GPS - DESCRIPTION AND OPERATION
AMM-34-50-10-081-B-801
1.
Introduction
A. Global Positioning System/Wide Area Augmentation System (GPS/WAAS) is a U.S.
satellite-based navigational, positioning and time transfer system operated by the
Department of Defense (DOD). The GPS 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 a world fixed coordinate system.
GPS operation is based on the concept of ranging and triangulation from a group of 24
satellites in space which act as precise reference points. A minimum of five satellites are
always observable by a user anywhere on earth. A GPS receiver measures distance from
a satellite using the travel time of a radio signal. The GPS receiver needs at least four
satellites to yield a three-dimensional position (latitude, longitude and altitude). It also
yields time solutions for navigational values such as distance and bearing to a way point
and ground speed.
B. The GPS system is made up of the components that follow, refer to
•
Two GPS antennas (Combination Antennas)
•
Two GPS 400W units
C. Garmin GPS 400W
(1) The GPS 400W has an internal GPS receiver, a 240 by 128 pixel color LCD display
and a re-moveable data card containing a Jeppesen data base. It presents an active
flight plan and moving map on its display and provides guidance and status display
on its LCD and outputs guidance, flight plan and status data to external devices.
(2) The GPS 400W has a WAAS GPS engine that is TSO C146a certified for primary
domestic, oceanic and remote navigation including en route, terminal and non-
precision approaches and approaches with vertical guidance, such as LPV and
LNAV/VNAV (when connected to an antenna of appropriate standard).
(3) The two GPS 400Ws function as autonomous units and can, in principle, have
different active flight plans. However a serial data bus interface between two units
enables a “cross fill” function that permits the two GPS 400W units to directly
communicate and, depending on the crossfill mode selected, to have their active
flight plans synchronized continuously or with pilot action. This allows one pilot to
build or modify a flight plan on one GPS without affecting active navigation to the
other GPS and when, the crew is satisfied, crossfill to synchronize the flight plans in
the two units. Alternatively, one crew member can update the active flight plan
knowing that the other GPS is continuously reflecting the changes that were made.
EA500 Aircraft Maintenance Manual — 06-117751
Temporary Revision No. 34-21
EFFECTIVITY: 0001-0262 POST SB 500-99-005; AND
0266-0267; ALL POST MB 500-31-018
34-50-10
CONFIG B
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Sep 30/20
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