Pilotage – is Navigation by reference to landmarks only.
Dead Reckoning – Navigation by use of pre-determined vectors of wind and TAS and pre-calculated headings Groundspeed and on the basis of these information calculated estimated time of arrival.
Radio Navigation – Navigation by Radio aids.
Celestial Navigation – Navigation by measuring angle to heavenly bodies, (Sun, Moon and Stars) to determine the position on the Earth.
Inertial Navigation – is Navigation by self-contained airborne gyroscopic equipment or Electronic computer that gives a continuous display of A/c position.
Dip – The earth’s magnetic lines of forces are horizontal at the equator but becomes vertical towards the poles. This causes the compass to tend to DIP or bend or go vertical in higher latitudes.
Dip must be corrected or compensated for in a compass during construction.
DIP is the angle of tilt a freely suspended magnet makes with the horizontal plane.
Magnetic Variation/Magnetic Declination – Angle between Magnetic and true North or meridian.
Agonic lines – No variation/Zero Variation.
Isogonics lines/ISOGONALS lines means Equal Variation
Deviation – Magnet mounted in simple direct reading compass do not point directly in the direction of magnetic North, but, due to the influence of magnetic fields associated with the airframe metal and engine, deflects slightly to what is known is COMPASS NORTH.
DEVIATION – is the Angle through which the compass needle is deflected from the magnetic meridian/ NORTH.
(GHA) Greenwich Hour Angle – of a heavenly body is the angular distance between the Greenwich Meridian and the meridian of the body. It is measured westward through 3600.
The Declination of a heavenly body is its angular distance between North or South of the Celestial equator (hence it corresponds to latitude), in degrees and minutes North or South of the celestial equator, it is same as latitude.
(SHA) Sidereal Hour Angle – of a star is the angular distance between the First point of the Aries and the meridian of the star measured westward from Aries through 3600.
First Point of the Aries (Y) – is also known as Vernal Equinox, is a point on the celestial equator arbitrarily chosen as a reference point from which to measure the hour angles of the stars.
(LHA) Local Hour Angle – of a heavenly body is the angular distance between your meridian and the meridian of the body, measured westward.
It is the algebraic sum of GHA of body and your longitude.
Sub Stellar Point is bringing (thinking/assuming) the heavenly body from the sky to earth, Since it is easier to measure the hour angle of the heavenly bodies, when they are assumed to be on the Earth.
Therefore we can say that the Sub Stellar Point is a point on the surface of the earth directly beneath the heavenly body.
Convergency – Angle which one meridian makes with the other on the Earth near either poles. At equator there is no convergency between meridians.
On VFR Navigation Charts and VFR terminal charts an elevation legend is printed to show what color are used for different locations. It is also called HYPSOMETRIC Tint Scale.
Relief is used to represent the elevation above sea level. It is shown by contour lines, layer tinting and spot lights.
Contour lines are used to show equal elevation above mean sea level. The closure the contours, the steeper is the slope of a hill or valley. The highest spot (elevation of hill etc) on a particular map is represented by the largest size of numerals and the numerals are boxed with the layer tinting removed with in the box.
The highest elevation is also indicated on the white border of the chart, with its geographical co-ordinates.
ISOGONIC lines – – – – – – – – – – – REPRESENT Equal Variation
Albedo – is the refraction of the light due to the clouds reflecting light in the sky.
Meridian and Equator are Great circles and Rhumb lines.
Earth is an Oblate Spheroid.
A Great Circle cuts Earth into 2 equal parts. Smaller arc of a great circle shows shortest dist between 2 points.
Heading must be changed at frequent intervals to enable the a/c maintain Great Circle route. All parallel of latitudes are Rhumb lines.
Parallel of latitudes are small circle whose plane is parallel to the plane of Equator.
Meridians are Semi – Great Circle joining the poles.
A Meridian and its Anti-Meridian makes one Great Circle.
Graticule – is a network of meridians and latitudes.
