Wing Spar Inspection
So I just saw something depressing on FB. It seems the FAA is considering putting a life limit on our wing spars. I didn't read the entire missive, but I'd like to hear opinions from those more knowledgeable than me. I had my Arrow II tested, and it passed. I thought that was that. Is it possible our planes could have an expiration date now?
Comments
Your timing is impeccable. Scott just posted the Airworthiness Bulletin the news story you mention was based upon. In it, FAA does a decent job of describing the science and rationale underlying their actions, and points out the spar of the Seminole is already life-limited to between 14/16K hours, depending on usage. Contact information for the supervising structural engineer is given at the end, and they invite you to contact him with questions or comments.
Scott posted the SAIB in another spot on the forum, here:
and we have posted a story on our regular website, here.
I will add that it's interesting to note that we sent a link to that article above to the FAA, and they approved its content. And it says "this might lead to another AD" right in it, they didn't have us redact that.
Digital Product Manager
Piper Owner Society
If the ramp at your local airport was a car show, it would be a bunch of old classic cars.
These airplanes are getting old, and I'm not really sure the engineers designed them to be around 70 years later.
I think periodic inspections is probably wise, but what will that entail? Constantly pulling bolts can't be that healthy for the spar.
Would there happen to be a list of approved eddy current inspection facilities that could be provided?
Hey fellows, I posted it the moment I got it. I own a PA-28, too, and here's how I look at it. The FAA is saving our bacon at the expense of some money. While money is important, we are more important.
If that doesn't help, maybe Jack Daniels does :)
Scott Sherer
Wright Brothers Master Pilot, FAA Commercial Pilot
I must be missing something. That service bulletin is asking for feed back on availability of eddy current testers, Asking how people feel about the factored hours. Was there any other damage that wasn't reported. And anything else you want to contribute.
That is currently it?? Yes, to me it means they will issued some kind of regular check up as long as they determine there are enough eddy current testers around the country.
If that is the extent of it and we can get the test done with our annual. I am not that upset. The only possible bad will be if they determine usable life of the spar and planes have to become sold for parts at some point. But if it goes like the Pa44 at 15,000 hours not too much of an issue. If they go with 10,000 that becomes more of a problem for flying school planes.
I really don't want my wing to fall off. Just saying!
But am I missing something else?
Andy Sikora
1972 PA28R-200
X51
Retired Miami ATCT/Tracon
Nope, it's just a warning of another AD to come.
Scott Sherer
Wright Brothers Master Pilot, FAA Commercial Pilot
Agree that it seems like we may expect more ADs.
Focus also seems like it is a fishing expedition to discover damage from previous ADs just as much as intent to find spar failures.
Also agree with comments that this is both good and bad. Nobody wants structural failre. And nobody wants secondary effect damage while repeatedly groping around trying to figure this out.
In terms of the possibility of a life limit, composite airframes have this. But then again, IIRC composites hit the market after the regs changed and engineering life limits turned into a requirement. Our aircraft were built prior to this requirement and nobody really wants to go back and pay for the math. The tragedy I see from the current slate of life limited parts is that they require death of the aircraft upon expiration, as opposed to replacement of the life-limited part and a reset of the timer. Put another way, unless I am missing something, upon the aircraft reaching its expiration, it is Ok to salvage parts / components and install them in other aircraft, but not the timed-out parts. Given this, I am not clear on the logic of how we cannot swap-out the expiered parts for new, and keep on flying.
Expired parts only good for man cave art,, all other parts would be ok to use pending serviceability checks. Carl
48 yrs A/P IA DAL aircraft inspector. 172N
Thanks Carl!
Scott Sherer
Wright Brothers Master Pilot, FAA Commercial Pilot
Just a comment on life limited parts. Its all relative. In the helicopter world, the Robinson R22 for example, a popular two place helicopter, the main rotor and tail rotor have a life limit of 2200 hours or 12 years whichever comes first 😱.
If necessary, 16,000 hours on a wing spar might not be too bad 😬
The part about secondary damage is something to be concerned about. They had to remove, inspect, and replace with new bolts. But how many times can they safely remove and replace the bolts without causing damage. There were problems getting many of the bolts out. So that is the problem and the biggest down side that I now see, after reading numerous comments here and other places. It seems many, especially those trying to sell, had the test done, even if they were not at the 5000 factored hours.
It is a peace of mind test. But I am not so sure I do the test again until I get to 5000 factored hours or are mandated to have it done. Risk vs reward.
