Aircraft Survivability Equipment

REFERENCES Aircraft Operator’s Manual DOD AIMS , 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

MODE 2 MODE 4 MODE 3/A TEST OUT ONON AUDIO OUT LIGHTLIGHT IDENT MIC OUTOUT REPLY MODE 1 TEST M-1 M-C M-3/A M-2 RAD TEST OUT ALT KITANT STATUS TOP BOT ANTANT DIVDIV TEST GOGO TEST/MON NOGONOGO CODE

TEST CODE MODE 4 IFF Mode 4 Code Switch MODE 4 TEST OUT ONON AUDIO OUT LIGHTLIGHT REPLY M-1 M-C M-3/A M-2 RAD TEST 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 ONON AUDIO OUT LIGHT MODE 4 REPLY RAD TEST OUT M-1M-2 M-3/AM-C TEST

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 ONON AUDIO OUT LIGHT MODE 4 REPLY RAD TEST OUT M-1M-2 M-3/AM-C TEST

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 ONON AUDIO OUT LIGHT MODE 4 REPLY RAD TEST OUT M-1M-2 M-3/AM-C TEST

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 ONON AUDIO OUT LIGHT MODE 4 REPLY RAD TEST OUT M-1M-2 M-3/AM-C TEST

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-72AN/APX-64AN/APX-100 AN/APX-101 Compatible Mode 4 Key Received Incompatible Mode 4 Key Received ToneToneTone 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 light Illumination 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

MODE 2 MODE 4 MODE 3/A TEST OUT ONON AUDIO OUT LIGHTLIGHT IDENT MIC OUTOUT REPLY MODE 1 TEST M-1 M-C M-3/A M-2 RAD TEST OUT ALT KITANT STATUS TOP BOT ANTANT DIVDIV TEST GOGO TEST/MON NOGONOGO CODE

AN/APX-100 SHUTDOWN To Retain Mode 4 code: 1) MODE 4 CODE switch - Rotate to HOLD 2) Wait 15 Seconds 3) MASTER Switch - OFF To zeroize Mode 4 code: 1) MODE 4 CODE switch - Rotate to ZERO 2) MASTER Switch - OFF

MODE 2 MODE 4 MODE 3/A TEST OUT ONON AUDIO OUT LIGHTLIGHT IDENT MIC OUTOUT REPLY MODE 1 TEST M-1 M-C M-3/A M-2 RAD TEST OUT ALT KITANT STATUS TOP BOT ANTANT DIVDIV TEST GOGO TEST/MON NOGONOGO CODE MASTER

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