Flight Training - May 2014 - 49

TERMS AND
CONDITIONS
Some simple navigational terms and flying
conditions you should know.

SECTIONAL
CHARTS depict
the difference
between true north
and magnetic north
with isogonic lines.
They can be found
as dashed magenta
lines with a degree
marking the
variation.

True directions: Directions measured from
the geographic poles, which are used to
draw charts and maps using meridians of
longitude.
Magnetic directions: Directions that are
measured from the magnetic poles, which
are measured by azimuths and do not correlate with the geographic pole locations.
Variation: In aerial navigation, the difference between true and magnetic directions
is called variation. This same difference
in land surveying and navigation is called
declination. Variation must be taken into
account when flying, as airplanes are
equipped with magnetic compasses that
point to magnetic, and not true north.
Isogonic lines: Lines of equal variation that
are used to identify the number of degrees
of magnetic variation for geographic areas
from the magnetic poles.
Agonic line: A singular isogonic line
location where the two norths (true and
magnetic) are perfectly aligned and there
is no magnetic variation. All isogonic lines
east of the agonic line are areas where
magnetic north is west of the geographic
North Pole. All isogonic lines west of the
agonic line are areas where the magnetic
north is east of the geographical North
Pole.

runway numbers are used to update navigational aids
such as instrument landing systems and beacons, the
FAA requires that a magnetic variation change of more
than five degrees requires that airport's runways to be
renumbered.
Take for example Tampa International Airport (TPA),
which in 2011 was required to make just such an update.
Its west parallel runway was 36L-18R, to designate the
compass points of 360 degrees and 180 degrees respectively. But with the magnetic drift constantly taking
place, those runways were starting to line up more
accurately to 10 degrees and 190 degrees. As a result, if
you fly into TPA today, you'll find its west parallel runway designated 1L-19R, to accurately reflect the shifted
magnetic north.
Magnetic versus true north has many implications
to the success of your flying. Knowing tricks of the
trade, like runways lining up to magnetic azimuths and
magnetic variation calculations, will help you to be
successful on your checkride, and also in your future
aviation endeavors. Remember to take magnetic variation into account, and you'll end up at your intended
destination each time.
Jill Brown is an Anchorage, Alaska-based writer and student pilot.

You may have heard that several airports across the United States have been
renaming their runways. This isn't done
as a means to make you stock your flight
bag with new supplements. It's necessary for accuracy as magnetic poles shift
to the point of new compass orientations.
Because runways are designated according
to the points on a compass and magnetic
North is in a constant state of drift, runway
numbers will periodically need to be
changed in order to be accurate. Since

She shares her adventures flying in Alaska on her blog, www.The
DuchessGuide.com.

THINGS TO KNOW
All runways line up with magnetic azimuths that align with your compasses
azimuths, plus or minus a few degrees. Therefore if you have Runway 32/14,
an approach to land northwest would be on Runway 32 and a southeast
approach would have you landing on Runway 14. This can help you in determining safe landing approaches at nontowered airports. If you can see from
the windsock or hear on the ATIS the prevailing wind is blowing from the
northwest, line up for a landing on Runway 32 so you can land into the wind
(don't risk a tailwind landing!).
MAY 2014 FLIGHT TRAINING

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Flight Training - May 2014

Table of Contents for the Digital Edition of Flight Training - May 2014