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
Define Magnetic radio bearing
A radio bearing for which the reference direction is Magnetic North
How is the accuracy for tolerance for bearings for DF equipment categorised?
- Class A: +/- 2º
- Class B: +/- 5º
- Class C: +/- 10º
- Class D: Worse than class C
N.B. Each unit will have a classification for their own equipment
What can an ATCO use a DF for?
Assist a pilot who may be temporarily uncertain of his/her position. AKA lost!
What is the difference between an ACFTs heading and bearing?
An ACFTs heading is which way its nose is pointing. A bearing is a direction to or from the ACFT
What is QTE, QDR and QDM within DF?
- QTE - TRUE bearing of an ACFT in relation to the direction-finding station or other specified point
- QDR - MAGNETIC bearing of an ACFT in relation to the direction-finding station or other specified point. Magnetic bearing from. Can be calculated by adding ACFT heading to Relative bearing
- QDM - MAGNETIC HEADING to steer, with no wind, to make for the direction-finding station or other specified point. (aka Homing). Magnetic bearing to
How is triangulation achieved using DF?
Pilots can establish their approximate position by obtaining two or more bearings from separate DF stations, and plotting the point at which the bearings intercept
What is homing?
Using DF equipment at your radio station with radio bearing of an ACFT transmission, whereby the ACFT proceeds continuously towards the station following bearings obtained from your DF equipment
When should DF stations have the authority to refuse to give bearings?
- Conditions are unsatisfactory
- When bearings do not fall within calibrated limits of the station
- When to do so would monopolise the frequency due to the priority given to messages relating to DF - Below Emergencies (MAY DAY AND PAN PAN)
- When the above occurs, state the reason at the time of refusal
What frequency band does an ADF operate in?
Medium frequency band: 300KHz - 3MHz
What is an NDB, its coverage and frequency range that it operates in?
Non-Directional Beacon
- A ground based omnidirectional beacon that works with ADF in an ACFT
- Continuously transmits an audio tone with morse code signal identifier
- Average radius of coverage is between 10 and 500nm
- High powered NDBs are used for long range navigation on and off airways
- Operates in low and medium frequency band - 190KHz to 1750KHz
- Error +/- 5º
What is RMI?
Radio Magnetic Indicator
- An arrow is superimposed onto the compass rose so that a QDM can be read straight from the pointer
- The instrument can house more than one arrow to simultaneously display bearing information to more than one beacon
What is a Relative Bearing Indicator (RBI)?
- A relative bearing in relation to the ACFTs heading is continuously displayed on the Relative Bearing Indicator
- To obtain a bearing to the NDB, the ACFTs heading must be added to the RBI reading
What errors do NDBs suffer from? (7)
- Static Interference
- Station Interference
- Mountain Effect
- Night Effect
- Coastal Refraction
- Quadrantal Error
- System Malfunction
What is Static Interference? (NDB Errors)
Caused by heavy precipitation and thunderstorms. ADF needle will point directly at the centre of an active thunderstorm in preference to the NDB
What is Station Interference? (NDB Errors)
Large bearing errors caused by interference from transmitters operating on a similar frequencies to the one being interrogated. Often caused by inaccurate tuning
What is Mountain Effect? (NDB Errors)
LF and MF are surface waves and therefore reflected by any high ground in their path. This can result in direct and reflected waves being simultaneously received by the ACFT and causing bearing errors. Normally overcome by flying higher
What is Night Effect? (NDB Error)
- Changes in the Ionosphere at night cause interference from transmissions, particularly in the higher medium frequencies, that would normally be out of range
- Severe bearing errors are most likely to occur at sunrise and sunset
What is Coastal Refraction? (NDB Error)
- Radio waves travel slightly faster over the sea than they do over land
- A radio wave crossing the coast at an any angle other than 90º is going to be refracted
- ACFT flying over the sea and interrogating an NDB inland is likely to suffer a bearing error. The further inland, the greater the bearing error
What is Quadrantal Error? (NDB)
- The airframe of an ACFT tends to reflect, refract and re-radiate incoming radio waves so the loop aerial receives a strong signal from the NDB together with a weaker one that has been distorted by the fuselage
- Overall, the signal appears to bend towards the fuselage and this error is maximum when it arrives at the ACFTs quadrantal points
- Conversely, signals arriving at the ACFTs cardinal points do not suffer any error
What happens when an NDB malfunctions?
There is no failure warning device so constant monitoring is required
When are maximum and minimum NDB ranges experienced?
- Maximum- From a high powered NDB at night when flying over the sea
- Minimum - From low powered NDBs used as locator beacons at airfields
What are the advantages (2) and disadvantages (2) of NDB?
