Flying The Route
CHART UPDATE MANUAL (CHUM)
Use the latest CHUM or supplement to identify the current edition of the chart you need. It will list
additions or deletions concerning obstructions on the current edition of the chart. Here, too, use a
little imagination. What will additions look like? What change will be observable after a tower was
removed or added?
PILOT POINT OF VIEW
Altitude, airspeed, light conditions, and obstructions must be considered when selecting visual
navigation features. At high altitude, visibility may be as great as 100 miles with ample checkpoints,
but 100 miles ahead, only a large city might serve as a landmark. From 500 feet AGL, you have
limited radius of vision. Compare that with the extended field of view you have at 6,000 feet AGL.
Look for large features and consider the possibility of an undercast; in conjunction with time and
course, check directly under you as well as ahead. At low altitude, you must consider the oblique
perspective you will have from your cockpit (Figure 3). Experience is a great teacher in this respect.
As airspeed increases, you have less time to interpret, analyze and locate landmarks, intermediate
checkpoints and checkpoints.
Early or late in the day, consider the effect of shadows on checkpoints. A long shadow may make an
object more visible, or it may hide another, leading to dangerous situations when flying in moun-
tainous terrain. Shadows in northern latitudes will cause snow to remain in some places much
longer than in others; the presence of a large patch of white can make a landmark much easier to
see due to the contrast while also making it harder to identify because of glare.
Finally, consider vegetation and
terrain. Which way does the
ground slope? Is it higher than
your landmark? Might a ground
slope lead you to your landmark?
From any knowledge of the country
you have, what effect will vegeta-
tion have on your checkpoints? It
will have less effect around El
Centro, California, where there is
little vegetation. Mississippi, on
the other hand, is full of tall trees.
In northern locations the effect of
vegetation can be dramatic. If the
predominant vegetation is ever-
green trees, there will be little
seasonal difference, as is the case
with the ocotillo cactus in southern
California and the live oak trees of
south Texas. But grass turns
brown and disappears in some
places, and leaves fall off trees,
changing the overall appearance
of the surface. Imagine what it will
Figure 3: VIEW FROM 500 FEET AGL AND 1/2 MILE