General Navigation Flashcards
What is the shape of the earth?
Oblate spheroid
Which is the major and minor axis of the earth? What is the ratio? And what is the term defined for this ratio?
N/S minor axis - 297
E/W major axis - 298
Ratio of ellipticity
What are the following earth dimensions:
- circumference
- Equatorial diameter
- polar diameter
- 40000km or 21600nm circumference
- 12756km equatorial diameter
- 12713km polar diameter
What do navigation system manufacturers use as their world charting system?
WGS84 - world geodetic system of 1984
How were the north and south poles defined as such? How can you determine East from the earths spin?
By looking downward at the solar system it is observed that the planets spin anti-clockwise and therefore from the north pole the earth spins anti-clockwise
The earth spins in an easterly direction therefore, it spins in the direction of east.
What is a great and small circle? Give examples of both
A great circle passes through the centre of the earth, is the shortest route from point to point and always bisects every other great circle.
The equator is a great circle line and its plane is at 90degrees to the earths spin. Every line of meridian is a great circle passing from pole to pole
Everything that is not a great circle is a small circle - e.g. Parallel lines of latitude to the equator N and S
What are the 2 kinds of latitude and their differences?
Geographic and geocentric.
Geocentric latitude is an angle measured at the centre of the earth between the plane of the equator and a line joining the point and centre of the earth.
Geographic latitude assumes the earth is a perfect sphere and is an angle measured between the plane of the equator and the normal of the geoid
What is the maximum difference between geodetic and geocentric latitude?
Between 45N/S the max difference is 11.6minutes
Calculate the change is latitude from: 65N 18’ to 50S 25’?
Different hemisphere therefore add - 115 43’
What is a meridian and anti meridian? How do these relate to longitude?
The meridian corresponds to a great circle line starting and finishing at the poles. The anti meridian is the reciprocal great circle line completing the great circle on the other side of the planet. There are infinite amounts of meridians
Meridians of longitude are described as the angle away from the prime meridian (000E/W). Longitude is the angle measured at the polar axis between the plane of prime and local meridian.
Find the change in longitude from E178 21’ to E045 35’
Same hemisphere so subtract - 132 46’
What is departure? What is its equation?
Departure is the movement travelled across a parallel of latitude
Departure = change in longitude x 60 x cos(Lat)
What is 1nm in feet and km?
1nm = 6080ft 1nm = 1.852km
Do the following latitude and longitude coordinates indicate a polar transit and why?
N48 54’ E88 30’
N60 30’ W91 30’
The shortest path between the 2 coordinates is by crossing the North Pole because the easterly and westerly add to a total of 180 degrees
What is a rhumb line?
A rhumb line is one that has constant bearing
A rhumb line intersects each meridian at the same angle
Rhumb lines always lay on the equatorial side of great circles
The equator are rhumb lines and great circles
What is convergency and its equation?
Convergency is the principle that travelling on a great circle in a straight line the bearing will change over large distances. This is due to the converging meridians at the pole and as each individual’s local meridian changes at different locations the bearing upon departure in New York will be different in Mumbai
Convergency = chlong x sin(mean Lat)
What is the conversion angle and its equation?
The angle between the great circle and the rhumb line is known as the conversion angle
CA= 1/2convergency or 1/2[chlong x sin(mean Lat)]
What does the compass detect?
The directive force of the horizontal component of the magnetic field.
What is the difference between true track and compass track?
True north is read in relation to the geographic North Pole. This is what latitude and longitude is based on.
True north is corrected for variation to find magnetic track and then deviation for compass track.
What is an isognol?
These are lines on a chart that plot equal variation
What is dip and where is it strongest?
Dip is the phenomena that illustrates that flux lines are not horizontal everywhere you go on the earth. Compass dip is worst at the magnetic poles because the vertical component of the magnetic field is largest and the horizontal the weakest resulting in the magnetic field not being strong enough to move the compass.
What is magnetic variation and where is it most profound?
Magnetic variation is the difference between true north and magnetic north. It’s is most convergent when flying between the 2 poles in which it can vary between 0-180degrees.
What is deviation, how is this determinedly do minimised?
Deviation is a function of the aircraft structure and magnetic field in relation to the compass. Deviation is also dependent upon the heading flown.
