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Engineering Disasters: Cracked Fitting Brings Down DC-10

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tekochip
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Re: Sad memory, and what was learned.
tekochip   11/21/2014 9:06:53 AM
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This is why procedures are to be followed.  My own aircraft is in the shop now for a crack at the horizontal stabilizer.  The crack is caused by ground handling crews turning the aircraft by pushing down on the stab to get the nose gear off the ground.  The POH doesn't even hint at this practice, but I have seen ground crews do it time and time again.

William K.
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Platinum
Re: Sad memory, and what was learned.
William K.   11/20/2014 6:39:28 PM
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@R2, the one other lesson is that for all systems that may evenutally need to be serviced, design in a satisfactory service procedure. Satisfactory, in this case means that it does not overstress any parts, and also that it is not likely to be circumvented because of being too complex or difficult.

Designing in a set of lifting pads for use with a lifting frame would have prevented the overstressing of the pylon, and probably made the taskeasier as well. But it would have required additional design effort. 

And I wonder how the engines were installed when the DC10 was built. Does anybody know?

Charles Murray
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Blogger
Re: Sad memory
Charles Murray   11/20/2014 5:31:05 PM
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Battar, nice story earlier this year by NPR about Butch O'Hare. http://www.npr.org/2014/05/24/315259241/butch-ohare-the-heroic-namesake-of-chicagos-airport

Charles Murray
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Blogger
Re: Sad memory
Charles Murray   11/20/2014 5:23:18 PM
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In honor of Butch O'Hare, there's a nice F4F Wildcat on display in Terminal 2 at O'Hare, Battar.

Wayne Eleazer
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Iron
Was There a Real Root Cause?
Wayne Eleazer   11/20/2014 10:09:54 AM
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In October 1975, 18 months after I graduated with a Mechanical Engineering degree, I was rushed off to Myrtle Beach Air Force Base to look into a problem with their A-7D aircraft.

Air Force Logistics Command had just discovered that the bleed air ducts on the A-7D fleet had mysterious wrinkles in them, some quite large.  Since the ducts carried high pressure very hot bleed air out of the TF-41 engine the fear was that they would rupture and the hot air would damage the airplane.  By the way, there is a B-52 on display at the Oklahoma City Fairgrounds that had just that occur and it rendered the airplane useless for anything but a display item.  

Once I got to the base I found that various theories abounded that blamed the manufacturing process.  But then they let me observe a USAF maintenance team removing and reinstalling an engine and it all became clear.

The maintenance crews had devised a shortcut to aid in the engine removal and installation.  There was very limited access to the ducts and they normally had to come off to remove the engine.  But they had found that if you took safety wire and looped around the ducts you could pull them over against the fuselage skin far enough to clear the engine igniter box and thereby significantly ease the task.

The time-saving process wrinkled the ducts, subjecting them to forces similar to someone having his arm twisted behind his back.  The ducts were wrapped with a thick stainless steel foil for insulation and so the damage was not obvious.

However, at that time the A-7D was suffering from serious engine problems and the engines had to be removed and inspected frequently.  Ultimately, the problem was caused by those engine problems and the decision to require such inspections without considering the possible problems that could occur.

Working from my lofty height of an engineering degree, 18 months actual experience, my 2nd Lt rank  - and an urgent official message from my Colonel saying, "Never mind about his age and his rank!  He is a fully qualified engineer and representative of this Air Logistics Center  and if you want to fly your airplanes you will do just what he tells you to!" – I inspected and found enough flightworthy ducts to get half their airplanes back in the air.  The number of ducts sets I Okayed just happened to match the number of airplanes they had functioning engines for - and none of them crashed as result.

But whenever I think of that DC-10 mishap, I wonder what requirements might have been imposed on the mechanics that prompted that disastrous innovation.               

rsquared
User Rank
Iron
Re: Sad memory
rsquared   11/20/2014 10:05:42 AM
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Biggest lessons to be learned from the DC10 Crash in Chicago were

1) Design Reduancy into systems,

2) Design seperation of critical systems,

3) Develop an Inspection plan to detect damage and fatigue cracks,

4) Design Damage tolerance into systems and structure 

5) follow processes procedures.

