Navigation Flashcards
What shape is the Earth?
An oblate spheroid - not round although we assume it is
N.B. Flattened at the poles and bulges slightly at the equator due to rotation of the Earth
Define Great circle
A circle drawn on the surface of the Earth whose radius and centre are the same as the Earths
N.B. Examples are the equator and all lines of longitude. Great circles are the shortest route
Define Small Circle
A circle drawn on the surface of the Earth whose radius and centre are not the same as the Earth’s
N.B. Examples are all lines of latitude apart from the equator
Define Equator
A great circle whose plane is perpendicular to the Earth’s axis of rotation and which divides the Earth into two equal hemispheres
Define Meridian
A semi-great circle joining the poles. Lines of longitude (including prime meridian at 0º)
N.B. Geographic/True North and South poles
Define Rhumb Line
A regularly curved line on the surface of the Earth that cuts all meridians at the same angle
What are the names of the cardinal points?
- North - 000º/360º
- East - 090º
- South - 180º
- West - 270º
What are the names of the quadrantal points on a compass?
- NE - 045º
- SE - 135º
- SW - 225º
- NW - 315º
Distances along a great circle
1 minute = __________
60 minutes = __________
- 1nm
- 1 degree
Define Nautical Mile
The distance on the surface of the Earth along a Great Circle which subtends an angle of 1 minute of arc measured at the centre of the Earth
N.B. See Form of the Earth slides for examples in calculating the distance along the arc of a great circle
What is the circumference of the Earth?
21,600nm
N.B. Earth is 360º, 1 minute = 1nm, 1 degree = 60 minutes therefore 60nm, therefore 60 minutes x 360 degrees = 21,600nm
Define Kilometer
Generally accepted as one 10,000th of the average distance between the equator and either pole
What is a Foot (ft)
A unit of measurement that has no relationship with any Earth dimension. (Probably originated from Roman times) Used for vertical navigation
1ft = 0.3408m or 30.48cm
Conversions
- 1 nautical mile = __________km
- 1 nautical mile =__________ft (Mile high)
- 1 statute mile = __________ft
- 1 kilometre = __________ft
- 1 nautical mile = 1.852km
- 1 nautical mile =6080ft (Mile high)
- 1 statute mile = 5280ft
- 1 kilometre = 3280ft
Conversion Factors
- Feet to metres
- Metres to feet
- Nautical miles to kilometres
- Kilometres to nautical miles
- Nautical miles to statute miles
- Feet to metres = Feet x 0.3048
- Metres to feet = Metres x 3.2808
- Nautical miles to kilometres = Nautical miles x 1.852
- Kilometres to nautical miles = Kilometres x 0.5396
- Nautical miles to statute miles Nautical miles x 1.15
Comparisons
- 41 nautical miles ~ __________ km
- 41 statute miles ~ __________ km
- 41 nautical miles ~ __________ statute miles
- 41 statute miles ~ __________ nautical miles
- 41 nautical miles ~ 76 km
- 41 statute miles ~ 66 km
- 41 nautical miles ~ 47 statute miles
- 41 statute miles ~ 35.5 nautical miles
Which way does the Earth rotate?
Eastward or anti clockwise if viewed from above the North Pole
What is the tilt of the Earth?
23.5º
What causes seasons?
The Earths 23.5º tilt means that there is a resultant global heating differential throughout the year as the Earth moves around the sun. This creates seasons
At any point on the Earths surface, when the Sun reaches the highest point in the sky during any given day, the time is __________
Noon
N.B. Length of the day according to solar time is not the same throughout the year because apparent motion of the sun varies
Define Night
The hours between the end of evening civil twilight and the beginning of morning civil twilight
Define Civil Twilight
Civil twilight ends in the evening when the centre of the sun’s disc is 6º below the horizon and begins in the morning when the centre of the sun’s disc is 6º below the horizon
What is mean solar time and what sort of time is mean sun used to measure?
Based on the motion of an imaginary sun travelling at an even rate throughout the year
Used to measure:
- Coordinated Universal Time (UTC)
- Time Zone
- Local Time
What is UTC?
Coordinated Universal Time
- It assumes that the sun crosses the Greenwich Meridian at 1200 and uses a 24 hour clock
What is local time?
Clocks set to the same time within each time zone
N.B. Borders of time zones are bent to conform with international frontiers and the boundaries of regions within countries. It is convenient for a nation to use the same time all over, even if it stretches over several time zones
What is a time zone?
