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approved source. If the WP data is entered in the user
database, its accuracy must be checked before use.
3. Attempting to use LORAN information with degraded
signals.
Advanced Technologies
Global Navigation Satellite System (GNSS)
The Global Navigation Satellite System (GNSS) is a
constellation of satellites providing a high-frequency signal
which contains time and distance that is picked up by a
receiver thereby. [Figure 7-27] The receiver which picks up
multiple signals from different satellites is able to triangulate
its position from these satellites.
7-27
Figure 7-28. Typical GPS Satellite Array.
Three GNSSs exist today: the GPS, a United States system;
the Russian GNSS (GLONASS); and Galileo, a European
system.
1. GLONASS is a network of 24 satellites, which can be
picked up by any GLONASS receiver, allowing the
user to pinpoint their position.
2. Galileo planned to be a network of 30 satellites that
continuously transmit high-frequency radio signals
containing time and distance data that can be picked
up by a Galileo receiver with operational expectancy
by 2013.
3. The GPS came on line in 1992 with 24 satellites, and
today utilizes 30 satellites.
Global Positioning System (GPS)
The GPS is a satellite-based radio navigation system, which
broadcasts a signal that is used by receivers to determine
precise position anywhere in the world. The receiver tracks
multiple satellites and determines a measurement that is then
used to determine the user location. [Figure 7-28]
The Department of Defense (DOD) developed and deployed
GPS as a space-based positioning, velocity, and time system.
The DOD is responsible for operation of the GPS satellite
constellation, and constantly monitors the satellites to ensure
proper operation. The GPS system permits Earth-centered
coordinates to be determined and provides aircraft position
referenced to the DOD World Geodetic System of 1984
(WGS-84). Satellite navigation systems are unaffected
by weather and provide global navigation coverage that
fully meets the civil requirements for use as the primary
means of navigation in oceanic airspace and certain remote
areas. Properly certified GPS equipment may be used as a
supplemental means of IFR navigation for domestic en route,
terminal operations, and certain IAPs. Navigational values,
such as distance and bearing to a WP and groundspeed, are
computed from the aircraft’s current position (latitude and
longitude) and the location of the next WP. Course guidance
is provided as a linear deviation from the desired track of a
Great Circle route between defined WPs.
GPS may not be approved for IFR use in other countries.
Prior to its use, pilots should ensure that GPS is authorized
by the appropriate countries.
GPS Components
GPS consists of three distinct functional elements: space,
control, and user.
The space element consists of over 30 Navstar satellites. This
group of satellites is called a constellation. The space element
consists of 24 Navigation System using Timing and Ranging
(NAVSTAR) satellites in 6 orbital planes. The satellites in
each plane are spaced 60° apart for complete coverage and
are located (nominally) at about 11,000 miles above the
Earth. The planes are arranged so that there are always five
satellites in view at any time on the Earth. Presently, there are
at least 31 Block II/IIA/IIR and IIR-M satellites in orbit with
the additional satellites representing replacement satellites
(upgraded systems) and spares. Recently, the Air Force
received funding for procurement of 31 Block IIF satellites.
The GPS constellation broadcasts a pseudo-random code
timing signal and data message that the aircraft equipment
processes to obtain satellite position and status data. By
knowing the precise location of each satellite and precisely
matching timing with the atomic clocks on the satellites, the
aircraft receiver/processor can accurately measure the time
each signal takes to arrive at the receiver and, therefore,
determine aircraft position.
The control element consists of a network of ground-based
GPS monitoring and control stations that ensure the accuracy
of satellite positions and their clocks. In its present form, it
has five monitoring stations, three ground antennas, and a
master control station.
The user element consists of antennas and receiver/processors
on board the aircraft that provide positioning, velocity,
and precise timing to the user. GPS equipment used while
operating under IFR must meet the standards set forth in
Technical Standard Order (TSO) C-129 (or equivalent); meet
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