Latitude – is an angular dist along meridian measured from Equator in degrees 0° to 90° North or South of Equator.
Longitude – is an angular dist along Equator measured in degrees from Prime Meridian 00 to 1800 East or West of Prime Meridian.
Position can be shown by 3 ways
(i) Latitude and longitude of place.
(ii) Name of the place.
(iii) Bearing and Distance from the place.
Nautical Mile (N.M) – is the length of on arc which subtends on angle of one minute at the center of the Earth.
Length of N.M. is not constant. It is smaller at Equator and is bigger at Poles.
At Equator 6048”
At Poles 6170”
Therefore average length is taken as 6080 feet, which is at 47°30” North/South.
Statute Mile (S.M) – is a arbitrary distance when length is decided by the British law.
1 Statute mile = 5280 feets.
Kilo Meter (K.M) -. 1/1000 feet part of average dist between Equator/ either Pole.
In aviation why n.m. is used and not k.m. or S.m..
It is easier to convert N.M. into dist in terms of lat and long and vice-versa.
Going around Equator you will cover so many n.m. 360 X 60 = 21,600 n.m.
True North – Direction of geographical meridian from a place.
Magnetic North – Direction/North indicated by a freely suspended magnet.
Variation – is the Difference between Magnetic North and True North.
Maps give True directions, while flying a/c Compass gives magnetic directions. Therefore you need to convert one into another.
Isogonal – are lines joining place of equal Variation (In India Survey of India does this surveys). As we go towards higher latitude, value of variation increases.
Compass of a/c is affected by magnetic field of the aircraft.
Compass North – North indication by the Aircraft compass.
Deviation – Angular difference between Magnetic North and compass North, measured in degrees East or West of magnetic North.
Poles are two end of axis of rotation of the Earth.
Distance between two meridians is maximum at Equator and it decreases as we go towards the poles.
The distance between meridians decreases as we go higher and changes @ Cos latitude.
The distance between meridians is maximum at Equator and this is called Departure.
Departure is distance between 2 meridians in N.M. measured in East or West direction along a parallel of latitude.
Convergency – is the angle of inclination between two meridians on the Earth.
Convergence – is the angle of inclination between two meridians on a projection.
Conversion Angle – is the angular difference between direction of the Rhumb line and Great Circle between two places.
Conversion Angle = ½ Distance Longitude × Sine Mean Latitude
Convergency = Distance of Longitude × Sine Mean Latitude or
Convergency = 2 C.A.
The tracks on Jeppesen charts are Great Circle tracks and distances are Great Circle distances, they are different from the Rhumb lines tracks and distances.
Tracks given on Jeppesen charts are Magnetic tracks.
Movement of Earth is as follows:
(i) Rotation
(ii) Revolution
Velocity of Earth is not constant it is fastest when Earth is closest to the Sun and is slowest when Earth is farthest from the Sun.
4th Jan Perihellion – Earth closest to Sun.
4th July Aphellion – Earth farthest from Sun.
Apparent motion of Sun – is Imaginary motion of Sun around the Earth.
Perigee – Point where Sun is closest to the Earth.
Apogee – Point where Sun is farthest from the Earth.
Axis of plane of rotation of Earth is inclined at on angle of 66½ etc, plane of rotation. Therefore, Sun is never overhead a particular lat. Sun is overhead only with in 0 to 22° ’30” North or South latitude.
100- 66½ – 23½
Above 23° 30” North and Below 23° 30” South of latitude Sun is never overhead.
0- 23½ North or South lat Sun is overhead twice.
Above 23½ North or South lat Sun is overhead only once.
Seasons are caused by the inclination of the earth, because this causes Sun to be not overhead the some place throughout the year.
It varies between 23° 30” North and South.
Perigee and Apogee are used in consideration when considering orbit of Sun around earth.
Perhellion and Aphellion are used when considering orbit of Earth around the Sun.
21st June – Summer Solistice is the Longest Day, it occurs when the Sun is at 23° 30” North.
