General Navigation Flashcards
Polar diameter vs equatorial diameter
Polar diameter is 23NM less than equatorial diameter
Geoid definition
The shape the Earth would take if it were entirely ocean, ignoring tides and winds.
Value for compression of the Earth
0.33% (=1/298)
This is used to calculate semi-minor from semi-major axis of earth (or vice versa).
Geoid Model for ICAO
World Geodetic System 1984 (WGS84)
This is the system used by USA and therefore GPS.
UK Ordnance Survey use OS36, France and Europe use other systems. Can cause lat long differences.
Inclination of polar axis to orbit around the sun
23.5 degrees
Quadrantal directions
NW, SW, NE, SE
Meridians
Semi-great circles connecting the two poles through a point on the equator.
Anti-meridian
The meridian which makes up a great circle along with a given meridian.
Graticule
The grid formed on a map or globe by the Prime Meridian, equator, meridians and parallels of latitude.
Identification of positions on globe relative to lat/long (units)
Great circle divided into 360 degrees.
Each degree divided into 60 minutes (‘).
Each minute divided into 60 seconds (‘’).
Geocentric vs Geodetic latitude
Geocentric is angle from centre of the Earth (spherical) to the point on the surface.
Geodetic draws a normal line at the point on the surface we are identifying and extends a line at 90 degrees to the equator. Since Earth is not a sphere this doesn’t join centre of the Earth.
Do we use geocentric or geodetic latitudes?
Geodetic latitude is used
Where is the biggest difference between geocentric and geodetic latitude?
At about 45deg N/S, difference of about 11.6 minutes of arc.
Latitudes of:
Tropic of Cancer
Tropic of Capricorn
Arctic Circle
Antarctic Circle
Tropic of Cancer: 23.5 deg N
Tropic of Capricorn: 23.5 deg S
Arctic Circle: 66.5 deg N
Antarctic Circle: 66.5 deg S
[Note 90 - 23.5 = 66.5]
Resolution of reporting of lat & long
At first level report degrees & minutes.
Then can go to decimal minutes (one DP).
Next level is minutes & seconds.
For further accuracy, one or two DP can be added to seconds.
Recall 1 minute = 1NM (latitude, or longitude only @ equator)
Great Circle Vertices
Northern and Southern vertex of a great circle are the most Northerly and Southerly points on that great circle.
Calculating track angle and latitude of great circle intersection with equator, given Northern or Southern vertex.
Intersection latitude: 90 degrees either side of the latitude of vertices.
Track angle: 270 + longitude, 90 - longitude [one may need a reciprocal depending on direction across intersection]
Rhumb line
Curved line on surface of the Earth which intersects all meridians at the same angle (so parallel to parallels of latitude).
Appears straight on a mercator chart, but in reality is not the shortest distance between 2 points.
Note a meridian is also a rhumb line (intersecting at zero degrees).
Definition of km
1/10000th of average distance between equator and pole.
i.e. earths circumference is 40,000km
ICAO nautical mile definition
1852m
[Note 852 is line down middle of calculator]
Standard Nautical Mile definition
6,080 feet
Circumference of Earth
40,000km
360*60 = 21,600NM
Real length of nautical mile at equator and poles
Due to geodetic measurement of latitude, 1NM is shortest at the equator (6,048ft) and longest at poles (6,108ft).
How variation is stated
Degrees E or W (and minutes) from true North
Isogonal
A line on surface of the Earth joining points of equal magnetic variation
Points of maximum variation
180 degrees when in between the true and magnetic poles (either North or South)
Agonic Line
Line of zero variation
2 of them, together with lines of maximum (180deg) variation between true and magnetic poles, create a full circle around the Earth.
Regular changes in variation over time (3)
Secular: Long term movement of magnetic poles
Annual: Sinusoidal, due to orbit of Earth around the sun
Diurnal: Sinusoidal, due to ionosphere height, up to 0.1deg change over day.
Unpredictable changes in variation over time (2)
Solar activity: Due to 11 year cycles of solar activity. Solar flares are predictable but impact on Earth is not. Has impacted variation by up to 7 degrees.
