(2)  
The INS transfer switch on the captain's instrument panel controls the captain's and first officer's INS transfer relays. Both relays are paralleled to function as a single unit. A switch position annunciator adjacent to the switch illuminates to show which INS systems are supplying heading information to the captain's and first officer's HSI's. The captain's instrument normally operates from INS 1 while the first officer's is operating from INS 2. Heading information from INS 3 is switched between the captain's and first officer's HSI's.

 (3)  
The attitude/compass stabilization transfer switch on the captain's instrument panel controls two attitude/compass stabilization transfer relays. A switch position annunciator adjacent to the switch illuminates to show which INS systems are supplying attitude information to the captain's and first officer's ADI's. The captain's instrument normally operates from INS 1 while the first officer's is operating from INS 2. Attitude information from INS 3 is transferred between the captain's and first officer's ADI's.

 (4)  
The instrument switching accessory box contains arc suppression diodes which are connected across the relay coils.

 18. INS Cooling System (Fig. 12)
__________________
 A.  It is extremely important that inertial navigation units have an adequate cooling air supply since overheating will result in failure of the navigation units.
 B.  To ensure that the INS system will always have a supply of cooling air, an INS cooling air fan is installed in the cooling air exhaust plenum beneath each navigation unit. These fans operate independently from the main equipment blowers and provide the INS with a cooling air supply even if the main equipment cooling blowers are not operating.
 C.  Each INS cooling fan receives power from the same main INS power circuit breaker that provides power to the INS system. If these main INS power circuit breakers are closed, the INS cooling fans are operating whether or not the INS is turned on.
 19. INS Battery Warning Logic Module (Fig. 12)
________________________________
 A.  General
 EFFECTIVITY

 AIRPLANES WITH LTN-72RL OR  CONFIG LTN-92 INS  01 Page 32  Apr 25/91

34-41-00
DIGITAL DATA AND

INS-3 INERTIAL NAVIGATION UNIT
TRUE HDG VALID
NAV VALID
ALERT
TKE+DA
FROM/TO
DA
XTK
DIGITAL DATA
DIGITAL DATA VALID
TRUE HDG

F/O HSI (SAME SIGNALS AS CAPT HSI) INS-2 INERTIAL NAVIGATION UNIT
INS Nav Data Simplified Switching Schematic
Figure 13 (Sheet 1)

TRUE HDG VALID NAV VALID ALERT TKE+DA FROM/TO DA XTK DIGITAL DATA DIGITAL DATA VALID TRUE HDG
INS-1 INERTIAL
NAVIGATION UNIT

TRUE HDG VALID NAV VALID ALERT TKE+DA FROM/TO DA XTK DIGITAL DATA DIGITAL DATA VALID TRUE HDG
EFFECTIVITY AIRPLANES WITH LTN-72RL OR
CONFIG 3LTN-92 INS
799Page 33/34
34-41-00

Apr 25/91

VOR-3 INTERLOCK

AUTO INS APPROACH DC
A24 C28V DC ESS A43A AUTOFLT INST BUS A25AUTOTUNE INHIBIT NORMCAPT FLT INST SW A42 INS APPROACH

RELAYS - VOR/ILS-INS 28V DC FLT
DC
DCB
AUTO
APPROACH MODE RETAININST BUS 2 MAN

A38
F/O FLT INST SW

INS

DC NORM
RELAYS - VOR/ILS-INS
APPROACH
AUTOTUNE COMMON

28V DC ESS A34 APPROACH MODE ANNUNC A48
FREQ SELECTFLT INST BUS VOR-1 A1-A18 FREQ SEL WAFERS APPROACH MODE ONA2828V DC FLT D APPROACH MODE DC PWRFREQ SELECTINST BUS 2 VOR-2 A52B1-B18 FREQ SEL WAFERS

MAN CIRCUIT BREAKER PANEL P7
MANCOMMON DC
B23
COMMON A23COMMON

NORM VOR/ILS

VHF NAV CONTROL PANEL NO. 1 INS 1AUTOTUNE2x5 TUNING 1 FREQ SELECT COMMON
ILS FREQ TUNED APPROACH MODE 11 MAG/
(+28V DC)
MAG HDG DISCRETE 9

GND (HSI MAG)
TRUE INS
ANNUN
APPROACH
MODE DISCRETE

10 CAPT

VOR/LOC VALID VOR-ILS/INSVOR/LOC VALID
RELAY
VOR

SINE
SINE

VOR
COSINE

BEARING
BEARING
COSINE

INS UPDATING INS 3
VHF NAV RECEIVER NO. 1 12
MILES GND SPEED
CAPT INS APPROACH 3 TRANSFER RELAY
I
CAPT
N S
MODE DISCRETE
VOR/ILSDIST PULSE PAIR DME DIST

1
UPDATERELAY BVALID DME VALID

APPROACH MODE
A L E R

2X5 TUNING
T
INS NAV UNIT NO. 1 CAPT INS

DME NO. 1 INTERROGATOR
MAG HDG DISCRETE ANNUNCIATOR INS NAV UNIT
UPDATING
CAPT HSI 2x5 TUNING
A

NO. 3
ILS FREQ TUNED
(28V DC)

INTERNALS SAME AS CAPT'SVOR/LOC VALID 3 ANNUNCIATORVOR SINE BCOSINE F/O INS UPDATING ANNUNCIATOR BEARING
B231 INST B231 ACCESS
　
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