RNAV
Review
Area navigation (RNAV) is a method
of point-to-point navigation along any
desired course within the service area
of
a VOR/DME (VORTAC) station, without the
need for flight over the station. This course
is
defined by “waypoints”
What is a waypoint?
A
waypoint is a predetermined
geographic position located within the
service area of a VORlDME station.
It
may
be used for route definition and/or progress
reporting.
A
waypoint is often called a
phantom station because
it
provides the
same navigation information that a “real”
VOR/DME station at that location would
provide.
A waypoint is defined by its radial and
distance from the selected VORlDME sta-
tion. The waypoint below is located on the
255.0”
radial at a distance of
20.0
nautical
miles from
ANX
VORTAC.
WAVPOINT
I
VORTAC Staban
RNAV
Geometry
Waypoint radial, waypoint distance and
crosstrack deviation are supplied by the
RNAV computer as solutions
to
continuously
changing geometry.
Known inputs
to
the RNAV computer
are:
Waypoint radial (VORTAC station
radial passing through the waypoint).
Waypoht distance from the VORTAC
station.
Aircraft radial from the VORTAC station
to
the aircraft.
DME distance from VORTAC station
to the aircraft.
Selected course
(OBS)
through the
waypoint.
The RNAV computer continuously
processes this information
to
supply the
aircraft distance from the waypoint and
crosstrack deviation of the aircraft from the
selected course in nautical miles (linear
deviation instead
of
conventional angular
course deviation).
Linear
or
angular crosstrack deviation?
Linear crosstrack deviation on CDI
or
HSI
permits flying parallel
to
a selected
course by maintaining appropriate needle
deflection In RNAVlENR function each dot
represents one nm off course In RNAVIAPR
function each dot represents
114
nm off
course
In VOR function the RNAV computer
IS
by-passed
so
that deviation from selected
course is conventional angular crosstrack
deviation expressed in degrees off course
(one dot equals
2“)
In VOR/PAR function you have, in
effect, a waypoint located over the VORl
DME station and thus will be provided linear
crosstrack deviation as in RNAV
Linear
Crasstrack
Deviation
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