Local anomalies: Due to rock deposits and local magnetic phenomena. Small enough effect to ignore.
Directive Force
The horizontal component of magnetic force which is useful in determining direction of magnetic north.
Dip angle
The angle between horizontal and the magnetic force experienced by compass
Isoclinals
Lines on a map joining locations of equal magnetic dip
Aclinic lines
Isoclinals joining places with zero dip (the point on earth where compass is most accurate, as directive force is strongest and dip is weakest).
Deviation
The angle between direction indicated by compass needle and the direction of magnetic north (direction defined as from magnetic north to compass north).
Direction can be defined W or E, or alternatively - or +.
Vertical card compass
- description
- aka
AKA B-type or E-type
1 of the 2 types of direct reading compass
Circular compass card attached directly to magnet assembly, suspended in liquid.
This is the typical light aircraft compass.
Grid Ring compass
- description
- aka
AKA P-type
1 of the 2 types of direct reading compass.
Accurate, but bulky and expensive, has damping wires which give greater periodicity.
Can only be measured in S&L flight when grid ring is unclamped.
Features required for direct reading compass
- Horizontal
- Sensitive
- Aperiodic
Horizontality of compass
- How it is achieved/increased
Achieved by being “pendulously suspended”, i.e. hung from a higher point so that the weight of the magnet offsets the effect of dip, reducing tilt to about 2 degrees.
Sensitivity of compass
- How it is increased
Length of magnets is restricted so use 2, 4 or 6 short magnets, or circular magnet made of an alloy with high magnetism.
Also reduce friction by using iridium-tipped pivot in jewelled cup, lubricating the pivot with the compass bowl liquid and reducing the magnets effective weight due to the liquid.
Aperiodicity of compass
- What is it?
Compass needs to be “dead beat”.
Means that it settles down quickly after disturbance due to turbulence or manoeuvres.
Aperiodicity of compass
- How is it increased?
Several short magnets instead of one long one keeps mass central and reduces moment of inertia on turns.
Compass liquids primary purpose is as a damping liquid.
Grid ring compasses have damping wires.
Compass accuracy limit
CS-OPS1: +/- 10deg
Purpose of compass swing
1 - Observe deviations
2 - Correct/remove deviation as far as possible
3 - Measure residual deviation
Hard Iron Magnetism
(In relation to deviation)
Magnetic force at the compass position due to the aircraft, regardless of heading and not induced by external magnetic fields.
Hard Iron Magnetism
- Relationship with latitude
The magnetic force doesn’t change with latitude, however the resulting deviation does as the horizontal component of the Earth’s magnetic field reduces at higher latitudes. Thus the deviation effect of hard iron magnetism increases at higher altitudes.
Soft Iron Magnetism in relation to deviation
Magnetic force induced in the aircraft due to surrounding fields.
We focus on vertical soft iron (VSI) magnetism, induced by vertical component of Earths magnetic field.
[Note: Zero @ magnetic equator as no vertical component]
Soft Iron Magnetism
- Relationship with latitude
At increasing latitudes VSI increases due to effective increase in Z (vertical component) vs H (horizontal component) of earths magnetic force.
Thus max deviation = Z / H = tan(dip angle).
Soft Iron Magnetism
- Relationship with heading
This effectively creates a dummy magnet somewhere on the aircraft, which creates a sine wave impact on deviation as heading varies and its position moves relative to the compass and magnetic north.
A, B and C coefficients of correction of deviation
Coefficient A: Mechanical error due to lubber line positioning, corrected by adjusting compass body position.
Coefficient B & C: Corrections due to magnetic deviation forces acting on the compass. B measured on East/West heading, C on North/South heading.
RAM Rise
Difference between Total Air Temperature (i.e. measured) and Static Air Temperature (SAT) (i.e. real OAT) due to impact of compressibility, kinetic & adiabatic issues with measured OAT.
Roughly (TAS/100)^2 [TAS in kt], but use the blue part of CRP-5.
Calculating SAT/COAT from indicated OAT based on high speed (RAM rise)
True OAT (COAT) is less than indicated OAT
Use blue scale on CRP-5 to find the difference
Calibrated Air Speed (CAS)
AKA Rectified Air Speed (RAS)
IAS corrected for:
- Pressure (Position) error
- Instrument error
Equivalent Air Speed (EAS)
CAS corrected for compressibility error.
