(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:
(a)
Calculate deviation west. (Dw)
Dw = MHw - CHw
(b)
Calculate deviation east. (De)
De = MHe - CHe
(c)
Calculate single cycle=or.(B)
B = De - dw
2
(12)
Repeat step (11) for No. 2 system.
(13)
Correct for index error (coefficient A) in system No. 1 as follows:
(a)
Calculate index error. (A).
A = Dn + Ds + Dw + De
4
(b)
Calculated index error shall not exceed 1 degree.
(c)
Index error cannot be removed from standby magnetic compass.
(14)
Repeat step (13) for No. 2 system.
(15)
Tow airplane to northerly heading once more and commence 12 point residual error swing.
(16)
Record magnetic heading at each 30-degree compass heading and actual reading of master compass card for each system.
(17)
Check that residual deviation does not exceed 2 degrees on each 30-degree heading.
NOTE: Check transit calibration against heading markers before taking heading reading at each point.
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E. Restore Airplane to Normal
(1)
Remove all items of test equipment.
(2)
If there is no further need for external power, remove external power.
3. Swing Standby Compass System
NOTE: The standby compass may be calibrated using one of two different procedures. One of the procedures is contained in the following paragraphs. This procedure tows the aircraft to swing the compass. The other procedure is contained in Section 34-24-11, Magnetic Standby Compass - Maintenance Practices (Compass Swing). It uses a compass calibrator to swing the compass.
A. General
(1) Compensation for single cycle errors only, is provided on the standby compass.
B. Equipment and Materials
(1) All items listed in paragraph 2.B.
C. Prepare for compass swing.
(1)
Repeat paragraphs 2.C(1), (2), (3), and (5) thru (7).
CAUTION: BE SURE THAT THE GROUND DOWN LOCKS ARE IN PLACE BEFORE PROCEEDING WITH STEP (2), OR THE LANDING GEAR WILL BE IN DANGER OF COLLAPSE.
(2)
Energize the landing gear lever latch solenoid after observing above caution by grounding terminal A of latch solenoid. Allow at least 20 minutes before commencing swing.
CAUTION: DO NOT MOVE LANDING GEAR LEVER AFTER COMPLETING STEP (2).
NOTE: It is necessary to energize the landing gear latch solenoid since it is energized during flight, and its magnetic field can affect the accuracy of the standby compass system. When the solenoid is energized it frees the landing gear lever from its latching mechanism. It is then possible for the lever to be moved to UP.
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