Sometimes small metal chips/flakes (possibly from assembly of the aircraft) can get wedged at the interface stack-up within the hole. The eddy current will do its job and see this chip as the coil goes around within the hole. Scratches/pits/gouges, etc, may certainly give an indication, but the phase of the signal will differentiate between a separation of material, like a real crack, or a scratch, etc. Unfortunately, new eddy current technicians might reject a hole because they see an amplitude signal alone. This signal must be evaluated by looking at the phase of the indication. If the indication has amplitude AND crack-like phase (which they set-up on a 0.030” x 0.030” EDM notch to simulate that crack), then yes it would be rejectable. Using a bottle brush would be my first step after seeing a suspicious signal to eliminate any false indications. Cracks cannot go away, so if the repeated inspection passes, then most likely there was a spec of metal within the hole during the original eddy current test, and removed with a bottle brush.
BTW- We’ve performed 210 aircraft to date, with a 4% failure rate. If you have any question regarding this eddy current inspection, please feel free to contact me directly.
Jim Hofer Aerohoff NDT 760-567-4123 Sales@aerohoff.com FAA Repair Station I9OR058X
It’s all over the board. We’ve done a Piper with 25,000, 17,000, and 13,000 TT hours that passed. We’ve also done Pipers with 13,000, 10,000, 6,800, and 4,800 TT hours that have failed. Unfortunately I do not keep track of the factors hours, but the mechanics do. We just get called in to perform the eddy current inspections as needed.
From your response, it does not appear that factored hours or TT play a significant role in determining failures. The company that did my inspection (my plane passed) mentioned that the most common trends they observed on aircraft that failed were that they had either been subjected to heavy G stresses, or had suffered very hard landings. Or both.
My questions:
Have you seen any other trends in the failures?
If not, can you confirm the above observations?
Only trend was the the first 8 Pipers inspected, the crack-like indication was always in the right forward hole, at the lower surface of the wing spar itself, and the indication started at the hole and was protruding aft. Just over a week ago, we found our first left forward hole with 2 crack-like indications (one going aft and one going forward). Again it was in the lower part of the wing spar. This type of fatigue cracking in a hole is typical, as when a crack gets so large on one side, it will start fatiguing 180 degrees opposite. Needless to say, this spar didn’t have much time left.
Anyone in the Las Vegas area needing inspection, I have Aerohoff coming to KHDN on 4/19/21 for my plane. We can save $$ if we bundle!! Call me 702 501 3505, Dave Waters
Just had my 1968 arrow eddy current tested even though it wasn't required my wife and I decided to have it done, just for peace of mind. A little history on my Arrow. 2005 hard landing
The left wing spar was replaced with a new spar and 1 rib (All documentation in log ) by Williams (excellent work). Since wing was rebuilt and not a salvaged wing we went ahead with the inspection (minor issues).
Left wing FAILED, right wing good. The shop that did the R&R butchered the installation, Not only are there gouges in the holes it looks like they used a ratchet to drive the bolt up. There are thread marks in one hole almost like a tap was used. In another hole my A&P lightly tapped it with the handle of a screwdriver and it fell right out. Looks like someone honed out that hole during installation. Right now I have a call into the F.SD.O. and an e-mail to one of the people involved with this AD. Also wrong washers were used to reinstall wing.
These holes look like a train wreck. The wing is going back to Williams for another rebuild and thisn time installed correctly. there is at least a 2 mo. backorder o spars so we will be down for a while. How many other aircraft are flying with improperly installed wings?
e-mail me if you want to see HOW NOT to install a wing
This is exactly why some folks recommended AGAINST removing the wing for inspection the first time an AD of this kind reared it’s ugly head 30 years ago. Damage on removing and reinstalling those bolts.
Wow, even after 15+ years, even with all that damage to gtbor1 attach point, the wing did not fall off the airplane! It makes one wonder why a scratch in a bolt hole, that can be polished out for an eddy current PASS as in Harley’s case, can lead to a spar replacement under this AD if not polished out and reinspected. Do all eddy current inspectors do this?
I do applaud the FAA for making an attempt to limit the action to those aircraft most likely affected. I am aware of the anecdotal reports of time not correlating well with failures, but how many of THOSE could have been polished out for a pass saving spar replacement?