Deviation is determined and minimised by a procedure called a compass swing - this is a procedure where by an aircraft is positioned on a turn table and rotated in numerous directions whilst measuring the bearing from inside the aircraft by comparison to known good. The compass is then adjusted using tiny magnets within the housing and any remaining residual deviation is placed on a deviation card.
What is the maximum allowable deviation?
+-10 degrees
When should a compass swing procedure be carried out?
After new systems have been fitted
A new compass has been fitted
Upon magnetic cargo being carried
Aircraft struck by lightning
When instrument readings look suspect
Aircraft maintenance schedule in particular after heavy landing
After the aircraft has been parked for a long time
Work out the following:
Compass Deviation Mag track Variation True track
270 269 275
144 3E 147 3W
Compass Deviation Mag track Variation True track
270 1W 269 6E 275
144 3E 147 3W 144
Name three chart projections and their respective charts
Cylindrical - mercator (direct, transverse and oblique) - applicable from Equator to +/-8 degrees
Conical - lambert conformal conic - applicable from +/- 8 degrees to 78 degrees
Azimuthal - polar stereo graphic - applicable from 78-90 degrees
What are the properties of a direct Mercator chart?
- straight lines drawn on this map are rhumb lines
- great circles are concave toward the equator
- cylindrical projection
- chart convergence on the entire chart is zero
- lines of latitude are parallel, straight and unevenly spaced. Therefore, parallels of latitude have increasing space as latitude increases
- meridians of longitude are parallel and evenly spaced
- scale expands as the secant of latitude (constant within 500nm of equator)
What is the equation for the Mercator scale and what does it help ascertain?
ABBA - scale LatA x cos latB = scale latB x cos LatA
Given any one of these values and/or a scale distance across a direct Mercator map or a latitude will enable you to find the departure distance between 2 points and scale of the Mercator map
What are the properties of a lambert conformal conic chart?
Conic projection
Convergency is equal to the sine of the parallel of origin
Meridians of longitude are straight lines emanating from the pole
The graticule is at 90 degrees
Shows a great circle as approximately a straight line
scale is reasonably constant
Applicable from 8 degrees N/S to 78 degree N/S
What are standard parallels and the parallel of origin?
In a lambert chart the POO is where the witches hat touches the earth surface and therefore, is tangential to the meridian at that latitude. This is what determines convergency across the whole map.
A standard parallel is where the witches hat touches multiple places on the earth and as such the scale is correct at these latitudes and least at the POO. This is to extend the coverage of the map
What is the constant of the cone? What is the lambert project convergency equation?
If you produce a conical projection on a flat piece of paper, you do not produce a full 360 degree representation even though the earth projection is spherical. Therefore the constant of the cone is the same as the sine of the POO latitude.
Convergency = ch long x sin(PoO latitude) or constant of the cone
What are the properties of a polar stereographic chart?
- great circles and rhumb lines concave to the pole (great circles considered straight)
- convergency is change in longitude
- scale can be assumed constant but expands away from pole
- meridians are straight lines radiating from the pole
- parallels of latitude are concentric circles
How does scale contract and expand on a lambert conformal conic projection? What does the scale do at the parallel of origin?
The standards of parallel are where the scale is correct therefore, at the parallel of origin scale will be at its minimum
Standard of parallels -> P.O.O contracts
P.O.O -> standard of parallels expands
Standard of parallels away from P.O.O expands
The maximum spread of latitude is 24 degrees
What is grivation?
It is the algebraic sum of variation and grid north
How is grid track calculated?
GT=true track +- grid convergency
Grid convergency is found with respect to grid north
In polar regions, as the magnetic compass cannot be relied upon, what is used instead?
Gyroscopic compass
Gyro compass maintains a reference to a fixed point in space (gyro rigidity) and therefore as the aircraft follows a straight line track it also maintains a constant bearing relative to grid north
With respect to grid navigation what is convergence?
The difference between grid track and true track is referred to as convergence.
The value of convergence is made by measuring the change in longitude between the datum meridian (grid north based upon) and the local meridian
Permanent magnetism in aircraft arises chiefly from what?
