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SonicFlyer
04-17-2018, 08:53 AM
As rumored, wing came off in flight, looks like metal fatigue:


https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20180404X13226&AKey=1&RType=HTML&IType=FA


rickair7777
04-17-2018, 09:35 AM
This airplane probably led a life of high-cycles, with plenty of low-altitude maneuver and cruise in air that tends to be bumpy and salty. This could be the canary for PA-28's of that generation. Wouldn't surprise me to see bulletins or AD's to follow.

Fair winds and following seas.

dera
04-17-2018, 10:24 AM
What a horrible, horrible way to go :(

I wonder if this could have been detected by completing SB1006.


PotatoChip
04-17-2018, 10:33 AM
Absolutely horrible. So sad.

Whale Driver
04-17-2018, 11:37 AM
You rarely see pictures in Prelim reports. My guess is the NTSB is going after an Emergency AD.

"None of the surfaces exhibited visible evidence of corrosion or other preexisting damage. The right wing also exhibited fatigue cracks in the lower spar cap at the same hole location extending up to 0.047-inch deep."

SB1006 is for corrosion behind the fuel tank mid spar.

dera
04-17-2018, 12:00 PM
You rarely see pictures in Prelim reports. My guess is the NTSB is going after an Emergency AD.

"None of the surfaces exhibited visible evidence of corrosion or other preexisting damage. The right wing also exhibited fatigue cracks in the lower spar cap at the same hole location extending up to 0.047-inch deep."

That's scary. And yeah, not surprised if there's an (expensive) Emergency AD soon.

2StgTurbine
04-17-2018, 12:02 PM
This could be the canary for PA-28's of that generation.

The plane was made in 2007, so it really isn't that old for a trainer. I hope this aircraft had a unique history to explain the fatigue.

rickair7777
04-17-2018, 12:28 PM
The plane was made in 2007, so it really isn't that old for a trainer. I hope this aircraft had a unique history to explain the fatigue.

I know. I think the unusual history was the location and use of the aircraft. If a failure was going to occur, that's exactly the kind of operational history where it would happen first. Since the other wing exhibited fatigue as well, it wasn't a defect in just the one spar. May affect other aircraft in that general production run.

I'm *assuming* not a design flaw, since piston ASEL wing spars are pretty well-defined technology. Perhaps a material defect from the mfg... that might affect other hulls. Worst case they tried to use high-tech design tools to remove weight during a design update, and went too far.

Since both wings were affected, and the plane was so new, I suspect we're going to hear more on this one. If my kid went to school there, he'd be grounded until they checked the other planes, or determined that that the accident plane was over-stressed.

It's *possible* somebody over-stressed the plane at some point in the past and didn't report it, but frankly it would be hard to crack wing spars without bending anything first... I would think an event like that that would have left visible bent sheet metal and popped rivets. I've seen over-stressed planes that made it home and they were obviously jacked up.

rickair7777
04-17-2018, 12:32 PM
You rarely see pictures in Prelim reports. My guess is the NTSB is going after an Emergency AD.

"None of the surfaces exhibited visible evidence of corrosion or other preexisting damage. The right wing also exhibited fatigue cracks in the lower spar cap at the same hole location extending up to 0.047-inch deep."

SB1006 is for corrosion behind the fuel tank mid spar.

x2
.........

Blackhawk
04-17-2018, 05:14 PM
Iíll be the jerk to say it.
I hope this accident weighs heavily on every ERAU student and CFI who ever did unauthorized aerobatics in one of these airplanes.

2StgTurbine
04-17-2018, 05:43 PM
Iíll be the jerk to say it.
I hope this accident weighs heavily on every ERAU student and CFI who ever did unauthorized aerobatics in one of these airplanes.

I have seen some stupid stuff at a college flight school, but I have never seen or heard of CFIs or students routinely doing aerobatic maneuvers in an Arrow. Aerobatics are actually difficult to do in a trainer, so most of the pilots dumb enough to do that wouldn't have the skill to perform any maneuver more complicated than an 80 degree bank.

dera
04-17-2018, 06:10 PM
Overload fractures due to excess G's in an Arrow happen further out the wingspan. If you snap a wing on an Arrow (According to Piper, it happens at 163.7% of design limit load which is around 7G) it fails at approx. 40% span.
If this damage was caused by heavy loads that were within the design envelope, that's a serious design flaw in itself.
So I'd imagine if the fatigue crack was caused by constant abuse, it would have been in a different location (assuming that the failure point is where the highest stress also is during excessive G maneuvering).

121guy
04-17-2018, 08:59 PM
Iíll be the jerk to say it.
I hope this accident weighs heavily on every ERAU student and CFI who ever did unauthorized aerobatics in one of these airplanes.

