Avionics News November 2014 - 61

used, the instruments to which it connects, and the
antennas used. Also important is an ability to navigate
using VOR or localizer. Review the limitations of a VOR
or LOC system and problems that could cause errors.
Finally, know the various ways to test VHF navigation
systems.
Although not specifically called out in the standard,
the DNS addresses marker beacon and glideslope
systems within the ILS subject area, including theory of
operation of all ILS subsystems. Be prepared to recall
glideslope and marker beacon modulation types, radio
frequencies and modulating 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.
Review DME theory, including the type of
modulation, radio frequencies used and modes of
operation. Like other systems, the NCATT requires
technicians to understand how the DME works with
other systems, including transponders, FMS, navigation,
R-NAV and audio systems. You must also perform an
operational check of a DME.
Brush up on ADF frequencies and the type of modulation.
Furthermore, you must understand how the ADF uses BFO.
The standard also mentions the various types of errors
inherent in ADF systems. Like VHF navigation, technicians
will find it useful to understand how to navigate using ADF,
whether the navigation is related to an outer compass locator,
NDB or AM radio station.
Autonomous Navigation Systems
Endorsement
With the DNS endorsement in hand, begin studying
for the ANS endorsement by becoming familiar with
the purpose, types, components and configurations of
common forms of direction indicating systems.
Of course, the slaved compass system relies on a gyro.
You may be taken back to high school physics, since the
ANS tests on basic gyroscopic concepts that apply to all
types of gyros.
Become familiar with the various types of gyro power
systems, how they are configured, and at what speed
gyros spin. Not only should the technician know the
concept of precession and precessive forces, but also
what affect these forces have on the types of gyros used
in aviation. In addition, you should have a grasp of the
effects of bearing wear. Finally, understand how the
various types of gyros are gimbaled. Become familiar
with how vertical is interpreted and what can happen
when the limits of the gimbals are exceeded.

Not only is it important for the technician to
understand the mechanical gyros found in aircraft, but
also the various types of solid-state position sensing
and indicating systems. Study various types of laser
gyros and accelerometers, including microelectronic
mechanical sensors.
Today, solid-state position sensing is rapidly replacing
mechanical gyros. As a result, you will need to learn
about magnetometers that are used with attitude heading
reference systems. Most IRS- or INS-equipped aircraft
will have an air-data system. In addition, many smaller
aircraft will have an air-data heading reference system.
With an ADHRS, your study will take you into the world
of pressure-sensing instruments.
Review the components of a pitot-static system, the
various types of airspeed, and how all this ties together
for air data, or for air-data inertial reference units.
Essentially, INS and IRS do the same things. For
example, engineers will design an INS with navigation
in mind, but the nature of the system allows it to monitor
and display aircraft attitude. Conversely, an IRS system
is engineered with attitude in mind, but also the system
will be accurate enough to navigate. In many ways, what
you learn about one can be applied to the other.
You will need to know some details about how IRS
and INS systems align and calibrate. Furthermore, know
how to enter data and what components comprise the
systems. These systems monitor themselves, so the
technician should learn how.
As with the other endorsements, you must be familiar
with how the ANS or IRS integrates with global
navigation satellite systems, flight management systems,
various types of displays and autoflight systems.
Onboard Communication & Safety
Systems Endorsement
The best way to prepare for the OCS endorsement
exam is to take a look at a transport category aircraft
maintenance manual, along with a review of the
Federal Aviation Regulations regarding flight data and
voice recorders. Those interested in earning the OCS
endorsement should review passenger entertainment
systems, multiplexing and intercom systems used on
transport category aircraft.
There is no better time to get certified. You have study
options available at home, conventions and school. You
have testing options at CATS/Comira testing centers
and the AEA International Convention & Trade Show.
Become a card-carrying avionics technician today. For
more information about NCATT, the AET certification
and its endorsements, visit www.ncatt.org. q
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Avionics News November 2014

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