Quality impeding Reliability. What are your stories?
Quality impeding Reliability. What are your stories?
(OP)
Without tainting the thread with my own views, let's look at a few responces first. Do you have a story about quality getting in the way of reliability in aerospace products?





RE: Quality impeding Reliability. What are your stories?
If you mean 'better made components' then, no I don't think I've experienced them causing a problem (I'm excluding possible situations where there was a design problem that poor quality may have been hiding).
If you mean 'QA systems' such as ISO-9001 then maybe. I've heard the view espoused that because of the effort required to 'certify' design changes, or the like, that improvements sometimes aren't incorporated.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Quality impeding Reliability. What are your stories?
Many, many years ago, I was involved in a project for a European customer who insisted that we set up a QA process. The end result was that all the people who knew how to do the work wrote quality procedures, and we brought in contract people to do the actual work. Quality suffered.
If you are working with an organization controlled by rigid, procedure driven people, your QA process will be just another set of procedures to follow, and there will be no improvement in quality.
RE: Quality impeding Reliability. What are your stories?
RE: Quality impeding Reliability. What are your stories?
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Quality impeding Reliability. What are your stories?
Better quality leads to better reliability. A lot of QA processes (not all) lead to reduced quality, with all the attendant consequences.
I read the OP's use of "quality" as meaning QA. A strict literal intepretation of his question does not make sense.
During WWII, the Germans had problems controlling their Fritz_X glider bombs in combat. The controls worked fine on the ground. It was eventually found that a French slave worker had taken apart some coax cables, snipped the conductors inside, then reassembled everything. The resulting electronics worked on the ground, but did not work in the air with the airplane vibrating. One could argue that this was a quality program with the objective of reduced reliability.
I cannot find any mention of this in Wikipedia. I got it from an aircraft history at home. I will have to look it up.
RE: Quality impeding Reliability. What are your stories?
100,000 parts.
Didn't get full flow on maybe 1,300. Still functional but appearance not suitable.
Reran them and all looked good.
What we missed was that the braze alloy had Zinc in it. Every time it was heated it lost Zinc and the remelt temperature was maybe 50F higher.
Customer went to use the parts in a machine set for the proper temperature which turned out to be too low for the reworked parts.
Thomas J. Walz
Carbide Processors, Inc.
www.carbideprocessors.com
Good engineering starts with a Grainger Catalog.
RE: Quality impeding Reliability. What are your stories?
If the original design and analysis is wrong, if a shaft is running beyond its torque rating, if a transistor is running too hot, then all of the units will be built exactly the same; with a transistor which is going to fail and a shaft which is going to break.
KENAT's comment reminded me of what I see very often, "...because of the effort required to 'certify' design changes, or the like, that improvements sometimes aren't incorporated."
Sadly in aerospace, certification is so incredibly expensive, that faulty products are often sold even though the manufacturer knows that a simple fix will improve it. The FAA and ISO don't allow simple fixes though. I bet those O-rings on the Challenger had 20lb of paperwork with the word "Quality" stamped on each sheet.
RE: Quality impeding Reliability. What are your stories?
"The FAA and ISO don't allow simple fixes though" Rubbish. The FAA doesn't allow "fixes" based on wishful thinking, arm-waving and management BS. While the cert process isn't perfect, its a lot better than not having any process.
RE: Quality impeding Reliability. What are your stories?
"Good to know you got shoes to wear when you find the floor." - Robert Hunter
RE: Quality impeding Reliability. What are your stories?
We differentiate quality, reliability, consistency and many forms of each as distinct attributes of the same process. Remember the story of the blind men and the elephant. One felt it and determined it was a wall, another felt a tree trunk, a third felt a rope and a fourth felt a snake while the fifth felt a huge leaf.
Your question seems like playing with words. Much as in high school we devised elaborate math formulas to prove that 1+1 =0 and other nonsense.
Personally I am really impressed by the aircraft certification process. Many tens of thousands of parts all interacting and the planes rarely fall out of the sky. It is still a very safe method of transportation.
Thomas J. Walz
Carbide Processors, Inc.
www.carbideprocessors.com
Good engineering starts with a Grainger Catalog.
RE: Quality impeding Reliability. What are your stories?
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Quality impeding Reliability. What are your stories?
In the orignal question of this thread I was looking for actual examples from actual projects, and there ARE many stories.
RE: Quality impeding Reliability. What are your stories?
Inductor core cracking on an aircraft battery charger due to excessive core loss. Engineering found a simple alteration of the inductor was necessary. QA sais can't do. Re-certification would cost over $20k though. Fix was never implemented.
