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after each turn
Figure 3-20. Northerly Turning Error.
aircraft is operating with the radios on, the pilot should fly a
compass heading of 123°.
The corrections for variation and deviation must be applied
in the correct sequence and is shown below starting from the
true course desired.
Step 1: Determine the Magnetic Course
True Course (180°) ± Variation (+10°) = Magnetic Course (190°)
The Magnetic Course (190°) is steered if there is no deviation
error to be applied. The compass card must now be considered
for the compass course of 190°.
Step 2: Determine the Compass Course
Magnetic Course (190°, from step 1) ± Deviation (-2°, from
correction card) = Compass Course (188°)
NOTE: Intermediate magnetic courses between those listed on
the compass card need to be interpreted. Therefore, to steer a true
course of 180°, the pilot would follow a compass course of 188°.
To find the true course that is being flown when the compass
course is known:
Compass Course ± Deviation = Magnetic Course ± Variation
= True Course
Dip Errors
The lines of magnetic flux are considered to leave the Earth at
the magnetic north pole and enter at the magnetic South Pole. At
both locations the lines are perpendicular to the Earth’s surface.
At the magnetic equator, which is halfway between the poles,
the lines are parallel with the surface. The magnets in a compass
align with this field, and near the poles they dip, or tilt, the float
and card. The float is balanced with a small dip-compensating
weight, so it stays relatively level when operating in the middle
latitudes of the northern hemisphere. This dip along with this
weight causes two very noticeable errors: northerly turning error
and acceleration error.
The pull of the vertical component of the Earth’s magnetic field
causes northerly turning error, which is apparent on a heading
of north or south. When an aircraft flying on a heading of north
makes a turn toward east, the aircraft banks to the right, and the
compass card tilts to the right. The vertical component of the
Earth’s magnetic field pulls the north-seeking end of the magnet
to the right, and the float rotates, causing the card to rotate toward
west, the direction opposite the direction the turn is being made.
[Figure 3-20]
If the turn is made from north to west, the aircraft banks to the left
and the compass card tilts down on the left side. The magnetic
field pulls on the end of the magnet that causes the card to rotate
toward east. This indication is again opposite to the direction
3-14
Figure 3-21. The effects of acceleration error.
OBS
N
E
S
W
333
24
21
15
12
306
NAV
GS
View is from the pilots
perspective, and the
movable card is reset
after each turn
Figure 3-21. The Effects of Acceleration Error.
the turn is being made. The rule for this error is: when starting
a turn from a northerly heading, the compass indication lags
behind the turn.
When an aircraft is flying on a heading of south and begins
a turn toward east, the Earth’s magnetic field pulls on the
end of the magnet that rotates the card toward east, the same
direction the turn is being made. If the turn is made from south
toward west, the magnetic pull starts the card rotating toward
west—again, in the same direction the turn is being made. The
rule for this error is: When starting a turn from a southerly
heading, the compass indication leads the turn.
In acceleration error, the dip-correction weight causes the end
of the float and card marked N (the south-seeking end) to be
heavier than the opposite end. When the aircraft is flying at
a constant speed on a heading of east or west, the float and
card is level. The effects of magnetic dip and the weight are
approximately equal. If the aircraft accelerates on a heading
of east [Figure 3-21], the inertia of the weight holds its end of
the float back and the card rotates toward north. As soon as the
speed of the aircraft stabilizes, the card swings back to its east
indication. If, while flying on this easterly heading, the aircraft
decelerates, the inertia causes the weight to move ahead and the
card rotates toward south until the speed again stabilizes.
When flying on a heading of west, the same things happen.
Inertia from acceleration causes the weight to lag, and the
card rotates toward north. When the aircraft decelerates on a
heading of west, inertia causes the weight to move ahead and
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