- Earth divided into 24 time zones which each cover 15º of longitude (1hr)
- Midday at 15º East longitude will be an hour
before Midday at Greenwich - Midday at 15º west longitude will be an hour
after Midday at Greenwich
N.B. 360/24=15
What is the International Date Line and where is it?
- An imaginary line on the Earths surface defining the boundary between 1 day and the next.
- Located half way around the world from the prime meridian (0º longitude) at 180º East or West of Greenwich - The reference point for time zones
- Sudden change of 24 hours takes place here. Travelling East becomes yesterday, travelling Westbound becomes tomorrow
N.B. Varies around the 180º to suit Russia, Alaska and some Pacific Islands
Define True North
The direction that points directly towards the geographic North Pole. A fixed point on the Earths globe
Define Magnetic North
- Magnetic North is the direction that a compass needle points to as it aligns with the Earth’s magnetic field
- The Magnetic North Pole shifts and changes over time in response to changes in the Earths magnetic core. It is not a fixed point
Define Variation
- The angle between Magnetic North and True North
- It is positive East of True North and Negative West of True North
N.B. Sometimes called magnetic declination
N.B.B. East is least, West is best!
Define Deviation
The angle between Magnetic North and Compass North measured in degrees East or West from Magnetic North
N.B. Compass deviation card in ACFT used to correct for this
How can True North be calculated?
See example below. True, Variation, Magnetic, Deviation, Compass (The Virgin Mary Does Cocaine) and in reverse (Cadbury’s Dairy Milk Very Tasty)
What does the accuracy of a compass depend on?
Manufacture and irregularities and fluctuations in the Earths Magnetic Field
What is are Isogonal?
Lines across a map joining points of equal magnetic variation
What is a Marginal Diagram?
Shows True North (TN) and Magnetic North (MN) and the angle between them. Below diagram shows a magnetic variation of 2º30W’’
What is a Double Compass Rose?
Another method of showing variation. It is a large compass rose aligned to TN and a smaller inset compass rose aligned to MN
What causes deviation error?
Induced by local magnetic fields, e.g. an ACFTs metallic structure and rotating parts generating their own magnetic field
N.B. Results in compass North. Deviation card to correct the error
What is Magnetic Dip/Inclination?
The angle made by a compass needle with the compass horizontal at any point on the Earths surface
N.B. Dip needle sits horizontally at the magnetic equator and dips towards the pole more with increasing latitude
What is an isoclinic line?
A line on a map connecting points where the dip in the Earths magnetic field is the same
N.B. Range of dip is from -90º to 90º. North end will point downward in the Northern hemisphere and upward in the Southern hemisphere
What is a DME?
Distance Measuring Equipment
Accurate slant range indicator that requires dedicated equipment on the ground and in the ACFT
How does a DME work?
- DME replies with the same train of irregular pulses it
receives but on a different frequency - to avoid 2 ACFT interrogating each other - Interrogator recognizes own original pulse train and
calculates time taken from transmission to reception - The pulse train varies unpredictably to distinguish it
from one transmitted from another aircraft - Increased working range due to two transmitters.
- Operates in UHF waveband
- Accurate to within 1nm and can accept 100 ACFT interrogations simultaneously
What sort of error is a DME subject to?
Slant error - the closer to the beacon, the less accurate the readings become
What are the uses of a DME? (6)
- Co-located VOR/DME stations provide range and bearing
- Provides positive ranges for ACFT flying the same track and interrogating the same DME, therefore ATC separation
- Co-location with precision approach aid, therefore accurate range from touchdown
- Enhances accuracy of holding patterns
- Suitable computer and DME, therefore accurate area navigation
- Military use for air to air refuelling
What is a VOR?
VHF Omnidirectional Range
- A system that automatically and continuously provides an ACFT with an accurate magnetic bearing from a beacon
- The principle is ‘Bearing by Phase Comparison’
- Operates in wave band 108 -117.95MHz
- Identified by either a 3 letter morse code or speech
- Line for sight - operating range depends on ACFT height
- +/- 1.25° accuracy
What 2 signals does a VOR use?
- Reference signal - transmitted omnidirectionally
- Variable signal - transmitted by a circular array of aerials around the reference signal antenna, simulating a revolving antenna
What is the cone of silence/confusion in relation to VOR?
- The VOR beacon does not transmit a usable signal vertically upwards
- The period during which the ACFT receives no signal increases with height
How many spot frequencies does a VOR operate using?
