(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
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
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
coefficient A by slightly realigning the whole
corrects the south deviation by the same amount