Although the official cause was ruled not following maintenance procedure. The maintenance procedure called for removing the engine from pylon before removing the pylon from the wing.   The engine is cantilevered off the front of the engine leading to very large loads on the front pylon attach bolts to the wing.   The revised procedure was to remove the engine and pylon from the wing as a single unit.   Greatly reducing the time required to remove the engine and pylon from the airplane during maintenance.  This change in procedure over loaded of the pylon attach bolts initiating damage to the pylon fitting and bolts initiating damage that developed into fatigue cracks that lead to the seperation of the engine and pylon from the airplane.   This damage and resulting fatigue cracks were easily detected by visually inspectiing the fittings.   Several other airplanes were found to have damage and fatigue cracks at this location.    Seperation of the engine and pylon from the airplane damaged the hydraullic lines which power in wing slats.   Proper design of the systems which include check valves, redundancy and seperation of the systems would have prevented the slats from retracting and possibly allow the plane to continue to fly and return to the airport.

HarryB
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Gold
Re: Sad memory
HarryB   11/20/2014 9:52:02 AM
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To answer your question I have in indeed been in a "union" auto plant where I (the engineer) was not permitted to touch the touch the equipment I built for maintaining the system (a master workstation consisting of a networked computer).  Two union employees accosted me and demanded to know what I was doing with "their" equipment (typing in a command)... The insisted that only they could touch the equipment, it was their JOB and they would file a grievance if I continued. I gave them the keyboard and dictated what to type... I had to show them where the letters were and which key was "enter".   I should have known by the graffiti in the rest room. One said "UAW - usually avoids work" and that was crossed out and scrwaled beneath was "Salary - stupid @sshole liars always rip you".  A common expression was "Go scrub" which I leared was short for "go scrub your nuts with a wire brush" This was in the late '90s... things may have improved since then.

Other Union shops have had members who were more than happy to assist in any way possible... overall my experience with them is quite favorable.

Steve Heckman
User Rank
Gold
Re: Sad memory
Steve Heckman   11/20/2014 9:48:26 AM
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My intent was not to raise Union vs non-union, but to set the record straight, I have been a Union member, and yes, it CAN get that bad. Please do not focus on that point: my theme is hands-on engineers will most likely be better engineerrs in anticipating what could go wrong.

There is some value in watching machinists work... as greenhorn engineer I picked up a lot by watching some of our older machinists build my parts. But I was also allowed to operate many of the machines in our tool room. 

I will also add that you haven't lived until you replace a 30-pin connector in a F-4 cockpit while literally standing on your head (in the winter). I learned more about "design for maintenance" by performing maintenance than any test book could ever provide. The Air Force in the late 80's had a "Blue Too" program in an attempt to get engineers field experience, to make future designs more friendly to maintain (The F-16 had an avionics bay with swing down doors, the F-4 had black boxes under a number panels with 60+ screws each).

ChasChas
User Rank
Platinum
nature of the beast
ChasChas   11/20/2014 9:45:01 AM
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Personnel elevators have safety factor of 12 by code.

If comercial aircraft had a SF of 12, they would be so heavy they would barely be useful.

You have to admire what aerospace engineers can do with so little to work with.

The maintainance people have special training to work on these critically stressed machines.

No unauthorized procedures can be allowed.

 

bronorb
User Rank
Silver
Re: Sad memory
bronorb   11/20/2014 9:30:04 AM
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Mr. Heckman,

Are you saying that if you were working in the engineering department at a facility that had a union on the shop floor, you would not be able to enter the shop and build your own fixtures? I suppose they would stop you at the door so that you could not observe anything that they were doing either.

Just curious. Have you ever worked in such a place or is this just conjecture on your part?

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