E. The airplane's initial compass swing will normally require at least two complete circuits around the compass rose; once to take out the index error and the single cycle error, and once to make the compass correction chart. Passenger cabin seats and cockpit seats shall be installed prior to swinging.
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2. Swing Main Compass System
A. General
(1)
The tests described under Compass System - Adjustment/Test, should be carried out prior to this procedure, to ensure that a serviceable compass system is being swung.
(a)
Replacement of an RMI or CDI will not necessitate performing a compass swing if the unit has been properly tested at the component level.
(b)
Replacement of a flux valve does not require a compass swing on the compass rose. To verify that flux valve is operating properly, turn airplane 360 degrees and observe RMI’s. Check that one system closely follows the other.
(2)
Index errors may be eliminated or reduced by adjusting the differential synchro in the remote magnetic compensator (if installed).
(3)
Single cycle errors may be eliminated or reduced by adjusting the E-W and N-S potentiometers on the compensator (if installed).
B. Equipment and Materials
(1)
Compass rose having the following features.
(a)
A flat, obstruction free area, large enough to permit towing the airplane in a circle around a surveyors transit, and still leave 25 feet between its outer wing tip and the edge of the area (Fig. 201). The direction of the horizontal component of the earth’s magnetic field in the area should be constant within 0.2 degree throughout the test area.
(b)
A baseplate located in the center of the area to identify the position for the transit.
(c)
Control over an area extending 180 feet in all directions from the rose center, which may be used to exclude any type of traffic during a compass swing.
(2)
Two heading markers, whose magnetic bearing from the baseplate has been established
(3)
Tow tractor
(4)
Surveyors transit or equivalent (Accurate to 1 minute or less)
(5)
Compass Fixture Set, F80180-1 (Fig. 201)
(6)
Nonmagnetic tools for adjusting standby compass
(7)
One compass correction card (AN5823) for each compass
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H31442
567 Compass Swing Target Fixture
Aug 15/77 Figure 201 34-21-0
Page 203
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
(8) 3-Phase, 115-volt, 400-cps external power supply (5 KVA capacity)
C. Prepare for Compass Swing
(1) Assemble and attach compass swing target fixture to airplane as follows:
(a)
Remove apex bolt connecting upper and lower torsion links of nose gear. Move upper torsion link down to release spring tension in piston position spring cartridge. Remove upper bolt of piston position spring cartridge and release from position.
CAUTION: THE PISTON POSITION SPRING CARTRIDGE IS SPRING LOADED TO EXTENDED POSITION. THEREFORE, UPPER TORSION LINK SHOULD BE HELD WHILE APEX BOLT IS BEING REMOVED).
(b)
Adjust sliding scale on fixture so that its 0 position is located on -100 or -200 mark (to agree with airplane type body). Lock scale in position.
(c)
Position fixture under electronics compartment hatchway with vee end pointing forward.
(d)
Raise fixture and rest vee end of arm assembly against aft side of the nose gear shock strut and at the other end, the support bracket angle on the airplane structure flange at Sta 324 (Fig. 201). Adjust support bracket assy to engage support bracket assembly pin into keeper fitting of access door lock at Sta 324.
(e)
Raise hanger bracket and attach to door stop assembly at Sta 294.
(f)
Level assembly by adjusting hanger bracket.
(g)
Install scope on scope mounts.
(h)
Attach target cable assy to the up-lock rollers on the main gear struts with cable attachments. When in position, cable should be taut and ball situated to left of airplane centerline (Fig. 201 and 202).
(i)
Ensure that locknuts on support bracket assembly are loose, to permit movement of fixture from side to side using vee block as a pivot point.
(j)
Sight through telescope and adjust fixture at aft bracket in azimuth until ball is centered in telescope sight. Tighten locknuts in aft bracket to ensure that crosshair and 0 mark on scale will remain at a fixed angle to centerline of airplane.
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