Page 140 - Planning and Design of Airports

Air Traf fic Management 109

designated route penetrates into an area of thunderstorms, aircraft
have to be vectored around the storm by controllers on the ground.
This imposed an extra workload on the controllers that is compen-
sated for by the use of the severe weather avoidance program (SWAP).
Despite these inefficiencies, the vast majority of transient aviation
still fly along the victor airways and jet routes. This trend, however,
has begun to change dramatically since the beginning of the twenty-
first century, with the proliferation of GPS based navigation systems,
under what is known as RNAV.
Area navigation, RNAV, is a method of aircraft navigation that
permits aircraft operation on any desired course within the cover-
age of station-referenced navigational signals or within the limits of
a self-contained system capability. Area navigation routes are direct
routes, based upon the area navigation capability of aircraft,
between waypoints defined in terms of latitude and longitude coor-
dinates, degree and distance fixes, or offsets from established routes
and airways.
RNAV is possible due to the proliferation of onboard aircraft
technologies that take advantage of the global positioning system
(GPS). GPS is based on 24 satellites located approximately 12,000 mi
about the earth in a geostatic orbit. Technology that references an
aircraft’s position in relation to these satellites allows an aircraft to
navigate by referencing its position to a detailed database that identi-
fies airports, waypoints, terrain, and man-made infrastructure.
Enhancements to the accuracy of the GPS system, with technologies
such as the wide area augmentation system (WAAS) have made it
possible for the air traffic control system to approve defined approaches
to airport runways with far greater accuracy than with traditional
radio-frequency-based systems.
Area navigation provides a more flexible routing capability that
allows for better utilization of the airspace. The greater utilization
reduces delays in the airspace and results in more economical opera-
tion of the aircraft. For example, routes parallel to the designated
routes from one VOR to another can be established without requiring
additional aids to navigation on the ground. Another example is the
establishment of a more direct route from one point to another by
establishing waypoints that provide for a shorter trip. Routing around
a thunderstorm without continuous radar guidance from the ground
is another example.
Area navigation is not limited to the horizontal plane but can also
be utilized in the vertical plane, termed VNAV. It can also include a
time reference capability. A properly equipped aircraft could arrive at
a specified point in space, called a fix, with no need for ground vector-
ing or directions and could additionally be at that point at a specified
altitude and time. This is a four-dimensional capability giving lati-
tude, longitude, altitude, and time (4D RNAV). Thus area navigation