On Tue, 1 Dec 2015 12:38:44 -0500, Phil Hobbs
wrote:

On 12/01/2015 12:09 PM, wrote:
On Tue, 01 Dec 2015 15:28:43 +0000, N_Cook wrote:

On 01/12/2015 15:22, wrote:
On Tuesday, December 1, 2015 at 9:23:11 AM UTC-5, N_Cook wrote:
On 01/12/2015 14:00, N_Cook wrote:
Pure tin tinning on a component which should have had derogated Pb/Sn

If I were to render an opinion, pure tin as a mechanical joint is a very bad idea, nor would I think that a sophisticated manufacturer would do that as a matter of intent. Pure tin is extremely brittle, and should NEVER be depended upon in any sort of situation where mechanical stresses (expansion/contraction/flexing) will take place. Add to this the whole issue of tin whiskers (which NASA, at least now understands all too painfully). If what you suggest is accurate, this is a design flaw of significant magnitude. If it is present fleet-wide, it is time to ground these beasts until the problem is addressed specifically.

I would hope that aircraft manufacturers by now would have learned that some admixture to their solders is a necessary step to reliability. And would have learned by now from the Nuclear industry if not NASA that relying on pure tin is a dangerous practice.

All-and-at-the-same-time, counterfeit parts are getting into the OEM repair stream at every level. It would not be difficult to believe where such parts may get into the OEM first-install stream as well.

Peter Wieck
Melrose Park, PA


I know from someone in the medical electronics field, that is extremely
difficult , if not impossible, to guarantee that PbF components do not
get into the derogated product stream, without sample chemical testing
of each batch of componnts, done themselves. The supposed accredited
documentation is easily compromised and cannot be relied on. With all
the extra markup on derogated components, plenty of motive.
In 1990 a US fastener company, Voi-Shan, admitted to supplying
thousands of fasteners for aerospace use that were in essence
counterfeit in that they had not been tested and were of inferior
quality.

Interesting. AFAICT they weren't crappy fasteners--the tests were
faked, but the parts themselves were good (though probably not as good
as if any defective ones had been screened out, of course).

They falsified inspection reports and even made up names of
the inspectors. These fasteners were used in airplanes among other
places. So even a large company will supply crap that is meant to be
used in life critical situations. If I was making medical devices, or
anything that might hurt or kill someone, I would check all the
components supplied from others.
Eric


Cheers

Phil Hobbs
I remember the big stink at the time because I was making helicopter
and turbine engine parts. Really fussy stuff. When it hapened I
remember they started checking all the VSI supplied fasteners and a
whole bunch were below the FAA requirements for strength and proper
plating. I was talking to an FAA inspector who was checking some
shafts I made and he said the FAA was REALLY ****ed off. The parts I
made were small enough quantity that they were 100% inspected and the
FAA inspectors would drop by from time to time to check our inspection
procedure and numbers. VSI made such huge quantities, hundreds of
thousands of parts, that there was no way to easily check for bad
parts intentionally supplied. I'm still ****ed off about VSI because
they risked the lives of the people flying planes with their fasteners
on board.
Eric