160
How is VOR displayed in the cockpit?
Radio Magnetic Indicator
The magnetic bearing of the beacon (QDM) is indicated by an arrow at one end of the VOR pointer. The radial (QDR) must be shown at the opposite end
What is an OBS and its forms?
Omni-Bearing Selector
- Earlier Form- Displays only VOR information, shows deflection left or right of pre-selected QDM, shows whether the ACFT is generally heading to or from the beacon
- Later Form - Shows all the same information as earlier but allows ILS to be used as well. Includes fail flag when no signal is being received
How does OBS work, VOR limits and approximate ranges and accuracy?
How it works
- The OBS is a “demand” instrument.
- The pilot selects a track that he wishes to fly with respect to the beacon, and the left/right needle then tells him which way to turn to acquire that track.
- It does not tell the pilot his current heading.
Limits and accuracy
- Limited to line of site
- Accuracy +/- 1.25º
Approximate ranges obtainable for reliable (protected) VOR operation
- 50nm at 1000ft
- 90nm at 5,000ft
- 150nm at 15000ft
- 200nm at 25000ft
N.B. VOR spaced between 50nm and 100nm to ensure low level coverage
What errors are associated with a VOR? (4)
- Site Errors - Poor beacon siting can produce reflected signals from high ground and buildings that can cause bearing errors
- Propagation Errors - Caused by uneven propagation over long distance or irregular terrain
- Equipment Errors - Caused by incorrect tuning or calibration
- Interference Errors - Limited number of available frequencies so some VOR frequencies are duplicated so there is a risk that a high flying ACFT could pick up more than one signal. Spaced about 500nm apart to try to avoid this
N.B. PIES
What are the uses of a VOR? (7)
- Homing to a station
- Maintaining track along an airway centreline
- Obtaining a position line
- Flying a holding pattern
- Flying instrument approaches with a suitable positioned beacon
- Obtaining a fix with two or more VORs
- Broadcast ATIS (Local Aerodrome information) and other information
N.B. HOMBOFF
What are the basic principles of air navigation?
What does successful air navigation involve?
- Piloting an ACFT from place to place without getting lost
- Not breaking the laws applying to ACFT
- Not endangering the safety of those on board or on the ground
What origin/datum are directions on the Earth made from?
The prime meridian
What is the most widely accepted method of indicating position on the Earth?
By reference to a graticule that covers the globe
Define Latitude
- Angular distance from the equator to a point measured northwards or southwards along the meridian through that point
- Parallels of latitude circle the Earth and are expressed in ºN and ºS up to a maximum of 90º
N.B. The UK lies between 50ºN and 59ºN
Define Longtitude
- The shorter angular distance along the equator between the prime meridian and the meridian through that point
- Expressed in degrees East or West of a reference - the prime meridian - up to a maximum of 180º
N.B. The UK lies between 7ºW and 2ºE of the prime meridian which passes through Greenwich in London
How are coordinates expressed?
- Latitude precedes longitude
- Up to 6 numbers for latitude and up to 7 for longitude
- Letters N and S follow latitude coordinates
- Letters E and W follow longitude coordinates
- See below for format in geographical terms
How are coordinates expressed in aviation terms?
- The letters N, E, S and W precede the coordinates
- The º and ‘ symbols are omitted
- 6 figure group used for latitude: the 1st 2 figures for whole numbers of degrees and the last 4 figures give minutes to within 2 decimal places. E.g. 19° 27’ 45” S = S1927.75
- 7 figure group used for longitude: 1st three figures for whole number of degrees, last 4 figures for minutes to within 2 decimal places. E.g. 029° 52’ 27” E = E02952.45
Examples of other methods of positioning reporting other than coordinates
- Using the names of published waypoints
- Using approved abbreviations for beacons
- VOR/DME stations provide constant information of positions in terms of range and bearing
What are ICAO codes?
4 letter code given to each airport based upon regions, country and then main airports and subsidiary airports
What are the common scales for ordnance survey maps? (2)
1:25,000 (Popular with walkers)
1:50,000 (Used by emergency services)
What are the accuracies of OS references using the national grid?
- 4 figure (accurate to 1000 meters)
- 6 figure (accurate to 100 meters)
- 8 figure (accurate to 10 meter)
- 10 figure (accurate to 1 meter) used by GPS
What are OS references used for?