Major cause of permanent magnetism in the airframe is bending, thumping and banging during the manufacturing process which induces magnetism with the alignment of the earths magnetic field
What is the Agonic line?
An Agonic line is a line joining points of zero variation. The Agonic line is a form of isognol specifically one joining points of zero variations.
It follows several irregular paths o of the north polar regions
What is the maximum possible value of dip caused by the vertical component of terrestrial magnetism?
90 degrees
What is density altitude?
It is pressure altitude corrected for non standard temperature
What is QFF and QNE?
QFF - pressure observed at the airfield datum reduced to sea level using ambient conditions
QNE - height indicated upon touch down with Standard pressure setting applied 1013.25
What is TAT and SAT? When are they equal and what is their relationship with an aircraft in flight?
Total air temperature - static air temp + ram rise
Static air temp - the actual temperature of the air
TAT > SAT UNLESS airspeed is zero where TAT = SAT
What is the formula for temperature error correction and what is its datum?
TEC = 4x(height/1000)xISA DEV
temperature error correction is the correction applied to give a true altitude due to the ambient temperature conditions being higher or lower that ISA
How is Mach number calculated? What does Mach number compensate for?
The Mach no indicator is susceptible to compressibility error.
Mach can be calculated by: TAS/LSS
What is the rule of thumb for getting a rate of descent on a 3 degree glide slope approach?
ROD = ground speed x 5
If the glide slope differs from 3 degrees the ROD can be calculated by:
5 x ground speed x (theta/3)
With CAS constant and the temperature reducing, what occurs to TAS?
TAS decreases with decreasing temperature and increasing air density (due to colder air)
Remember ECTM:
Climbing:
-ECTM+
Descending:
+ECTM-
How do you calculate a height above a navigational marker with a known distance from a touchdown point and a threshold?
Touch down = theta x (distance(ft)/60)
Threshold = touchdown + 50 ft
What is the gradient of slope and what is the relationship between glide angle?
Slope gradient is the vertical rise divided by The horizontal run. Therefore, the altitude difference(ft)/ ground distance(nm).
Given a gradient in ft/nm you can work out the gradient percentage which is the alt (difference(ft)/ground distance(ft))x100. This has a direct relationship with glide angle and is 0.6
On a lamberts chart rhumb lines are?
Curves convex to the equator
Remember on a lamberts that parallels of latitude are curves concave to the pole which is also convex to the equator
When plotting on a Mercator chart in temperate latitudes to and from radio bearings what must be done with convergency?
Half the convergency must be applied to radio bearings to make them straight lines on the chart.
Radio bearings are great circles which appear as curves on a Mercator chart. As curves cannot be plotted they must be converted to the equivalent straight lines, which on a direct Mercator is a rhumb line. Conversion angle must be added or subtracted
Great circles always lie on the poleward side of a rhumb line. True or false?
True
On any chart the great circle always lies to the polar side of the rhumb line and they never reverse this on any chart.
A good example is London to Tokyo - it would fly over the pole (great circle) whereas Japan lies almost due east (Rhumb line)
In which direction are true bearings measured?
Clockwise from North!!!
An aircraft at a constant indicated altitude flies into a colder air mass. What will the altimeter indicate?
It will over read because the air mass is colder more dense and if you remember TEC will decrease with a lower than ISA temp therefore, the altimeter will OVER READ and believe it is higher than true altitude
What is the outside air temperature at FL390 if the environment is ISA+5 degrees C?
FL390 ISA = -56.5 (temp is constant above FL360 at -56.5)
FL390 OAT = ISA+5 therefore, -56.6 +5 = -51.5
What are the common conversion rates between volumes: litres, imperial gallons, USG. Mass: lbs, kgs and distance: nm, and km?
Volume:
1 Imp Gallon = 1.2 USG = 4.54 litres
Weights and volumes:
4 litres is approximately 10 pounds in every gallon and is 1 litre is approx. 1 kg.
Distances:
1nm = 1.852km =6080ft
The time at which the shortest period of night time occurs is called what?
Summer solstice
The summer solstice occurs exactly when the Earths axial tilt is most inclined towards the sun at its maximum of approx 23.5 degrees. This is the day at which the longest amount of daylight occurs
During he apparent solar day, the Earth rotates by how much?
