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system unpowered is automatically enabled when the IFF system is powered. To enable the complete
altitude encoding mode, enabling mode C also enables mode 3. Disabling mode 3 also disables mode C.
The altitude encoding mode uses 29.92 in. hg. as a reference.
Mode 1 and mode 3 codes may be changed depending on which mode was last selected to be enabled
or disabled. If mode 1 data entry is available, 1- is displayed in the scratchpad. If mode 3 data entry
is available, 3- is displayed in the scratchpad. Touching two valid numbers (mode 1) or four valid
numbers (mode 3), verifying these numbers in the scratchpad, and touching ENT changes the
respective code. If invalid data is entered, ERROR is displayed in the scratchpad.
23.7.2.1 IDENT (ID) Pushbutton. The ID button is used to manually squawk ident. Pressing the ID
button enables the IFF system to transmit momentary identification of position.
23.7.2.2 IFF Control Panel. The IFF control panel contains an IFF MASTER switch, an IFF MODE
4 switch, and an IFF CRYPTO switch. The IFF MODE 4 and IFF CRYPTO switches are used for mode
4 on aircraft which have the mode 4 transponder computer KIT-1A installed. With the IFF MASTER
switch in EMERG, the IFF r/t replies with the emergency code. With the switch at NORM, the IFF
r/t replies to interrogations with selected codes.
23.7.2.2.1 MODE 4 Switch. This switch has positions of OFF, DIS, and DIS/AUD.
OFF Disables M4 OK advisory, mode 4 audio tone, IFF 4 caution, and voice alert.
Figure 23-24. IFF Sublevel
A1-F18EA-NFM-000
VII-23-34 ORIGINAL
DIS Mode 4 advisory (M4 OK) appears when the IFF is responding to mode 4 interrogations.
IFF 4 caution and voice alert enabled.
DIS/AUD M4 OK advisory and audio tone enabled when IFF is interrogated with valid mode
4 is interrogations. IFF 4 caution and voice alert enabled.
23.7.2.2.2 CRYPTO Switch. This switch has positions of HOLD, NORM, and ZERO. Placing the
switch to HOLD with the landing gear handle in the DN (down) position retains the mode 4 codes if
power to the system is lost. In the NORM position, mode 4 codes are available as long as power is not
lost. Putting the switch to ZERO erases (zeroizes) the mode 4 codes.
With the landing gear down, the status of the MIDS crypto logic is displayed in the status area of
the MIDS terminal control format. HOLD indicates that crypto variables will be retained at terminal
shutdown. HOLD is the normal preflight indication. ZERO indicates that crypto variables will be
erased at terminal shutdown. A zero condition is automatically set by the MC when the landing gear
is lowered after the aircraft has been flying. A zero condition can be changed to HOLD by setting the
CRYPTO switch to HOLD. Crypto can be erased at any time by setting the CRYPTO switch to ZERO.
23.7.2.3 IFF 4 Caution/Voice Alert. An IFF 4 caution is displayed on the DDI caution display
whenever the mode 4 codes are zeroized, there is a fault in the KIT, or when the transponder is not
replying to valid mode 4 interrogations because mode 4 is not enabled or because of a failure. At the
same time that the caution condition occurs a corresponding voice alert message is heard twice in the
headset. The voice alert message is ªmode 4 reply, mode 4 replyº. The IFF 4 caution and voice alert are
disabled whenever the mode 4 switch is in the OFF position.
23.7.2.4 Emission Control Pushbutton Switch. The emission control pushbutton switch on the right
side of the UFCD is labeled EM CON. Pressing the pushbutton switch changes the IFF, if ON, to a
standby mode so that it cannot transmit. At the same time, EMCON is displayed in the scratchpad for
top level displays or vertically in the left options for DDI displays on the UFCD. When EMCON is
turned off by pressing the pushbutton again, the IFF returns to the previous operating mode.
23.7.2.5 IFF BIT Check. A manually initiated IFF BIT check is done by pressing the TCN/IFF
pushbutton on the BIT display on the DDI. IFF status is displayed on the BIT status display.
23.7.2.6 IFF Antenna Selector Switch. The antenna selector switch is on the left console.
UPPER Selects upper antenna.
BOTH Provides automatic antenna selection.
LOWER Selects lower antenna.
23.7.3 IFF Emergency Operation. The IFF emergency mode automatically becomes active upon
ejection.
23.8 COMMUNICATION-NAVIGATION-IDENTIFICATION INTERFACE
The radios, ADF, TCN, ILS, data link, radar beacon, and IFF interface with the aircrew through the
UFCD. The UFCD power and symbology are provided by the MPCD. As commands are entered into
the UFCD, the MPCD transmits those commands to the mission computer. The MC accepts those
commands and transmits them either directly to the CNI equipment if it is MUX compatible or to the
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NATOPS Flight Manual 飞行手册 2(87)
