AIRCRAFT SURVIVABILITY EQUIPMENT (ASE)
Lesson Plan and Program Text
I. Introduction:
A. Annual Review of ASE
B. References:
Aircraft Operator’s Manual
DOD AIMS 86-100, Mode 4 Handbook, May 1987
C. Instructions: Review the attached information on Aircraft Survivability
Equipment and complete the written exam. Program text should be
supplemented with the PowerPoint presentation when appropriate.
II. Outline:
A. Overview of Identify Friend or Foe (IFF)
B. AN/APX-100 Control Head
C. Mode 4 Faults
D. Shutdown Procedures
III. Lesson Plan:
A. Overview of IFF
(1) Mode 4 IFF is a secure means of identification
(2) Mode 4 uses a secure challenge/password means to identify
friendly aircraft.
a. Interrogator system generates a challenge code word
using the current mode 4 key.
b. The signal is then transmitted and received by the
aircraft.
c. If the transmission is compatible, the transponder will
generate a time-coded reply.
NOTE: Compatible indicates a key that matches that of your transponder.
Valid refers to a key that is theoretically possible but not the correct Mode 4
key for the period
d. If the transmission is valid but not compatible, the aircraft
will not generate a reply and will cause illumination of the IFF caution light.
Faults will be covered further in Mode 4 Operations.
B. AN/APX-100 Control Head. The AN/APX –100 transponder control
head’s description and functions will be described. If your aircraft is equipped
with a different transponder, please consult your operator’s manual.
(1) The control head has four controls and indicators that will be
described here:
a. Mode 4 Code Switch – A multi-function knob used to
select between Hold, Zero, A and B.
1. Hold – In the Hold position, the hold circuits are
enabled. This allows the user to retain the Mode 4 key after the power has been
removed from the system.
2. Zero – The Zero function allows the transponder to
zero (clear) the current code held in the computer.
3. A - Selects the corresponding Mode 4 key stored
in the A position.
4. B – When selected, will select the Mode 4 key for
the next crypto period without the need to rekey the transponder computer.
b. Mode 4 On/Out Switch – A 3-position switch that allows
the transponder to reply to mode 4 interrogations.
1. On – In the “ON” position the transponder is able
to generate Mode 4 relies.
2. Out – With the switch in the “OUT” position, the
transponder will not generate a reply when interrogated by a compatible Mode 4
code. If no rely is generated, the Mode 4 caution light will illuminate, indicating
that the system was interrogated with a compatible key but did not reply.
c. Mode 4 Audio/Out/Light Switch – This switch is used to
select between modes.
1. Audio – In the audio position, the Mode 4 reply
light and the audio tone are enabled.
2. Out – In the out position, both the Mode 4 reply
light and the audio tones are disabled. The press-to-test light of the Mode 4 rely
light is also disabled.
3. Light – In the light position, the Mode 4 light is
enable but the audio is disabled.
d. Mode 4 Reply Light – Provides a visual indication that
replies are being transmitted. For the light to function, the audio/out/light switch
must be in either the audio or the light position.
(2) The last switch of the Mode 4 control head is the Rad Test
switch that is used to select bit 1. This is intended as a test mode and is not
commonly used.
C. Mode 4 Faults. Each transponder is equipped with a Mode 4 caution
light (IFF) to indicate one of the following conditions:
(1) The transponder computer is installed, with power applied, but
is not loaded with a valid Mode 4 key
(2) The transponder has failed its self-test cycle.
(3) A compatible Mode 4 interrogation was received but no rely
was transmitted: This condition occurs if:
a. The transponder is in standby
b. A malfunction in the receiver-transmitter does not allow a
reply to be generated or transmits the reply at low power.
c. The Mode 4 On/Out switch is in the “OUT” position.
(4) Faults 1 and 2 above will generate a steady illumination of the
IFF caution light. Fault 3 can result in a blinking IFF caution light depending on
the recurrence of the interrogations.
D. Shutdown Procedures. Procedures for shutting down the AN/APX-100
will differ depending on whether or not the codes are to be held or zeroed.
