Aircraft Survivability Equipment
REFERENCES
Aircraft Operator’s Manual
DOD AIMS 86-100, Mode 4 Handbook, May 1987
OUTLINE
Mode 4 IFF
Overview of IFF
AN/APX-100 Control Panel
Mode 4 Operations
Shutdown Procedures
PRINCIPLES OF IFF
1. Interrogator transmits computer generated interrogation signal
2. Aircraft transponder receives signal
3. If the interrogation is compatible, the transponder will transmit a time-coded reply
Mode 4 IFF is a secure means of identification
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MODE 2 MODE 2
MODE 4
MODE 3/A
TEST
OUT
ON
AUDIO
OUT
LIGHT
IDENT
MIC
OUT
REPLY
MODE 1
TESTM-1 M-CM-3/AM-2
RADTEST
OUT
ALT KIT ANT
STATUS
TOP
BOT
ANT
DIV
TEST
GO
TEST/MONNO
GO
CODE
TEST
CODE
MODE 4 IFF
Mode 4 Code Switch
MODE 4
TEST
OUT
ON
AUDIO
OUT
LIGHT
REPLY
M-1 M-CM-3/AM-2RADTEST
OUT
Rad Test Switch
Mode 4 On/Out Switch
Mode 4 Audio/Out/Light switch
Mode 4 Reply Light
MODE 4 OPERATIONS
1. Selects Mode A/B - In the A or B position, the switch selects the corresponding Mode 4 operational key
2. Enable Mode 4 hold - In the ‘HOLD’ position, switch activates the hold circuits. Code hold circuits prevent the loss of the Mode 4 key if power is removed from the system.
3. Zeroizes Mode 4 - In the zero position, Mode 4 is zeroized
Mode 4 Code Switch
TEST
OUT
ON
AUDIO
OUT
LIGHT
MODE 4
REPLY
RADTEST
OUT
M-1 M-2 M-3/A M-CTEST
MODE 4 OPERATIONS
1. ON Position - Used to allow transponder to reply to a compatible Mode 4 interrogation. Switch must be in the “ON” position before aircraft can generate a Mode 4 reply
2. OUT Position - With the switch in the “OUT” position and the Mode 4 otherwise functional, the computer will not generate a reply to a compatible interrogation.
Mode 4 On/Out Switch
TEST
OUT
ON
AUDIO
OUT
LIGHT
MODE 4
REPLY
RADTEST
OUT
M-1 M-2 M-3/A M-CTEST
MODE 4 OPERATIONS
1. AUDIO - In the audio position, Mode 4 reply light and audio are enabled
2. OUT - In the Out position, both the reply light and the audio are disabled. The pres-to-test light is also disabled.
3. LIGHT - In the light position, Mode 4 reply light is enabled and the audio is disabled
Mode 4 Audio/Out/Light Switch
TEST
OUT
ON
AUDIO
OUT
LIGHT
MODE 4
REPLY
RADTEST
OUT
M-1 M-2 M-3/A M-CTEST
MODE 4 OPERATIONS
The reply light provides a visual indication that Mode 4 replies are being transmitted.
Reply light will only function when the audio/out/light switch is in either the audio or light position.
Mode 4 Reply Light
TEST
OUT
ON
AUDIO
OUT
LIGHT
MODE 4
REPLY
RADTEST
OUT
M-1 M-2 M-3/A M-CTEST
MODE 4 OPERATIONS
Mode 4 Audio Tone
With most transponders, audio indicates that you have been interrogated by a Mode 4 key compatible with the key in your transponder computer.
AN/APX-72 AN/APX-64 AN/APX-100 AN/APX-101
Compatible Mode 4 Key Received
Incompatible Mode 4 Key Received
Tone Tone Tone
Tone
** “Compatible” - Indicates a key that matches that of your transponder ** “Valid”- Indicates a key that is theoretically possible but not the correct Mode 4 key for the period
NOTE: A tone in the headset of AN/APX-100 means that you have been interrogated by a valid but incompatible Mode 4 key
MODE 4 CAUTION LIGHT
Every transponder is equipped with a Mode 4 caution lightIllumination of the caution light will indicate:
1. Transponder computer is installed, with power applied, but is not loaded with a vaild Mode 4 key.2. The transponder computer has failed its self-test cycle.3. A compatible Mode 4 interrogation was received but no Mode 4 reply was transmitted
This occurs if:- The transponder system is in standby- The Mode 4 On/Out switch is in the Out position- A malfunction in the receiver/transmitter will not allow the Mode 4 reply to be
transmitted or transmits the reply at low power
**NOTE: Fault 1 or 2 will result in a steady illumination of the IFF caution light. Fault 3 may result in the IFF caution light cycling On and Off depending on the recurrence of the interrogations**
IFF MASTER CAUTION
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MODE 2 MODE 2
MODE 4
MODE 3/A
TEST
OUT
ON
AUDIO
OUT
LIGHT
IDENT
MIC
OUT
REPLY
MODE 1
TESTM-1 M-CM-3/AM-2
RADTEST
OUT
ALT KIT ANT
STATUS
TOP
BOT
ANT
DIV
TEST
GO
TEST/MONNO
GO
CODE
AN/APX-100 SHUTDOWN
•To Retain Mode 4 code:1) MODE 4 CODE switch - Rotate to HOLD2) Wait 15 Seconds3) MASTER Switch - OFF
•To zeroize Mode 4 code:1) MODE 4 CODE switch - Rotate to ZERO2) MASTER Switch - OFF
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MODE 2 MODE 2
MODE 4
MODE 3/A
TEST
OUT
ON
AUDIO
OUT
LIGHT
IDENT
MIC
OUT
REPLY
MODE 1
TESTM-1 M-CM-3/AM-2
RADTEST
OUT
ALT KIT ANT
STATUS
TOP
BOT
ANT
DIV
TEST
GO
TEST/MONNO
GO
CODE
MASTER
QUESTIONS?
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