(6)  
The ECS miscellaneous card will command the forward overboard valve to close any time that the pressurization ICU high cabin altitude switch activates or the CARGO FIRE - FWD switch is set to the ARMED position.

 (7)  
BITE

 (a)  The ECS miscellaneous card has a built in power up test and capability for CMC initiated ground test. The FWD OVBD VALVE SYS ground test checks for proper operation of the ECS miscellaneous card including a command of the forward overboard valve.
 B. Control - Forward Overboard Valve
 (1)  The forward overboard valve operates automatically when power is supplied to the airplane and the cabin pressure control system is enabled.
 C. Functional Description - Flight Deck Ventilation Fan
 (1)  The flight deck fan operates when the airplane is on the ground. A current sensor is used to detect fan failure when the fan is commanded on and does not operate, assuming the airplane is on the ground.
 D. Control - Flight Deck Ventilation Fan
 (1)  To operate the fan, push the FLT DECK FAN switch on the overhead P5 panel to ON.
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747-400
MAINTENANCE MANUAL

 E. Functional Description - Forward Cargo Overboard Valve System
 (1)  
The ECS freighter card controls the forward cargo exhaust system valves.

 (2)  
The overboard exhaust stack is used to regulate outflow when the airplane is in the air. The overboard exhaust stack consists of the multi-position overboard valve, the overboard back-up valve and a check valve. The overboard and overboard back-up valves are fully open during ground operation. During flight the overboard back-up valve remains open and the overboard valve is commanded to one of four intermediate positions. Both valves are closed when forward cargo air conditioning is selected off or when the cargo fire bottles are armed. The check valve swings open to allow outflow of exhaust air. The valve flapper closes to provide airplane ditch protection.

 (3)  
CMC initiated BIT

 (a)  The Central Maintenance Computer (CMC) provides built-in testing for the forward cargo exhaust system. To perform a ground test for the forward cargo exhaust system, cargo air conditioning must be selected off and the airplane must be in the ground mode. The test is initiated by selecting GROUND TESTS, then FWD CARGO OVBD from the CMC main menu. The test takes approximately 1.5 minutes.
 F. Control - Forward Cargo Overboard System
 (1)  The forward cargo overboard system operates automatically whenever forward cargo air conditioning is selected on. System operation is fully automatic. No control functions are exercised.
 G. Functional Description - Forward Cargo Ventilation Fan
 (1)  The forward cargo ventilation fans will operate on the ground when the forward cargo air conditioning system is off and the forward cargo door is open. The fan will turn off if the cargo fire switch is armed.
 H. Control - Forward Cargo Ventilation fan
 (1)  To operate the forward cargo ventilation fans on the ground, make sure that the forward cargo air conditioning system is off and the forward cargo door is open. Put the VENT FANS switch on the P86 panel (next to the forward cargo door) to ON.
 I. Functional Description - Aft and Bulk Cargo Ventilation Fan
 (1)  The aft and bulk cargo ventilation fans will operate on the ground when the aft cargo air conditioning system is off and the aft or bulk cargo door is open. The fans will turn off if the cargo fire switch is armed.
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 ALL  ú ú 04F Page 11 ú Jun 18/00
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

 J. Operation - Aft and Bulk Cargo Ventilation Fan
 (1)  To operate the aft and bulk cargo ventilation fans on the ground, make sure that the aft cargo air conditioning system is off and the aft or bulk cargo door is closed. Put the VENT FANS switch on the P59 panel (next to the aft cargo door) to ON.
　
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