(1) To Hold Mode 4 Code:
a. MODE 4 CODE switch - Rotate to HOLD
b. Wait 15 Seconds
c. MASTER Switch - OFF
(2) To Zero Mode 4 Codes:
a. MODE 4 CODE switch - Rotate to ZERO
b. MASTER Switch – OFF
MODE 4 MYTHS AND FACTS
Below are some common misconceptions referencing the Mode 4 IFF. All
information below has been taken out of the DOD AIMS 86-100, Mode 4
Handbook.
MYTH: The KIT-1 transponder computer will not accept the Mode 4 key if the
code switch on the transponder control head is left in the zero position.
FACT: The transponder will accept the Mode 4 key if the code switch was left in
the zero position. When the code switch is not returned to the normal
position (A or B), the zeroize circuits associated with the zero switch are
not re-armed so they are not ready to be activated again. Also, with the
code switch left in the zero position, the transponder computer is
signaled that cod A has been selected. Normal operation of the Mode 4
function will continue. If you discover that the code switch is in zero,
move it to its correct position, normal Mode 4 operation will continue.
The zeroize circuits associated with the code switch will be armed again.
MYTH: When either crypto computer is loaded with the open door maintenance
key, the computers can be zeroized from their remote control locations.
FACT: This is not true. Unless the code changer front door is closed, none of
the zeroizing mechanisms are enabled. Personnel using the open door
maintenance key must ensure that they zeroize the key by closing and
then opening the code changer front door when they are finished using
the key.
MYTH: Interrogator and transponder computers will accept any random key that
might be loaded into the KIK-18A key loader.
FACT: The computer’s circuits can detect is a Mode 4 key is a valid one or one
that was randomly generated or incorrectly entered in the KIK-18A key
loader. If the Mode 4 key is invalid, the crypto computers will not accept
it.
MYTH: An operational Mode 4 key will be automatically zeroized from either
computer if the code changer front door is not closed within a specific
amount of time after the Mode key is inserted.
FACT: No mechanism in the two computers zeroizes the Mode 4 key if the code
changer front door is not closed within a specific amount of time. It is a
good security procedure not to allow the computer’s code changer front
door to remain open with Mode 4 operational keys loaded.
MYTH: Mode 4 should only be used in time of war or in hostile situations.
FACT: This is emphatically not true. By direction of the highest command
authority in the Department of Defense, exercise Mode 4 daily to ensure
maximum efficiency. Use it as a positive means of identifying friendly
forces. It is a well-learned lesson of war that you fight like you train.
Therefore, become familiar with the tools of your trade.
MYTH: Mode 4 should be interlaced with SIF modes.
FACT: No. Mode 4 is not to be used as a search mode or a tracking mode; it is
used as override or sector enable. In fact, many units are under
operational directive to use Mode 4 in override or sector only.
MYTH: It is acceptable to transmit Mode 4 through a complete 360 degrees.
FACT: Because Mode 4 is not a search or tracking mode, there should be no
need to transmit more than 15 or 20 degrees at a time. This helps to
limit the adversary’s access to the library of Mode 4 interrogations/reply
pairs, thus protecting the security of the Mode 4 function.
MYTH: Mode 4 can identify hostile aircraft.
FACT: No cooperative identification system can positively identify a target as
hostile. If a target cannot be positively identified as a friend, its identity
remains unknown until it can be positively identified by other means.
MYTH: The Mode 4 system is classified secret.
FACT: The highest classification usually attached to any Mode 4 equipment or
key is confidential. An undue lack of secrecy has contributed to a lack of
working knowledge of and thus a low condition of readiness for the Mode
4 function. This is not to say an appropriate amount of security is not
necessary. All users of the Mode 4 function must be familiar with the
security regulations governing the storage, access, and use of Mode 4
equipment and key lists.
MYTH: An aircraft will reply in Mode 4 even if it is loaded with an incorrect Mode
4 key.
FACT: For the transponder to reply to Mode 4 interrogations, those
interrogations must be generated from the same Mode 4 key that is
loaded into the transponder computer. This feature is part of what gives
Mode 4 its security.
MYTH: Mode 4 equipment is used by U.S. Military units only.
FACT: Many of our allies have the Mode 4 equipment and are capable of
interrogating and replying in Mode 4
MYTH: Once Mode 4 is interrogated, its key is no longer secure.
FACT: Because only encrypted words, which are formed using the Mode 4 key,
are transmitted, the daily Mode 4 key is not compromised merely by
interrogating Mode 4.