Advantages
- Reception not limited to line of sight. The MF waves follow the curvature of the Earth
- Maximum range is dependent on the power of the NDB
Disadvantages
- Subject to atmospheric (electrical storm) interference, coastal and night refraction,which affects bearing accuracy
- Not as accurate as VOR
What is an ILS?
Instrument Landing System
- ILS is a Precision RWY Approach that provides accurate
guidance both in azimuth and elevation - Runways served by ILS are known as Precision Approach Instrument Runways
- Pilot interpreted aid
- Designed for conditions of low cloud base or poor visibility
- Assists in achieving an orderly flow of landing traffic
- Operates continuously without assistance from ATC
What does an ILS consist of?
- Localiser transmitter - Indicates deviation from the optimum lateral approach path
- Glide path transmitter - Indicates deviation from the optimum vertical approach path - Defines safe descent slope (Normally 3º)
- Marker beacons - Normally 2 or 3 beacons to define ranges from threshold. DME can be used
Within an ILS, what can a DME provide?
- Range information instead of Marker Beacons
- DME is frequency paired with localiser so it is automatically tuned when ILS selected
- Range information is zero referenced to the runway threshold
- Accurate only within localizer coverage and up to 25,000ft.
How does a localiser work?
- Signal transmitted in the 108-112MHz band
- 2 lobes are radiated which overlap by 5º
- Flight receives signals of equal intensity from both lobes when on centreline
- Deviation left or right results in unequal signals being received
- Coverage out to 35º either since of centreline out to 17nm, reducing to 10º thereafter up to max range
What is the ILS protected range?
- Coverage out to 35º either side of the centreline out to 17nm, reducing to 10º thereafter up to 25nm
How does a Glide Path work?
- Signal transmitted in the 329.3-335MHz band
- Radiates 2 lobes which overlap by 1º out to a maximum range of 10nm along extended approach path
- Flight down the correct descent path will receive signals of equal intensity from both lobes
- Deviation above or below results in unequal signals being received
- Coverage extends horizontally 8º either side of centre line and vertically 0.45 x GP below the surface to 1.75 x GP above the surface
- Glide path aerial is also known as as the ILS reference point
- Overlapping area normally subtends an angle of 3º to give continuous descending approach to the touchdown point
What is the glide path protected range?
Coverage in the sectors 8° azimuth each side of the Localiser centre-line to a distance of 10 nm from threshold
What does the location of the glide path aerial and approach angle depend on?
- ACFT likely to use the aerodrome
- Terrain
- Obstacles within the approach and missed approach areas
- Local meteorological conditions
- RWY length
What is the ILS reference datum?
Affects the location of glide path aerial
The point at a specified height, located vertically above the intersection of the centreline, and the threshold, through which the downward extended straight portion of the ILS glidepath passes
Rate of loss of height depends on approach angle
2.5° = 250ft per NM
3° = 300ft per NM (Normal setting)
3.5° = 350ft per NM
N.B. Not a point on the ground. It is up in the air, usually about 50ft
Why are the localiser and glide path transmissions are frequency paired?
- Reduces pilot workload
- Guards against mismatching
- Only the localiser frequency needs to be published and selected on the flight deck
How is the ILS monitored?
- Automatic equipment which monitors radiation fields of localiser, glide path and markers
- If power drops below an acceptable level or anything abnormal happens, the ILS will switch off
- ILS will also switch off if the monitoring equipment fails
- ATC and pilot is warned of the failure
How is an ILS station identified?
- Modulating a 3 letter morse code identifier onto the localiser carrier wave
- When undergoing maintenance or radiating for test purposes, it is removed or replaced by continuous tone
What are the categories of ILS? (7)
- ILS Category I - DH not lower than 200ft, RVR not less than 550m, Visibility not less than 800m
- LOWER THAN STANDARD CAT I - CAT I decision height but lower RVR than would normally be associated with Dh but not lower than 400m
- ILS Category II - DH below 200ft but not lower than 100ft, RVR not less than 300m
- LOWER THAN STANDARD CAT II - Some or all of CAT II light system unavailable, DH below 200ft but not lower than 100ft, RVR not less than 350m
- ILS Category IIIA - DH lower than 100ft or no DH, RVR not less than 200m
- ILS Category IIIB - DH lower than 50ft or no DH, RVR less than 200m but not less than 75m
- ILS Category IIIC No DH or RVR limitations - blind landing
What does the space between contour lines on vertical chart relief depend on?
