Form of the earth/Lat and Long

Question 1

Isogonal line

Answer 1

Lines joining places with equal variation.

Isogonals converge at both the geographic and (˚M) N and S poles

Question 2

Agonic line

Answer 2

Lines joining areas of zero variation

Question 3

Isoclinic line

Answer 3

Lines of equal dip

Question 4

Aclinic line

Answer 4

Lines joining areas of zero dip

Question 5

Variation is?

Answer 5

The angular difference between ºT and ºM

Question 6

Deviation is…?

Answer 6

The angular difference between ˚C and ˚M

The max difference is normal 3˚ E/W however EASA accuracy limit for the DRC is 10˚

Question 7

What is a graticule?

Answer 7

All lines of parallels of latitude and longitudes are collectively known as graticule.

Question 7

What is a rhumb line?

Answer 7

Is a regularly curved line that cuts all the meridians of longitude at the same angle.

Rhumb lines are ALWAYS convex to the EQ side while great circles are always convex to the polar side.

Question 8

What is a great circle?

Answer 8

A circular track which has the centre of the earth as it’s centre of radius. Thus the radius of GC is equal to the earth’s radius.

All GC pass through the the EQ while small circles do not.

Question 9

What are parallels of latitude?

Answer 9

Latitudes stretch W to E but are measured N or S of the EQ.

Latitudes have a max angle of 90˚

Question 10

What are meridians of longitude?

Answer 10

Longitudes stretch N and S but measured E and W.

Longitudes max at 180˚ therefore a meridian and it’s anti meridian make a great circle (360˚).

Question 11

What is a prime meridian?

Answer 11

It is the meridian which goes through London and it’s angle is at 0˚

Question 12

What is the problem with flying GC?

Answer 12

Due to increasing convergency as you fly further north or south, to fly a GC you must continually change track.

Question 13

What is a vertex?

Answer 13

A point on the GC where you are at the highest latitude.

So there will be a northern and southern vertex; 2 points, and are antipodal

Question 14

A GC crosses the EQ at 2 points, what are these 2 points called?

Answer 14

Crossing point or the node.

For calculations, to check if you have correctly calculated the nodes, the 2 points has to add up to 180˚

Question 15

At either vertex the track direction is either 090˚ or 270˚, why?

Answer 15

This is because vertices are antipodal, exact opposite ends from each other. That is why the 2 points add up to 180˚.

As vertices are GC. A GC is made up of a meridian and anti meridian. Since meridians are measured E to W, the points on a compass would be 090˚ and 270˚. Thus vertices must have a track direction of either 090˚ and 270˚.

Question 16

Deviation west, magnetic best

Deviation east, magnetic least

Answer 16

Deviation west, compass best

Deviation east, compass least

Question 17

What is a dip angle?

Answer 17

This is when a compass points directly to the strongest horizontal magnetic field being emitted by the earth’s core.

Due the magnetic field emitting from the South Pole to the North Pole, the point of:

• max dip occurs at the (˚M) North Pole i.e. 90˚ dip
• min dip occurs at the (˚M) South Pole i.e. 0˚ dip

Question 18

What is a compass swing?

Answer 18

A compass swing is the checking of the direct reading compass (DRC) and whether it is accurately aligned to ˚M north.

Question 19

When is a compass swing required?

Answer 19

• Change of base
• A/C hit by lightening
• major change in A/C equip
• A/C parked in same direction for a long period of time
• when new compass is fitted
• when carrying magnetic freight or freight with large ferrous content
• when suspect deviation
• when scheduled for A/C maintenance

+/- 10˚ is the acceptable error (according to EASA)

Question 20

What causes deviation?

Answer 20

Interference of the A/C as both A/C and it’s instruments carry large quantities of ferrous metals e.g. Magnets in instruments

And

Electrical equip also create electromagnetic fields also causing erroneous reading

Question 21

What is a compass card?

Answer 21

A card advising adjustments that should be made for deviation errors.

Deviation values change for different HDGs.

Question 22

What is a latitude?

Answer 22

A latitude is a point on the surface in relation to the EQ.

This angular difference between the EQ and the point can be indicated as a latitude.

Latitude max 90˚

Question 23

When using the term departure, what do we mean by this?

Answer 23

The distance along the parallel of latitude.

Question 24

Define geocentric latitude?

Answer 24

The angle between a line drawn on the surface of the earth to the centre of the earth and the plane of the equator.

Geocentric latitudes assume a perfect sphere where the line drawn from any point on the surface will always end at the centre of the earth.

Question 25

Define Geodesic.

Answer 25

The shortest distance between 2 points will always be a straight line. A straight line on a curved surface is called geodesic.

Question 26

Define geodesic (or geographic) latitude

Answer 26

We have learnt that on a perfect sphere any geocentric latitude has earth’s centre as it’s centre of radius.

But because the earth is an oblate spheroid, not all points on the surface are perpendicular to the earth’s centre. With the exception of the points along the equator and at the N/S poles. This is therefore called the geographic latitude.

Question 27

Where is the difference between the geodetic and geocentric the greatest?

Answer 27

Mid Lat at exactly 45˚ N/S

The min is therefore at the EQ and at the poles. In fact geographic and geocentric latitudes are the same here.

Question 28

Due to earth’s ellipsoid, what is 1˚ in NM near the Eq compared to the poles?

Answer 28

1˚ NM at Eq/nearer Eq/low altitudes < 60nm

1˚ NM at the poles/nearer poles/high altitudes > 60nm

Question 29

What is the maximum difference in mins between the geocentric and geodesic (or geographical) latitude?

Answer 29

11.6’ (mins)

Question 30

Magnetic variation is applied at the AC or at the VOR?

Answer 30

Always at the VOR because you are working in radials.

Radials are from the VOR so variation must be applied there.