It seems the FAA IS fishing for answers that they don't really have and aren't sure what to do next. Just my opinion
Andy Sikora
1972 PA28R-200
X51
Retired Miami ATCT/Tracon
The eddy current test performed on our 1982 Archer indicated a crack in the left fwd, outboard hole. Strangely, we performed that test the very day the service bulletin was issued. The mechanic had difficulty removing that bolt and only that bolt, because there was corrosion on the bolt. The testing indicated all the other holes were clean and OK. The airplane was grounded, we found a used wing from a 77 Archer, had the holes inspected, painted and installed it, and all is good. The right wing is still original, nearly 11,000 TT, 9500 as a trainer. The left wing has 2500 TT. I’m still skeptical that there was actually a crack. I think there was some surface damage to the inside of the hole when the rusty bolt was removed and that looked like a crack to the eddy current equipment. I find it interesting that when I spoke to the FAA about this, they didn’t seem interested in our old wing which is now probably been made into a beer can, but they seem to have all this data about cracks in spars. I also find it interesting that the vast majority of the cracks in the data are from Cherokees that have the NACA tapered wing not the Hershey bar wing. The corrosion on the spar bolt in our Archer, was due to an aged and leading wing root seal. I haven’t looked yet, but does the Hershey bar wing have the same or similar seal?
just my 2 cents on the matter.
1982 Archer II with a 1977 wing on one side :/
You bring up some very valid points.
The bolts and holes are close tolerance and every disassembly/reassembly introduces a little wear.
Eddy current testing can mistake a scratch for a crack. There were cases where a crack was detected, then a gun bore brush was run through the bolt hole a few times and upon retesting, it passed. I believe you lived through that exact scenario before you had the wing replaced.
Jim "Doc Griff" Griffin
PA28 - 161
Chicago area
About that corrosion. When I got the plane last year, there were for locations on the wing root seals (two each side) where the seal delaminated from the wing root. Each was coincidentally right above a spar. Logs are not clear on when that might have happened (aside from years ago when the root seals were replaced). The A&P who did my Annual was not overly happy with me on one work order item as I requested a wing root seal replacement, and the job occurred in an unheated hanger, during Winter. At least I now have some corrosion mitigation back in place.
From the territory that I know enough to be dangerous, one of the non-intrusive spar tests included a red dye which IIRC was petroleum based. Intent was for the stuff stuff to wick its way into crevices and make visual inspection easy to spot a spar crack. Except the stuff would wick into any crevice (including washers and bolt heads) and stay there. Last I checked, oil attracts dirt and moisture. So, no potential for second order corrosion there either. Especially at the exact locations where we are trying to maintain structural integrity.
So to me, the fishing needs to stop as it has the potential to do more harm than good. Yes, I am all-in for safe aircraft, but not for death by a thousand inspections. At this point, my senses are that we are saving our Government a lot of money by way of doing the testing for the Government, but we are spending our money without entrance crieteria, no test duration, and no exit criteria.
Oddly enough, my friend who owns the scrap metal recycling yard here, kept the old wing. He had planned to use it to decorate his “man cave”. So, I took a sawzall and lopped of the end of the spar.
The hole with the circle penciled around it is of course the left, fwd, outboard hole that condemned the airplane to a $10,000 investment. I don’t know if it has any value to the FAA, Piper, the Piper owners group or for anything but a coffee table ornament, but I’ll be damned if I can see anything with 3 pairs of reading glasses and a penlight, that looks like a crack. Some pitting maybe, and very maybe.
On another note, the fuel tank is in pretty good shape if anyone needs one.
With respect to eddy inspections mistaking a scratch for a crack,, what you see is a (indication), whether it is a crack is up to additional steps at that point. Yes, running brushes is the first attack. IF the hole is damaged due to corrosion or removal issues,,, the next attack is to oversize the hole to the next nominal size for a fastener. Anyway, the only way to be totally sure, wing removal and a FPI dye check, not the red stuff, FPI is very sensitive to surface cracks.
I had one plane with damaged holes from repeated removals,, oblong and lots of thread damage. Made the FBO remove from fleet . It will crack. Piper is not going to give you a AMOC to oversize the holes,
Carl
48 yrs A/P IA DAL aircraft inspector. 172N
Correct, an AMOC was not a feasible option. We actually ran a hone inside the hole to see if the “indication” would go away, but it didn’t. As I recall, there was discussion about Air Tractors and an AMOC that allows for over sizing the hole in those aircraft, and using a larger bolt, but there wasn’t any provision for that process with respect to PA type aircraft and although I was told it was possible to apply for one, it would be prohibitively expensive and still not likely to be accepted. I still find it curious that the NACA wing Piper show up with more occurances than the Hershey bar wing. ie: Warriors and Archers.
I think I was actually able to photograph what was “indicated” as a crack by the eddy current examination. Maybe it is. I think it’s the one on the left. The NDT technician said it was at the 5:00 position and that would be about right.
Nice photo spike. From the phot it appears you also had what looks like some good exfoliation corrosion starting. Not a good combo for sure. As mentioned, the best way to verify is with a FPI inspection. We also use a 4mm rigid scope with a very close focal range. Can actually see the cracks most of the time. You have to be cautious on using a actualy "hone" you have the potential to peen over the indication, making it very hard for follow up NDT. CArl
48 yrs A/P IA DAL aircraft inspector. 172N
I noticed that too with regard to the overwhelming qty of testing failures with tapered wing versions. What i didn’t see was the total qty of tapered and Hershey bar wing aircraft tested. At least there could be a determination if it is more relevant to a certain wing design.