Not being a structural engineer, I also wonder how a crack of any kind near ONE bolt hole means the wing could fail when there are 17 other bolts to bear the load? It would seem that in those accident aircraft (a total of 3) to the best of my knowledge, there was a whole lot of cracking going on. In fact, in the first case, apparently very large wing skin cracks were stop drilled before the accident occurred.
Gtbor1;
First of all, sorry to hear. I have some questions. You wrote that there were issues with the holes (threading and possibly honing, both of which would seem to be previous installation issues), but were any actual cracks detected? Damage to the bore may cause an errant reading on the eddy current machine, but did it detect an actual crack?
Good points Mike, and yes, that article is a very interesting read.
Unfortunately, the 1,000+ pages of the FAR/AIM regulations were written in blood. When a fatality occurs, there is no CYA. Whatever led to the fatality will be exposed.
From an engineering standpoint, I would tend to agree with Mike that an improperly installed bolt in an otherwise sound spar should not cause wing failure, whereas a crack is definitely a point of failure. It sounds like the ERAU aircraft involved in the fatal accident was severely abused and had not followed Piper's maintenance recommendations. Now we all pay the price.
Like it or not, the FAA had to make a decision. The downside is it forced all of us to dig into our wallets, some deeper than others. The upside is that finding a cracked spar on the ground may have saved you and/or your family's lives.
I have read these posts a number of times, then let them soak for a day or two. Your comments are sound. But finding a bad wing isn't the issue. My arrow didn't have to be tested according to the AD. The damaged wing was rebuilt with a new spar from piper, all documented in the logs. The problem is the shabby and dangerous work performed by the repair station. I felt if there was an issue it would be with the right wing seeing that its 53 yrs old ( nice and clean no issues).
The damage is about .030 deep, honing them out would make the holes out of tolerance, so that's not an option.
Would the damage develop into a crack, who knows. But what I do know is damage of this type can develop into a crack.
1 quick example:
I own a towing company, I noticed a thin vertical line of rust on the chassis of one of my trucks. upon closer look it was a hairline crack originating from a factory hold that had a small gouge in it. I can give you more but again, that's not the issue.
I was hesitant about buying this arrow because of the wing, but the repair was a new spar and not a salvaged wing. The shop that did the R&R seemed like a good shop so we bought the plane 5yrs ago.
I have e-mails and calls out to the FAA and organizations:
F.S.D.O. in my area and where the work was performed- no response.
AOPA connected me to their A&P sent him pictures of damage
Called this mag. "crickets" not happy with them.
E-mailed a person involved with this AD. He said there is no database tracking faulty repairs but gave address to large a complaint.
This Arrow will be fixed and fix correctly. I'm going to everything I can to hold this shop and the A&P who signed off on the repair accountable. If it doesn't fit you don't use a bigger hammer.
all comments welcomed.
pictures upon request
Jim Hofer (AeroHoff, www.aerohoff.com, 760-567-4123) was fantastic! He has now done 248 aircraft, and this man knows his business. He's had 9 failures, 8 with right forward hole as the issue. Wing off retests and dye penetrant tests confirmed all were really bad. So the Eddy Current test really works.
Don't hammer the bolts out. Take it easy...rubber mallet if needed, lift up on wingtip to relieve pressure. The bolts come out cleanly.
Next, use a gun bore brush to clean the holes to ensure no foreign material is stuck in the hole from the factory that may lead to a false positive.
Next, call all your Piper friends and bundle. The more planes done at once, the cheaper it is for everyone. We did three today (all passed).
Next, Piper has updated the parts catalog, and it no longer specifies the AN172-14A & AN176-13A bolts. It specifies the stronger NAS6606-15 (rear) & NAS6606-13 (front) bolts. Some kit sellers are still supplying the AN-176 bolts, and this is technically wrong (even though original equipment), because the AD specifies the work per the SB-1345, and that points to the IPC which now calls for the NAS bolt. My shop is insisting on NAS bolts and certification documentation, so make sure when you get the hardware, make sure you get the correct h/w and cert.
Your mileage may vary, but this was my experience.
