Specifications

Variations in along-tram aisrance while
operating in RNAV modes
Under certain conditions, VOR scalloping
can contribute significant variation in the
smoothness of the along-track distance
while operating in the RNAV modes
VOR scalloping is defined as
imperfection or deviation in the received
VOR signal which causes radials to deviate
from a standard track VOR scalloping
IS
generally the result of reflection from
buildings, terrain or other aircraft This
deviation or scalloping effect causes the
CDI needle
to slowly or rapidly shift from
side
to side
are
Factors contributing to VOR scalloping
0 The VORTAC is located in
mountainous terrain and is not a
Doppler VOR
0 Snow cover on the ground around
the VORTAC station
The effects of VOR scalloping are
minimized under the following conditions
C
1.
the VORTAC (not illustrated). The waypoint
may also be located on the flight path with
the VORTAC behind the aimlane and the
waypoint in front
(3).
NT
2.
NT
3* VORTAC
4.
4
D
FLIGHT PATH
When the waypoint offset distance is short,
’ then the acute angle formed by the flight
path and the waypoint offset radial from the
VORTAC
to the waypoint can approach
909 (4)
...... -.,..
m WAYPOINT
. ..
Note that, when the angle is large,
the distance needs to be short; con-
versely, when the distance is long, the
angle needs
to be small. Another way
of saying this is that the along-track
distance will have the least variation
if the geometry is such that DME
information is the major factor in
computing along-track distance.
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