magnetic compass

Question 1

what is the operation of a magnetic compass?

Answer 1

functions according to the properties of magnetism.

this aligns itself with the lines of magnetic flux surrounding the earth, which run from the north pole to the south.

Question 2

what is the construction of a magnetic compass?

Answer 2

consists of two bars or needly type magnets which are attached to a compass card. which are suspended from above the CoG in an arrangement known as pendulous suspension.

Compass card is free to rotate and will do so as the two magnets will sign themselves in a north-south direction.

all of it sits inside the compass bowl which is filled with a liquid that is there to lubricate to provide some buoyancy to the compass card and dampen any motion of the card.

Question 3

within the compass case, the magnet is suspended from above (above its COG) for what reason?

Answer 3

to contrast the effects of dip. which is the indirection of the compass magnet away from the horizontal as it seeks to align itself with lines of magnetic flux.

Question 4

where does acceleration error occur?

Answer 4

at the pivot point, through which acceleration acts, and the centre of gravity is offset.

Question 5

what is acceleration error in regards to magnetic compass?

Answer 5

Depict aircraft flying with a heading to the east, as it accelerates it’ll cause the compass to turn to the south.

the acceleration force will be felt on the magnet system through its pivot point. the weight of the magnet system acts through the CoG making it want to lag behind during acceleration.

These two forces make a couple which serves to want to turn the magnet system which can be viewed by the pilot as the compass card turning to the south.

Question 6

in a deceleration what happens to the magnetic compass?

Answer 6

the centre of gravity of the magnet system goes in front of the pivot point making the compass card turn to the north, (heading east),

Question 7

how can acceleration error be remembered in the southern hemisphere?

Answer 7

SAND - south accelerating north decelerating.

meaning that on an east-west heading, acceleration will cause your compass to swing to the south, and deceleration will cause it to swing north.

Question 8

what is turning error caused by?

Answer 8

residual dip pulls the compass card around, making the compass turn too fast when we turn onto northerly headings.

turning onto southerly headings it’ll turn too slow.

Question 9

how does turning error work?

Answer 9

say an aircraft has a southerly heading, the magnetic dip force (wanting to pull the compass needle down) causes the compass card to swing in the same direction that the card is turning.

meaning that the card is actually in front of the aircraft heading, other words the compass is telling you the turn is actually too high a number and to stop the turn prematurely for proper heading

Question 10

what is the mnemonic to remember for turning error in the southern hemisphere?

Answer 10

ONUS, overreading north, under reading south

to determine what magnetic heading to roll out of the turn on to achieve a desired actual heading.

Question 11

compass turns are made at what rate and what would the max turning error be?

Answer 11

rate one turns and 30 degrees when turning through north or south, reducing to 0 at east or west.

Question 12

what are the serviceability checks of the compass? (6)

Answer 12

• secure in its mounting and sits well
• compass is facing straight ahead
• no cracks or leaks
• liquid is clear and no bubbles
• compass deviation card installed within validity date.
• compass indication correct direction

Question 13

when doing taxi turns what should happen to the compass?

Answer 13

compass card should move freely and not oscillate when turn is stopped. heading change indicated on compass should match the direction of the turn, decreasing in left increasing in right.

lining up for takeoff compass should be checked for indication of runway heading.

Question 14

being magnetic the compass must not be what?

Answer 14

near metal or other magnetic things due to potential deviation or damage.

Question 15

when the compass is installed, following changes to aircraft that are considered major (engine change) and it remains stationary for a long time what should happen to the compass?

Answer 15

must be swung meaning placing the plane on a known magnetic heading and recording the compass readings.

used to determine coefficients of deviation which are then used to calculate compensation factors.

Question 16

a magnetic heading corrected for deviation is known as what? and what should this deviation be reduced to and where should it be placed?

Answer 16

compass heading.

deviation should be reduced to 3 degrees or less and placed next to the compass for other people.

Question 17

if the deviation is east correction should be what, and what should it be for west?

Answer 17

deviation east, correction should be subtracted and west added.

deviation east compass least
deviation west compass best

Question 18

what is the lubber line?

Answer 18

the white vertical line in front of the compass that you line up with the numbers to tell you your compass direction.

Question 19

what causes magnetic dip?

Answer 19

over the equator, the force pulling down on each pole of the magnet is the same, but if we move away from the equator, say south, the south pole seeking end of the compass needle will be drawn downwards to the magnetic south pole.

In other words, the compass needle will have a dip towards the south. Closer you get to the south pole the greater the angle of dip.

Question 20

where can the NZ magnetic dip be found?

Answer 20

61 degrees at north cape top of the north island, 72 degrees, Bluff bottom of the south island.

Question 21

what is residual dip?

Answer 21

The leftover dip which wasn’t removed through pendelous suspension where having the CoG of the compass card below the suspension point cancel out most of the magnetic dip

Question 22

how is the magnetic dip increased?

Answer 22

the close you are to the poles

Question 23

during turns in the southern hemisphere what should you do with a southerly or northerly heading regarding turning error.

Answer 23

southerly heading you should stop a bit before your destined heading depending on what the ONUS says.

northerly you should pass the desired heading.

Question 24

how is magnetic dip prevented and why?

Answer 24

pendulous suspension as having the CoG of the compass card below the suspension point helps cancel dip out