21 May 2007

EAA Sport Aviation Magazine
ATTN: David Hipschman, Editor
Oshkosh WI 54903

Via email.
Ref: Sport Aviation, May 2007, pp 108-110

Dear Mr. Hipschman:

I have written several times over the years about articles from Mr.
Wilhelmsen. As yet, I have not gotten any good answers to my comments or a
short rebuttal in the magazine. I would hope that the least you would do is
answer my comments and if you felt them worthy, then give them some ink in
your publication.

In the journalism business, we generally expect expertise from our authors.
This expertise can come in the guise of formal education, certificates or
licenses, or practical experience. Indeed, with a technical subject such as
avionics we expect that an author have some credentials in that field before
(s)he is published at face value. Indeed I know for a fact that my editors
over the last 30 years of magazine authorship considered my degree in
Electronics Physics, my FCC and FAA licenses and certificates, and my 50
years of practical experience in electronics, 43 years in the avionics
field, the last 40 as a professional avionics engineer before they would
publish my articles without some sort of professional review. Even then,
from time to time I would have to justify my designs, calculations, or
assertions with credible reference before they would publish a controversial
or unique project.

I find no such expertise in the field of avionics, much less aviation law
from Mr. Wilhelmsen ("the author"). The author has a degree in "engineering
technology" which may or may not have had a smattering of electronics. I
find no certificates or licenses, and not a minute of formal professional
work in the avionics field.

Be that as it may. Let me take a few points that the author makes and
examine them in the light of reality.

The author hangs his hat on section 43.13 to assert that "Each person
performing maintenance … shall use the methods … prescribed in the …
maintenance manual … [from] the manufacturer." Simple blind reliance on
this sentence without the practical experience to back it up says that if I
have an old King KX-170 transceiver and I want to perform repair or other
maintenance that I need (among other things) a Heath IP-20 Power Supply, a
Heath IM-13 Voltmeter, and an Eico 261 Wattmeter (listed in the
manufacturer's manual as required test equipment).

Let's examine these requirements, and I beg of you to note the three pieces
of test equipment for a later comment. In the first place, Heath and Eico
have been out of business for twenty years or so. The only place you will
find this test equipment will be on ebay auctions under Antique Radio
Equipment. Even then your odds of finding one of these pieces of gear is
slim to none. So is the KX-170 then not to be repaired because these pieces
of test gear are unavailable? No, of course not. The FAA has more sense
than that. They expect a shop or technician that wants to work on this
transceiver to use a bit of common sense. A garden variety power supply is
a power supply is a power supply. Dozens of manufacturers make much better
voltmeters and wattmeters than these listed units. If an FAA avionics
inspector comes to my shop and asks where the Heath voltmeter is I will
point them to the Hewlett-Packard voltmeter (ten times the accuracy, ten
times the price) as a perfectly valid equivalent. And if the inspector has
been in the field for more than ten minutes, they will understand that.

Let's go a step further. The FAA will not enforce a requirement that it has
not approved. That is, the KX-170 manual was never approved by the FAA in
any manner, way, shape, or form. It never saw that test equipment list,
much less approved it. Nowhere in the manual will you find the words,
"Official FAA Document". That leaves WIDE space for interpretation, which
is why some FSDOs are known to be sticklers and some are reasonable.
Interpretation is everything.

Finally, there is a requirement for "manuals" postulated by the author.
While it is a minor point, you do not need the manual, you only need the
section(s) that pertain to your work. If you are doing a repair, you do not
need the installation section, nor the license requirements section.

Another point the author makes is that you must use a "diode…from the same
brand and batch" to do a replacement. That is simply not true. There are
dozens of 1N4148 diodes in our illustrative King receiver. They were
probably made by RCA back in 1977 when this transceiver was new. RCA got
out of the semiconductor business twenty years ago, and the odds of King
having a diode from that batch are just about zero. Does that mean the
transceiver is junk? Hardly. Most parts in a piece of avionics meet what
are called "Jedec" and "Retma" specifications which are to electronics what
MS and AN are to aircraft hardware. It matters not the manufacturer nor the
batch in which it was manufactured. If it meets the generic specification
it is good to go.

Incidentally, the term is "mean time BETWEEN failures" and not "mean time
BEFORE failure."

As to the difficulty of soldering SMD on SMT boards, it takes me something
on the order of half an hour with regular soldering equipment to have a new
student successfully remove and replace a SMD capacitor or resistor. SOIC
devices take me a bit longer … an hour or so. It is not rocket science as
the author would have you believe.

Let me take what to me is the crux of this article … the section on
owner-made parts for a standard airworthiness aircraft. The author says
that the "…[kit avionics] device may be used in your aircraft" but that the
"interpretation is interesting". It is also interesting to the FAA Office
of the Chief Counsel who wrote in the official FAA magazine FAA Aviation
News Magazine July/August 2002 that this is exactly the interpretation of
the FAA lawyers. (See additional articles at
150cessna.tripod.com/parts.html and
150cessna.tripod.com/obrienonownermadeparts.html ).

As a side note, remember the Heath and Eico equipment required to service
the King transceiver above? They were only available as … KITS. That's
right, owner assembled kits. Now if kits are acceptable for TESTING the
equipment, why is the equipment itself not acceptable in kit form?

The advice to find a mechanic skilled in minor installations is a perfectly
valid admonition. The FAA publication "Plane Sense" on "Aircraft
Alterations" published by the FAA Western Region states over and over again
that it is the INSTALLING MECHANIC that determines whether a modification is
major or minor. A good avionics mechanic might spend ten minutes evaluating
a modification before approving it while a skilled engine mechanic (both
with the same A&P after their names) might take five hours before
DISapproving it. Finding a mechanic skilled in the art of avionics is a
treasure indeed.

The paragraph on soldering is hogwash. It is not applying heat incorrectly
that makes a cold solder joint (a common mistake among many who don't
understand the soldering process) but the movement of the joint while the
solder is solidifying.

As to the "heat sinking" required on transistors and integrated circuits,
hogwash again. This old wives tale started out with the first transistors,
which were made of germanium and COULD be damaged by heat. Today's silicon
devices require no heat sinking under any but the most extreme of
circumstances.

The second to last paragraph makes no sense to me at all. "…the required
equipment…the FAA assumes must be approved." What does that mean? That all
required equipment must be approved? ANY equipment at all must be approved
in some form. The author goes on to say that the product must be "PMA, TC,
TOS (sic), or STC approved". In the first place, that is untrue on the face
of it. One manufacturer of altitude encoder and another manufacturer of
emergency equipment relies on the wording of Part 91 which requires that the
equipment MEET the TSO standards, but does not require TSO approval. Again,
anybody working in the avionics field knows this hiccup in the regulations
by heart, but again, it requires experience in the field.

The long and the short of it does NOT come down to a simple truth. The long
and the short of it is that if you know what you are doing and perform the
work in an airworthy manner (however that is locally defined) then you can
in fact legally work on your own avionics.

Hanging out your shingle on this advice, though, will in all probability
bring you a visit from the FAA, who "Isn't happy until you aren't happy."



Jim Weir
VP Engineering, RST
A&P, IA
California Community College Professor, Electronics