A bit more than 360 degrees
Earth rotates 360 degrees in a sidereal day. 2 passages of the sun over the same meridian is referred to as an apparent solar day. The earth is a prograde planet (rotates round its polar axis) - the sidereal day is always less than apparent solar day because of the rotation around the ecliptic and over the same meridian would take a little longer therefore more than 360
In the norther hemisphere winter the sun does not rise for some time at latitudes above what?
66.5 degrees north
The sun is below the horizon for 24 continuous hours at least once per year. This occurs at the winter solstice.
When does morning and evening civil twilight start and end?
Morning - 6 degrees below the horizon and ends at sunrise
Evening - from sunset until the sun is 6 degrees below the horizon
Where is the Tropic of Capricorn and cancer?
Cancer - 23.5 N
Capricorn - 23.5 S
What are the reasons for the seasonal changes in climate?
Because the earths spin axis is inclined to the plane of its orbit round the sun
The seasons are caused by the change in declination (celestial latitude) of the sun due to the tilt of the spin axis compared to the plane of the earths orbit
What are the approximate dates of the perihelion and aphelion?
Perihelion - 3rd Jan
Aphelion - 4th July
The main reason that day and night throughout the year have different durations is due to what ?
Inclination of the ecliptic to the equator
The changing length of a day is caused by the change in declination of the sun due to the inclination of the spin axis compared to the plane of the earths orbit (ecliptic)
At what times of the year does the length of the hours of daylight change most rapidly?
Spring (vernal) Equinox and Autumn Equinox
The rate of change of the length of daylight depends on the rate of change of declination (latitude) of the sun. This will be most rapid as the sun crossed the equator at the equinoxes.
What is the definition of a meridian and their direction of travel?
Meridians are straight lines connecting the poles. It is half a great circle which is completed with its anti meridian. All meridians run in true direction from south to north. It will change direction by 180 degrees when it crosses a pole
An aircraft is lined up on runway 05, which is aligned with magnetic bearing of 047M. In order to comply with maximum permissible deviation errors, the DRMC readings should be between?
+- 10degrees
Therefore, 037/057
On an oblate spheroid representing the earths shape, 1 min of arc along the equator measures is longer of shorter are northerly or southerly latitudes?
The ratio of elipcity is 298:297 I.e. At the equator 298 and 297 stretching to the poles. Therefore, 1 min of arc along the equator measure a greater distance than 1 min of arc along the meridian at a latitude of 45 N/S
By the term transit of a heavenly body what does this mean?
The body is passing the meridian of the observer or another specified meridian
What projections surfaces maybe used in the production of charts?
Plane
Cylinder
Cone
There are also projections purely produced mathematically rather than based in geometric projections
On a lambert conformal conic chart Earth convergency is most accurately represented where? How does scale vary with latitude?
Chart convergency = earth convergency at the POO
Scale varies with the secant of latitude and is NOMINALLY correct (same as scale of the globe/reduced earth) at the standard parallels
What are transverse Mercator projections used for?
Direct Mercator - equatorial regions
Lamberts - extensive East/West coverage
transverse Mercator - extensive North/South coverage e.g. Ordnance survey mapping
What does a large scale mean?
Large scale = 1:25000 - 1cm = 250m therefore lots of good details
Small scale = 1:500000 - 1cm =5000m therefore less detailed
What happens when the pressure of the atmosphere decreases over night, with a higher pressure setting on the altimeter, what will it read (at sea level)?
The altimeter will read the height of the pressure change - it will have climbed
In what conditions, does the altimeter over and under read?
Hi - Low: look out below - altimeter will over read, if unchanged
Low - Hi: plenty of sky - altimeter will under read, if unchanged
Warm air mass - cold air mass: look out below
Cold air mass - warm air mass: plenty of sky
What are the direct reading compass acceleration/ turning errors?
UNOS - undershoot north, overshoot south
Northern hemisphere:
Accelerate on an easterly heading, this will indicate a decrease
Accelerate on a westerly heading, this will indicate an increase
Southern Hemisphere:
Accelerate on an easterly heading, this will indicate an increase
Accelerate on a westerly heading, this will indicate a decrease