82 archer, 12k + TT. 9200 as a trainer. Left front hole failed by a crack indicated by eddy current test even after honing several times. The A/P performing bolt removal noted excessive corrosion in that hole only. We were early enough in this wing spar pandemic that we located a low time used wing from a 77 Archer. I doubt there’s many, if any out there any more. Of course we had the donor wing inspected, painted, fitted and installed. There were a number of unexpected issues in the process. The donor wing either didn’t have wheel pants or different ones, the pitot static lines entered the fuselage in different places, slightly different wiring, etc. But she flies again. Total cost around $10,000 and 7 months grounded. By the way I just happen to have a left wing, with a tiny little crack in 1 of 18 bolt holes if anyone wants a lawn decoration or perhaps a bar top.
Comments
If the indication has amplitude AND crack-like phase (which they set-up on a 0.030” x 0.030” EDM notch to simulate that crack), then yes it would be rejectable. Using a bottle brush would be my first step after seeing a suspicious signal to eliminate any false indications. Cracks cannot go away, so if the repeated inspection passes, then most likely there was a spec of metal within the hole during the original eddy current test, and removed with a bottle brush.
BTW- We’ve performed 210 aircraft to date, with a 4% failure rate. If you have any question regarding this eddy current inspection, please feel free to contact me directly.
Jim Hofer
Aerohoff NDT
760-567-4123
Sales@aerohoff.com
FAA Repair Station I9OR058X
Jim
Thanks so much for the info, Jim. This is valuable stuff and we're grateful to have you on the forum. Stay healthy!
Scott Sherer
Wright Brothers Master Pilot, FAA Commercial Pilot
Jim Hofer;
Excellent analysis, thank you for posting.
From your response, it does not appear that factored hours or TT play a significant role in determining failures. The company that did my inspection (my plane passed) mentioned that the most common trends they observed on aircraft that failed were that they had either been subjected to heavy G stresses, or had suffered very hard landings. Or both.
My questions:
Have you seen any other trends in the failures?
If not, can you confirm the above observations?
Thanks in advance.
Jim "Doc Griff" Griffin
PA28 - 161
Chicago area
Good question, Griff, thanks for the post.
Scott Sherer
Wright Brothers Master Pilot, FAA Commercial Pilot
Just over a week ago, we found our first left forward hole with 2 crack-like indications (one going aft and one going forward). Again it was in the lower part of the wing spar. This type of fatigue cracking in a hole is typical, as when a crack gets so large on one side, it will start fatiguing 180 degrees opposite. Needless to say, this spar didn’t have much time left.
Jim
Thanks so much, Jim.
Scott Sherer
Wright Brothers Master Pilot, FAA Commercial Pilot
Just had my 1968 arrow eddy current tested even though it wasn't required my wife and I decided to have it done, just for peace of mind. A little history on my Arrow. 2005 hard landing
The left wing spar was replaced with a new spar and 1 rib (All documentation in log ) by Williams (excellent work). Since wing was rebuilt and not a salvaged wing we went ahead with the inspection (minor issues).
Left wing FAILED, right wing good. The shop that did the R&R butchered the installation, Not only are there gouges in the holes it looks like they used a ratchet to drive the bolt up. There are thread marks in one hole almost like a tap was used. In another hole my A&P lightly tapped it with the handle of a screwdriver and it fell right out. Looks like someone honed out that hole during installation. Right now I have a call into the F.SD.O. and an e-mail to one of the people involved with this AD. Also wrong washers were used to reinstall wing.
These holes look like a train wreck. The wing is going back to Williams for another rebuild and thisn time installed correctly. there is at least a 2 mo. backorder o spars so we will be down for a while. How many other aircraft are flying with improperly installed wings?
e-mail me if you want to see HOW NOT to install a wing
gtbor@yahoo.com
Yikes!!!
I love to defy gravity!
1979 Arrow IV
Wow, even after 15+ years, even with all that damage to gtbor1 attach point, the wing did not fall off the airplane! It makes one wonder why a scratch in a bolt hole, that can be polished out for an eddy current PASS as in Harley’s case, can lead to a spar replacement under this AD if not polished out and reinspected. Do all eddy current inspectors do this?
I do applaud the FAA for making an attempt to limit the action to those aircraft most likely affected. I am aware of the anecdotal reports of time not correlating well with failures, but how many of THOSE could have been polished out for a pass saving spar replacement?
Not being a structural engineer, I also wonder how a crack of any kind near ONE bolt hole means the wing could fail when there are 17 other bolts to bear the load? It would seem that in those accident aircraft (a total of 3) to the best of my knowledge, there was a whole lot of cracking going on. In fact, in the first case, apparently very large wing skin cracks were stop drilled before the accident occurred.
