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Revision to SB-00036 document and replacement parts

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Try with the elevator down (there was more room on my -4 in this config) and put a 1/2” step bit in an extension so the drill isn’t in the way. I was able to do it that way and only needed to enlarge a little bit. Also, get a borescope with two cameras so you have a good quality image at 90deg to the main camera.

ditto.
Still tight but doable.

My scope articulates 90 deg., so no issue seeing in there.

RV6, 900 hours, occasional acro, no cracks.
 
Try with the elevator down (there was more room on my -4 in this config)

I find that rather odd since the nominal maximum elevator travel is 35 degrees up, but only 25 degrees down... with the tooling hole centered on the coard line, elevator full up should provide better access.
 
Spider Web!

Thanks all for the suggestions. I did a swab with a pipe cleaner, then took some more pics. Sure enough, it was a piece of web--can still see a portion stuck to the rivet. I used a 12" long 1/4" drill bit to slightly enlarge the tooling hole. The small Teslong camera fits nicely thru the hole. Attached are before and after pics. To reiterate, 228 hours, no acro, no rough field landings, and no cracks.
 

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Latest parts

Maybe I missed it here ….but what were the changes / improvements made to new parts ? Edge distance on non pre punched kits seemed a concern ? Is a “ doubler “ part of the SB now ? Thanks. Stew
 
Other than high time and aerobatics, is rivet orientation contributing to the cracks?
 
Other than high time and aerobatics, is rivet orientation contributing to the cracks?

Webb, your question is valid and will one day be answered when we've amassed enough poll data.

We knew before we started that high time would be associated with higher likelihood of finding cracks. The cracks weren't there when our planes were completed and got their AW certificates. Once formed, cracks never heal themselves. It's an inescapable conclusion that building flight time will raise the chances for cracks to appear. Time in service may not be causative (okay, it almost certainly is), but it will absolutely correlate...

Reminds me of a time on morning rounds when one of us interns, attempting to impress our attending physician, noted that the patient under discussion had a condition 'more commonly found in first-born children.' Our mentor replied that the only finding he knew of that wasn't more common in firstborns was the presence of hand-me-down clothing. "How many families in this hospital even have a ninth- or tenth-born child," he asked. "Would you expect to find very many of that birth-order presenting in derm clinic this afternoon with skin tags? Therefore, doctor, skin tags are highly correlated with being a firstborn, aren't they. Do you impress yourself with your deductive skills?"

We all paused to take in this new information: when it came to correlation and causality, we realized then that the 'retrospectoscope' could lie to us if we weren't careful. The following year, Graham Martin published in The Lancet (1984) his classic hit piece on the malicious manipulation of clinical trial data by scoundrels, titled 'Munchausen's Statistical Grid, Which Makes All Trials Significant.' This is fun reading if you are in a Lewis Carrol sort of mood and want a rabbit hole to ponder.

I just bought a 5mm sideview boroscope and will be adding my findings to the thread one day this year. Not expecting to see anything amiss at 100 hours TT, but perhaps, eventually, the correlation between time in service and finding things that weren't there at the beginning will play itself inevitably out. At my age, I can only hope I live long enough to put that many hours on the new gal.
 
RV-6a no cracks

RV-6a
0-320, carb, FP
800 hrs in 22 years
No acro
Yes severe turb +4G / -2G
Shop head on forward side
No cracks
 
Does anyone know what vans kit includes? It almost seems like if you’re going to replace these hinges you will be taking off your rear spar so why not buy a new one to zero out the time on it and thus longevity of the repair.
 
Have you ever watched the horizontal stabilizer of an RV (or any airplane, really) during an engine runup? The tail vibrates like crazy from the prop blast.

Every time I see that, I think to myself how impressive it is that cracks aren't found more often.

--Ron
 
We all paused to take in this new information: when it came to correlation and causality, we realized then that the 'retrospectoscope' could lie to us if we weren't careful.

This is very good advice, considering that 100% of people who confuse cause and effect end up dying.

- mark
 
Inspection results.