Diodes within a rocket thruster subject to voltages beyond their rating. Fortunately, this would only occur during a worse case condition not seen with typical conditions yet. QA would require expensive recertification of the entire unit if the fix were installed. Simple change to a different diode never took place.
Unstable oscillations from a voltage supply to software unit in a satellite. Engineering found a simple chip capacitor added solves it. Change was tested in lab over temperature extremes and CAD analysis. QA sais no. Change would require vibration tests, certified thermal chamber tests, re-writing documents like build procedures, certification compliance, etc...too expensive and time-consuming. Units were shipped with unstable supply lines. They were all built the same. QA was satisfied.
If you are an engineer in aerospace, I know you've seen similar stories.
RE: Quality impeding Reliability. What are your stories?
"Tip:
Be very careful about where you apply zero defects. If what you're doing contributes towards a mission critical or complex goal, you'd better adopt a zero defects approach, or things could quickly unravel.
However, if you fanatically follow a zero defects approach in areas which don't need it, you'll most likely be wasting resources. One of the most important of these resources is time, and this is where people are accused of time-destroying "perfectionism.""
B.E.
RE: Quality impeding Reliability. What are your stories?
Originally it looked like you were after a philosophical discussion about the relationship between quality and reliability. Now it looks like you are talking about quality specifications that are not perfect. To me those are two entirely different topics.
Thomas J. Walz
Carbide Processors, Inc.
www.carbideprocessors.com
Good engineering starts with a Grainger Catalog.
RE: Quality impeding Reliability. What are your stories?
In my time in Aerospace/Defense it was up to Engineering and the Customer Desk officer to decide the types of decisions you're talking about.
It was Engineering's Names that went on the Certificates of Design, not QA.
It was up to QA to ensure units built actually met the data pack referenced by the Certificate Of Design.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Quality impeding Reliability. What are your stories?
I have worked with people who have aggressively demanded consistency, in my opinion, frustrating efforts to improve processes.
You need to distinguish between QA procedures, and actually achieving quality. QA is just like any other job. It is futile if you do it badly.
RE: Quality impeding Reliability. What are your stories?
Are these conflicts with your QA department, or are they conflicts with management? QA requires you to follow procedures and submit documentation. It is management that decides that it is not worth the effort.
RE: Quality impeding Reliability. What are your stories?
As KENAT stated, QA should have nothing to do with certification; that is an engineering responsibility. Engineering should discuss the certification requirements with the customer/FAA and determine the required data/testing/etc.
Sounds like in the cases quoted, insufficient testing was originally done, and now management doesn't want to pay to fix the problem. Hard to have sympathy.
Perhaps the real question should be "why wasn't the customer/FAA informed about the defective conditions?"
RE: Quality impeding Reliability. What are your stories?
Mainly it's the high cost of re-certification which is demanded by the certification agencies which I am attempting to aim this discussion at.
Again, the question was, What are your stories. . . ?"
Surely some of you have seen cases of product improvements and corrections which weren't made because of the high cost of certification.
RE: Quality impeding Reliability. What are your stories?
Well I looked at the prints, talked to manufacturing and came up with a list of something like 30 items.
A lot of these looked like simple changes - swapping custom parts for similar off the shelf parts. Changing materials/treatments to lower cost ones etc.
However, when you looked at what testing would have been required to certify many of these changes, be it vibration tests, ultimate strength tests, salt spray or similar tests, drop tests, flight tests... almost none of them were viable.
Now my guess is a lot of them probably would have been fine. So you could argue that this is one of the examples you're asking for. However, when you're talking about parts that not only get flown around over our heads, but in my case also go 'bang', then I'm OK with erring on the side of caution.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Quality impeding Reliability. What are your stories?
Of course if you say these simple changes need no recert at all you now are on that slippery slope that ends at "We just exchanged the main aluminum structural spar for an equivalent design in fiberlass. So no retest is needed." Of course this is a ridiculous extreme, but defining that line is difficult, and the damage that could be caused by making an unacceptable but apparantly minor change severe for example the KC hyatt disaster.
The problem could be greedy management. The problem could also be clueless management who don't know how to argue effectivly with the FAA that a specific test is not needed, or that an alternate test is acceptable. For the diode I would have suggested the diode be mounted in a similar maner in a test board and vibration tested. If the individual compontent passes, then the swap is accpetable. QED.
Sometimes the FAA makes you go through the hoops of comeing up with a test plan and then saying you can skip the test.
-Kirby
Kirby Wilkerson
Remember, first define the problem, then solve it.