This was an interesting read:
https://piperowner.org/talk/uploads/editor/qz/xquw0pusv13i.pdf
Gtbor1;
First of all, sorry to hear. I have some questions. You wrote that there were issues with the holes (threading and possibly honing, both of which would seem to be previous installation issues), but were any actual cracks detected? Damage to the bore may cause an errant reading on the eddy current machine, but did it detect an actual crack?
Jim "Doc Griff" Griffin
PA28 - 161
Chicago area
Good points Mike, and yes, that article is a very interesting read.
Unfortunately, the 1,000+ pages of the FAR/AIM regulations were written in blood. When a fatality occurs, there is no CYA. Whatever led to the fatality will be exposed.
From an engineering standpoint, I would tend to agree with Mike that an improperly installed bolt in an otherwise sound spar should not cause wing failure, whereas a crack is definitely a point of failure. It sounds like the ERAU aircraft involved in the fatal accident was severely abused and had not followed Piper's maintenance recommendations. Now we all pay the price.
Like it or not, the FAA had to make a decision. The downside is it forced all of us to dig into our wallets, some deeper than others. The upside is that finding a cracked spar on the ground may have saved you and/or your family's lives.
Jim "Doc Griff" Griffin
PA28 - 161
Chicago area
I have read these posts a number of times, then let them soak for a day or two. Your comments are sound. But finding a bad wing isn't the issue. My arrow didn't have to be tested according to the AD. The damaged wing was rebuilt with a new spar from piper, all documented in the logs. The problem is the shabby and dangerous work performed by the repair station. I felt if there was an issue it would be with the right wing seeing that its 53 yrs old ( nice and clean no issues).
The damage is about .030 deep, honing them out would make the holes out of tolerance, so that's not an option.
Would the damage develop into a crack, who knows. But what I do know is damage of this type can develop into a crack.
1 quick example:
I own a towing company, I noticed a thin vertical line of rust on the chassis of one of my trucks. upon closer look it was a hairline crack originating from a factory hold that had a small gouge in it. I can give you more but again, that's not the issue.
I was hesitant about buying this arrow because of the wing, but the repair was a new spar and not a salvaged wing. The shop that did the R&R seemed like a good shop so we bought the plane 5yrs ago.
I have e-mails and calls out to the FAA and organizations:
F.S.D.O. in my area and where the work was performed- no response.
AOPA connected me to their A&P sent him pictures of damage
Called this mag. "crickets" not happy with them.
E-mailed a person involved with this AD. He said there is no database tracking faulty repairs but gave address to large a complaint.
This Arrow will be fixed and fix correctly. I'm going to everything I can to hold this shop and the A&P who signed off on the repair accountable. If it doesn't fit you don't use a bigger hammer.
all comments welcomed.
pictures upon request
N9394W just passed eddy current inspection!
What I learned...
Jim Hofer (AeroHoff, www.aerohoff.com, 760-567-4123) was fantastic! He has now done 248 aircraft, and this man knows his business. He's had 9 failures, 8 with right forward hole as the issue. Wing off retests and dye penetrant tests confirmed all were really bad. So the Eddy Current test really works.
Don't hammer the bolts out. Take it easy...rubber mallet if needed, lift up on wingtip to relieve pressure. The bolts come out cleanly.
Next, use a gun bore brush to clean the holes to ensure no foreign material is stuck in the hole from the factory that may lead to a false positive.
Next, call all your Piper friends and bundle. The more planes done at once, the cheaper it is for everyone. We did three today (all passed).
Next, Piper has updated the parts catalog, and it no longer specifies the AN172-14A & AN176-13A bolts. It specifies the stronger NAS6606-15 (rear) & NAS6606-13 (front) bolts. Some kit sellers are still supplying the AN-176 bolts, and this is technically wrong (even though original equipment), because the AD specifies the work per the SB-1345, and that points to the IPC which now calls for the NAS bolt. My shop is insisting on NAS bolts and certification documentation, so make sure when you get the hardware, make sure you get the correct h/w and cert.
Your mileage may vary, but this was my experience.
New type bolts = exactly what are the technical differences & standards between the old OEM bolts and the new bolts? New type of nuts as well???
NAS 160,000 psi tensile strength
Not sure spec differences on nuts, but NAS spec is stronger than AN