If you replace or change the magnetic compass or components on your aircraft’s compass system, it is appropriate to swing the compass to verify or align it to minimize errors.
The following alignment steps apply to all make/model aircraft and are based on MIL-STD 765A. Your aircraft’s compass system may have different methods of alignment. Always refer to and use the manufacturer’s procedures if they differ from this method.
Formulae:
North (N) / South (S) Correction = ½ [N error - S error]
East (E) / West (W) Correction = ½ [W error - E error]
Index Correction =
¼ [N error + E error + S error + W error]
Compass Swing Procedure with example:
South
- Align the aircraft to the South magnetic heading (180°) per the compass rose
- Note the indicated heading (Example: 175°)
- Note the deviation error (-5)
- Positive (+) if greater than 180° and negative (-) if less
West
- Align the aircraft to the West magnetic heading (270°) per the compass rose
- Note the indicated heading (Example 276°)
- Note the deviation error (+6)
- Positive (+) if greater than 270° and negative (-) if less
North
- Align the aircraft to the North magnetic heading (0°) per the compass rose
- Note the indicated heading (6°)
- Note the deviation error (6)
- Positive (+) if greater than 0/360° and negative (-) if less
East
- Align aircraft to the East magnetic heading (90°) per the compass rose
- Note the indicated heading (90°)
- Note the deviation error (0)
Swing Results
Actual Indicated Deviation error
N 000 006 +6
E 090 090 +0
S 180 175 -5
W 270 276 +6
N/S Correction = ½ [N error - S error]
= ½ [(+6) – (-5)]
= ½(+11)
= +5.5° error
Align the aircraft to 5.5° indicated and adjust the N/S correction to read 0° indicated
E/W Correction = ½ [E error - W error]
= ½ [(+0) – (+6)]
= ½(-6)
= -3° error
Align the aircraft to 87° indicated and set E/W adjustment to read 90°
Index Correction = ¼ [N error + E error + S error + W error]
= ¼ [(+6) + (+0) + (-5) + (+6)]
= +1.75° error
Align Flux Valve to subtract 1.75° from existing indicated heading
If you have any questions about this procedure, feel free to reach out to Duncan Aviation Avionics Instrument Tech Rep, Curt Campbell.
Curt Campbell