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Sherlock Ohms

Skepticism Prevented a Nasty Crash

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tekochip
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Frightening
tekochip   10/3/2012 8:49:11 AM
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That's why it's so important to do a complete and thorough preflight, especially after any service.  Thankfully I've never found any problem other than compass deviation.  From time to time I've mentioned that people should do predrive with automobiles as well.  At the very least, check all your tires every time you get in the car, and stomp on the brakes to see if they work.


Dave Palmer
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Re: Frightening
Dave Palmer   10/3/2012 11:28:09 AM
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This is indeed "frightening." Maybe Design News should be highlighting this kind of scary story as we approach Halloween.

What stands out to me is how the crew's attitude changed when Len hit the "gear up" switch.  He was right from the beginning, but no one took his concerns seriously until he had a physical demonstration.  Then he quickly won everyone to his side.

This should be a lesson to all engineers that "show" is better than "tell."

naperlou
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Re: Frightening
naperlou   10/3/2012 1:24:38 PM
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Dave, that is a good point.  Showing is better.  Maybe we should all be from Missouri. 

It is amazing that aircraft, being as complex as they are, are so reliable.  You are more likely today to hear that there was a problem with a pilot than with a airplane. 

Charles Murray
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Re: Frightening
Charles Murray   10/3/2012 6:56:09 PM
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Indeed, showing is better. I could easily imagine a group of engineers saying this isn't a problem. It's a lot easier to assume nothing's wrong.

TJ McDermott
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Re: Frightening
TJ McDermott   10/3/2012 11:27:04 PM
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The spirit (or should I say ghost) of Richard Feynmann lives on.

I'm really, really surprised that the sliver wasn't accounted for during the modification.  Aircraft maintenance and fabrication is normally much more focused on accounting for everything that goes in and out of an aircraft.  Lost fasteners must be found and so forth.

SparkyWatt
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Re: Frightening
SparkyWatt   10/4/2012 2:04:44 PM
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What surprises me is that a critical harness was checked for continuity, but not for isolation!

Rob Spiegel
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Re: Frightening
Rob Spiegel   10/4/2012 12:25:58 AM
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Good point about show being better than tell, Dave. The story is also a good arguement for healthy skepticism.

kenish
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Platinum
Re: Frightening
kenish   10/4/2012 11:58:14 AM
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I always preflight my plane, truck and motorcycle.  On the C-130 in the article a preflight probably would not have found the problem.  The elevator isn't visible from the cockpit, so "Flight Controls Free and Correct" would not help.  The first sign of trouble would have been at gear retraction as the author pointed out.

I do wonder a bit on the veracity....the flight controls in a C-130 "Herky Bird" are mechanical...pushrods, bellcranks, cables, and pulleys.  AFAIK even the latest "J" version is not fly-by-wire.

McG
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Iron
Re: Frightening
McG   10/4/2012 4:33:47 PM
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The problem described would have been in the autopilot system, not the primary flight controls.  As kenish correctly notes, C-130's have hydraulically-booseted manual controls, not fly-by-wire.  The Functionl Check Flight crew would not have the autopilot engaged during takeoff, but could have had an unexpected surprise when they engaged the autopilot in flight.  However, they could have quickly disengaged the autopilot, and most autopilots have clutches that will allow the crew to overpower the autopilot inputs with the cockpit controls.

TJ,  the metallic sliver was likely introduced by drilling of the structure near the harness, which introduced shavings into the harness that were not properly cleaned up.  Have seen this several times.  You would be shocked at the lack of QA at some of the military overhaul depots.  One major depot that one of my aircraft went through had no independant inspection.  They relied on the technician performing the work to inspect his own work (all in the interest of cost savings). 

notarboca
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Gold
Re: Frightening
notarboca   10/18/2012 2:13:33 PM
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Wow, the lack of good QA at the depot level is extremely scary.  I worked 12 years in the general/commercial avionics world, and EVERYTHING had to be checked by an in-house FAA approved inspector.  Techs certifying their own work is a recipe for disaster.

