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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




Global Positioning System
The GPS is a satellite-based radio navigation system. Its
RNAV guidance is worldwide in scope. There are no symbols
for GPS on aeronautical charts as it is a space-based system
with global coverage. Development of the system is underway
so that GPS is capable of providing the primary means of
electronic navigation. Portable and yoke mounted units are
proving to be very popular in addition to those permanently
installed in the aircraft. Extensive navigation databases are
common features in aircraft GPS receivers.

The GPS is a satellite radio navigation and time dissemination
system developed and operated by the U.S. Department of
Defense (DOD). Civilian interface and GPS system status
is available from the U.S. Coast Guard.

It is not necessary to understand the technical aspects of
GPS operation to use it in VFR/instrument flight rules (IFR)
navigation. It does differ significantly from conventional,
ground-based electronic navigation, and awareness of those
differences is important. Awareness of equipment approvals
and limitations is critical to the safety of flight

The GPS navigation system broadcasts a signal that is used
by receivers to determine precise position anywhere in the
world. The receiver tracks multiple satellites and determines
a pseudorange measurement to determine the user location.
A minimum of four satellites is necessary to establish an
accurate three-dimensional position. The Department of
Defense (DOD) is responsible for operating the GPS satellite
constellation and monitors the GPS satellites to ensure proper

The status of a GPS satellite is broadcast as part of the data
message transmitted by the satellite. GPS status information
is also available by means of the U.S. Coast Guard navigation
information service at (703) 313-5907 or online at http://
www.navcen.uscg.gov/. Additionally, satellite status is
available through the Notice to Airmen (NOTAM) system.

The GPS receiver verifies the integrity (usability) of the
signals received from the GPS constellation through receiver
autonomous integrity monitoring (RAIM) to determine if
a satellite is providing corrupted information. At least one
satellite, in addition to those required for navigation, must be
in view for the receiver to perform the RAIM function; thus,

RAIM needs a minimum of five satellites in view, or four
satellites and a barometric altimeter (baro-aiding) to detect an
integrity anomaly. For receivers capable of doing so, RAIM
needs six satellites in view (or five satellites with baro-aiding)
to isolate the corrupt satellite signal and remove it from the
navigation solution. Baro-aiding is a method of augmenting
the GPS integrity solution by using a nonsatellite input
source. GPS derived altitude should not be relied upon to
determine aircraft altitude since the vertical error can be quite
large and no integrity is provided. To ensure that baro-aiding
is available, the current altimeter setting must be entered into
the receiver as described in the operating manual.

RAIM messages vary somewhat between receivers; however,
generally there are two types. One type indicates that there
are not enough satellites available to provide RAIM integrity
monitoring and another type indicates that the RAIM integrity
monitor has detected a potential error that exceeds the limit
for the current phase of flight Without RAIM capability, the
pilot has no assurance of the accuracy of the GPS position.

Selective Availability
Selective Availability (SA) is a method by which the accuracy
of GPS is intentionally degraded. This feature is 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.

The GPS constellation of 24 satellites is designed so that a
minimum of five satellites are always observable by a user
anywhere on earth. The receiver uses data from a minimum of
four satellites above the mask angle (the lowest angle above
the horizon at which a receiver can use a satellite).
VFR Use of GPS

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.

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. In all
cases, VFR pilots should never rely solely on one system
of navigation. GPS navigation must be integrated with
other forms of electronic navigation as well as pilotage
and dead reckoning. Only through the integration of these
techniques can the VFR pilot ensure accuracy in navigation.