Sherlock Ohms

Skepticism Prevented a Nasty Crash

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Re: Frightening - Show versus Tell
oldpartsnrust   10/11/2012 3:34:32 PM
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.

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Re: experience counts
Tool_maker   10/11/2012 3:59:54 PM
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.

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Re: Frightening
notarboca   10/18/2012 2:13:33 PM
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.

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GuidoBee   10/22/2012 5:09:07 PM
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. 

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dbues   7/1/2013 11:49:49 AM

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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