User Guide

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Flight Instruction
Flight Instruction
THE BACK COURSE
The localizer and glideslope are exactly aligned for use with
only a single runway. At some airports, however, the localizer’s
“back course” can be used for a nonprecision approach to the
other end of the same runway, landing in the opposite direction.
There are only two significant things to remember about such a
back-course approach:
1. Since the OBS is not functional and the localizer provides only
a single course signal, you can’t set the indicator to “work the
other way” as you could on a VOR. Thus, when on the back
course, you must make your corrections by turning away from
the needle rather than toward it. (If you’re lucky enough to
have an HSI - see “Radio Flyer” - you can fly normally as long
as you keep its course arrow set to the front course value.)
2. The back course approach provides no vertical guidance.
Although the glideslope needle may deflect due to local
reflections, these are false signals and must be ignored.
NDBs and the ADF
Your airplane is equipped with a further navigation radio,
called an Automatic Direction Finder (ADF). Actually, this unit is
better described by its old-fashioned name of “Radio Compass.”
Just as a magnetic compass points toward magnetic north, the nee-
dle of the ADF will point toward simple ground stations called
Nondirectional
Beacons, or NDBs.
Thus, unlike a VOR,
the ADF can tell you
your heading with
regard to the station,
but not necessarily
where you are.
Note, in this illustration, that each of these airplanes is in a
different location - but the ADF indicator would appear as it is
shown in all of them.
In addition to this ambiguity, the ADF is inherently less accu-
rate than a VOR. In recent years it’s fallen into disrepute, sup-
planted largely by GPS. In fact, it probably would have disap-
peared entirely in the USA were it not for its one redeeming fea-
ture: in addition to the low-frequency NDBs, it can also receive
(and, for that matter, point at) commercial AM broadcast stations -
a feature much appreciated on long, boring flights, particularly
during the World Series or NFL playoffs! It’s also still a primary
basis for navigation in the developing world, largely because an
NDB ground station is orders of magnitude simpler, easier to main-
tain, and cheaper than a VOR.
IT’S ALL RELATIVE
Absent any other information, the only thing you can tell
from the ADF is the relative bearing to a station - starting at 0 if it’s
right in front of you, going to 90 if it’s at your 3 o’clock position,
180 if it’s right behind you, etc. To determine where you are in
relation to the station, and which way you have to fly to get to it,
you need to combine this relative bearing with your current com-
pass heading to get a magnetic bearing. For example, in this illus-
tration our heading is 045 degrees magnetic. The relative bearing
is 030 (the station is 30
degrees right of the
nose), so its magnetic
bearing is 075 degrees
- our heading plus the
relative bearing. That’s
the heading we’d have
to turn to if we wanted
to fly right over the
NDB.