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 34-11-03
 ALL  ú ú 01 Page 405 ú Feb 10/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
 AIR DATA SYSTEM - DESCRIPTION AND OPERATION
___________________________________________
 1.  General (Fig. 1)_______
 A.  The air data computing system provides air data information to the integrated display system and other interfacing systems. The system consists of these components:
 (1)  
Three air data computers (ADC)

 (2)  
Two angle of attack (AOA) sensors

 (3)  
Two total air temperature (TAT) probes

 (4)  
Two air data source select relays

 (5)  
Two air data source select switches

 (6)  
A gear down dispatch switch

 (7)  
A fifth engine carriage switch

 B.  The inputs to the air data system are pitot and static air pressure from the pitot-static system (Ref 34-11-00), angle of attack from the AOA sensors, total air temperature (TAT) from the TAT probes, and barometric pressure correction from the EFIS control panels.
 C.  A number of discrete signals are also applied to the air data system. These discretes perform functions such as selection of SSEC curve, selection of maximum operating speed curve, definition of status of the air data sensor heaters, and selection of desired mode of operation.
 D.  The air data system outputs are available on four ARINC 429 buses. One test only data bus, which is electrically connected to the No. 1 bus, is available on the ADC front panel. All four of the buses are identical and contain the same data.
 (1)  
The No. 1 bus supplies data to the following autopilot and flight director system and warning interfaces:

 (a)  
Flap control units (FCU)

 (b)  
Stabilizer trim/rudder ratio modules (SRM)

 (c)  
Flight management computer/thrust management computers (FMC/TMC)

 (d)  
Flight control computers (FCC)

 (e)  
Yaw damper modules (YDM)

 (f)  
Modularized avionics and warning electronics assembly (MAWEA) The MAWEA contains the altitude alert logic, speed tape barber pole logic, and stall warning functions.

 (2)  
The No. 2 bus supplies data to the following instrument display interfaces:

 (a)  
Inertial reference units (IRU)

 (b)  
EFIS/EICAS interface units (EIU)

 (c)  
MAWEA

 (3)  
The No. 3 bus supplies data to the electronic engine controls (EEC).

 (4)  
The No. 4 bus supplies data to the following general purpose and alternate interfaces:

 (a)  
Cabin Pressure Controllers (CPC)

 (b)  
Ground proximity warning computer (GPWC)

 (c)  
Air traffic contol transponders (ATC)

 (d)  
Data management unit (DMU)

 (e)  
Alternate source input for the following: 1) SRM

 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

 34-12-00
 ALL  ú ú 04 Page 1 ú Feb 10/96
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

PILOTS' CENTER 
INSTRUMENT PANEL 
SEE  E  F 
CAPTAIN'S 
INSTRUMENT PANEL 
SEE  A  B 
AFT ELECTRONICS 
CONTROL PANEL 
SEE  G 
FLIGHT COMPARTMENT
SELECTED 
AIRSPEED 

AIR DATA SOURCE
AIRSPEED SELECT SWITCH
MACH
SOURCE SELECT MODULE
METERS BUTTON
A
PILOTS' LIGHTSHIELD SEEC D
FIRST OFFICER'S
INSTRUMENT PANEL
SEEA B
FORWARD ELECTRONICS CONTROL PANEL
SEE G
145  10475 
200 
700 
10400 
180  6 
UP 
5  2 
V1 
160  VR  10  10  10200  1 
142  10 100 
　
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