Since last Wednesday and today i have inspected 4 RV Aircraft using a TESLONG Digital Endoscope Camera. Only requires a 1/4" diameter hole; Model NTS500B with the following results:


RV6
1994
868 hours.
Very light aero.
No Cracks: rivets installed with bucked head on bracket side.
Prop Dynamically balanced.


RV4
1995
1,995 hours
Lots of Aero.
No Cracks: rivets installed with bucked heads on front spar side. And has a 5-rivet pattern on both sides of bracket.
Prop Dynamically balanced.

RV-6A
2001
2,000 hours
Only Aileron Rolls.
No Cracks: rivets installed with bucked heads on bracket side.
Prop never Dynamically balanced.


RV-8
2005
1,700 hours
Medium Aerobatics.
No Cracks: rivets installed with bucked heads on bracket side.
Prop Dynamically balanced.
 
Crack data........

RV-6a
0-320, carb, FP
800 hrs in 22 years
No acro
Yes severe turb +4G / -2G
Shop head on forward side
No cracks

Is anyone keeping track of this data? Or are we just talking to ourselves? Is there one design, activity, hours, etc that is more prone to cause cracking? It would be nice to compile the data so some conclusions can be drawn.

RV-4; O-320-160hp; wooden fix pitch; 1210 hours; mild acro. Love to pull G's. No cracks. Shop head forward.
 
RV7 no cracks found

RV-7
180hp IO360M1B
72 inch BA Hartzell
164 TT
Some grass, mostly pavement
No dynamic prop balance yet
Light acro 3g or less
Shop head on forward side

No cracks found
 
Tracking data.

Is anyone keeping track of this data? Or are we just talking to ourselves? Is there one design, activity, hours, etc that is more prone to cause cracking? It would be nice to compile the data so some conclusions can be drawn.

RV-4; O-320-160hp; wooden fix pitch; 1210 hours; mild acro. Love to pull G's. No cracks. Shop head forward.

I PM my results to Greg Hughes & vans. That said, Vans wants to implement a change in design to prevent any future occurrences in new builds and any potential structural failure in the existing fleet.
 
Is anyone keeping track of this data? Or are we just talking to ourselves? Is there one design, activity, hours, etc that is more prone to cause cracking? It would be nice to compile the data so some conclusions can be drawn.

RV-4; O-320-160hp; wooden fix pitch; 1210 hours; mild acro. Love to pull G's. No cracks. Shop head forward.

The reports appearing here constitute an extremely small sample of the fleet, not sure how valuable statistically it will be.
 
Well, for it to be the least bit helpful, somebody is going to have to collate it. Either here as a poll or someone taking the time to spread-sheet it, or the mothership will have to do the same with the presumably much larger sample they are privy to. Vans should ask its customer base to report results of their inspections for this purpose as part of the SB - perhaps they did (too lazy to look right now).
 
Well, for it to be the least bit helpful, somebody is going to have to collate it. Either here as a poll or someone taking the time to spread-sheet it, or the mothership will have to do the same with the presumably much larger sample they are privy to. Vans should ask its customer base to report results of their inspections for this purpose as part of the SB - perhaps they did (too lazy to look right now).

And as you stated in post 106 and Webb's question in post 105, the data collected needs to be relevant to the possible causes. Any data can be correlated to show a trend, especially with the small sample size.
 
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I brought this up early in this thread when folks where making assumptions about the direction of the rivet. I stated that this would be "statistically irrelevant" due to the small sample size.
However, folks still seem to think rivet direction as an important piece of data, or there just stepping in line as others have reported same. Why not shop head driven dimensions then? That's the real point of this theory, not enough surface area compared to the manufactured head? That would be fun to measure.
Again, as I stated before, since the beginning of aluminum aircraft construction, it has always been acceptable for the shop head to be on any side. It is preferred on the thicker material, but very few airplane are built with shop heads on the outside of the aircraft, even in areas where it doesn't matter aerodynamically. If it was critical to the design, Vans would have redesigned it as that marginal difference is thin, at best, if any....
Two cents and all that is worth.

I believe this is a design issue. As good as any engineer or manufacturer is, covering all the bases for the life of a machine isn't easy to do. Perhaps it is impossible to do.
 
Are folks using dye penetrant or just plain visual inspections? Many of the photos in the SB look to have dye on them but most of the photos on this thread are without.
 