You said what I was thinking.

TiredSoul
04-18-2018, 02:38 AM
Itís not that difficult to roll or loop in a trainer. Depending on the airplane and the proficiency of the pilot the proper execution and if not the recovery may be very difficult.
No airplane I know off came apart during a spin. They do come apart in a botched recovery.
Considering a plane used for CPL Training does a lot of landings that plane may have had 25000+ landings including its share of unreported hard landings.

FlyJSH
04-18-2018, 04:21 PM
Overload fractures due to excess G's in an Arrow happen further out the wingspan. If you snap a wing on an Arrow (According to Piper, it happens at 163.7% of design limit load which is around 7G) it fails at approx. 40% span.
If this damage was caused by heavy loads that were within the design envelope, that's a serious design flaw in itself.
So I'd imagine if the fatigue crack was caused by constant abuse, it would have been in a different location (assuming that the failure point is where the highest stress also is during excessive G maneuvering).

That would be a positive G overload you have described. I wonder where the failure would be if after a zillion student pilot smack-it-into-the-ground landings would be. In those sorts of landings, from the wing's perspective, they are negative G events.

Blackhawk
04-19-2018, 10:29 AM
Itís not that difficult to roll or loop in a trainer. Depending on the airplane and the proficiency of the pilot the proper execution and if not the recovery may be very difficult.
No airplane I know off came apart during a spin. They do come apart in a botched recovery.
Considering a plane used for CPL Training does a lot of landings that plane may have had 25000+ landings including its share of unreported hard landings.

The problem is when the maneuver is not done correctly normal category airplanes are not stressed to the G-loading necessary to sustain such maneuvers. And since such maneuvers are not authorized the offenders rarely, if ever, fess up.
This was not a very old airplane by any stretch of the imagination and, according to the preliminary report, no sign of corrosion.

Blackhawk
04-19-2018, 10:31 AM
I have seen some stupid stuff at a college flight school, but I have never seen or heard of CFIs or students routinely doing aerobatic maneuvers in an Arrow. Aerobatics are actually difficult to do in a trainer, so most of the pilots dumb enough to do that wouldn't have the skill to perform any maneuver more complicated than an 80 degree bank.

I've been around aviation long enough (32 years), that I've seen some pretty dumb stuff. Don't sell pilots short- they will try aerobatics in just about anything, often with spectacular (in a bad way), results.

Blackhawk
04-19-2018, 10:37 AM
My emphasis.


https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20180404X13226&AKey=1&RType=Prelim&IType=FA


" Preliminary examination of the left wing main spar revealed that more than 80% of the lower spar cap and portions of the forward and aft spar web doublers exhibited fracture features consistent with metal fatigue (see figure 1).The remainder of the lower spar cap, spar web doublers, and upper spar cap displayed fracture features consistent with overstress fracture. The fatigue features originated at or near the outboard forward wing spar attachment bolt hole (see figure 2). None of the surfaces exhibited visible evidence of corrosion or other preexisting damage. The right wing also exhibited fatigue cracks in the lower spar cap at the same hole location extending up to 0.047-inch deep."

TiredSoul
04-19-2018, 12:13 PM
Would a couple of high speed ( > Vne) dives (low passes) sufficiently weaken the wing.
I was glad when the owner of the flightschool I worked for switched to a whole new fleet.
I knew and flew every airplane from zero hours, hired the CFIís that flew them and was very friendly with our Head of MX.
I knew what was wrong with each airplane and how it was repaired.
We at one point considered data loggers ( altitude & airspeed).

Blackhawk
04-19-2018, 12:49 PM
Would a couple of high speed ( > Vne) dives (low passes) sufficiently weaken the wing.
I was glad when the owner of the flightschool I worked for switched to a whole new fleet.
I knew and flew every airplane from zero hours, hired the CFIís that flew them and was very friendly with our Head of MX.
I knew what was wrong with each airplane and how it was repaired.
We at one point considered data loggers ( altitude & airspeed).

If I were a flight school owner today I would have data recorders in all airplanes that could give me FOQA type data. I understand ERAU has this but doubt they were in this airplane from day 1.

Yoda2
04-19-2018, 02:51 PM
Would a couple of high speed ( > Vne) dives (low passes) sufficiently weaken the wing.
I was glad when the owner of the flightschool I worked for switched to a whole new fleet.
I knew and flew every airplane from zero hours, hired the CFI’s that flew them and was very friendly with our Head of MX.
I knew what was wrong with each airplane and how it was repaired.
We at one point considered data loggers ( altitude & airspeed).