Dan
Dan
Private Pilot, ASEL & Instrument
1975 PA-28R-200
As a Dakota owner, I'm thinking since the 236 wing has a beefed up spar, it should not be in the same situation as the thinner spar. I included the Aircraft Components YouTube video of the differences in the Piper spars. This video did mention the Hershey and tapered wings have the same spars, just for information.
https://youtu.be/tnbvlXEq5kQ
We have performed over 350 wing spar eddy current inspections throughout the US, with 12 rejectable spars (3.4% rejection rate). As someone mentioned earlier, scratches do produce indications, but scratch-like indications are in a different “phase” than a crack (or separation of material), and can be separated out. We do not reject scratches. Also mentioned earlier was honing or brushing of the hole with an indication. This would be the next step to see if there is any loose aluminum flake (possibly from fabrication) that is wedged at the interface). Often I would see material exit the hole after brushing, and indications during re-inspection, do not appear again. Now, regarding the 3.4%, I have had the opportunity to re-eddy-current inspect many of these aircraft, and when indications re-appear, perform a best-effort fluorescent penetrant inspection. The penetrant indications would “bleed-out” after wiping, thus validating the eddy current inspection. Some of the 3.4% rejected aircraft had flaws that were extremely large, and even started cracking 180 degrees around the hole (yes, 2 indications in that one hole). Some were so small, only eddy current would detect that indication (I.e. 0.030” x 0.020”; 0.010” x 0.010”). A borescope is not a good tool for these extremely small indications. All cracks we detected were in the forward holes, at the lower interface of the spar, and propagating aft at the 6 o’clock position.
A properly trained eddy current NAS410 Level 2 technician, can determine if there are scratches or crack-like indications. I did watch a You-Tube video from an NDT company in Texas that an un-experienced “Level 2” eddy current technician put together trying to show how the inspection works. They actually showed on the video using the wrong reference standard…. And this was suppose to be an informational video. I called them and the FAA regarding the video and it was pulled immediately.
This last photo revealed a 0.030” x 0.020” crack-like indication.
I’m not sure about life-limiting the wings, but my experience would be to re-inspect these holes at an interval inspection Piper stress analysis determines safe.
Jim Hofer
Aerohoff Mobile NDT
E: sales@aerohoff.com
This all started as a fishing expedition to see if they were going to expand or not.
Jim, excellent phots.. Try doing one of these!! LOL
IA. Level 2 Eddy DAL Inspector
Carl
48 yrs A/P IA DAL aircraft inspector. 172N
Having done a lot of these inspections, what were the “factored hours” of the aircraft that come back positive for cracks? Is the 5000 factored hours an accurate way to determine whether we should have the test performed? I read elsewhere that it seemed there were more positive results from the tapered wings. Have you seen that as well?
We’ve performed the ET inspection on aircraft with 25,000 hours that have passed, 17,000 hours that have passed, and 17,000 hours that have failed (all total time, not factored hours). We’ve performed the ET inspection on an aircraft that had 4800 hours, and it failed. Owner was just doing the inspection for peace-of-mind. The consortium of aircraft that we’ve performed, doesn’t appear to have any rhyme or reason to when the aircraft start cracking.
Also, replying to Carl, that hole may create too much eddy current noise, and may need some “working” prior to getting any distinct eddy current results. It happens. We’ve seen it too.
Great photo Carl. Thanks.
Jim
I covered this issue in depth when the NPRM was issued. Fell on deaf ears at the FAA.
carl
48 yrs A/P IA DAL aircraft inspector. 172N
Jim and Carl,
thank you for keeping us safe, and posting about your inspection and NDT experience. As another poster commented a few days ago, "aviation often suffers from a lack of objective information."
that thought in mind, I vaguely recall about 20 years ago there was significant concern about spars in the 400-series Cessnas, and subsequent corrective actions issued by FAA. As part of the investigation there was a "road show," touring the country, chaired by Cessna and including FAA, the structures group at AFRL, and the maintenance director from Cape Air (who had a large fleet of 402s). The two-hour presentation up in Boston was attended by roughly half A&Ps and half structural engineers, and the Cessna team reviewed the history and details of the investigation, the analysis, fleet sampling and Instron work they had performed, and talked about the potential options for mitigating the risk. Of course, ECT was a big part of the solution. The panel spent over an hour fielding questions and recommendations from the audience. Although the work wasn't perfect, I was left with the impression they did a competent job, and were relatively transparent about the process.
Have any of your seen similar "road shows," for the Piper spars? I'm sure they're all doing a good job, but I'd feel better if I could "check their math."
Bob
So, I haven’t talked to anyone with the experience you have. I have under 4000 total hours on my 1967 PA-32-260. Factored hours is just over 1000. There were 9 100 hour inspections early on in her history. Is this something you would recommend doing?