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AIM
second type indicates that the RAIM integrity
monitor has detected a potential error and that there
is an inconsistency in the navigation solution for the
given phase of flight. Without RAIM capability, the
pilot has no assurance of the accuracy of the GPS
position.
4.
Selective Availability. Selective Availability
(SA) is a method by which the accuracy of GPS is
intentionally degraded. This feature was designed to
deny hostile use of precise GPS positioning data. SA
was discontinued on May 1, 2000, but many GPS
receivers are designed to assume that SA is still
active. New receivers may take advantage of the
discontinuance of SA based on the performance
values in ICAO Annex 10.
b. Operational Use of GPS.
U.S. civil operators
may use approved GPS equipment in oceanic
airspace, certain remote areas, the National Airspace
System and other States as authorized (please consult
the applicable Aeronautical Information Publica
tion). Equipage other than GPS may be required for
the desired operation. GPS navigation is used for both
Visual Flight Rules (VFR) and Instrument Flight
Rules (IFR) operations.
1. VFR Operations
(a)
GPS navigation has become an asset to
VFR pilots by providing increased navigational
capabilities and enhanced situational awareness.
Although GPS has provided many benefits to the
VFR pilot, care must be exercised to ensure that
system capabilities are not exceeded. VFR pilots
should integrate GPS navigation with electronic
navigation (when possible), as well as pilotage and
dead reckoning.
(b)
GPS receivers used for VFR navigation
vary from fully integrated IFR/VFR installation used
to support VFR operations to hand
−
held devices.
Pilots must understand the limitations of the receivers
prior to using in flight to avoid misusing navigation
information. (See TBL 1
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1
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6.) Most receivers are
not intuitive. The pilot must learn the various
keystrokes, knob functions, and displays that are
used in the operation of the receiver. Some
manufacturers provide computer
−
based tutorials or
simulations of their receivers that pilots can use to
become familiar with operating the equipment.
(c)
When using GPS for VFR operations,
RAIM capability, database currency, and antenna
location are critical areas of concern.
(1)
RAIM Capability. VFR GPS panel
mount receivers and hand
−
held units have no RAIM
alerting capability. This prevents the pilot from being
alerted to the loss of the required number of satellites
in view, or the detection of a position error. Pilots
should use a systematic cross
−
check with other
navigation techniques to verify position. Be
suspicious of the GPS position if a disagreement
exists between the two positions.
(2)
Database Currency. Check the curren
cy of the database. Databases must be updated for
IFR operations and should be updated for all other
operations. However, there is no requirement for
databases to be updated for VFR navigation. It is not
recommended to use a moving map with an outdated
database in and around critical airspace. Pilots using
an outdated database should verify waypoints using
current aeronautical products; for example, Chart
Supplement U.S., Sectional Chart, or En Route
Chart.
(3)
Antenna Location. The antenna loca
tion for GPS receivers used for IFR and VFR
operations may differ. VFR antennae are typically
placed for convenience more than performance,
while IFR installations ensure a clear view is
provided with the satellites. Antennae not providing
a clear view have a greater opportunity to lose the
satellite navigational signal. This is especially true
in the case of hand
−
held GPS receivers. Typically,
suction cups are used to place the GPS antennas on
the inside of cockpit windows. While this method has
great utility, the antenna location is limited to the
cockpit or cabin which rarely provides a clear view
of all available satellites. Consequently, signal losses
may occur due to aircraft structure blocking satellite
signals, causing a loss of navigation capability. These
losses, coupled with a lack of RAIM capability, could
present erroneous position and navigation informa
tion with no warning to the pilot. While the use of a
hand
−
held GPS for VFR operations is not limited by
regulation, modification of the aircraft, such as
installing a panel
−
or yoke
−
mounted holder, is
governed by 14 CFR Part 43. Consult with your
mechanic to ensure compliance with the regulation
and safe installation.
(d)
Do not solely rely on GPS for VFR
navigation. No design standard of accuracy or
Navigation Aids
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