(a)  If FAIL> shows: 1) Push the LSK that is adjacent to FAIL> to see the GROUND TEST MSG pages for the failure. 2) Push the NEXT PAGE key until you find all the GROUND TEST MSG pages. 3) Make a list of all CMCS messages, CMCS message numbers, and ATA numbers that show on the GROUND TEST MSG pages.
 4)  Go to the CMCS Message Index of the Fault Isolation Manual (FIM) to find the corrective action for each CMCS message.
 E.  Put the Airplane Back to Its Usual Condition
 S 864-022
 (1)  
Set the GND TESTS switch to the NORM position.

 (2)  
Install the floor panels that you removed.

 (3)  
Install the cargo handling hardware that you removed.

 S 864-024

 (4)  
Remove the electrical power if it is not necessary
 (AMM 24-22-00/201).

 S 414-023
 S 434-025
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

 21-23-03
 ALL  ú ú 02F Page 405 ú Feb 10/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
 1.

2.

3.

A
747-400 MAINTENANCE MANUAL
 VENTILATION - DESCRIPTION AND OPERATION
_______________________________________General
_______
 A.  The ventilation system is used to improve cabin air circulation and remove odors from confined spaces.
 B.  The ventilation system consists of the following:
 (1)
A forward overboard system.

 (2)
A flight deck ventilation system.

 (3)
A forward cargo ventilation system.

 (4)
An aft cargo ventilation system.

 (5)
A bulk cargo ventilation system.

 (6)
A lower forward cargo overboard system.

 C.  The forward overboard valve system promotes air circulation in the forward section of the airplane. Some compartment air, after exiting the sidewall return air grilles, is drawn into an inlet adjacent to the nose gear wheel well and exhausted overboard. The forward overboard valve system consists of a bell shaped inlet, exhaust valve and a flow regulating venturi attached to the airplane skin.
 D.  The flight deck ventilation system consists of a fan which provides for air circulation in the flight deck with the packs on or off and when the airplane is on the ground.
 E.  The forward cargo ventilation system consists of two fans installed in the ceiling area with localized intake from the area above the ceiling lining. The fans have localized exhaust at diffusers in the compartment ceiling linings.
 F.  The aft and bulk cargo compartment ventilation system consists of two fans and two flapper valves. The two fans draw air from the compartment sidewall areas and discharge the air into the aft and bulk cargo air conditioning distribution ducts. The flapper valves allow air to flow from the compartment through the sidewall lining and aft to the pressurization outflow valves.
 G.  The lower forward cargo compartment exhaust system is used to exhaust air during forward cargo air conditioning system operation. The system provides compartment ventilation both in-flight and during ground operations.
Forward Overboard Valve
_______________________
 A.  The forward overboard valve is a 28 volts dc, motor-operated valve attached to the airplane skin adjacent to the nose gear wheel well. The valve, with two positions, open or shut, has limit switches which shut off power in either direction. An override handle, which acts as a position indicator during electrical operation, is provided to allow positioning the valve when power is unavailable or the valve fails.
Flight Deck Ventilation Fan
___________________________
 A.  The flight deck fan is a 3-phase 115 volt fan which provides flight deck air circulation. The fan will operate with the packs on or off and when the airplane is on the ground. The fan is controlled by the ECS Freighter card.
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

 21-26-00
 ALL  ú ú 04F Page 1 ú Oct 18/00
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

747-400
MAINTENANCE MANUAL

FORWARD OUTBOARD VALVE ASSEMBLY
　
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