Johnathamilton
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Iron
Frightening - Show versus Tell
Johnathamilton   10/4/2012 9:20:15 AM
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Good points - I agree it is always more convincing to show than tell. We as engineers are often too busy to spend the time to figure out how to show - it's not always easy. But definitely worth it - especially when it comes to mission critical issues.

oldpartsnrust
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Iron
Re: Frightening - Show versus Tell
oldpartsnrust   10/11/2012 3:34:32 PM
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My wife relayed a story one of the tubing bender operators told her about a young "hot-shot" engineer that had designed a tube that he was convinced saved money, material, and maintenance cost by eliminating a few fittings.  He had spent days checking that the tube could be installed in one piece as opposed to being made in 3 pieces and assembled on the aircraft.  The tubing bender operator rejected the part several times, only to have it resubmitted without any changes.  This resulted in a "face to face" requested by the tubing bender operator.  He took the engineer, who was still adamantly defending the viability of the part, down to the bending machine and proceeded to "bend" the newly engineered part.  The tubing bender started whipping the tubing around wildly to make the multitude of small bends necessary resulting in large chuncks of tubing kinking, snapping off and flying around the shop.......  Obviously the engineer agreed to re-work the part......this time with fittings.

mblazer
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Silver
Stupid Questions
mblazer   10/4/2012 10:11:16 AM
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It is always better to ask stupid questions before the accident than having to testify before the Accident Review Board.

If doesn't look right, investigate until you're certain there is no problem or there is one.  Is someone's word that "it's good enough" equal to an aircrews' life?

benmlee2
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Gold
Re: Stupid Questions
benmlee2   10/4/2012 11:03:35 AM
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The longer I am in engineering, the longer I realize intuition is as important as math and numbers. Learning to listen to your intuition is as important as learning theories. There are so many interactions in a system, is impossible for anyone to systematically troubleshoot. Sometime when you are faced with a problem, is best to stand back and ask yourself what do you think. What does your little voice tell you.

Charles Murray
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Re: Stupid Questions
Charles Murray   10/4/2012 9:07:54 PM
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Good point about asking dumb questions, MBlazer. For that to happen, a certain attitude is needed at the top -- one that welcomes all kinds of questions, not just those that sound intelligent but may, in fact, be worthless.

rv8iator
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Iron
Single point failure
rv8iator   10/4/2012 11:12:12 AM
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 After reading the story I don't believe that Lockheed designed a single point failure mode of the primary flight control system.   All aircraft are designed with redundancy based on risk.  Flight control failure though low in risk is high in severity and thus qualifies for redundancy.

Tim
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Platinum
Almost right
Tim   10/4/2012 6:56:01 PM
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This story reminds me of a physics professor that refused to give partial credit on complex problems. His reasoning was that in real life even tiny mistakes like an errant punch slug can have disastrous consequences. We as engineering students had to learn that there is no almost wrong or almost right.

GlennA
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Gold
experience counts
GlennA   10/4/2012 10:19:12 PM
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The story doesn't say how many years of experience the mechanic had.  After spending several years working on stone machines I could diagnose many problems by a slight difference in the noise the machine made.  A new operator couldn't distinguish the difference.  So the twitch that was of no concern to a less experienced mechanic, obviously caught the attention of the more experienced mechanic.

Tool_maker
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Platinum
Re: experience counts
Tool_maker   10/9/2012 12:51:33 PM
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  I have been in manufacturing since 1964 and I love to hear a younger voice admit that there are occasions when experience counts for something. As another poster on this thread has said, sometimes things just did not sound right. It is amazing to me how much seat-of-the-pants knowledge is rejected by people new to the field because it does not appear in a textbook nor is there an algorithm written to which it can be tested.

  It goes without saying that a dinosaur like me also needs to be receptive to innovation. It is called teamwork.

oldpartsnrust
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Iron
Re: experience counts
oldpartsnrust   10/11/2012 3:26:25 PM
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Experience does count.  When I had my automotive electrical shop, I could "diagnose" a number of problems just from the customer's description...  Certain GM automobiles would have the radio shut off when the driver's door was opened.  This was a blown Cigarette lighter fuse, most likely caused by coins in the ashtray,,,, Certain Fords would trigger the intermittent wipers whenever the headlights were turned on, or the high beams activated.  This was a loose Driver side wiring harness body ground.  Imagine tracking those down the first time!

