Preliminary results of the ERAU PA-28 accident

Stress corrosion cracking? It shouldn’t have failed so early in its life but it did. Tensile stresses. Humid environment. Cracks at fuselage-wing joint on both sides.

Wonder what they’ve been using to wash the planes?
 
kyleb said:
I expect they will find or infer something bad happened to that airplane during usage, maintenance, or construction. Arrows have been around long enough that if there was a design flaw that led to premature wing removal, it would have come to light before now.
Click to expand...
Yeah, like fuel selector labeling.
 
We are just going to have to wait and see what the actual report is on the failed part. I think the FAA will initially order large schools like this to inspect all their Arrows, and possibly have them pull a few wings. If there is no pattern and this plane is unique, I believe a visual inspection AD will result. So not bad. If they find more damaged planes the %^$# will hit the fan and the inspections will likely spread to the larger Charokee family.

This is just conjecture on my part. But the FAA seems to be expediting this investigation because of the possible ramifications.

One potential positive. They have not taken the step of grounding all Arrows at this point. Hopefully that means they realize this is a rare events, and they can't over react.

Sent from my SM-G950U using Tapatalk
 
Last edited:
drotto said:
We are just going to have to wait and see what the actual report is on the failed part. I think the FAA will initially order large schools like this to inspect all their Archers, and possibly have them pull a few wings. If there is no pattern and this plane is unique, I believe a visual inspection AD will result. So not bad. If they find more damaged planes the %^$# will hit the fan and the inspections will likely spread to the larger Charokee family.

This is just conjecture on my part. But the FAA seems to be expediting this investigation because of the possible ramifications.

One potential positive. They have not taken the step of grounding all Archers at this point. Hopefully that means they realize this is a rare events, and they can't over react.

Sent from my SM-G950U using Tapatalk
Click to expand...

It was an Arrow.
 
The only good thing--if you can call it that--is they haven't found an obvious smoking gun issue which would cause an immediate bulletin or grounding. Comparing the spar picture to others I've seen it appears the spar has been cracked for an extended period. Just as they found on the R/H side. But as referenced above after a pass under the microscope we'll know the exact failure cause and rate which will probably determine the mitigation process, i.e., AD note.
 
Last edited:
I love the insanity of this hobby. A cohort of derelicts take a new rental car and proceed to tokyo drift the livin shiatsu out of it until the axles snap, car runs through an intersection without brakes and the occupants get killed. So the govt decrees it a crisis and all vehicles of the same make get told to replace axles every 50 hours or 2 years, at owner's expense!

How do you think that would go? Ground dwellers....
giphy (1).gif





.....Pilots?
giphy.gif

Ugh.
 
hindsight2020 said:
I love the insanity of this hobby. A cohort of derelicts take a new rental car and proceed to tokyo drift the livin shiatsu out of it until the axles snap, car runs through an intersection without brakes and the occupants get killed. So the govt decrees it a crisis and all vehicles of the same make get told to replace axles every 50 hours or 2 years, at owner's expense!
Click to expand...
Please promise me that you are going to be very sorry for making misleading analogies when the investigation finds that Piper used junk aluminum after the bankrupcy.
 
overdrive148 said:
uN9W8vb.jpg


:(:(:(
Click to expand...

Since I am not a mechanic or metallurgist or NTSB investigator...... I 'assume' the blackened parts are what was previous cracked/damaged and the shiny part is what broke in flight?
 
DeeG said:
Since I am not a mechanic or metallurgist or NTSB investigator...... I 'assume' the blackened parts are what was previous cracked/damaged and the shiny part is what broke in flight?
Click to expand...
Looks like the areas centered on 3 1/8 and 4 5/8 are cross sections of the bolt holes.
 
Checkout_my_Six said:
yup....a PA-28 Cherokee.
Click to expand...
Again I ment to say Arrow. My initial though is that the whole line may not initially be subject to investigation, because of the changes made to the wing structure and weight to hold the retractable gear. I know the differences are minor, but there may be just enough to hold back from this spreading to all PA28's

Again the PA28's are historically very tough and durable airplanes. This event is very rare, and we are not seeing a rash of events. I think it is very likely there is a history of rough use of this plane, because that is the best case situation for everyone. I am just pessimistic about what the FAA may do just based on past history.

