400W Series Installation Manual Page 2-3190-00356-02 Rev. G3. ARINC 429 from GTX 33/3304. RS-232 FADC2.3.3 Multiple Heading SourcesThe 400W Series can accept heading data from an ARINC 429 INS/IRU, ARINC 429 EFIS, GAD 42,EHSI, GTX 33/330 transponder, ARINC 429 traffic advisory system, RS-232 FADC, and RS-232WX-500 Stormscope®.If multiple sources of heading data are supplied to the 400W Series unit, only valid data from the highestpriority source is used – preference is given to true heading (ARINC 429 label 314) if both true heading(label 314) and magnetic heading (label 320) are received. If the highest priority source becomesunavailable, data is taken from the next-highest priority source. The priorities of the heading sources areas follows (from highest to lowest):1. ARINC 429 INS/IRU2. ARINC 429 EFIS3. ARINC 429 from GAD 424. ARINC 429 from Sandel EHSI5. ARINC 429 from GTX 33/3306. ARINC 429 traffic advisory system7. RS-232 FADC8. RS-232 WX-500 Stormscope2.4 Antenna ConsiderationsThis section contains mounting location considerations for the antennas required for the 400W Seriesunits.The GPS 400W requires a GPS/WAAS antenna, the GNC 420W/420AW requires a GPS/WAAS andCOM antenna, and the GNS 430W and GNS 430AW require four antennas: a GPS/WAAS antenna, aCOM antenna, a NAV antenna, and a Glideslope antenna. Structural substantiation for mounting ofantennas is beyond the scope of the 400W Series unit STC. For mounting the GPS/WAAS antenna, referto Garmin GA Antenna AML STC SA01695SE or other FAA approved data. For mounting the COM,NAV, and Glideslope antennas, refer to the aircraft manufacturer’s data.2.4.1 GPS Antenna LocationThe GPS antenna is a key element in the overall system performance and integrity for a GPS/WAASnavigation system. The mounting location, geometry, and surroundings of the antenna can affect thesystem performance and/or availability. The following guidance provides information to aid the installerin ensuring that the most optimum location is selected for the installation of the GPS antenna. Theinstallation guidelines presented here meet the intent of AC 20-138A section 16. The greater the variancefrom these guidelines, the greater the chance of decreased availability. Approach procedures with verticalguidance are the most sensitive to these effects. LNAV only approaches, terminal operations, and enrouteoperations may also be affected. Because meeting all of these installations guidelines may not be possibleon all aircraft, these guidelines are listed in order of importance to achieve optimum performance. Items 3below are of equal importance and their significance may depend on the aircraft installation. The installershould 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 flightattitude 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.
