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Pilot's Handbook of Aeronautical Knowledge

Radio Navigation

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Pilot's Handbook of Aeronautical Knowledge



Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making




Some critical concerns in VFR use of GPS include RAIM
capability, database currency and antenna location.

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 crosscheck
with other navigation techniques would identify this
failure, and prevent a serious deviation.

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. 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display may be outdated and offer erroneous information to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 .y 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by using an outdated database.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 there is not a current data
base in the receiver, disregard the moving map display when
making critical navigation decisions.

In addition, waypoints are added, removed, relocated, or renamed
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 A/FD, sectional chart, or en route chart.

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.

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 aircraft
windows. While this method has great utility, the antenna
location is limited by aircraft structure for optimal reception

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.

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. Pilots should consult with a mechanic to ensure
compliance with the regulation and a safe installation.

Tips for Using GPS for VFR Operations
Always check to see if the unit has RAIM capability. If no
RAIM capability exists, be suspicious of a GPS displayed
position when any disagreement exists with the position
derived from other radio navigation systems, pilotage, or
dead reckoning.

Check the currency of the database, if any. If expired, update
the database using the current revision. If an update of an
expired database is not possible, disregard any moving map
display of airspace for critical navigation decisions. Be aware
that named waypoints may no longer exist or may have
been relocated since the database expired. At a minimum,
the waypoints planned to be used should be checked against
a current official source, such as the A/FD, or a Sectional Aeronautical Chart.

While a hand-held GPS receiver can provide excellent
navigation capability to VFR pilots, be prepared for
intermittent loss of navigation signal, possibly with no RAIM
warning to the pilot. If mounting the receiver in the aircraft,
be sure to comply with 14 CFR part 43.

Plan flights carefully before taking off. If navigating to user de
fined waypoints, enter them before flight, not on the fly.
Verify the planned flight against a current source, such as a
current sectional chart. There have been cases in which one
pilot used waypoints created by another pilot that were not
where the pilot flying was expecting. This generally resulted
in a navigation error. Minimize head-down time in the aircraft
and keep a sharp lookout for traffic, terrain, and obstacles.
Just a few minutes of preparation and planning on the ground
makes a great difference in the air.

Another way to minimize head-down time is to become very
familiar with the receiver's operation. Most receivers are not
intuitive. The pilot must take the time to 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.
Take the time to learn about the particular unit before using
it in flight.