- Combines Civil and Military Search and Rescue services over land (e.g. mountain)
- Airfield crash maps made available to Fire, Ambulance and Police
- Enables controller to give precise position of an accident
N.B. Think emergencies!!!
Define Ground Position and Bearing of an Object
- The position on the ground directly beneath the ACFT at a given time
- The horizontal direction of an object measured in degrees clockwise from the direction of North at the pilot’s position
How can ground position be determined?
Pinpoint - Identification by direct observation of the ground beneath
Fix - Use of bearings and position
What is meant by Dead Reckoning Position?
The assumed ground position of the aircraft based on calculation. Deduced from the forecast winds
What is an ADF?
Automatic Direction Finder
- Non-visual navigation device
- An older type of radio navigation equipment
- Also known as a radio compass and is a tuneable receiver inside the ACFT
- Indicates relative bearing to NDB in relation to ACFTs heading using a pointer on a Relative Bearing Indicator
How can True Bearing be calculated?
True Heading + Relative Bearing
What is a position line?
A line drawn on a chart along which an ACFT is known to have been at a certain time
Visual position lines are not practical, therefore radio aids are used
- What is Bearing Information provided by?
- What is Range Information provided by?
- What are position lines obtained by radio aids called?
- VHF Direction Finding (VDF), VHF Omni-Directional Radio Range (VOR), Automatic Direction Finding (ADF)
- Distance Measuring Equipment (DME)
- Radio position lines
What is a fix?
- The intersection of two or more position lines obtained simultaneously which provides ground position of the ACFT
- Typical combinations:
What is WGS84?
- The world geodetic system. It is the reference system for GPS/GNSS
- It is geocentric - based on the centre of the Earth
- Very accurate when combined with terrestrial data
- Globally consistent within +/-1 metre
What do charts show and what are they normally used for?
- Lines of latitude and longitude
- Coastal outlines
- Normally used for plotting
What do maps show and what may they be used for?
- Significant additional detail
- Topographical detail
- May be used for visual map reading
What is chart scale?
- The ratio between the chart distance and the Earth distance that it represents
- Scale = Chart Distance/Earth Distance
- The larger the scale denominator, the greater the distance shown, therefore less detail will be shown - Small scale
- The smaller the scale denominator, the smaller the distance shown, therefor more detail will be shown - large scale
Ways scale can be represented
- Fraction
- Ratio
- Statement in words
- Graduated scale line such as below
When is a chart conformal? (5)
- All angles and bearings on the Earth are accurately represented on the chart
- Scale distortion at any point must be the same in all directions
- Each parallel must cross every meridian at right angles
- Enables all directions, headings and bearings to be measured correctly - chart would be unsuitable for flight navigation without this
- “Conformal” will appear in the name of the chart
Examples of classic conformal projections
- Azimuthal stereographic - used to produce topographical and specialist aeronautical charts for polar regions and large area MET forecast charts
- Mercator - See other flash cards
- Lamberts conformal conic - Used for plotting radio bearings and long distance flights using great circle tracks
What is the only conformal cylindrical projection?
Mercator Cylindrical Projection
- Cylinder touching the equator - Antarctica and Greenland enormously stretched in an attempt to keep shapes undistorted
- Cylinder touching the poles - Used to produce topographical charts for countries that extend for long distance North to South but not East to West e.g. UK, New Zealand, Italy, Chile and Argentina
- Cylinder touching chosen great circle - Used to produce topographical charts for countries that extend a long distance in one direction not North to South e.g. Malaysia and Indonesia
How do rhumb lines and great circles appear on a Mercator projection?
Rhumb lines appear straight and great circles appear as shallow curves, concave to the equator
With a Lamberts Conformal conic, when the imaginary cone is inset inside the Earth. The scale __________ within the parallels of origin and __________outside the parallels of origin. The scale is __________ where the cone touches the Earth
- Contracts
- Expands
- Correct
N.B. A Lamberts projection chart is said to exhibit a constant scale
How do rhumb lines and great circles appear on lamberts conformal conic projection?
- Great circles appear as straight lines and rhumb lines are projected as curves concave to the nearest pole
- Used for plotting radio bearings and long distance flights using great circle tracks
Define Direction Finding (DF)
The measurement of the direction from which a received signal was transmitted
N.B. AKA Radio Direction Finding (RDF)
Define Radio Bearing
The angle between the apparent direction of a definite source of emission of radio waves and a reference direction, as determined at DF station
Define True radio bearing
A radio bearing for which the reference direction is True North