Not likely a couple Vne dives would cause damage, if performed carefully and in smooth air. As a maintenance test pilot I routinely took aircraft to Vne during return to service flights after any flight control surfaces were replaced. I've also, slightly, exceed Vne per FAA request during flight test of external Mods. This said, Don't recommend it for any other reasons, and it was always done without passengers.

In a flight school environment, I have seen the results of pilots screwing around beyond their or the aircrafts ability. Actually had a renter pilot get a guilty conscience once and confess. He couldn't get to sleep later that evening. He suggested that the aircraft be inspected. Unfortunately, That's not the Norm.

Blackhawk
04-19-2018, 03:01 PM
Not likely a couple Vne dives would cause damage, if performed carefully and in smooth air. As a maintenance test pilot I routinely took aircraft to Vne during return to service flights after any flight control surfaces were replaced. I've also, slightly, exceed Vne per FAA request during flight test of external Mods. This said, Don't recommend it for any other reasons, and it was always done without passengers.

In a flight school environment, I have seen the results of pilots screwing around beyond their or the aircrafts ability. Actually had a renter pilot get a guilty conscience once and confess. He couldn't get to sleep later that evening. He suggested that the aircraft be inspected. Unfortunately, That's not the Norm.
I remember watching a special on the development of the A380. When it came time for the flutter testing and high speed dives the test pilots were not as jovial as they were on previous flights.

Yoda2
04-19-2018, 03:26 PM
I remember watching a special on the development of the A380. When it came time for the flutter testing and high speed dives the test pilots were not as jovial as they were on previous flights.

True statement. Another one that test pilots dislike is the aft CG tests. Thankfully as a maintenance pilot, all those were above my qualifications and pay grade. I was only issued the small set of brass balls:)

Blackhawk
04-19-2018, 08:15 PM
True statement. Another one that test pilots dislike is the aft CG tests. Thankfully as a maintenance pilot, all those were above my qualifications and pay grade. I was only issued the small set of brass balls:)

I knew a test pilot killed along with two others testing the aft CG of the C-23 Shirpa. They got into a flat spin at 10,000í and couldnít get out.

rickair7777
04-20-2018, 07:04 AM
I knew a test pilot killed along with two others testing the aft CG of the C-23 Shirpa. They got into a flat spin at 10,000í and couldnít get out.

Ideally you install a drogue chute for that kind of stuff.

Blackhawk
04-20-2018, 01:11 PM
Ideally you install a drogue chute for that kind of stuff.

Don't know if they use them on larger airplanes during test flights. I know the crew had personal parachutes. The flight engineer was found close to the door so it was assumed he was trying to bail but couldn't get out if I remember correctly (this was in 1992).

rickair7777
04-20-2018, 04:46 PM
Don't know if they use them on larger airplanes during test flights. I know the crew had personal parachutes. The flight engineer was found close to the door so it was assumed he was trying to bail but couldn't get out if I remember correctly (this was in 1992).

The CRJ had a fatal stall spin test because the drogue deployed but then detached. IIRC one of the pilots may have accidentally pulled the release handle before the deploy handle.

Yoda2
04-20-2018, 06:48 PM
The CRJ had a fatal stall spin test because the drogue deployed but then detached. IIRC one of the pilots may have accidentally pulled the release handle before the deploy handle.

That wasn't a spin test; they don't normally spin test multiengine airplanes. It was a side slip test, I believe in '93. Several things went wrong on that deal.

The original Canadair Challenger business jet also crashed, at Mojave during certification, aft CG flight test... I remember that well as I stopped into Mojave that morning to get gas; about an hour before it crashed.

CaptainYoda
04-20-2018, 09:09 PM
We at one point considered data loggers ( altitude & airspeed).

Wouldn't be surprised of data loggers became the norm at ERAU then every other flight school and renting company.

aeroengineer
04-21-2018, 08:45 AM
Personally I've only flown the older Hershey Bar wing Arrows. I can't imagine how many hours some of them had and never an issue I was aware of beyond the old radios sucked. I'm sure the NTSB will check but I'd really like to know if the bolts were properly torqued.

rickair7777
04-21-2018, 05:45 PM
Wouldn't be surprised of data loggers became the norm at ERAU then every other flight school and renting company.

Maybe they should.

CaptainYoda
04-21-2018, 06:59 PM
Not to over simplify, but isn't the process relatively pretty simple?

Inspect aircraft of similar build, chronological age and flight time.
If multiple instances of failure found, point to manufacturing failure.
If no other instances of failure found, point to previous operator failure.

ERAU really IS the best place to start the inspections. Similar aircraft, usage, age, and maintenance practices.



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