Section 7
Columbia 400 (LC41-550FG)
Description of the Airplane and Systems
Initial Issue of Manual: November 10, 2004
RC050002
Latest Revision Level/Date: A/12-01-2004
7-123
GARMIN GNS 430 SYSTEM
General –
The GPS is a United States satellite based radio navigational, positioning, and time
transfer system operated by the Department of Defense. The system provides highly accurate
position and velocity information and precise time on a continuous global basis to an unlimited
number of properly equipped users. The system is unaffected by weather and provides a
worldwide common grid reference system based on the earth fixed coordinate system. The GPS
constellation of 24 satellites is designed so that a minimum of five are always observable by a
user anywhere on earth. The receiver uses data from the best four satellites above its horizon,
adding signals from one as it drops signals from another, to continually calculate its position.
The GPS receiver verifies the integrity of the signals received from the GPS constellation
through receiver autonomous integrity monitoring (RAIM) by determining if a satellite is
providing corrupted information. At least one satellite, in addition to those required for
navigation, must be in view for the receiver to perform the RAIM function; thus, RAIM needs
five satellites in view, or four satellites and baro-aiding to work. RAIM needs six satellites in
view (or five satellites with baro-aiding) to isolate the corrupt satellite signal and remove it from
the navigation solution. Baro-aiding is a method of augmenting the GPS solution equation by
using a non-satellite input source. Baro-aiding uses the pressure altitude corrected for the local
barometric pressure setting to provide accurate altitude information to the GPS receiver.
The Global Positioning System, when receiving adequate and usable signals, can be used as a
primary means of navigation in oceanic airspace and certain remote areas. GPS equipment may
be used as a supplemental means of IFR navigation for domestic en route, terminal operations,
and certain instrument approach procedures. This approval permits the use of GPS in a manner
that is consistent with current navigation requirements. The system can be used as one of the
required items for long-range oceanic navigation and as the only device for short-range oceanic
routes that require one source of navigation.
The GNS 430 System is a fully integrated, panel-mounted instrument, which contains a VHF
Communications Transceiver, a VOR/ILS receiver, and a Global Positioning System (GPS)
Navigation computer. Dual GNS 430 units are installed. The system consists of a GPS antenna,
GPS Receiver, VHF VOR/LOC/GS antenna, VOR/ILS receiver, VHF COMM antenna and a
VHF Communications Transceiver. The primary function of the VHF Communication portion of
the equipment is to facilitate communication with Air Traffic Control. The primary function of
the VOR/ILS Receiver portion of the equipment is to receive and demodulate VOR, Localizer,
and Glideslope signals. The primary function of the GPS portion of the system is to acquire
signals from the GPS system satellites, recover orbital data, make range and Doppler
measurements, and process this information in real-time to obtain the user’s position, velocity,
and time. Navigation is accomplished using the WGS-84 (NAD-83) coordinate reference datum.
Navigation data are based upon use of only the Global Positioning System (GPS) operated by the
United States of America. A picture of the GNS 430 System is shown in Figure 7 - 48.
Provided the GARMIN GNS 430 GPS receiver is receiving adequate usable signals, it has been
demonstrated capable of and has been shown to meet the accuracy specifications for:
•
VFR/IFR en route, terminal, and non-precision instrument approach (GPS, Loran-C,
VOR, VOR-DME, TACAN, NDB, NDB-DME, RNAV) operation within the U.S.
National Airspace System in accordance with AC 20-138.
