(but in the opposite sense). The south heading on

for zero effect by turning both adjusting screws

the compass will now read 181°. The coefficient

until the dots on the screws match with the dots

of north-south deviation, which is 5 1/2° in this

on the compensator case.

case, is called coefficient **C.**

Then, place the aircraft on a south magnetic

On the loose-magnet type compensator, you

heading over the compass rose, with the tail in

adjust north-south deviation by inserting the

a level flying position. The aircraft engine(s)

should be turning, and as many pieces of avionics

necessary number of magnets into the lateral

(athwartship) chamber of the compensator. If the

equipment as possible turned on. This will create

compass has a universal compensator, you make

as many stray magnetic fields as possible and

the adjustment by turning the north-south (N-S)

simulate the condition of the aircraft in flight.

Note the compass reading and record it. From this

compensator screw.

reading, it is simply a matter of algebraic

The next step is to determine the east-west

subtraction (or subtraction of numbers having

deviation. Turn the aircraft heading to magnetic

east, according to the compass rose. Record the

plus and minus signs) to determine the deviation

compass reading on that heading. Now determine

on the south heading. The deviation is the

algebraic difference between the magnetic heading

the coefficient of east-west deviation, otherwise

and the compass reading. Deviation is the error

known as coefficient **B.**

in a magnetic compass caused by electromagnetic

Assume, for example, that the compass reads

2760 when the aircraft was on the west (270°,

disturbances in the aircraft.

heading. Also assume it reads exactly 90° on the

After doing this, place the aircraft on a west

heading. Again, note the compass reading and

east (90°) heading. You find coefficient **B **b y

determine the deviation or difference between the

algebraically subtracting the deviation on west

magnetic heading and what the compass reads.

( 6°) from the deviation on east (O°) and dividing

by two.

Next, turn the aircraft heading to magnetic

north. Take the compass reading on this heading

and determine the deviation. Now subtract,

algebraically, the south heading deviation from

the north heading deviation and divide the

remainder by two.

While the aircraft is on the east heading,

For example, if the compass reads 175 1/2°

adjust the east-west (E-W) compensator to

while on the south heading (180°0), record this as

add 3° to the compass reading. This reading

a deviation of +4 1/2°(180° 175 1/2°). If the

becomes 93° on the east heading, and the

compass reading is too low, the deviation is plus;

compass would read 273° on the west heading.

if the reading is too high, the deviation is minus.

Make this adjustment by turning the E-W screw

Suppose that on the north (000°), heading, the

on a universal compensator. On the loose magnet

compass reads 006 1/2°. Such a reading is 6 1/2°

type compensator, add the necessary magnets in

too high. You would record this as a deviation

the longitudinal (fore-and-aft) chamber. Leaving

of 6 1/2° (000° 006 1/2°).

the aircraft on an east magnetic heading, next

The next job is to determine the coefficient

compute an overall deviation correction based on

of north-south deviation. You accomplish this by

coefficient **A. **This coefficient is equal to the

subtracting, algebraically, the deviation on the

algebraic sum of the compass deviations on all

south heading from the deviation on the north

four cardinal headings (north, east, south, and

heading. You then divide the remainder by two.

west) divided by four.

You must compensate instrument panel

The aircraft is still on the north heading and the

compasses for coefficient **A **if it amounts to 2°

compass reads 006 1/2°. Since the coefficient of

or more in either direction. When making this

the north-south deviation is 5 1/2°, you must

correction, leave the magnetic compensators

adjust the north-south compensator by this

alone. To compensate for coefficient **A, **move the

amount. The compass reading on the north

instrument in its mounting.

heading will now be 001°. This adjustment also

Compensate panel-mounted compasses for

coefficient **A **by slightly realigning the whole

corrects the south deviation by the same amount