Chapter 12 - Direct Reading Magnetic Compass

Question 1

Purpose of Direct Reading Magnetic Compass in an airline?

Answer 1

Standby instrument

Question 2

What is the task of a Direct Reading Compass?

Answer 2

indicate direction on the surface of the Earth, relative to Magnetic North.

Question 3

What is the fluid in a direct reading magnetic compass?

Answer 3

Damping fluid

Question 4

How do we balance a Direct reading mag compass?

Answer 4

compensating magnet

Question 5

What is the serviceability check of a Direct Reading mag compass?

Answer 5

• Glass clean
• No discoloration of the fluid
• No bubbles visible
• Indications within 5° of known heading, e.g. runway heading

Question 6

The compass sensing magnets must lie as nearly as possible in the …… plane during normal straight and level flight.

Answer 6

horizontal

Question 7

Where does the NORTH SEEKING end of a direct reading magnetic compass point?

Answer 7

Magnetic North Pole

Question 8

What are the three major limitations of a direct reading magnetic compass?

Answer 8

• Turning and acceleration errors due to dip.
• Closeness to sources of deviation (electric lights, electric motors and ferrous metal).
• The instrument is self-contained. It is not possible to take a magnetic heading and input it into other equipment.

Question 9

What is magnetic dip?

Answer 9

Acceleration and turning errors only occur where the vertical component (Z) in the earth’s field is large.

Question 10

What are the turning principles?

Heading increase?
Heading decrease?

Compared to the compass card

Answer 10

Heading increase – compass card anticlockwise

Heading decrease – compass card clockwise

Question 11

What are acceleration errors with a direct reading mag compass?

Answer 11

acceleration on a heading of west in the northern hemisphere causes the compass card to rotate anticlockwise indicating an apparent turn to the north, or nearer pole.

NH: Acceleration North Deceleration South (ANDS)
SH: North Deceleration South Acceleration (NDSA)

Question 12

What causes acceleration errors on a direct reading magnetic compass?

Answer 12

Caused by inertia acting on a magnet with residual dip.

Question 13

What does the size of the acceleration error depend on in a direct reading magnetic compass?

Answer 13

aircraft heading, acceleration, latitude and design of the magnet system.

Question 14

What are the size of acceleration errors on a direct reading magnetic compass on a east/west or north/south heading?

Answer 14

Acceleration / deceleration errors are MAX on East and West Headings (M) and ZERO on North and South Headings (M).

Question 15

What is the apparent turn due to acceleration errors in the northern and southern hemisphere on a direct reading magnetic compass?

Answer 15

Apparant turn North in the Northern hemisphere.

Apparent turn south in the southern hemisphere.

Question 16

What is DEAP (Dip) of a direct reading magnetic compass?

Answer 16

DEAP (dip): Deceleration toward Equator / Acceleration toward Poles

Question 17

In the northern hemisphere, during a take-off run in a westerly direction, a direct reading magnetic compass indicates:

Answer 17

An apparent turn to the north.

Question 18

In the southern hemisphere, during deceleration following a landing in a northerly direction, a direct reading magnetic compass indicates:

Answer 18

No apparent turn.

Question 19

When are turning errors of a direct reading magnetic compass max and min?

Answer 19

MAX when turning through North and South and ZERO when turning through East and West.

Question 20

The Plane Pushes the Pivot near the Pole

Answer 20

Southern Hemisphere

Question 21

What is lag through the turn?

Answer 21

moment set up by the turn causes an anti-clockwise rotation of the compass card causing its reading to lag in the turn.

Question 22

How is turning error of a direct reading magnetic compass further magnified?

Answer 22

The error will be further magnified by liquid swirl – think viscosity.

Question 23

Because of a turning errors of a direct reading magnetic compass is it over or under reading?

Answer 23

because the reading is lagging behind the aircraft, we call this under-reading.

Therefore, if we wish to roll out of our turn on a magnetic heading of 315 ̊, we will need to roll out when our compass reads, say, 335 ̊ or apparently early.

Question 24

When turning away from the nearer pole the your direct reading magnetic compass will…? Due to turning error

Answer 24

Your compass will lead in the turn

Question 25

Turning error

Turning away from the pole in the SH, the damping fluid will, increase or decrease the error of your direct reading magnetic compass?

Answer 25

Decrease, as compass is trying to lead in the turn.

Question 26

Is the heading indicated on the compass leading the aircraft, over or under reading?

Answer 26

over-reading if leading the aircraft heading

Question 27

What is compass sluggish and lively?

Answer 27

sluggish - under reading in the turn
lively - leading, over reading in the turn

Question 28

What is UNOS and ONUS

Answer 28

Northern Hemisphere - U N O S - Under-reads turning through North, Over reads turning through South

Southern Hemisphere - O N U S – Over-reads turning through North, Under-reads turning through South

Question 29

Timed turns are a solution for?

Answer 29

Turning errors on the direct reading magnetic compass

Question 30

what causes turning errors?

Answer 30

Dip of the compass

Question 31

The effect of the turning error of a direct reading magnetic compass increases when?

Answer 31

The magnetic latitude increases