Deals with the fact that air density isn’t 1.225kg/m3.
Only relevant for TAS over 300kt, if below this figure don’t carry out a correction in test.
Which speed is “air distance” based on?
TAS
CRP-5: Compressibility correction
Set up for CAS conversion to TAS using airspeed window (altitude and temp).
If TAS > 300kt, use COMP. CORR. window, calculate TAS/100 - 3 (as indicated) and turn the correct number of divisions in COMP. CORR.
Now read off CAS against TAS again.
CRP-5: Mach to TAS
Line up mach number indicator in air speed window with temperature.
Now read mach number off inner ring against TAS in outer ring.
NOTE - DOES NOT DEPEND ON ALTITUDE/FLIGHT LEVEL!
CALC - TAS = MN x 38.95 x sqrt(K)
CRP-5: Indicated altitude to true altitude
Line up temperature and pressure altitude in the ALTITUDE window. Read off indicated altitude in inner window against true altitude in outer window.
NOTE: Indicated altitude = QNH, pressure altitude = 1012, use both here.
Density Altitude calculation
Can use CRP-5 but not accurate - Line up pressure alt and temp in the AIRSPEED window, read off the density altitude window.
Use Density Altitude =
Pressure Altitude + (ISA Deviation x 120)
CRP-5: Multi-drift winds
Take 3 estimates of drift @ 60 degrees to each other.
Centre the dot on TAS and select each heading, drawing a line along the relevant drift angle (e.g. draw over the 5 port line).
The 3 lines should cross together at a point you can measure using the wind section.
Note on 2 drift winds
This can be done reasonably accurately if estimating drift using VOR tracking (figure out the heading required to maintain VOR radial gives you drift).
Don’t get a third cut to confirm drift, but shouldn’t need it due to better drift estimates.
CRP-5: Combine multiple wind vectors
Plot first wind on grid section, with dot at zero. For next wind, set direction, line the first “x” up with the top line of the grid and count down the grid by appropriate speed. Keep going with all winds.
NOTE: Final speed needs to be divided by number of wind vectors (an average speed, not a distance)
Consequence of 1 in 60 rule on assessing height based on glide slope
Height = Glidepath angle x Distance to go (ft) / 60
[NOTE: If question refers to runway threshold, add 50ft to height]
Consequence of 1 in 60 rule on rate of descent based on 3 degree glide slope
For a 3 degree glide scope:
ROD (feet per minute) = 5 x Ground Speed (kts)
Other glide slopes adjusted linearly
[Change in speed calculations also just 5 x change in ground speed]
Convert glidescope degrees to %
Percentage glidescope x 0.6 = Degrees glidescope
Relative bearing
This is the bearing relative to your current heading, e.g. 270 is directly to your left, regardless of which direction you are headed.
Look out for this in triangulation problems.
Adjusting True Mach No to achieve different ETA
Calculate TAS from mach using CRP-5.
Calculate Ground speed using information given.
Difference gives you head/tailwind component.
Calculate desired new TAS.
New True Mach No =
Original TMN * (New TAS / Old TAS)
Relationship of EAS, TAS, CAS and Mach no with altitude (assuming one is constant)
ECTM (if one is constant, the ones to the left are decreasing with alt, to the right are increasing).
Except T&M together in isothermal layer, reversed in inversion.
Convergence
Angle of inclination between two selected meridians, measured at a given latitude.
At the equator it is zero as meridians all parallel at equator, at the poles it will be equal to the difference in longitude (imagine looking down on the pole, meridians initially head off at exactly their own longitude).
Calculation for convergence angle
Convergency = Change in longitude x
Sine (Latitude)
Using convergence angle to calculate change in heading during great circle track
Change in heading will be equal to the convergence angle between the two points.
As latitude is different between the two points use mid-latitude (this is a simplification, mean latitude is actually different).
Change in heading = change in longitude x Sine (mid-latitude)
Conversion angle
This is the difference between rhumb line track and great circle track between two points.