Sent from my SM-G950U using Tapatalk
 
paflyer said:
Looks like the areas centered on 3 1/8 and 4 5/8 are cross sections of the bolt holes.
Click to expand...
Yes those areas appear to be the bolt holes. Somebody higher up said the darkened areas on the outer portion of the cross beam are the old chronic fractures. The shiny area is the part that catastrofically failed.

Sent from my SM-G950U using Tapatalk
 
yup....shiny is new damage....black (fretting) and dull is old damage.
 
When looking at fractured/ruptured metals generally the shiny areas are the recent break and the corroded areas are older cracks. Sorta interesting that the crack on the right appears on both sides of the bolthole. That had to be one heck of a stress concentration after about half the flange material failed.
 
the damage was there for a while....and shoulda been seen during the last inspection. IMHO. ;)
 
Checkout_my_Six said:
the damage was there for a while....and shoulda been seen during the last inspection. IMHO. ;)
Click to expand...
Black corrosion on aluminum seems a bit out of place without heat and moisture. OTOH, I live in a desert. Do you guys closer to a coast see black corrosion on aluminum?
 
Tell me there are other pilots who, when they discover how the wings are held to the plane, say to themselves, “man, I was hoping there’d be like 20x more bolts holding the wings on!” As far as bounced landings in a PA28, I can’t imagine...those things don’t want to touch the pavement...they float for damned near forever.
 
Clark1961 said:
Black corrosion on aluminum seems a bit out of place without heat and moisture. OTOH, I live in a desert. Do you guys closer to a coast see black corrosion on aluminum?
Click to expand...
think.....smoking rivets. movement between the two surfaces causes it.
 
Would be very interesting to see some of the really detailed photos of those bolt holes. From a former structural assembler, they look weird. One looks like it is oversize and the other looks like it had some smearing from the bolt.
 
Hershey Bar wing Arrow prior to 73 is similar to a UH-1 in Autorotation when you pull the power...I swear...and the old ones don't float. I sure hope they find some good answers since I own two PA-28's...
 
Checkout_my_Six said:
think.....smoking rivets. movement between the two surfaces causes it.
Click to expand...
Hmmm, that's going to be a tough sell particularly on the crack which extends past the bolt hole to the interior portion of the flange.
 
Checkout_my_Six said:
the damage was there for a while....and shoulda been seen during the last inspection. IMHO. ;)
Click to expand...
And that is ok ne of the big picture questions here. With a plane subject to 100 hrs inspections, should that have been seen. Here is a ok view of the underside of the Arrow wing. Between the access ports and the wheel well, I am not sure how visable that joint is. This shot shows several aces ports at the leading edge, and the spar lies just forward of the wheele well
cf17e6342f74ccd6a8af6b8def952f6e.jpg


Sent from my SM-G950U using Tapatalk
 
A better wing shot, but it is the older Hershey bar wing.
d954a1e1574761f8d5d645472edba97a.jpg


Sent from my SM-G950U using Tapatalk
 
Gerhardt said:
Tell me there are other pilots who, when they discover how the wings are held to the plane, say to themselves, “man, I was hoping there’d be like 20x more bolts holding the wings on!” As far as bounced landings in a PA28, I can’t imagine...those things don’t want to touch the pavement...they float for damned near forever.
Click to expand...
Gerhardt said:
Tell me there are other pilots who, when they discover how the wings are held to the plane, say to themselves, “man, I was hoping there’d be like 20x more bolts holding the wings on!” As far as bounced landings in a PA28, I can’t imagine...those things don’t want to touch the pavement...they float for damned near forever.
Click to expand...
I was surprised at how short the spar connection to the carry thru is. Just looking at the lever arm.
 
There are cover plates over the bolts on the bottom of the fuselage and access to the center section once the rear seats and plywood cover are removed. As noted previously the cracks would have been visible to diligent inspection.
 
Just found Piper bullitan SB 968A that was issued in August 6, 1999. Sounds very similar to what we may see here. It gave Piper guidelines how to pull the wing and inspect that exact area, including guidelines based on usage and TT.
545b13a38e9059664e066587d80dfe21.jpg


Sent from my SM-G950U using Tapatalk
 
Hard to see for sure but it looks like at least three fatigue crack initiation sites. Quite a lot of propagation before final failure. You really need striation density counts to know what really happened over the life of the plane. That’s in addition to basic material properties testing.

