Verifying and Aligning Aircraft Compass Systems: Essential Steps and Manufacturer Guidelines

September 2024

This describes a technology that has essentially gone unchanged since before WW II. However, many aircraft supported by Duncan Aviation Component Services have at least one compass system that requires this alignment procedure.

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

1. Align the aircraft to the South magnetic heading (180°) per the compass rose
2. Note the indicated heading (Example: 175°)
3. Note the deviation error (-5)
   1. Positive (+) if greater than 180° and negative (-) if less

West

1. Align the aircraft to the West magnetic heading (270°) per the compass rose
2. Note the indicated heading (Example 276°)
3. Note the deviation error (+6)
   1. Positive (+) if greater than 270° and negative (-) if less

North

1. Align the aircraft to the North magnetic heading (0°) per the compass rose
2. Note the indicated heading (6°)
3. Note the deviation error (6)
   1. Positive (+) if greater than 0/360° and negative (-) if less

East

1. Align aircraft to the East magnetic heading (90°) per the compass rose
2. Note the indicated heading (90°)
3. 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 and contact us directly.