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

4 1 26 71

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?