22nd December– Winter Solistice is the Longest Night, it occurs when the Sun is at 23° 30” South.
Winter in Northern Hemisphere Summer in Southern Hemisphere.
Winter in Southern hemisphere is more severe than in Northern hemisphere. Therefore, size of Antarctica in Southern Hemisphere is more than Arctic Ocean in Northern Hemisphere.
21st March – Spring Equinox Day = Night, it occurs when Sun is at Equator.
22/23rd September – Autumn Equinox Day = Night, it occurs when Sun is at Equator.
Equinox = Day and Night are equal.
First point of Aries is a point in the space, when Sun crosses equator.
E.g. 21 March- Sun moves from Southern Hemisphere to Northern Hemisphere.
Sun is overhead Equator and between 23° 30” North and South twice a year. Sun is overhead 23° 30” North and South once a year.
At Madras 13° 00” North- twice
At Bombay 19° 10” North – Twice
At Delhi 28° 00” North- Never
Rotation of Earth about its own axis gives rise to Day and Night.
(i) Sidereal Day is measured with reference to a fixed point in the space. (First point of Aries).
(ii) Apparent solar Day is measured with reference to True Sun.
(iii) Mean Solar Day is measured with reference to Mean Sun.
Mean Sun / Imaginary Sun is considered as a Sun, which goes around the Earth at a constant velocity.
First point of Aries has a very small westward motion therefore a Tropical year is smaller than a Side Real year.
Tropical Year Duration- 365 days 5 hours 42 minutes and 48 seconds.
We use Tropical Year, because it is related to the seasons.
Seasons will come at a fixed time year after year because Tropical year is cal with reference to a fixed point of Aries, whose movement is related to the movement of the Sun, which causes Seasons.
A Civil Year has 365 days. Every 4th year is a Leap year it has 366 days but every 100th year is not a Leap year but every 4th century is a Leap year.
| 1600 | 1700 | 1800 | 1900 | 2000 |
| Leap / Year | X | X | X | Leap Year |
Century ÷ 400 is a Leap year.
When Sun is overhead your Meridian it is 1200 hrs LMT. When Sun is overhead your Anti Meridian it is 2400/0000 hrs LMT.
0000 means End of Previous Day or Start of New Day.
Earth rotates in a Easterly direction, therefore Places in East Zone are ahead in time.
Places in West are behind in time.
GMT/UTC- Universal Time Co-ordinated.
UTC is LMT of Greenwich Meridian.
The World is divided into different time zones according to their Longitudes.
Indian Standard time is taken from the Allahabad, which is located at 82° 30” East
On calculating we get 82° 30” ÷15 = 5½ hours, since it is in the East direction it is ahead of UTC.
In Northern Hemisphere, In Summer Sun rises early and sets late therefore day becomes longer.
Day Light saving time is a procedure adopted by the countries at higher Latitudes to utilize the Day Light time to maximum.
The countries located at higher Latitude follow D.S.T. during which they reduce the time difference from UTC by 1 hour in Summer.
This is usually done between 1st April to 30th September and is notified.
e.g. Difference between UTC and IST become 5½ hour-1 = 4½hours
UTC = 0300 I.S.T. 08.30
D.S.T. but UTC= 0400 I.S.T. 08.30
Moon takes 29½ Days to go around the Earth.
Geo-Stationary – Stationary with reference to a fixed point on the Earth.
Waning – Moon increasing in size.
Waxing – Moon decreasing in size.
Moon has four cycles. In 1 and 2 cycles Moon is Waning and in 3 and 4 cycles Moon is Waxing.
This cycle of moon takes 24 days.
Every day Moon rises or sets 50 minutes late, therefore in a day in a month, there is no Moon rise and one day when no Moon set is visible.
This phenomenon gives rise to a Full Moon day.
On a full Moon day, Moonrises at Sun set, because on a Full Moon day Sun and Moon are 1800 apart from Earth.
i.e. When Sun is on Western horizon Moon will be on Eastern horizon ( because all bodies rise from East) When moon rises Sun can be seen on Western horizon setting.