Rhumb line track never changes and we know the change in great circle track between two points (convergency).
Conversion angle is therefore half of convergency.
[Conversion angle at each end of the route adds up to make the full expected convergency over the route]
Departure
The distance between two meridians along a given latitude.
Departure (NM) = change in longitude (in minutes) x cos(latitude)
Conversions
- NM in feet
- 1m in feet
- 1 inch in cm
- NM to km
- 1NM = 6080 ft
- 1m = 3.28 ft
- 1 inch = 2.54 cm
- 1NM = 1.852km
Large scale vs small scale charts
Large scale - lots of detail, high representative fraction, BIG fraction, SMALL divisor (e.g. 1/50,000)
Small scale - low level of detail, small representative fraction, SMALL fraction, BIG divisor (e.g. 1/500,000)
Reduced Earth
The mini version of Earth (globe) reduced in size by a scale factor, which is used to make charts (using projections).
Perspective vs non-perspective charts
Perspective charts use geometric projections, whilst non-perspective charts use mathematical models.
Most used models are non-perspective but can be thought of as projections which are modified matematically.
3 types of projection chart
- Azimuthal/Plane: Simple projection of globe onto paper underneath, works @ poles
- Cylindrical: Project from light inside earth onto cylinder wrapped around it (touching at equator)
- Conical: Similar to cylindrical but touches at a higher/lower latitude.
2 ideal features of charts that can’t be achieved
- Scale can’t be constant and correct
- Shapes of large areas can’t be represented perfectly
However over small enough areas the errors in this can be manageable.
Orthomorphic or conformal charts
- 2 key features (ie benefits)
A chart where navigation bearings are correct, i.e. angles on the Earth must be represented correctly on the chart and shapes are shown correctly.
Essential for navigation charts, but a chart focussing on land areas may not have this property.
Conditions for chart to be orthomorphic (2)
1) Meridians and parallels must be at 90 degrees
2) At any point on a chart, scale should be the same in all directions, or should change at the same rate in all directions
What single characteristic of a chart means a straight line will approximate a great circle
Chart convergency = real world convergency [approximately]
The two orthomorphic conditions together achieve this.
Mercator chart
Adjusted version of the cylindrical projection which adjusts latitudes so that N-S changes in scale are same as E-W changes in scale.
Thus is a mathematically adjusted, non-projection chart.
Looks like the map of the world we are used to seeing.
Rhumb lines and great circles on mercator charts
- Impact on plotting
Since meridians of longitude are all parallel, rhumb lines are straight lines, great circles aren’t.
When plotting (e.g. position from VOR) we use straight lines. VOR information gives us great circle headings so need to convert these to rhumb to allow a straight line plot on mercator.
Mercator scale change
Meridians are shown as parallel so chart makes departure appear constant.
Need to adjust scale at higher latitudes based on true departure.
Scale @ latitude =
scale @ equator x (1/cos(lat))
[if scale = 1/500,000, do 500,000 x cos(lat)]
Secant
This is 1/cos(angle). Used in the mercator scale calculation, so that:
Scale @ latitude =
scale @ equator x secant(lat)
Accuracy of measurement on mercator map near equator
At 8 degrees from equator, scale is x 1/cos(8) = x 1/0.99 so 1% change in scale.
Thus measurements accurate to within 1% up to 8 degrees (c. 500NM) from equator.
Shape of mercator graticules
Rectangular
Great circles (on mercator) represented as concave or convex to the equator/nearest pole?
Great circles are concave to the equator (convex to the poles).
i.e. show the concave side to the equator
Standard parallel in conical chart
This is the parallel of latitude that touches the cone in the projection.
Scale expands either side of this latitude.
AKA parallel of tangency
Apex angle of conical chart
Angle of the triangle at the point of the cone.
Calculated as 2 x standard parallel latitude.
e.g. 60 deg latitude, apex angle is 120, creating a 180 triangle with 30 degrees at the base where cone is tangential with latitude 60
Arc of sector of conical chart
Conical chart is laid out flat by cutting up one median, leaving a circle with a chunk cut out.
The arc of the chart (or sector of the chart) is based on the latitude of the chart.
