Quality impeding Reliability. What are your stories? 2

[DHambley]

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?

 

[DHambley]

To avoid confusion I shouldn't have used the word "quality" in the first paragraph. Most of the engineers at the companies I have worked with throw this term around loosely to mean, "quality control procedures" or, "government paperwork requirements" or similar. In some instances the problem could be attributed to "management greed" as SWcomposties wrote because indeed, it all boils down to cost. My opinion is that the management of aerospace firms didn't make the expensive paperwork requirements in the first place. We're just stuck with them.

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.

 

[KENAT]

One of my first tasks as an Engineer was to look at a certain 'aircraft accessory' that my company made, compare it to similar more modern items and see where we could share parts/techniques or otherwise save money. This item was essentially expendable & made by the thousand so there was a real drive on cost.

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.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[KirbyWan]

I think it's important to have some moderatly high bar to pass before an aircraft part is considered airworthy. Without that we will end up with crappy airplanes. Once that is passed we ask ourselves what hurdles must be jumped to make a change to an already acceptable design. The FAA usually want's the same hurdles to be jumped, but in some cases they will accept an argument from similarity that most of the tests can be skipped. If you were changing one diode for another, and both diodes were structurally similar why recertify the vibration test. You probably do need to recert any electrical functional test.

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.