Section One: 4. The Magnetic Compass and Direction

Question 1

045, 135,225 and 315 degrees are what kinds of directions?

Answer 1

Quadrantal points

Question 2

Grid north is the same as

Answer 2

True North

Question 3

What is ‘variation’?

Answer 3

Angular difference between North Geographic and Magnetic Poles

Question 4

Why is magnetic variation not uniform across the Earth’s surface?

Answer 4

Due to the angular difference between the two kinds of Poles

Question 5

What is an isogonal?

Answer 5

Line joining locations of equal magnetic variation

Question 6

What kind of variation is experienced over the UK currently?

Answer 6

Western

Question 7

What is an agonic line?

Answer 7

Indication of where magnetic variation is 0

Question 8

Isogonals are shown for every what increment in mag variation?

Answer 8

0.5 degrees

Question 9

If mag north is WEST of true north (westerly direction), the magnetic direction will have a

Answer 9

Higher angular value than true direction

Question 10

If mag north is EAST of true noth (easterly direction), the magnetic direction will have a

Answer 10

Lower angular value than true direction

Question 11

If magnetic direction has a higher angular value than true direction, what variation exists?

Answer 11

Westerly

Question 12

If magnetic direction has a lower angular value than true direction, what variation exists?

Answer 12

Easterly

Question 13

Rhyme to remember for mag/true variation

Answer 13

Variation west - Magnetic Best, Variation East - Magnetic Least

Question 14

The metallic structure and equipment of an aircraft has what effect on navigational ability?

Answer 14

Compass deviation occurs

Question 15

Rhyme to remember for compass deviation

Answer 15

Deviation west - compass best, deviation east - compass least

Question 16

Why is magnetic compass reliability poor near the magnetic poles?

Answer 16

Magnetic dip is greater
Weaker horizontal component

Question 17

At what approximate latitudes does do magnetic compasses become unreliable?

Answer 17

60 degrees North or South

Question 18

The horizontal component of magnetic flow is greatest where?

Answer 18

Equator

Question 19

How do magnetic compass cards minimise the effect of magnetic dip?

Answer 19

The float is displaced

Question 20

What is the drawback to having the float displaced on magnetic compasses?

Answer 20

It causes turning and acceleration errors

Question 21

Why do compasses give incorrect readings in turns?

Answer 21

The pivot and float’s C of G are not correctly aligned with magnetic north

Question 22

When turning through the nearest magnetic pole, the compass will…

Answer 22

Underestimate the actual magnetic heading

Question 23

When turning through the furthest magnetic pole, the compass will…

Answer 23

Overestimate the actual magnetic heading

Question 24

Why does a compass turning error not occur during turns through 90 or 270 degrees?

Answer 24

The pivot and float’s C of G are aligned during the turn

Question 25

Acceleration errors in compasses walkthrough

Answer 25

Aircraft accelerates
Float CoG’s inertia causes clockwise rotation
Compass heading underestimates

Question 26

Decceleration errors in compasses walkthrough

Answer 26

Aircraft decelerates
Float’s CoG thrown forwards causing anti-clockwise rotation
Compass heading overestimates

Question 27

Why do acceleration errors not occur on headings of 360 and 180?

Answer 27

Pivot and float’s CoG are aligned

Question 28

A compass pivot and float’s CoG rotate clockwise in a change of speed. What is occuring?

Answer 28

Aircraft is accelerating and the compass will overestimate

Question 29

A compass pivot and float’s CoG rotate anti-clockwise in a change of speed. What is occuring?

Answer 29

Aircraft is decelerating and the compass will underestimate

Question 30

A compass will underestimate during what change of speed?

Answer 30

Acceleration

Question 31

A compass will overestimate during what change of speed?

Answer 31

Deceleration

Question 32

An aircraft accelerates on a heading of 360 degrees. What compass error will occur?

Answer 32

None, as the pivot and float CoG are aligned

Question 33

An aircraft turns from 060 to 120. What compass error will occur?

Answer 33

None, as the pivot and float CoG are aligned

Question 34

Northern Hemisphere compasses are compensated how?

Answer 34

Displaced towards the south pole to compensate for dip

Question 35

The Earth rotates how many degrees an hour?

Answer 35

15 degrees

Question 36

Directional indicator (gyro) drift occurs how?

Answer 36

Indicator axis is fixed in space by the gro and drifts in accordance with the Earth’s rotation

Question 37

Why can the correct functioning of the HI only be checked when the engine is running?

Answer 37

The vaccum system needs to be operational