Arc of sector = change of longitude x sin(parallel of origin)
[for full 360 degree chart just sin(parallel of origin)]
Conical chart convergence
This is the same as the arc of sector (i.e. change in angle of medians over given longitude).
Chart convergence = change of longitude x sin(parallel of origin)
Constant of the cone
Represented by “n”, this is the sine of the parallel of origin.
Used to determine chart convergence over a given change in longitude.
Lambert Conical Chart
Brings the cone inside the reduced earth, so parallel of tangency now a parallel of origin (doesn’t touch the cone).
2 points where the cone touches earth are the standard parallels.
The scale contracts between the standard parallels and expands outside them.
One sixth rule
On lambert conical chart, upper standard parallel should be 1/6th from top of chart, lower standard parallel 1/6th of the way from bottom of chart.
This way scale is fairly regular over the whole chart.
Impact on cone angle, convergency (etc.) of lamberts conical (vs standard conical)
No impact, the cone is reduced in size (or pushed down), but shape is identical.
Lambert chart properties
- Orthomorphic?
- Angle of parallels to meridians
- Shape of rhumb lines
- Shape of great circles
- Yes, orthomorphic
- Parallels 90deg to meridians
- Rhumb lines concave to pole
- Concave to the parallel of origin, but only very little, can use straight lines in practice
Conversion angle on lambert chart
Conversion angle is based on Earth convergence, so:
0.5 * ch. long. * sin(mid lat)
DON’T use half of chart convergence.
Conversion angle at different latitudes on lambert chart
A straight line between two points is at an angle to the rhumb line of 1/2 chart convergence.
So @ parallel of origin this is equal to earth convergence and great circle is a straight line, but at other latitudes earth convergence is different and great circles are concave to the parallel of origin.
Mid-meridian on a lambert chart route
At the mid-meridian point of a route on lambert chart, all types of line between 2 given points (straight line, rhumb line, great circle) will be parallel to each other.
Scale error on lambert chart
Depends on how far apart the standard parallels are, the further apart, the less the accuracy.
UK CAA 1:500,000 chart covers 5 degrees latitude so only has 1% error.
Limit on lambert chart coverage to maintain accuracy
24 degrees total latitude, 16 degrees between the standard parallels.
Issue with plotting bearings on Lambert
Plotted straight line headings will correctly follow great circles.
However, heading will change along the line (just as in real life along a great circle), so it is critical to plot the line from the same position where heading is measured.
Plotting VOR, VDF, ADF/NDB and AWR on Lambert
Lambert great circle lines need to be plotted from the point of measuring heading.
VOR & VDF headings measured at the stations, so plot from there.
ADF & AWR headings measured from aircraft, so plot from there.
Converting Lambert headings from point heading is measured to another point
Difference will be based on chart convergence between the two points.
Draw a diagram of the lines to figure out whether to add or take away.
Need to draw a dummy meridian line at the same angle as at the origin point at the new point.
Co-latitude
= 90 degrees - latitude
Polar Stereographic chart
Projection from the pole itself onto a flat piece of paper under the other pole. Creates a circle covering up to the entire hemisphere, with straight line meridians and concentric circles for parallels of latitude.
Polar Stereographic scale
Correct at the pole it touches.
Elsewhere expands at the rate of sec^2(0.5 x co-latitude)
[secant squared of half the co-latitude]
Polar Stereographic scale accuracy
@ 78 latitude, scale is a factor of:
(1 / cos( (90-78) / 2 ) )^2 = 1/0.989
So around 1% accuracy down to 78 latitude (down to 3% at 70 latitude)
Polar Stereographic chart properties:
- Orthomorphic?
- Angle of parallels to meridians
- Shape of rhumb lines
- Shape of great circles
- Yes, orthomorphic
- Parallels 90 deg to meridians
- Rhumb lines concave to pole
- Great circles concave to pole (less so than rhumb lines)
Polar Stereographic chart convergence
Basically a special case of lambert conical with n = 1
So = change in longitude
Polar Stereographic chart
- Angle between great circle and straight line for track over pole
Great circle over the pole is a straight line.
