Garmin Antenna placement

[Paul Sharp]

On the $ I know the feeling - one or two potential buyers have wondered why I ask a high price for my aircraft. You can buy at $50K and then spend another $100K or just buy for $150K and have it already done. If they want one fixed up with all new guts, engines, and major components they'll have to put out the money one way or another. Well, I'm not dying to sell, so it's OK.

On the Garmin 396, I put mine right in the panel (Airgizmos panel mounting bracket) and LOVE IT. I also have it slaved to the 430 (a very simple connection) so that whatever flight plan I put into the 430 goes to the 396. I know there was a lot of controversy over the legality of the panel mount back whenever (haven't checked lately), but when all was said and done my A&P/IA people, who are excellent and very careful, went to a seminar of A&P/IAs and they all concluded the way the regulation was written means it was OK and they mounted it and signed it off and I've had no trouble. (I had a licensed avionics man do the slaving connection.)

I ran the antenna cable from the 396 up behind the panel (since it was already behind the panel given the 396 is panel-mounted) and put a piece of heat-resistance velcro on the bottom of it with the coupling piece on the glareshield surface, so the actual round pickup of the antenna sits well forward on top of the glareshield and never has a bit of trouble. I have never lost signal when I'm outside the hangar and have flown it in all kinds of weather, as in from Salt Lake to Atlanta, and north and south. It's another one of those things you wonder how you ever flew IFR before without.

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For anyone who didn't see the original post from back then, here's some information that may be helpful - caveat: these notes are over a year old now:

1 - Had to enlarge the holes for cables in the Airgizmos bracket since things are too tight the way they make it. I enlarged them before mounting so that the following cables would slide in and out with ease when moving the 396 into or out of the aircraft:

* Audio cable
* GPS cable
* XM antenna cable
* Auxiliary 396 cable for power and interface to the 430 in my panel

2 - To interface the 396 to the 430 Garmin box you need to know what port to connect the data wire of the auxiliary cable to on the other box's RS232 bus. That meant contacting Garmin tech support because evidently it isn't the same for every model and S/N. You also have to know which pin that equates to on your box, so you have to ask Garmin both questions. This requires the purchase of the Garmin 396 auxiliary cable which is needed for power connection anyway.

3 - Then for that interface between the boxes to actually work you have to set the 396 itself to "Aviation" INPUT on the setup page and also set the RS232 port OUTPUT on the other box to "Aviation" on its setup page.

4 - DO NOT use the "Audio" wire in the 396's auxiliary cable for connecting audio to your audio panel in the airplane! This feed can blow audio panels, etc. So for audio use the 1/8" stereo audio connector on the back of the 396 instead. I just connected it to my intercom stereo input jack, but the output could feed an audio panel directly.

5 - The Airgizmos mount is specified on their own website as needing a field approval-meaning a form 337-for installation in certified aircraft. AOPA claimed the same thing when I talked to them. But Airgizmos mentioned a FSDO that recently told an owner that a simple log entry could be used, citing AC20-138A. I passed on this input to my shop and they brought it up at a local A&P/IA meeting where all agreed that this was an acceptable approach. So they made a logbook entry referring to AC20-138A and attached a placard (label) that reads "For VFR Use Only" on the 396. (Mucho better than having to do a form 337.) The inspector at the Salt Lake FSDO even said if we HAD submitted a field approval form he'd have rejected it and told us it was "a minor modification" and that this was the operative phrase (meaning have the mechanic specify "minor modification" in the logbook entry). Included below is Appendix 5 of AC20-138A which details this kind of VFR GPS installation.

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(NOTE: Following quoted from over a year ago, also

12/22/03 AC 20-138A Appendix 5

APPENDIX 5. INSTALLATION OF EN ROUTE GPS EQUIPMENT FOR VFR USE ONLY
1. GENERAL. This appendix provides guidelines for the installation of stand-alone GPS systems used for en route, VFR navigation only.
2. APPLICABILITY. All un-pressurized aircraft less than 6000 pounds where the modification is classified as a minor alteration.
3. TECHNICAL INSTRUCTIONS. Install the GPS as follows:
a. The GPS equipment should be located in a position which is viewable and accessible to the pilot from his/her normally seated position. The installed GPS equipment should not:
(1) Restrict access to or view of any control, display or indicator;
(2) Restrict movement of the flight controls;
(3) Interfere with the pilot's vision along the flight path; or
(4) Restrict pilot/passenger egress.
b. The installation should be carried out in accordance with the manufacturer's installation instructions, the aircraft maintenance manual and the guidelines in AC43.13-2A. The installation should conform to the following requirements:
(1) Manufacturer-supplied or standard parts should be used.
(2) If a 'non-standard' method of installation is used, the manufacturer's recommended procedures are to be followed.
(3) The GPS mounting should be tested to ensure that it will be restrained throughout the flight envelope.
(4) Where a modification is required to the aircraft structure to show compliance with paragraph 3b(3), the modification is to be carried out in accordance with the aircraft maintenance manual and the guidelines in AC43.13-1B and AC 43.14-2A.
c. If required, install a remote GPS antenna as follows:
(1) Determine a suitable location for the GPS antenna on the upper fuselage. Particular care should be taken to ensure that at least the minimum separation is maintained between the GPS antenna and VHF communications and ELT antennas.
(2) Install the manufacturer-approved GPS antenna in accordance with the manufacturer's installation instructions, the aircraft maintenance manual and the guidelines in AC 43.13-2A. The GPS antenna installation should be tested to ensure that it would be restrained throughout the flight envelope.
(3) If using an internally mounted, manufacturer-supplied remote antenna, install the antenna in accordance with the manufacturer's installation instructions. Ensure that the antenna and associated cable will not interfere with pilot's vision, aircraft controls or displays, or pilot/passenger egress.
d. Install and placard an appropriately rated circuit breaker or fuse.
e. If required, install a remote GPS indicator as follows:
(1) Determine a suitable location for the GPS indicator. The indicator should be located in the instrument panel and readily viewable to the pilot from his/her normally seated position.
(2) Install the indicator in accordance with the manufacturer's installation instructions, the aircraft maintenance manual and the guidelines in AC 43.13-2A.
(3) Interconnect the GPS, power supply, indicator and antenna (as required) in accordance with the manufacturer's installation instructions.
f. Unless the equipment automatically displays a message on start-up and pilot action is required to clear the message, install the following placard in the vicinity of the GPS and in clear view of the pilot: GPS APPROVED FOR VFR USE ONLY.
g. Close the GPS circuit breaker or install the fuse.
h. Carry out a functional test of the GPS installation in accordance with the manufacturer's installation/operation instructions. Checks are also to be carried out to determine satisfactory operation of all disturbed systems, that there is no interference between GPS and other systems, no effect on the aircraft compass system and that there is no interference with the aircraft flight controls.

[Paul Sharp]

Sorry about the double-post; the site said I wasn't logged in but evidently I was.