I believe this is a design issue. As good as any engineer or manufacturer is, covering all the bases for the life of a machine isn't easy to do. Perhaps it is impossible to do.

Fatigue and Damage Tolerance is often difficult, and like many things, only as good as the underlying assumptions made. And I'm not sure that F&DT was given much thought on the early RV designs.

When I first got into flutter engineering for a large commercial transport maker, other engineering disciplines would joke (out of ignorance) that flutter was a Black Art. After 35+ years experience and seeing how the other disciplines did their work, my comeback was that Loads was a Black Art, Flutter was a Black Science, and Fatigue and Damage Tolerance was just Voodoo and Black Magic! :D
 
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When I first got into flutter engineering for a large commercial transport maker, other engineering disciplines would joke (out of ignorance) that flutter was a Black Art. After 35+ years experience and seeing how the other disciplines did their work, my comeback was that Loads was a Black Art, Flutter was a Black Science, and Fatigue and Damage Tolerance was just Voodoo and Black Magic! :D

From my 37+ years in aircraft design I have the same opinion.
I worked a project in the early days trying to combine aerodynamic CFD analysis in a closed loop optimization with structural FEM. At that time it was really smoke and mirrors. Better tools now.
 
From my 37+ years in aircraft design I have the same opinion.
I worked a project in the early days trying to combine aerodynamic CFD analysis in a closed loop optimization with structural FEM. At that time it was really smoke and mirrors. Better tools now.

Boy that is for sure. Excuse the thread drift (others might find it interesting)

A leader in the field is a long-time colleague, Kim Martins (Joaquim R. R. Martins) now at University of Michigan. His PhD thesis long ago coupled an Euler CFD analysis and a FEM structural analysis with an adjoint-based optimization to do MDO design (Multi-Disciplinary Optimization) of a supersonic transport.

Among the early lessons is that the optimization must couple the disciplines simultaneously, rather than sequentially, or the approach will converge nicely to a wrong answer.

The MDO field has grown tremendously in fidelity of analysis tools as well as range of applications, and speed. Kim has been a leader at the forefront of that growth.
 
I'm going to don the moderator hat for a moment and respectfully request that we keep this thread on track for its intended purpose as titled:

"Revision to SB-00036 and replacement parts"

This topic is too relevant to the safe operation of our RVs to allow it to be detoured in directions that Greg at Vans didn't intend when he started this thread.
 
Compilation of crack reports in this thread

I've compiled a table of the crack reports I've seen in this thread so far, and posted it on Google Drive at this location.

The first column in the table is the post number in this thread. The next column is the aircraft model number following "RV-". The third column is the number of hours on the airframe. If you said something like "500+", I just entered 500. The fourth column is the number of cracks reported. Out of 41 airplanes with reported inspections, cracks were found in three (or maybe four, inspector wasn't sure). The fifth column is the location of the rivet factory heads (opposite the shop heads), if reported, FWD or AFT of the HS rear spar.

A friend who is building a -7A says his drawing shows the manufactured heads on the AFT side of the spar, i.e., on the hinge bracket side, not inside the HS. We both recall an instruction we saw somewhere that says the manufactured head should be on the side with the thinner material, but there are reasons to put it on the hinge bracket side in this instance (e.g., elevator leading edge rubbing). Also, neither of us recalls that instruction saying anything about steel vs. aluminum.

Please PM me if you spot any errors.

Follow-up edit in response to #125 below:
The instructions my friend refers to for his RV-7A are in DWG 5, Detail D, which is referred to from DWG 3. That detail inset shows the manufactured heads of the elevator hinge bracket rivets on the elevator hinge brackets and the shop heads on the forward side of the spar.
 
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A friend who is building a -7A says his drawing shows the manufactured heads on the AFT side of the spar, i.e., on the hinge bracket side, not inside the HS.

My -7's and 8 instructions make no mention of rivet directions (first picture), plan revision 3/2014.

Only the -10 and -14 mention this detail. (maybe the 9 but I don't have a set of plans to confirm).
 

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My -7's and 8 instructions make no mention of rivet directions (first picture), plan revision 3/2014.