Polar Stereographic chart
- Angle between great circle and straight line @ lat 70 for 90 degree longitude change
Straight line to rhumb line angle is 1/2 chart convergence = 45 degrees.
Rhumb line to great circle is conversion angle =
1/2 x change in long x
sin(70) = 42.3 degrees
This 2.7 degree error is acceptable, so down to 70 latitude can take great circles to be straight lines.
Polar Stereographic chart
- Calculations (e.g. track on great circle)
Great circles taken to be straight lines.
Draw the circular chart (NH draw meridian from bottom of circle to pole, SH draw meridian from pole to top of circle, that way East is always on the right).
Draw in the points and the track between them, use geometry of triangle with the pole to determine angles.
REMEMBER: Answer will be TRACK, not the angle in the triangle!
Gyro error factors (3)
- Real drift: 1/100th of a degree per hour for INS, 1/10th of a degree per hour for DG mode. Small enough to ignore.
- Earth rate: Due to gyro syncing to a fixed point in space, error factor is 15 x sin(latitude) / hour
- Transport Wander: Essentially convergence
Gyro adjustment for grid navigation
Real drift can be ignored. Transport wander can also be ignored as we want to keep a static version of north in grid navigation.
Therefore only need to adjust for earth rate.
Polar grid navigation:
Grid North used in NH & SH and convergence at longitudes
Use Greenwich meridian as grid north in both hemispheres.
In NH, convergence is negative of longitude.
In SH, convergence is equal to longitude.
Types of bearing you can be given (Q codes)
Fix vs pinpoint
Fix: Position determined from radio aids
Pinpoint: Position found by map reading
VOR bearings true or magnetic?
Magnetic so they can be easily utilised by pilot in flight
Margin to add to MSA (Minimum Safe Altitude) for flight
Below 5,000ft - 1,000ft
Above 5,000ft - 2,000ft
Viewed from North Celestial Pole, what is the orbit of Earth around the sun (shape and direction)?
Anticlockwise
Elliptical
Kepler’s first law
Orbit of each planet is an ellipse with the Sun as one of the foci
Kepler’s second law
The line joining the planet to the sun sweeps an equal area in an equal amount of time.
Thus the planet has to go faster when it is closest to the Sun.
Kepler’s third law
The square of the time a planet takes to orbit the sun (sidereal period) proportional to the cube of mean distance from the sun.
Square of time (ST)
Cube of distance (CD)
Perihelion & Aphelion
Perihelion - When sun is closest to the earth (app. 4th Jan)
Aphelion - When sun is furthest from the earth (app. 4th July)
Approx dates in NH:
Summer Solstice
Autumn Equinox
Winter Solstice
Spring (Vernal) Equinox
approx.
Summer Solctice: 21st Jun
Autumn Equinox: 21st Sep
Winter Solstice: 21st Dec
Spring (Vernal) Equinox: 21st Mar
Plane of equinoctial
Plane of elliptic
Their angle through the year
Phrase for this
Plane of equinoctial is the plane of the equator. Plane of elliptic is the plane of the Earths path around the sun.
These two are at 23.5 degrees to each other AT ALL TIMES.
This is called the “obliquity of the elliptic”.
Analemma
The shape in the sky if you plot the midday position of the sun through the year. Roughly a figure of 8 (one loop much bigger than the other).
AKA Eliptic
Celestial sphere
Imaginary sphere around a planet. Can imagine all other celestial bodies as being projected onto points on this sphere.
Zenith
The point on the celestial sphere directly “above” a point on Earth. Above meaning opposite direction to gravity, opposite direction to the centre of Earth.
Declination of the sun
Analogous to the latitude at which the Sun appears directly overhead.
Follows sine pattern over the year.
Sidereal day vs apparent solar day
Sidereal day is as measured from a distant planet, time taken to see the same point again. Apparent solar day based on when the sun passes overhead and is slightly longer as the planet moves anti-clockwise around the sun so the planet needs to turn a little more to get the sun back overhead.
Mean solar day
- description
- max difference from apparent day
Because apparent days are affected by the earth going around the sun, length isn’t constant and varies through the year:
16 min max difference in November, second peak of 14 min in February
[between mean solar day and apparent solar day]
Mean sun
The mean sun is an imaginary sun travelling along the celestial equator at a uniform speed. Related to difference between apparent solar day (when the real sun appears overhead) and our adjusted mean solar day.
