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Sherlock Ohms

Skepticism Prevented a Nasty Crash

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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.

SparkyWatt
User Rank
Platinum
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!

McG
User Rank
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). 

Tim
User Rank
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.

Charles Murray
User Rank
Blogger
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.

GlennA
User Rank
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.

TunaFish#5
User Rank
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.
User Rank
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.

Tool_maker
User Rank
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
User Rank
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!

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