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H30367
502  Target Fixture and Transit Arrangement 
May 15/67  Figure 202  34-21-0 
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(2)  
Fit ground downlocks to landing gear and tow airplane around compass rose at least once, then position airplane on compass rose to meet following conditions:

(a)  
Airplane heading within 2 degrees of magnetic north

(b)  
Heading roughly tangential to a circle drawn about transit base

(c)  
Compass swinging fixture readily seen from transit base (Fig. 202).

(3)  
Provide external electrical power to airplane.

(4)  
Energize both compass systems by closing circuit breakers listed in Compass Systems -Adjustment/Test. Set compass transfer switches, if fitted, to normal configuration for the systems.

(5)  
Set up transit on baseplate in center of compass rose and calibrate as follows:

(a)  
Level off transit and sight on marker No.1. Unlock transit lower motion and set scale to read magnetic bearing. of marker minus 66 degrees for 737-200 airplanes and 67 degrees, 58 minutes for 737-100 airplanes. Lock lower motion.

NOTE:  If bearing thus calculated results in a minus quantity; add 360 degrees to it in order to validate it.

(b)  
Check transit calibration with marker No. 2. Transit should read marker's magnetic heading minus 66 degrees for 731-200 airplanes and 67 degrees 58 minutes for 737-100 airplanes. Correct as necessary.

(c)  
Repeat steps (a) and (b) until transit is correctly calibrated.

NOTE:  The transit is purposely calibrated to read magnetic heading minus 66 degrees for 737-200 airplanes and 67 degrees 58 minutes for 737-100 airplanes, since it is used to measure airplane heading through the target fixture.
(6)  
Place radio power switches to ON. Select a localizer frequency on VHF NAV control panel.

(7)  
Set flight director MODE selector to VOR-LOC and weather radar MODE selector to STBY.

(8)  
Check that landing gear downlocks are in place. Energize landing gear lever latch by placing a mild steel slug against sensitive surface of air sensing sensor (S106). Do not move landing gear lever while solenoid is energized. The solenoid shall be energized at least 20 minutes before proceeding with test.

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D.  Swing Compass
(1)  
Deleted.

(2)  
Check that compass transfer switch is in NORMAL.

(3)  
Using SYNC knobs, set captain's and first officer's master compass cards to airplane heading. The annunciators shall indicate a null.

(4)  
Determine true magnetic heading of airplane and North Heading Deviation for each compass.

(a)  
Sight transit on cross hair of target fixture and record transit angle T°.

(b)  
Sight through fixture crosshair (with transit) to fixture scale. Read and record fixture scale angle F°, which is negative if read to left of zero mark, and positive if read to right.

(c)  
Calculate true magnetic heading of airplane thus:

MHn = T° - F°
(5)  
Read and record heading (CH) shown by each compass system's main instrument (i.e., two instruments receiving information direct from DG No. 1 and DG No. 2) and STBY compass.

NOTE:  Allow time for dials to settle before taking readings.

(6)  
Repeat steps (4) and (5) for a westerly heading.

(7)  
Repeat steps (4) and (5) for a southerly heading.

(8)  
Correct for N-S single cycle error (coefficient C) in system No. 1 as follows:

(a)  
Calculate deviation north. (Dn)

(b)  
Calculate deviation south. (Ds)

Ds = MHs - CHs

(c)  
Calculate single cycle error. (C)

Dn = MHn - CHn
C = Dn - Ds
 2

NOTE:  It is important that plus and minus signs are taken into account when making calculations.
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(9)
Repeat step (8) for No. 2 system.

(10)
Repeat steps (4) and (5) for an easterly heading.

(11)
Correct for E-W single cycle error (coefficient B) in system No. 1 as follows:
　
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