NOTE: WIRING AND CONNECTOR DETAIL
 OMITTED FOR CLARITY.

Flight Instrument Switching Relay Panel
Figure 12

825069
EFFECTIVITY

CONFIG 2AIRPLANES WITH LTN-72 INS 799 Page 29
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Apr 25/86
 (1)  
The captain's VOR-ILS/INS switch controls the captain's VOR-ILS/INS transfer relay which allows the captain' HSI to display heading information from either the VOR/ILS and magnetic heading reference systems or the INS. The first officer's VOR-ILS/INS switch and transfer relay function in a similar manner for the first officer's HSI.

 (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.

 11. INS Cooling System (Fig. 13)
__________________
 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 independantly 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.
 12. INS Battery Warning Logic Module (Fig. 13)
________________________________
 A.  General
 (1)  
If the INS system is operating and ground power is removed, the INS automatically transfers to battery power. In order to protect the INS batteries from inadvertent discharge when the airplane is sitting on the ground, a ground crew call horn, located in the nose wheel well, activates 30 (| 10) seconds after the INS transfers to battery power.

 (2)  
The battery warning system consists of a battery warning logic module, an INS warning relay and a ground crew call horn.

 EFFECTIVITY AIRPLANES WITH LTN-72 INS  
  CONFIG  01 A Page 30  Apr 25/86

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INS Cooling and Battery Warning
Figure 13

EFFECTIVITY CONFIG 2AIRPLANES WITH LTN-72 INS

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 (3)  The ground crew call horn is activated: (1) when any one or more INS systems operates on battery power for approximately 30 seconds;
 (2) if the equipment cooling airflow detector detects "no airflow"; or (3) if the ground crew call button (on overhead panel P5) is pressed.
 B.  Battery Warning Logic Module

 (1)  
The battery warning logic module is a relay driver that provides dc power to energize the INS warning relay, when the INS has been operating on battery power for about 30 seconds.

 (2)  
When any INS is not off, a 28-volt dc INS NOT OFF signal is applied to the input of OR gate A, resulting in an output applied to the INS NOT OFF side of AND gate C.

 (3)  
When any INS is operating on battery power, a 28-volt dc BATTERY IN USE signal is applied to the input of OR gate B, resulting in an output applied to the BATTERY IN USE side of AND gate C. There is a time delay of approximately 30 seconds between the input to gate B and input to gate C.

 (4)  
When both the INS NOT OFF signal and the BATTERY IN USE signal are applied to gate C, the output of gate C causes the INS warning relay to close. When the relay is closed dc power is applied to the ground crew call horn, causing the horn to sound.
　
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