Tool_maker
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Platinum
Re: experience counts
Tool_maker   10/11/2012 3:59:54 PM
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I take my hat off to anyone who is able to diagnose any electrical problem in an automobile. Perhaps with the right equipment and schematic, but to just be able to walk in and solve seems impossible.

TunaFish#5
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Gold
missing facet of the story
TunaFish#5   10/5/2012 10:14:30 AM
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Explained neither in the story nor in the comments I've seen is what moved the quality guy to hit the gear limit switch when the elevator motion showed a transient behavior.

OK, somebody mentioned intuition -- fine; I'll buy that.

Another mentioned autopilot system.  Well, OK, but how does that get you into the wheel well when autopilot's off?

Still a great story, but this omission leaves this engineer a bit dissatisfied the inspector's "whimsical" reach into the wheel well.

William K.
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Platinum
Preventing the nasty crash
William K.   10/5/2012 9:11:45 PM
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"Intuition" is not just wild hunches popping out of the air! Most often it is built on both experience and understanding of a system, or systems. A complete ubderstanding does not need to come from experience, and experience alone does not bring understanding. But some few people develope both, and hence become quite valuable.

What I wonde is just what kind of test would have spotted that problem, and how often are tests like that done? A short circuit between circuits on a harness plug is not something that one person would check for with a multimeter alone. Finding the problem by dignostics would have meant looking at the circuits and finding what wires could have a problem that would cause the symptom, , and then tracing that circuit to find the problem. Not a simple task by any means.

GuidoBee
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Iron
JDLR
GuidoBee   10/22/2012 5:09:07 PM
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Before retiring in the Pengagon I had a USN Captain boss who firmly believed in the JDLR theory: just does'nt look right.  When planes were prepared to be "shot off the pointy end of the boat", there is a collection of maintenance people who are looking at the plane on the catapult and all are giving a "thumbs up" before the catapult officer "fires" the cat and launches the plane.  Any one of those "checkers" who may be very junior airmen, though highly trained, are given the authority to halt the launch if he / she sees something irregular.  It is a big deal to take a plane off the cat, as it has to be taken backwards to a position where the problem can be evaluated / resolved.  Making the call must be supported by the maintenance officers, as the consequence of a fault on launch can be catastrophic in terms of both costly material and lives.  Very often the "JDLR" is hard to define exactly, but when it is finally figured out, it may have been something very subtle and almost impossible to explain why it triggered a concern on the part of the guy who suspended the event.  Also, the system has to tolerate the occassional wrong guess: when there really is nothing wrong: the technician still has to be ready to do the same thing again the next time he sees something that JDLR.   Lots of the comments above bring familiar memories to mind from my 26 years of AC maintenance in the USN, USAF and aircraft manufacturer environment.  None are unbelievable to me.  Thanks for the memories. 

dbues
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Gold
Re: JDLR
dbues   7/1/2013 11:49:49 AM
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All,

I appreciate the interest that this article has drawn.  I am sorry to say that I no longer have access to the individual that related the story to me, so some questions will remain unanswered.  

What happens with refurbishment of complicated systems in an airplane can never be simulated, because there are too many "degrees of freedom" to explore.  You would have to be able to simulate Murphy's Law for each individual who had a hand in the work.

What I CAN say, after having assembled wiring harnesses like these over a few Summers during college, is that a Service Bulletin may have required a slightly larger whole to be punched (could be 1/16th inch larger) to accommodate a few more signal paths in the harness.  This would be punched out of the bulkhead panel and then, the new harness could be installed.  

Airmen usually think of FOD (Foreign Object Damage) OUTSIDE the aircraft, but this is an example of one INSIDE.  This is the reason that the Apollo spacecraft components were vibrated upside down to rid the spacecraft of FOD.  I can imagine that inhaling a rivet head in zero gee could ruin your whole day.

 

 

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