On a new Moon day the Moon rises at the same time as Sun rises but we cannot see it but Moon does rise.
Why does Moon rise/set late every day by 50 minutes, because direction of rotation of earth about its axis and direction of revolution of Moon around Earth is same.
This is also known as the RHETROGRATE period of Moon
Difference between the Maps & Charts
Maps – Maps has Geographical features.
Charts – Charts are made for a specific purpose and has less Geographical features.
Relief – Relief means high features on a Map/Chart. It is shown by following.
(i) Contours– Contours are lines joining places of equal Elevation on a given map. Contours are always numbered towards higher side. When contours are closer together hill is Steep and when they are far the hill is Shallow.
(ii) Spot Height reads *2200, and gives the exact location and elevation of the hill.
(iii) Layer tinting – Higher places are shown by darks colors.
(iv) Hachure – Hachure are tilted lines towards high features.
(v) Hill Shading – A part of the map is shaded off. Light is presumed to come from one side and the area next to the hill (shadow) is shaded.
Civil twilight – 6o Sun below the horizon.
Astronomical twilight – 18o Sun below the horizon.
Nautical twilight – 12o Sun below the horizon.
Graticule is a network of Meridians & parallel of Latitudes on the Earth.
Latitude is the angular distance along Meridians, measured in degrees “North” or “South” from the Equator.
Longitude is the angular distance along Equator, measured in ‘East’ or ‘West’ degrees from the Prime Meridian (Greenwich, London).
The Earth is not a perfect sphere.
If Equator diameter – is 300 nm, the pole diameter is 299 nm.
Actually Equatorial diameter is 12,748.6 km.
Polar diameter is 12,705.6 km
All Maps & charts are based on assumption that Earth is a perfect sphere because the error is negligible.
Distance between Equator & North Pole is 10,000 km, Therefore one km. is 1/10,000 part of average distance between Equator & either pole.
Dist. in nm between Equator & North Pole is 5400 nm, because 90 x 60o = 5400 rm.
ONE Nautical Mile is length of an arc which subtends an angle of one minute at the centre of the Earth.
Ground position is position of A/c on ground directly beneath the A/c.
Pin point is ground position of A/c obtained by direct visual references to the ground.
Fix is ground position of A/c obtained by other means than visual references to the ground.
Dead Reckoning is ground positioning of A/c, calculated by known data of flight.
It is only an estimated position.
Air position is ground position of A/c not affected by wind velocity.
The winds at upper levels are given in True direction.
Ground speed is speed of A/c with relation to the ground.
Earth has 2 motions.
1) Rotates about its axis.
2) Rotates around the sun.
The rotation of Earth on its own axis causes day & night.
The movement of Earth around the sun causes the seasons.
The rotation of earth on its axis causes measurement of the Time.
1 day consists of 24 hours.
When Earth completes one revolution around the Sun we say 1 year has passed
1 year = 365 ¼ days.
Because of this ¼ day after every 4 years there are 36 days, which is called Leap Year.
But every century is not a Leap year, Century divided by 400 is a Leap year.
2000 was a Leap year, 2100 2200 2300 were not a leap year, but 2400 is a Leap year.
12.00 LMT – when sun is overhead your Meridian
00.00 LMT when sun is overhead your Anti-Meridian.
The time is measured from Prime Meridian in a clockwise direction manner from 0000 hours to 2400 hours.
UTC = Universal Time Coordinated
Places east of Prime Meridians are ahead of UTC.
Places west of Prime Meridians are behind of UTC.
The Whole World is divided into 24 time zones 326 ¸ 24 = 15o.
Each zone is 15o of longitude wide.
Orthomorphic projection – Bearings are shown correctly (directions) Two properties of Orthomorphism.
(1) Meridians & Parallels of latitudes should cut each other at 90o.
The scale in vicinity of Equator point in all directions should be same.
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