General Navigation Flashcards
What are the lines which run from pole to pole called?
Meridians of longitude
What are the lines that run east to west called?
Parallels of latitude
Latitude is measured as an angle from the _______.
Equator
Longitude is measured as an angle from the ______.
Prime meridian
To calculate the change in latitude of two points in the same hemisphere ____ the angles.
subtract
To calculate the change in latitude of two points in different hemispheres ____ the angles.
add
To calculate the change in longitude of two points in the same hemisphere ____ the angles.
subtract
To calculate the change in longitude of two points different hemispheres ____ the angles.
add
What do you do if chlong is greater than 180°?
Subtract it from 360° to find the shortest way round.
How do you find the position of the opposite point on the earth?
Latitude: same ° but opposite hemisphere
Longitude: 180 - ° and in the opposite hemisphere
What is the ratio of elipticity of the earth?
1/298
Geocentric latitudes are measured from the ______.
Centre of the earth
They do not intersect the surface at 90°
Geodetic lattitudes are measured _______.
At 90° to the earth’s surface.
They are used for charts.
What is the difference from equator to pole in km?
10,000km
What is the earth’s circumference in km?
40,000km
1’ = ___NM
1
1° = ___NM
60
What is departure used to calculate?
The east/west distance along a parallel of latitude (not the shortest distance)
(needed as the distance between meridians of longitude decreases as latitude increases)
What is the formula for departure?
Departure (NM) = Chlong (minutes) x cos lat
If asked to find the shortest distance between points with different longitudes AND diferent latitudes…
It will be over the pole from a meridian to its antimeridian
What is convergency?
How much the great circle track changes because of converging meridians.
What are directions referenced to the geographic north pole called?
True north
Give 2 examples of great circles
Describe great circles in terms of track direction and distance between two points.
Equator, all meridians of longitude
Constinuously changing track direction (unless both points on equator or same longitude)
Shortest distance between points
What is the formula for convergency?
Convergency = chlong x sin(mean lat)
Rhumb lines have ________ direction and lie on the __________ side of the equivalent great circle.
constant
equatorial
Where do the great circle track and rhumb line track have the same direction?
halfway
What is the conversion angle and how is it calculated?
The angle between the great circle and the rhumb line.
Conversion angle = ½ convergency
Which lines on the earth are rhumb lines?
All parallels of latitude.
Whch angle does magnetic variation represent?
The angle between the true meridian and the magnetic meridian.
Which lines join points of equal variation?
Isogonals
‘Variation east, magnetic _____
variation west, magnetic ____’
least
best
Concerning variation, consider east as ______ and west as ______.
positive
negative
What is the difference between the direction of magnetic north and compass north called?
Deviation
‘Deviation ____ compass least,
deviation ____ compass best.’
East
West
What causes deviation to vary?
Magnetic latitude (strength of Earth’s magnetic field)
Aircraft heading (orientation of aircraft to magnetic field)
Changes of aircraft electrical equipment (production of interfereing magnetic fields)
Cadbury’s Dairy Milk Very Tasty is a pneumonic for what?
Compass Deviation Magnetic Variation True
The directive force is the component of the Earth’s magnetic field that ________________.
Aligns the compass needle.
When should a compass swing be carried out?
Transfering bases with significant latitude change
After major changes of aircraft equipment
After lightning strike
After its been parked facing one direction for a long time
When a new compass is fitted
When compass or recorded deviation is suspect
When specified in the maintenance schedule
What is the maximum permissable deviation for a magnetic compass (current EASA regulations)?
+/- 10°
If variation is west then true north is ____ of magnetic north.
east
What 3 properties do conformal/orthomorphic charts have?
Shows shapes, angles and distances correctly
Same scale used for latitude and longitude
Meridians and parallels are perpendicular
What is the formula for chart scale?
chart scale = chart distance / earth distance
Where is a projected chart most accurate?
The parallel of origin (where it touches the model)
How is a simple conic projection derived?
Convergency is ________ and calculated using the formula : _______
Placing a cone on a wire globe
constant
convergency = chlong x sin parallel of origin
How does the accuracy of convergency effect great circles on a map?
Accurate convergency shows great circles as straight lines
Increasing inaccuracy makes great circles more curved
Where is the parallel of origin on a Lamberts Conformal Projection?
Parallel to the tangent of the sphere
On Lamberts conformal projections how does scale vary with the standard parallels and parallel of origin?
Contracts between standard parallels, expands outside them
Scale at minimum value at parallel of origin
Can be assumed constant though
What 2 conditions must be met by a lamberts conformal projection in order to assume the great circle lines to be straight and the scale to be constant?
max latitude spread of 24°
max 2/3rds of chart between the standard parallels
On lamberts conformal projection rhumb lines are concave to _______.
the nearest pole
On a polar stereographic chart _____ can be assumed constant. Rhumb lines are concave to ______. Great circles are assumed straight but are actually _______.
Convergency = ________
scale
the nearer pole
concave to the pole
convergency = chlong
(sin lat at pole, 90°, is 1)
On a mercator projection chart scale can be assumed constant within ____ NM of the equator.
Which lines are straight and which are curved?
(great circles, rhumb lines, meridians, parallels)
500NM
rumb lines, meridians, prallels and the equator are straight
great circles are concave to the equator
On a mercator projection what is convergency?
zero
How is scale calculated on a mercator projection?
Scale at any latitude = scale at equator x sec(lat)
Great circles always lie on the ________ side of rhumb lines.
poleward