Cheers
 
Last edited:
drotto said:
A better wing shot, but it is the older Hershey bar wing.
d954a1e1574761f8d5d645472edba97a.jpg


Sent from my SM-G950U using Tapatalk
Click to expand...

I am new to this airplane stuff, but am I looking at this correctly? When interpret the pic, it looks like the wing only attaches at two small points? That can’t be correct.


Sent from my iPhone using Tapatalk Pro
 
Peter Anderson said:
I am new to this airplane stuff, but am I looking at this correctly? When interpret the pic, it looks like the wing only attaches at two small points? That can’t be correct.


Sent from my iPhone using Tapatalk Pro
Click to expand...
The main spar attaches with about 18 bolts and that is what you are probably looking at. In addition there are fore- and aft- attachment points that are single pined.
 
Gerhardt said:
ell me there are other pilots who, when they discover how the wings are held to the plane, say to themselves, “man, I was hoping there’d be like 20x more bolts holding the wings on!”
Click to expand...
Same here. I had the same thought the first time I saw all the cowlings off a plane, and a puny little engine sticking out there on some metal tubes
drotto said:
A better wing shot, but it is the older Hershey bar wing
Click to expand...
Yeah... I mean, there must be an incredible amount of stress on that joint and the associate bolts right there. My hats off to the engineers that design and build these things

Anyone ever looked up at that one tiny little bolt that chairlifts swivel on that connect it to the cable? 6 fat guys sitting in a chairlift with all their ski gear on held to the cable by one bolt that appears grossly undersized.. and chairlifts dangle out there in the snow and moisture for decades

Metal is an incredible thing.. until you push it past its limits and it begins to fatigue

I wonder how a Diamond 20 or other composite plane treated the same as the accident bird would have behaved. We've been told composites are unforgiving when they give up the ghost.. but I can't imagine too many things more unforgiving then your wing coming off
 
Clark1961 said:
The main spar attaches with about 18 bolts and that is what you are probably looking at. In addition there are fore- and aft- attachment points that are single pined.
Click to expand...

So that protrusion that looks like a rail w/ all the holes is what you're referring to Clark? I count about 10 holes on the top portion.
 
zaitcev said:
Please promise me that you are going to be very sorry for making misleading analogies when the investigation finds that Piper used junk aluminum after the bankrupcy.
Click to expand...

Do you have any evidence to support your claim they used junk aluminum?
 
SkyDog58 said:
Do you have any evidence to support your claim they used junk aluminum?
Click to expand...
The thing that bothers me is that I haven't seen the flange of a beam fail with that signature. The corroded cracks existed for awhile before the final failure. Were the material properties different in the center portion of the flange? Obviously I don't know. the cracks which existed prior to failure look a little suspicious.
 
Tantalum said:
Same here. I had the same thought the first time I saw all the cowlings off a plane, and a puny little engine sticking out there on some metal tubes

Yeah... I mean, there must be an incredible amount of stress on that joint and the associate bolts right there. My hats off to the engineers that design and build these things

Anyone ever looked up at that one tiny little bolt that chairlifts swivel on that connect it to the cable? 6 fat guys sitting in a chairlift with all their ski gear on held to the cable by one bolt that appears grossly undersized.. and chairlifts dangle out there in the snow and moisture for decades

Metal is an incredible thing.. until you push it past its limits and it begins to fatigue

I wonder how a Diamond 20 or other composite plane treated the same as the accident bird would have behaved. We've been told composites are unforgiving when they give up the ghost.. but I can't imagine too many things more unforgiving then your wing coming off
Click to expand...
I have talked to mechanics about metal vs. composit. Many of them like the metal planes because they say you can usually tell visually when metal is fatiguing. It warns you that is is going to have a problem. You can see wrinkles, cracks, changes in color, etc.

Composites on the other hand do not show issues to the naked eye till failure. Apparently, you can do things like ultrasound the composite to see hidden damage, but that is expensive and time consuming. So there is damage there, but you can not see it. So when it does fail there appears to be no warning.

Sent from my SM-G950U using Tapatalk
 
You must log in or register to reply here.
Back
Top