Only the -10 and -14 mention this detail. (maybe the 9 but I don't have a set of plans to confirm).

Drawings on my 9A (2008) show the shop head on the spar side, factory head on the hinge bracket.
 
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Shop vs manufactured head

Drawings on my 9A (2008) show the shop head on the spar side, factory head on the hinge bracket.

I'd have to drag out the plans for the -4 (paper; rolled up in a large tube) but I don't recall any callout for the direction of the rivet. I may have had the shop head on the spar side because the manufactured head on the bracket just looked better. Sometimes it's better to be lucky than good....;)
 
Cracks in the horizontal spar...

I've compiled a table of the crack reports I've seen in this thread so far, and posted it on Google Drive

Thank you for doing this! This is what we needed to see! So it looks like it is NOT a common problem (albeit a small sample size) and limited to certain models. Good to know!:)

But it will still be a condition inspection item (should be anyway) and it will be interesting to see if the list of problem aircraft grows (if results are reported....which they also should be.....)
 
oh yeah...

...I forgot to mention mine --

2015 RV-7 Kit, 2018 A/W, 238 hours TT. Light acro, Dynamically Balanced Hartzell BA on 200HP Lyco (A1B6). Holes dressed/deburred, manufactured heads on thinner material - inside on .032" spar. No Cracks.
 
RV-3B - 475 Hours - Rights Side, 2 rivets with cracks - Heads are FWD

My plane operated out of grass previously. Was also used extensively for aggressive airshow work prior to my purchase. Prop dynamically balanced when I bought it 120 hours ago.
 
I've compiled a table of the crack reports I've seen in this thread so far, and posted it on Google Drive at this location.

The first column in the table is the post number in this thread. The next column is the aircraft model number following "RV-". The third column is the number of hours on the airframe. If you said something like "500+", I just entered 500. The fourth column is the number of cracks reported. Out of 41 airplanes with reported inspections, cracks were found in three (or maybe four, inspector wasn't sure). The fifth column is the location of the rivet factory heads (opposite the shop heads), if reported, FWD or AFT of the HS rear spar.

A friend who is building a -7A says his drawing shows the manufactured heads on the AFT side of the spar, i.e., on the hinge bracket side, not inside the HS. We both recall an instruction we saw somewhere that says the manufactured head should be on the side with the thinner material, but there are reasons to put it on the hinge bracket side in this instance (e.g., elevator leading edge rubbing). Also, neither of us recalls that instruction saying anything about steel vs. aluminum.

Please PM me if you spot any errors.

I have not reported in yet. Only saw three higher time RVs in your spreadsheet. Me: RV-6, 3,500 hours, NO Cracks found, Factory Heads FWD.

Prop has almost always been balance. Three times, twice same guy, third time different guy and machine. Maybe there are 50 hours that have been flown unbalanced.
 
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No cracks.

Early -4, completed 1987. 1500hrs. Shop head forward, 5 rivet pattern.

New to me, but builder tells me it did no hard acro, and I've done nothing above 3.5g
 
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Don't know if it means anything...

I don't know if it means anything, but so far it looks like all but one of the airplanes with cracks are taildraggers. But then 33 of the 51 airplanes reported on so far on this thread and reports from Van's are taildraggers. Might be time for a chi-squared test of independence (cracks/no cracks vs taildragger/nosedragger). The sample size is still kinda small, though. I'm adding three airplanes (nosedraggers) for which I have PM reports from friends, albeit no reported hours or factory head locations on any of them. That brings the numbers up to 33 taildraggers out of 54 airplanes.

Once again, the table is here.
 
Why include the -10?

My impression is that the -10 and -14 are not showing any cracks. Why does this SB apply unless it is just seeking statistics?

If zero show cracks, will these models be burdened with repetitive inspections or replacement that might do more damage than it repairs?
 
RV6 - 1 crack on LH side, short, horizontal, shop head on forward face of spar, no cracks on RH side, 1650 hrs, 200hp Angle Valve, some acro.

Thought I would post as it looks like someone is trying to collect some good trend data. Thanks!
 
S B rear spar cracks

RV 8 1250 hours some acro many races at or above vne shop heads to the rear no cracks.
RV 10 1000 hours no cracks.
 
