S 972-020
 (10) Calculate the north-south single-cycle error coefficient (C) as follows:
 C = 0.5(Dn - Ds)
 S 822-021
 (11)
 Turn the N-S adjustment screw on the standby compass (while at the south magnetic heading) to give a compass heading indication of (CH)s - C.

 S 582-022

 (12)
 Turn the airplane to a direction that is less than 2 degrees of a west magnetic heading (MH)w.

 S 972-023

 (13)
 Make a record of the magnetic heading (MH)w and the compass heading (CH)w.

 S 972-024

 (14)
 Calculate and make a record of the west heading deviation (Dw) and its sign as follows:

 Dw = (MH)w - (CH)w
 S 972-025
 (15) Calculate the east-west single-cycle error coefficient (B) as follows:
 B = 0.5(De - Dw)
 S 822-026
 (16) Turn the E-W adjustment screw on the standby compass (while at the west magnetic heading) to give a compass heading indication of (CH)w - B.
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

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747-400 MAINTENANCE MANUAL
 F. Standby Compass Accuracy Check
 NOTE: The steps that follow are for the 12 point accuracy swing:
____ S 582-029
 (1)  
Turn the airplane near the center of the compass swing area for these ND magnetic headings: 0, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, and 330 degrees.

 S 972-030

 (2)  
Make a record of the magnetic heading (MH) and standby compass heading (CH).

 S 972-031

 (3)  
Calculate and make a record of the difference for each 30 degree heading in the steer column on the compass correction card as follows:

 D = MH - CH
 S 972-028
 (4)  During these steps, make sure each difference is less than | 5 degrees. Make sure the difference between the maximum positive and maximum negative value is 10 degrees or less.
 G. Put the airplane back to its usual condition.
 S 862-060
 (1)  
Set the mode selector switch for each IRS to OFF.

 S 862-061

 (2)  
Remove the electrical power if it is not necessary
 (AMM 24-22-00/201).

 TASK 34-22-00-822-039
 3.  Standby Compass Calibrator Procedure____________________________________
 A. Equipment
 (1)  
Tow Tractor

 (2)  
Non-magnetic tools to adjust the standby magnetic compass.

 (3)  
One compass correction card - AN5823-1.

 (4)  
Standby Compass Calibrator Kit, Honeywell
 2591553-901

 (5)  
Non-Magnetic Tripod

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A
747-400
MAINTENANCE MANUAL

 B. References
 (1)  
AMM 9-11-00/201, Towing

 (2)  
AMM 24-22-00/201, Electrical Power - Control

 (3)  
AMM 31-61-00/501, Integrated Display System

 (4)  
AMM 34-21-00/501, Inertial Reference System

 C. Access
 (1)  Location Zones
 221 Control Cabin, LH

 D. Calibrator Adjustment (Fig. 201).
 S 822-080
 (1)  Do this procedure to calibrate the standby compass calibrator (SCC) to the magnetic field at the location of the compass rose.
 (a)  
Make sure that there are no vehicles or airplanes less than 250 feet away.

 (b)  
Make sure that there are no buildings less than 250 feet away.

 (c)  
Put a nonmagnetic tripod at the center of the compass swing area.

 (d)  
Remove the magnet assembly from the SCC.
　
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