FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 12. Aircraft Avionics Systems | 2. Ground Operational Checks for Avionics Equipment (Electrical) | 12-15. Marker Beacon
AC 43.13-1B CHG 1
9/27/01
be degraded by lightning activity, airframe
charging, ignition noise and atmospheric phe
nomena.
12-14. INSTRUMENT
LANDING
SYSTEMS (ILS). The ILS consist of several
components, such as the localizer, glide slope,
marker beacon, radio altimeter, and DME.
Localizer and glide slope receivers and marker
beacons will be discussed in this section.
must be conducted under visual flight rules
(VFR) conditions. A failed or misleading
system must be serviced by an appropriately-
rated repair station. Ground test equipment
can be used to verify glide slope operation.
c. Localizer/Glide Slope (LOC/GS) may
have self test function, otherwise the proper
ground test equipment must be used. Refer to
manufacturer’s or aircraft instruction manual.
a. Localizer receiver operates on one of
40 ILS channels within the frequency range of
108.10 to 111.95 MHz (odd tens). These sig
nals provide course guidance to the pilot to the
runway centerline through the lateral dis
placement of the VOR/localizer (LOC) devia
tion indicator. The ground transmitter is
sighted at the far end of the runway and pro
vides a valid signal from a distance of 18 NM
from the transmitter. The indication gives a
full fly left/right deviation of 700 feet at the
runway threshold. Identification of the trans
mitter is in International Morse Code and con
sists of a three letter identifier preceded by the
Morse Code letter I (two dots). The localizer
function is usually integral with the VOR sys
tem, and when maintenance is performed on
the VOR unit, the localizer is also included.
The accuracy of the system can be effectively
evaluated through normal flight operations if
evaluated during visual meteorological condi
tions. Any determination of airworthiness af
ter reinstallation before instrument flight must
be accomplished with ground test equipment.
b. The glide slope receiver operates on
one of 40 channels within the frequency range
329.15 MHz, to 335.00 MHz. The glide slope
transmitter is located between 750 feet and
1250 feet from the approach end of the runway
and offset 250 to 650 feet. In the absence of
questionable performance, periodic functional
flight checks of the glide slope system would
be an acceptable way to ensure continued sys
tem performance. The functional flight test
12-15. MARKER BEACON. Marker bea
con receivers operate at 75 MHz and sense the
audio signature of each of the three types of
beacons. The marker beacon receiver is not
tunable. The blue outer marker light illumi
nates when the receiver acquires a 75 MHz
signal modulated with 400 Hz, an amber mid
dle marker light for a 75 MHz signal modu
lated with 1300 Hz and, a white inner marker
light for a 75 MHz signal modulated with
3000 Hz. The marker beacon system must be
operationally evaluated in VFR when an ILS
runway is available. The receiver sensitivity
switch must be placed in LOW SENSE (the
normal setting). Marker audio must be ade
quate. Ground test equipment must be used to
verify marker beacon operation. Marker bea
con with self test feature, verify lamps, audio
and lamp dimming.
12-16. LONG RANGE NAVIGATION
(LORAN). The LORAN has been an effective
alternative to Rho/Theta R-Nav systems. Hy
perbolic systems require waypoint designation
in terms of latitude and longitude, unlike
original R-Nav (distance navigation) systems,
which define waypoints in terms of distance
(Rho) and angle (Theta) from established VOR
or Tacan facilities. Accuracy is better than the
VOR/Tacan system but LORAN is more prone
to problems with precipitation static. Proper
bonding of aircraft structure and the use of
high-quality static wicks will not only produce
improved LORAN system performance, but
can also benefit the very high frequency
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