TM 1-1500-204-23-4
6
Return aircraft to the north magnetic
heading. Add coefficient C, shown below, algebraically
to compass reading on that heading to determine what
compass should read when compensated. Adjust MS
compensating screw (of polyplane compensator) or
insert magnets in compensating drawer, which is at right
value angles to needle, until compass indicates
compensated value.
Coefficient C= N-S = (+8) - (-4) = 12 = +6
2
2
2
7
Head aircraft east. Add coefficient
B, as shown below, algebraically to compass reading on
that heading. Adjust EW compensating screw (or insert
magnets in that chamber of compensating drawer at
right
angles
to
needle)
until
compass
indicates
compensated value.
Coefficient B= E-W = (-4) - (+8) = -12 = -6
2
2
2
NOTE
·
The spread between maximum
positive and maximum negative
deviation after compensation shall
not exceed 5 degrees.
·
Coefficient
A
represents
total
deviation from the formula given
on DD Form 1613. All additions
and subtractions are algebraic.
Coefficient A = N + E + S +W =
4
(+8) + (-4) + (-4) + (+8) = 8 = 2
4
4
8
After adjustment has been made,
residual swing can begin on any heading. Record actual
heading (M) Column 3, and aircraft compass reading (c)
Column 4; repeat every 45 degrees around the circle.
As indicated in the example in figure 4-22, C to M DEV
is calculated by (3) - (4) or M to C by (4) - (3).
NOTE
The
spread
between
maximum
positive deviation and the maximum
negative deviation after compensation
shall not exceed 5 degrees.
9
Fill in back of the DD Form 1613.
Detach heading correction card portion of the DD Form
1613 at the perforation and place in the cockpit. The
location for the card may vary due to night vision goggle
requirements. See applicable aircraft manual for
location of Compass Correction Card.
10
Place the balance of the form with
the aircraft historical record as a record of compass
swing until completion of the next compass swing.
Upon transfer of aircraft, this portion of the form will
accompany the aircraft with other records.
(d)
B16
master
sighting
compass
method of compensating. The compensator assembly is
removed from the compass and a special sighting
device fitting is substituted. During compensating
procedure with this instrument, aircraft is turned to
desired heading as indicated by aircraft compass. A
sight is then taken by the swinging compass 2 points on
the fore-and-aft axis of aircraft being lined up with
hairline in collimator lens, as shown in figure 4-23. The
compass used for this purpose will be painted red,
indicating that it has been remagnetized 180 degrees
from normal. This permits observer to read magnetic
heading of aircraft directly when sighting from in front of
aircraft. When a compass drawn from stock is used as
a swinging sight, 180 degrees must be added to
compass reading to obtain magnetic heading of aircraft.
Corrections, as indicated by master compass, are made
on each of the cardinal headings in the conventional
manner. In every other respect, compensation is
exactly the same as in the use of the compass rose.
NOTE
When using a sight compass on
helicopters, line up with any two
objects that are parallel with the
centerline of the aircraft.
(e)
Using
AHRS
and
INS
to
compensate compasses. If the aircraft is equipped with
a functional Attitude and Heading References System
(AHRS) or an Inertial Navigation System (INS) and the
variation is known to within 0. 2 degree, the standby
compass system may be swung using either of these
systems as a heading reference in place of a compass
rose.
The
standby
compass
system
is
then
compensated by using the procedures in paragraph (c).
Special care must be exercised in the alignment of
aircraft and the use of nonmagnetic materials.
4-28
