RNAV
Review
Area
navigation
(RNAV)
is a method
of point-to-point navigation along any
desired course within the service area
of a
VOWDME
station, without the need
for flight over the station. This course is
.-
-
-.
A
waypoint
IS
dined
as
a geo-
graphic position located within the
service area
of
a
VORTAC
station.
It
may
be
used for route definition and/or
progress reporting.
A
waypoint is often
called a "phantom" station because
it provides the
RNAV
user with the
same
navigation information that a
real
VORTAC
station at that location would
provide:
A
waypoint is described by its
radial and distance from the selected
VORTAC
station. The waypoint below
is located on the
255.0"
radial at a
distance of
20.0
nm from the
ANX
VORTAC.
WAWOlNT
114
255
waypoints close together-a technique
that involves unnecessary planning
and execution.
Good
RNAV
technique
s
gests that you should 'reach out"
least
100
nm or
so
apart. Experience will
tell you what your technique should be.
But the whole idea behind
RNAV
is
to
reduce pilot workload and shorten flight
time. Remember, when selecting away-
point from a particular
VORTAC,
the
aircraft must
be
in the service range of
the
VORTAC
for proper operation.
if
two
sides of a trian le and the angle
angles can be calculated. This is what
the
RNAV
computer does.
Calculations based on waypoint
radial, waypoint distance, and cross-
wit
Y
the waypoints by placing them at
F
basic
Q
netry we know that
they form are given,
t
1
e other sides and
track deviation are supplied by the
RNAV
computer as solutions
to
continuously changing trigonometric
equations during flight.
Known inputs
to
the
RNAV
com-
puter are:
(1)
the
VORTAC
station radial
that passes through the wa point;
(2)
to
the waypoint;
(3)
the radial from the
VORTAC
station that the aircraft is on at
any particular point in time;
(4)
the
DME
distance from the
VORTAC
station
to
the
aircraft, and
(5)
the selected course
(OBS
to
the waypoint.
he
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 the angular
deviation used in conventional
VOR
navigation).
the
distance from the
VO
d
AC
station
VOR
Radial
A
Waypoint Radial
Linear or angular crosstrack
deviation?
Linear crosstrack deviation on a
CDI
or
HSI
permits flying parallel
to
a
selected course by maintaining appro-
priate needlb deflection.
In an
RNAV
enroute mode, each
dot represents
1.0
nm
off
c;ourse. In an
RNAV
approach modeyefrch
dot
repre-
sents
0.25
nm
off
course.
In a
VOR
mode, the
RNAV
CM-
puter
is
by-passed
so
that deviation
Lmar
Crosstrack
Deviation
10
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