9,10,14

Note that the RV-9, 10 & 14 all have lightening holes in the HS ribs making inspection easy….unless, of course, you have glassed them in.
 
RV-8 Crack

RV-8 inspected:

1 small crack found on left side.

1192 hours, lots of acro, flight into “buffet”, and air racing. Hinge bracket rivet shop heads on forward face of spar.

Skylor
 
NOTE: Reporting has been set up on its own thread so we can more effectively communicate the SB revision info here. If you've come here to report your airplane's results, please visit this thread instead and post there - thanks!

The reports appearing here constitute an extremely small sample of the fleet, not sure how valuable statistically it will be.

It's interesting info from a discussion perspective to be sure, but it's also incomplete and therefore not really statistically valuable. Also, some of the questions/assumptions being asked/made are not all that meaningfully relevant to the actual problem that needs to be addressed.

Our team's analysis and decision to release the SB and parts is not based solely or principally on field data. Obviously, real-world info from the field predicated our initial investigation, but the decision to issue the bulletin and changes was based on a deeper engineering analysis using modern computer design and stress analysis tools. Note that these are tools that were not available when the models on which we are currently seeing occasional cracks were designed.

To be ultra-clear, this is what matters most: Eventually, whether it happens in 100 hours or 100,000 hours, all of the RV-3/4/6/7/8 models can and quite possibly will develop cracks if they are flown/operated enough hours/cycles. There will be some significant number of airplanes that won't develop cracks within the lifetime of the airframe - but when it does happen, it matters. Regardless, the necessary fix is essentially the same.

A few key points...

  1. Inspection per the SB is necessary, annually, regardless of any airplane-specific configuration or feature. For example, the location/orientation of the shop/manufactured heads does not modify the need or requirement to comply and is not statistically relevant based on our engineering assessment.
  2. The fix, when needed due to an inspection that reveals cracks, is the only approved/supported fix. Do not fly with cracks present.
  3. Even after implementing the fix, it is prudent and smart to inspect the areas described in the SB as part of routine condition inspections. To extend that point to the whole airplane, any area where forces are concentrated is worth closely inspecting routinely. For some people that might mean a deeper inspection than they have conducted in the past. In that case, this is a great opportunity to step up their inspection game to where it needs to be.

Model-by-model update and availability of parts:

  • RV-9/10/14 models remain inspect-only, and report to Van's support team should you find something.
  • RV-8/7/6-prepunched (very late RV-6 empennages only) will see parts shipping this week. Inspect annually. Install SB parts per the (soon-to-be released) revised SB. There will be two "flavors" of installing the revised parts: one for airplanes where cracks were found and strop-drilled, and another for those without any cracks present. The details of this will be described in the revised SB doc when it is published this week.
  • RV-6 (non-pre-punched)/4/3 will also have revised parts available soon, potentially as early as this week but timing of availability is still TBD pending manufacturing completion and validation.
 
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Just to confirm... If no cracks on completed builds we should not install the new hinge? Install new hinge on completed builds with cracks or non completed builds. Is that correct?

Thanks
 
Just to confirm... If no cracks on completed builds we should not install the new hinge? Install new hinge on completed builds with cracks or non completed builds. Is that correct?

Thanks

It will be the option of the owner to comply with the SB by inspection or via installation of the new parts if cracks are not found at each inspection. Either will be acceptable in that case. We will release the revised SB this week, which will explain the options and the difference when installing before cracks form, vs. after cracks have formed. That info will be shareable when it’s gone through our review and approval process and is publishable.

  • Cracks found and extend into the flange radius: Replace rear spar
  • Cracks found that can be stop drilled: Install the SB kit per the instructions before flying
  • No cracks found: Either inspect no less than annually or install the SB kit before cracks form as a preventative measure
  • Still building: I'd suggest the best/smartest option is to install the SB kit before you fly it and remove it from the list of things to think about and look after
 
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Rivet direction...update...

My -7's and 8 instructions make no mention of rivet directions (first picture), plan revision 3/2014.

Only the -10 and -14 mention this detail. (maybe the 9 but I don't have a set of plans to confirm).

