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in a manner that is consistent with current navigation
requirements as well as approved air carrier
operations specifications.
b. VFR Use of GPS
1. GPS navigation has become a great asset to
VFR pilots, providing increased navigation capability
and enhanced situational awareness, while
reducing operating costs due to greater ease in flying
direct routes. While GPS has many benefits to the
VFR pilot, care must be exercised to ensure that
system capabilities are not exceeded.
2. Types of receivers used for GPS navigation
under VFR are varied, from a full IFR installation
being used to support a VFR flight, to a VFR only
installation (in either a VFR or IFR capable aircraft)
to a hand−held receiver. The limitations of each type
of receiver installation or use must be understood by
the pilot to avoid misusing navigation information.
(See TBL 1−1−6.) In all cases, VFR pilots should
AIM 2/19/04
1−1−26 Air Navigation Aids
never rely solely on one system of navigation. GPS
navigation must be integrated with other forms of
electronic navigation (when possible), as well as
pilotage and dead reckoning. Only through the
integration of these techniques can the VFR pilot
ensure accuracy in navigation.
3. Some critical concerns in VFR use of GPS
include RAIM capability, database currency and
antenna location.
(a) RAIM Capability. Many VFR GPS receivers
and all hand−held units have no RAIM
alerting capability. Loss of the required number of
satellites in view, or the detection of a position error,
cannot be displayed to the pilot by such receivers. In
receivers with no RAIM capability, no alert would be
provided to the pilot that the navigation solution had
deteriorated, and an undetected navigation error
could occur. A systematic cross−check with other
navigation techniques would identify this failure, and
prevent a serious deviation. See subparagraphs a8 and
a9 for more information on RAIM.
(b) Database Currency
(1) In many receivers, an up−datable
database is used for navigation fixes, airports, and
instrument procedures. These databases must be
maintained to the current update for IFR operation,
but no such requirement exists for VFR use.
(2) However, in many cases, the database
drives a moving map display which indicates Special
Use Airspace and the various classes of airspace, in
addition to other operational information. Without a
current database the moving map display may be
outdated and offer erroneous information to VFR
pilots wishing to fly around critical airspace areas,
such as a Restricted Area or a Class B airspace
segment. Numerous pilots have ventured into
airspace they were trying to avoid by using an
outdated database. If you don’t have a current
database in the receiver, disregard the moving map
display for critical navigation decisions.
(3) In addition, waypoints are added,
removed, relocated, or re−named as required to meet
operational needs. When using GPS to navigate
relative to a named fix, a current database must be
used to properly locate a named waypoint. Without
the update, it is the pilot’s responsibility to verify the
waypoint location referencing to an official current
source, such as the Airport/Facility Directory,
Sectional Chart, or En Route Chart.
(c) Antenna Location
(1) In many VFR installations of GPS
receivers, antenna location is more a matter of
convenience than performance. In IFR installations,
care is exercised to ensure that an adequate clear view
is provided for the antenna to see satellites. If an
alternate location is used, some portion of the aircraft
may block the view of the antenna, causing a greater
opportunity to lose navigation signal.
(2) This is especially true in the case of
hand−helds. The use of hand−held receivers for VFR
operations is a growing trend, especially among
rental pilots. 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 only and is
rarely optimized to provide a clear view of available
satellites. Consequently, signal losses may occur in
certain situations of aircraft−satellite geometry,
causing a loss of navigation signal. These losses,
coupled with a lack of RAIM capability, could
present erroneous position and navigation information
with no warning to the pilot.
(3) While the use of a hand−held GPS for
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