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Instrument Flying Handbook
Flight Instruments
Basic Aviation Magnetic Compass

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Instrument Flying
Handbook

Preface

Table of Contents

Chapter 1. Human Factors
Chapter 2. Aerodynamic Factors
Chapter 3. Flight Instruments
Chapter 4. Section I
Airplane Attitude Instrument
Flying
Using Analog Instrumentation
Chapter 4. Section II
Airplane Attitude Instrument
Flying
Using an Electronic Flight
Display

Chapter 5. Section I
Airplane Basic
Flight Maneuvers
Using Analog Instrumentation
Chapter 5. Section II
Airplane Basic
Flight Maneuvers
Using an Electronic Flight
Display

Chapter 6. Helicopter
Attitude Instrument Flying

Chapter 7. Navigation Systems
Chapter 8. The National
Airspace System

Chapter 9. The Air Traffic
Control System

Chapter 10. IFR Flight
Chapter 11. Emergency
Operations

compass correction card
Figure 3-19 A compass correction card shows the deviation
correction for any heading.

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 he 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 he interpreted. Therefore, to steer a true
course of 180°, the pilot would follow a compass course of 188°.
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 fight. 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
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.

Northerly Turning Error.
Figure 3-20. Northerly Turning Error.

 

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