...and for completeness/accuracy, Van's did update the RV-7/8 plans in 2014, the drawing for the elevator includes a depiction of the entire stack-up that clearly shows the shop heads going against the elevator spar (DWG 5, Detail D). Excerpt attached...

I suspect this detail was added in support of SB 14-02-05, Cracks in Elevator Spar.

I wish I could find that Disney movie that showed how to rivet correctly -- I think that's where I learned to put the "dome" on the thinner material...
 

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Early vs late RV6

NOTE: Reporting has been set up on its own thread so we can more effectively communicate the SB revision info here. If you've come here to report your airplane's results, please visit this thread instead and post there - thanks!





  • RV-9/10/14 models remain inspect-only, and report to Van's support team should you find something.
  • RV-8/7/6-prepunched (very late RV-6 empennages only) will see parts shipping this week. Inspect annually. Install SB parts per the (soon-to-be released) revised SB. There will be two "flavors" of installing the revised parts: one for airplanes where cracks were found and strop-drilled, and another for those without any cracks present. The details of this will be described in the revised SB doc when it is published this week.
  • RV-6 (non-pre-punched)/4/3 will also have revised parts available soon, potentially as early as this week but timing of availability is still TBD pending manufacturing completion and validation.

Greg, do you have data by serial number that would let us know if we own a pre punched horizontal or the earlier one? I ordered the earlier kit because I did not know.
 
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I have a question regarding this SB. I am in the process of building my Horizontal Stab and have the rear spar out and available for a fix. My tail kit was ordered in Jan 2022, and shipped sometime in April 2022.

I understand there are parts to order but I have not seen the plans for the fix itself. My question is; would it be wise while the spar is out and available; put a doubler on the opposite side of the hinge to spread the load of the rivets holding the hinges?

Thank you for all the information of this SB!

Dave


NOTE: Reporting has been set up on its own thread so we can more effectively communicate the SB revision info here. If you've come here to report your airplane's results, please visit this thread instead and post there - thanks!



It's interesting info from a discussion perspective to be sure, but it's also incomplete and therefore not really statistically valuable. Also, some of the questions/assumptions being asked/made are not all that meaningfully relevant to the actual problem that needs to be addressed.

Our team's analysis and decision to release the SB and parts is not based solely or principally on field data. Obviously, real-world info from the field predicated our initial investigation, but the decision to issue the bulletin and changes was based on a deeper engineering analysis using modern computer design and stress analysis tools. Note that these are tools that were not available when the models on which we are currently seeing occasional cracks were designed.

To be ultra-clear, this is what matters most: Eventually, whether it happens in 100 hours or 100,000 hours, all of the RV-3/4/6/7/8 models can and quite possibly will develop cracks if they are flown/operated enough hours/cycles. There will be some significant number of airplanes that won't develop cracks within the lifetime of the airframe - but when it does happen, it matters. Regardless, the necessary fix is essentially the same.

A few key points...

  1. Inspection per the SB is necessary, annually, regardless of any airplane-specific configuration or feature. For example, the location/orientation of the shop/manufactured heads does not modify the need or requirement to comply and is not statistically relevant based on our engineering assessment.
  2. The fix, when needed due to an inspection that reveals cracks, is the only approved/supported fix. Do not fly with cracks present.
  3. Even after implementing the fix, it is prudent and smart to inspect the areas described in the SB as part of routine condition inspections. To extend that point to the whole airplane, any area where forces are concentrated is worth closely inspecting routinely. For some people that might mean a deeper inspection than they have conducted in the past. In that case, this is a great opportunity to step up their inspection game to where it needs to be.

Model-by-model update and availability of parts:

  • RV-9/10/14 models remain inspect-only, and report to Van's support team should you find something.
  • RV-8/7/6-prepunched (very late RV-6 empennages only) will see parts shipping this week. Inspect annually. Install SB parts per the (soon-to-be released) revised SB. There will be two "flavors" of installing the revised parts: one for airplanes where cracks were found and strop-drilled, and another for those without any cracks present. The details of this will be described in the revised SB doc when it is published this week.
  • RV-6 (non-pre-punched)/4/3 will also have revised parts available soon, potentially as early as this week but timing of availability is still TBD pending manufacturing completion and validation.
 
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