Section III. NAVIGATION
Section IV. TRANSPONDER AND RADAR
3-5. TRANSPONDER APX-100.
a. Description. The transponder (APX-100)
system is a position tracking, identification, altitude
reporting, and emergency-tracking device. This set
receives, decodes, and responds to interrogations by
search radar. Range of the set is normally limited to
b. Operating Controls and Functions. The
operating controls of the transponder system are
described as follows and illustrated in Figure 3-3.
indicates successful completion of built-in-test (BIT).
(2) TEST / MON Indicator Illumination
indicates unit has malfunctioned, or interrogation by a
ground station (MON).
(3) ANT Switch.
Place the TOP / BOT / DIV switch in the DIV
position during flight operations. Do not
use the TOP or BOT position. This does
not preclude using the TOP or BOT switch
position for ground based system checks.
(a) TOP Selects use of top antenna.
(b) DIV Selects diversity operation
using both antennas.
(4) RAD TEST OUT Switch. Enables an
appropriately equipped transponder to reply test mode
interrogations from an AN/UPM-92 or similar test set.
(5) MASTER Control.
(a) OFF Turns set OFF.
(b) STBY Places set in warmup
(standby) condition. Red NO-GO light is ON in
(c) NORM . Operates set at normal
(d) EMER. Transmits emergency reply
(6) STATUS ANT Indicator Illumination
indicates the BIT or MON failure is due to high VSWR
(7) STATUS KIT Indicator Illumination
indicates the BIT or MON failure is due to external
(8) STATUS ALT Indicator Illumination
indicates the BIT or MON failure is due to Altitude
(9) IDENT MIC Switch.
(a) IDENT Activates transmission of
identification (IP) pulse.
(b) MIC Enables the POS IDENT
button located only on the pilot's side CONTROL
wheel to activate transmission of IDENT signal from
(c) OUT Disables IDENT MIC.
(10) MODE 4 REPLY Indicator Illumination
indicates that a REPLY has been made to a valid
MODE 4 interrogation or will flash when in standby
position and interrogated for MODE 4.
(11) MODE 4 AUDIO / LIGHT / OUT Switch.
If the MODE 4 computer is installed in the
aircraft, place the AUDIO / LIGHT / OUT
switch in the AUDIO or LIGHT position
during flight operations. Do not use the
(a) AUDIO Permits aural and REPLY
light monitoring of valid MODE 4 interrogations and
(b) LIGHT Permits REPLY indicator