Message-ID: <3787865A.46952AAA@mr.net>
Date: Sat, 10 Jul 1999 12:43:54 -0500
From: Michael D Smith <msmith1@mr.net>
To: "lancair.list@olsusa.com" <lancair.list@olsusa.com>
Subject: GPS Certification
Mime-Version: 1.0

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Has anyone certified a Garmin 430 for IFR enroute and
approach in the 4?

I mounted the antenna in the aft portion of the fuselage
just forward of the beginning edge of the vertical
stabilizer per recommendations of Regan and others.  The
avionics guy, who makes a living revising and upgrading
military spec and biz jet class electrical systems, is an
extremely knowledgeable and skilled individual who  has
consisted opined that I should have mounted it high in the
tail. (read mistake on my part)   Given the noteworthy
opinions I received, I chose the more forward and less
elevated position.

Does anyone have thoughts or experience in this area?

I will post his comments to me after my signature.

Michael D Smith

Mike,
I've been doing some reading on the subject of GPS IFR
certification. Since
you've paid for an IFR capable box, I assume you're going to
want it
certified. The easiest method is to use an existing,
certified airplane
installation as the certification basis. You might want to
put out a feeler
on the Lancair internet forum and ask what others have done.
Has anybody done
an IFR certification (en-route or approach) in a Lancair 4
or 4P with the
Garmin 430 and your antenna location?  If not, the process
gets a little
involved. The other question is weather or not we need the
external
annunciators. Garmin was claiming we don't, but it's really
up to the local
FAA office. We have provisions for them if needed. My main
concern is still
with the antenna location. According to AC 20-138, the FAA
accuracy
predictions assume a 5 degree "mask angle", which I am
assuming to mean that
the sky is obstructed from the horizon to 5 degrees above
the horizon. I'm
guessing yours will be more like 30 or 40 degrees through a
significant
azimuth arc in the forward direction. If I can find somebody
that knows how
to calculate the effects of the obstruction, we can try it
that way.
Otherwise we can do a ground test which would involve
recording position data
every 5 minutes for 24 hours to see if it stays within
limits (.056 nm for
non precision approach). This could probably be done
automatically with a
laptop P.C., so you wouldn't have to watch it the whole
time.
More stuff to think about.

Jim

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