Avionics News February 2014 - 60

THE DEPENDENT NAVIGATION SYSTEMS
AET ENDORSEMENT
Continued from page 59

dard has a slight overlap with the
Autonomous Navigation Systems
endorsement. This makes sense, as
an IRS-equipped aircraft will use
great circle navigation and have
the system closely integrated with
the GPS and the FMS.
Of course, the navigation workhorse for the last 60 years has
been the VHF navigation system,
or VHF omnirange with localizer. Those preparing for the
DNS endorsement exam should
be familiar with theory behind
this system. They must know the
radio and modulating frequencies
used, the instruments to which it
connects, and the antennas used.
Also important for technicians is
an ability to navigate using VOR
or localizer, since this knowledge
helps one understand and interpret
the various indicators used by the
system. Technicians should be
familiar with the limitations of a
VOR or LOC system, and problems which could cause errors.
Finally, they should be familiar
with the various ways to test VHF
navigation systems.
Although not specifically called
out, the DNS addresses marker
beacon and glideslope systems
within the ILS subject area. Like
the other systems, those wishing
to earn the endorsement must be
familiar with the theory of operation of both systems. Technicians
must be familiar with glideslope
and marker beacon modulation
types, radio frequencies and modu60

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february

2014

lating frequencies. In addition, the
standard asks technicians to be
familiar with approach categories
and airport lighting. Regarding the
integration of these systems, the
DNS standard requires technicians
to be familiar with radar altimeters.
Traditionally, avionics schools
used an engineering model to
develop programs. Because
of this, classes were designed
around technology types or spectrum used. Thus, most programs
included DME coursework with
other radar systems using L-band
frequencies and above. NCATT
groups the endorsements in a different, groundbreaking fashion.
As a result, DME is very sensibly
grouped with other navigation systems. Like VOR and GPS, those
preparing for the DNS endorsement should become familiar
with DME theory. This would
include the type of modulation,
radio frequencies used and modes
of operation. Some readers may
be confused by my separation of
modulation types and modes. In a
generic sense, the modulation type
is the mode; however, in the case
of DME, the system uses different
modes (X and Y) within the same
modulation (pulse) scheme. Like
other systems, NCATT requires
technicians to understand how the
DME works with other systems,
including transponders, FMS, navigation, R-NAV and audio systems.
Technicians also must be able to
perform an operational check of a
DME.
In today's navigation environment, the ADF seems like an
antique; however, there are enough

around to warrant inclusion in the
DNS endorsement. Technicians
must be familiar with radio frequency and the type of modulation.
Furthermore, they must understand
how the ADF uses BFO. The standard also mentions the various
types of error inherent in ADF
systems. Like VHF navigation,
technicians will find it useful to
understand how to navigate using
ADF, whether the navigation is in
relation to an outer compass locator, NDB or AM radio station.
Regarding operational theory of
all these systems, technicians wishing to earn the DNS should learn
block diagrams. Those wishing to
earn the endorsement should be able
to draw an external block diagram
of each system. In addition, they
should be able to draw and analyze
simplified internal block diagrams.
There are study materials available online. For guided study,
visit www.avotek.com. If you are
a technician attending the AEA
International Convention & Trade
Show in Nashville, Tenn., March
12-15, and have earned the AET
certification, consider taking time
to study and take the RCS endorsement exam. You may find the test
easier than you expected.
Finally, all exams are free
to those attending the AEA
Convention and AEA Regional
Meetings throughout the year,
courtesy of the AEA Educational
Foundation. A complete list of dates
and locations for this year is available online at www.aea.net. For
more information about NCATT, the
AET certification and its endorsements, visit www.ncatt.org. q
http://www.avotek.com http://www.aea.net http://www.ncatt.org
Avionics News February 2014

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