks. The fact that this happens at or near a weld in this case is simply because that is where the most stress is focused, where the lever/step is attached.

I would recommend any one having problems with this, weld a strap on the bottom side that extends down about two inches, Vans actually does this on there demo planes because people of all sizes climb in and out of them all day long all the time.
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rvbuilder2002 said:
Listen to Russ...he has it exactly right.
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Looks like we've known the cause for quite some time (Russ post above is from 2011), but the simple fix he suggested has not been implemented for some reason (low priority obviously).
Having the supplier add a strap to the bottom certainly wouldn't add that much to the cost of the part, but Van's needs to change the drawing to make that happen....

I've seen plenty of broken and cracked steps, including my own, and it seems silly that we are still debating this 5 years later.
I'd like to at least be able to purchase a new step and not immediately have to find and pay a welder to modify it to correct a known deficiency.

Come on Van's, just change the drawing to incorporate the strap so Russ can start making them that way and we can fix this problem and be done with it, it's really not that hard, but somebody has to step up and say "do it".
I guess an alternative is to purchase the steps from Van's and have them drop ship to Russ for the fix, seems like the long way around though.
 
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Bird shot

I'm trying Alan's method. I drilled a 1/4" hole in the end of the step, but used bird shot instead of sand, then welded-up the hole. You should have seen how nervous I was emptying all those shot gun shells :eek:

 
Steps removed and out for repair

My RV-9A completed in 2004 had cracked steps when I purchased it in 2012.
I have recently removed both steps and sent them out for repair. I am having the I-beam type of repair done thanks to the great pictures and the information on this thread.

I found the removal of the steps, for a non builder to be somewhat difficult. Some tips I would make are:
Purchase a rivet removal tool. This was beneficial as it centered on the rivet head for drilling out the rivets on the steps.
Purchase a spring loaded center punch. This was beneficial to create a good center point for drilling out the flush rivets used for the nut plates.
Purchase a good 1/8 inch punch tool to help with removing rivets.
Use good quality sharp drill bits.

The right hand floor came up easier than the left hand floor. The left hand floor required loosening the flap actuator supports to get the flap actuator weldment out of the way of the two front nut plates on the floor.

Allan's method of drilling access holes would surely save a lot of work versus removing the floor. I decided to remove the floors to allow bucking new rivets when finally ready to reinstall the steps. I am hoping this is a one time repair.

I feel strongly that Van's should incorporate the I-beam modification into the manufacture of these steps. This is a rediculous amout of work to perform after the fact. I would be very upset as a builder, who took great care and had nice paint on everything, to have to go through this on a known issue sometime later. This is a serious amount of time and labor, and anyone building should think twice about installing these steps without modifcations.
 
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