Sidereal year length
Tropical (seasonal) year length
Sidereal year: 365 days 6hrs
Tropical year: 365 days 5hrs 48.75 mins
Leap years
To maintain tropical year length have a leap year every 4th year.
But for centennials only if the first 2 digits are divisible by 4.
e.g. 2000 is leap, 2100 is not.
Hour angle
Measured as # degrees from a given meridian, refers to the angle at which a given object appears overhead.
e.g. something at Greenwich hour angle 270 is currently overhead longitude 090E.
Converting longitude to time
1 hour = 15 degrees
On calculator use [deg ‘ “] key to input longitude and divide by 15 to get hrs:min:sec
UTC
Universal time kept by nuclear clocks. Gets regularly corrected to line up with GMT so can be considered the same, but isn’t exactly.
Local Mean Time (LMT)
The exact local time based on longitude adjustment from UTC (Greenwich). Adjusts by minutes and hours, not just hours.
Standard time
A time period adopted by a given country or land area to allow standard time keeping across it.
Convert time when given time zone as (e.g.) UTC + 4 or UTC - 5.
Whatever the time is at Greenwich, UTC + 4 means add 4 hours.
So midday at Greenwich is 1600 at UTC+4, is 0700 at UTC-5.
Paris is UTC+1 as it is later there.
Summer time/Daylight Saving Time (DST)
Always add one hour to Local standard time.
International Date Line
Roughly at 180W/180E, the line over which date changes.
WESTBOUND => ADD A DAY
[DO NOT get confused between “Easterly” and heading to Eastern Hemisphere, they are OPPOSITE!]
Mnemonic for adjusting time for time zones
Longitude East => Greenwich least
Longitude West => Greenwich best
[Go through Greenwich (not international date line) to keep things simple!]
Sensible horizon
The horizon that can be sensed by instruments (e.g. spirit level), i.e. straight line tangent to earth at a given point on the surface.
Time between sunrise and sunset @ equator
12hrs 6 mins.
Extra 6 mins is due to the last edge of sun dipping below sensible horizon when the centre of the sun is 0 deg 50’ below (i.e. 3 mins of time).
Civil twilight
When sun (centre of it) is between 0 deg 50’ and 6 degrees below the sensible horizon.
Nautical and Astronomical twilight
Nautical: Sun at 6 to 12 degrees below horizon
Astronomical: 12 to 18 degrees
Definition of night
From end of evening civil twilight to beginning of morning civil twilight, or such period between sunset and sunrise prescribed by local authority.
Length of twilight at equator
Time it takes sun to move from 0 deg 50’ to 6 deg is easily calculated at equator:
5 deg 10’ => 21 mins
Twilight at high latitudes
There is a special case at high latitudes where the sun goes below the equator but not quite below 6 degrees.
So there is only one twilight in the middle of the night, between sunrise and sunset.
Marked in almanac with //////
Effect of altitude on sunrise/sunset/twilight
At altitude sunrise is earlier and sunset later as you are “looking around” the earth at the sun.
Twilight will be shorter as the refractive effect of the atmosphere is reduced.
Plotting symbols
- Pinpoint fix vs dead-reckoned fix
- Track made good
- Radio bearing or DME arc
ICAO chart colours
- Water features
- Built up areas
- Woods
- Contours
Water features: Blue
Built up areas: Yellow
Woods: Green
Contours: Brown
ICAO line symbols
- FIR
- ATZ
- CTR
- Advisory airspace (ADA)
- Uncontrolled route
Altitude to use as reference for calculations when climbing or descending
Climbing: 2/3 of alt between bottom and top of climb
Descending: 1/2 of alt between top and bottom of descent
[For WINDSPEED ALSO!]
Whiteout
When snow covers the ground and can’t be distinguished from the sky to be able to identify a horizon.
Rate of movement of magnetic north pole around geographic north pole
1 degree every 5 years
Heading correction, track error angle, closing angle
Heading correction = track angle + closing angle
