Garmin GA 35 Installation Instructions Manual - page 11
GA 35, GA 36, and GA 37 Antenna Installation Instructions
Page 2-1
190-00848-00
Revision B
2. Installation
2.1 Introduction
One method of installing the GA 3X antennas is to follow Garmin GA Antenna AML STC SA01695SE
for installations not penetrating a pressure vessel for those aircraft that are included on the STC approved
model list. If installing antenna per Garmin GA Antenna AML STC SA01695SE, follow instructions
contained in STC Antenna Installation Manual 190-00569-00.
CAUTION
Antenna installations on pressurized cabin aircraft require FAA approved installation
design and engineering substantiation data whenever such antenna installations
incorporate alteration (penetration) of the cabin pressure vessel by connector holes and/or
mounting arrangements. For needed engineering support pertaining to the design and
approval of such pressurized aircraft antenna installations, it is recommended that the
installer proceed according to any of the following listed alternatives:
1. Obtain approved antenna installation design data from the aircraft manufacturer.
2. Obtain an FAA approved STC pertaining to and valid for the antenna installation.
3. Contact the FAA Aircraft Certification Office in the appropriate Region and request identification of
FAA Designated Engineering Representatives (DERs) who are authorized to prepare and approve the
required antenna installation engineering data.
4. Obtain FAA Advisory Circular AC-183C and identify a DER from the roster of individuals in it.
5. Contact an aviation industry organization such as the Aircraft Electronics Association for assistance.
2.2
Antenna Mounting Location
The GPS antenna is a key element in the overall system performance and integrity for a GPS/WAAS
navigation system. The mounting location, geometry, and surroundings of the antenna can affect the
system performance and/or availability. The following guidance provides information to aid the installer
in ensuring that the most optimum location is selected for the installation of the GPS antenna. The
installation guidelines presented here meet the intent of AC 20-138A section 16. The greater the variance
from these guidelines, the greater the chance of decreased availability. Approach procedures with vertical
guidance are the most sensitive to these effects. LNAV only approaches, terminal operations, and enroute
operations may also be affected. Because meeting all of these installations guidelines may not be possible
on all aircraft, these guidelines are listed in order of importance to achieve optimum performance. Items
3a, 3b, and 3c below are of equal importance and their significance may depend on the aircraft
installation. The installer should use their best judgment to balance the installation guidelines.
1. Mount the antenna as close to level as possible with respect to the normal cruise flight attitude of the
aircraft. If the normal flight attitude is not known, substitute the waterline, which is typically
referenced as level while performing a weight and balance check.
2. The GPS antenna should be mounted in a location to minimize the effects of airframe shadowing
during typical maneuvers. Typically mounting farther away from the tail section reduces signal
blockage seen by the GPS antenna.
3a. The GPS antenna should be mounted no closer than two feet from any VHF COM antenna or any
other antenna which may emit harmonic interference at the L1 frequency of 1575.42 MHz. An
aircraft EMC check (reference VHF COM interference check in Post Installation Checkout
procedures) can verify the degradation of GPS in the presence of interference signals. If an EMC
check reveals unacceptable interference, insert a GPS notch filter in line with the offending VHF
COM or the (re-radiating) ELT transmitter.