- The scale of the map
- The range of elevations displayed on the map
- The units of measurement being used
How is the gradient assessed? (Vertical Relief)
- Proximity of the contour lines. The closer they are, the steeper the slope
- Contour line method may be enhanced by tinting intervening layers
What is a spot elevation? (Vertical Relief)
A dot position indicator with the elevation printed along side it. It marks the location of the highest points
What are form lines? (Vertical Relief)
Replace contour lines when an accurate survey has not been carried out. Represented as dashed lines rather than solid
What are hachures? (Vertical Relief)
Short lines that radiate away from high ground
N.B. An older method used to indicate hill features in areas that have not been fully surveyed or when detailed information is not required
What is hill shading? (Vertical Relief)
- Simulation of a low sun angle casting shadows on high ground
- Used for displaying vertical relief in areas where detailed surveying has not been completed
- Most effective on relatively flat terrain (moorland/dunes)
What are the methods of displaying vertical relief? (6)
- Contours
- Spot elevation
- Form lines
- Tinting
- Hachures
- Hill shading
Examples of types of Precision Approach (4)
- ILS - Instrument Landing System
- MLS - Microwave Landing System
- RNP APCH - Required Navigation Performance Approach
- PAR - Precision Approach Radar
Examples of Non-Precision Approach (6)
- VOR - VHF Omni-directional Range
- NDB - Non Directional Beacon
- ILS Localiser only - Instrument Landing System Localiser only
- GNSS - Global Navigation Satellite System
- SRA - Surveillance Radar Approach
- VDF - VHF Direction Finder
What is a precision approach?
An instrument approach and landing using precision lateral and vertical guidance with minima as determined by the category of operation. Has a DA or DH!
N.B. Provided by ground based navaid or computer generated navigation data or controller interpreting the display on a radar screen
What is a non-precision approach?
An instrument approach and landing which utilises lateral guidance but does not utilise vertical guidance. Have MDA or MDH
Why is there a higher number of Controlled Flight Into Terrain Accidents associated with non precision approaches?
In part a result of loss of situational awareness, e.g., resulting in descent before the initial approach fix; and a consequence of the lack of precise vertical guidance, which may involve levelling off at intermediate points
What are the possible 5 segments of an instrument approach procedure
- ARRIVAL
- INITIAL - from initial approach fix (IAF)
- INTERMEDIATE - intermediate fix (IF)
- FINAL - Final Approach Fix (only on NPA - FAF) or Final Approach Point (PA only – FAP)
- MISSED– Missed approach point (MAPt)
What is a STAR?
Standard Instrument Arrival
- Permits transition from en-route to approach phase
- Normally ends at the Initial Approach Fix (IAF)
Where does the Initial Approach Segment begin and end?
Begins at the Initial Approach Fix (IAF) and ends at the Intermediate Fix (IF)
Where there is no suitable IAF or IF available to construct a straight in approach:
- Reversal procedure - Procedure or base turn
- Racetrack procedure
- Holding pattern required
What happens in the Intermediate Approach Segment?
- Speed and configuration adjusted to prepare for final approach
- Descent gradient kept as shallow as possible
- Obstacle clearance reduced from 1000ft to 500ft
What happens in the Final Approach Segment?
- Alignment and descent for landing made
- May be to a RWY for a straight in landing or to an aerodrome for a visual manoeuvre
- Must begin at the final approach fix and end at the Missed Approach Point (MAPt)
- The lowest point on the approach will be the MDA/MDH
What are the phases of the Missed Approach Segment? (3)
- Initial - Mapt to start of climb (SOC)
- Intermediate - SOC to 150ft Obstacle clearance
- Final - 150ft Obs clear. To point where new approach, hold or enroute begins
What could a Missed Approach Point (MAPt) be? (4)
- Glide Path/Decision Alt(Hgt)
- Nav facility
- Fix
- Specified distance from FAF
N.B. 1 MAPt for each MISAP. If required visual reference not established, MISAP must be initiated immediately
Define Obstacle Clearance Height
The lowest height above the elevation of the relevant RWY threshold or above the aerodrome elevation as applicable used in establishing compliance with the appropriate obstacle clearance criteria.
N.B. In other words, the height above which you won’t hit anything!
Minimum MDA/H for ILS localiser only, VOR, VOR/DME, NDB?
What is meant by VM(C)?
Visual Manoeuvring (Circling)
The term used to describe the visual phase of flight, after completing an Instrument Approach, where an aircraft is manoeuvred into position for a landing on a runway which is not suitably located for a straight-in approach
What is a VM(C) area and how is it determined?
- Area where obstacle clearance has been considered for ACFT manoeuvring visually before landing
- Determined by drawing arcs centred on each RWY threshold and jointing these arcs with tangent lines
In VM(C), what are the radius of arcs related to? (4)
- ACFT Category
- Speed for each Category
- Wind Speed: 25 kts throughout turn
- Bank Angle: 20 degrees average, or 3 degrees per second, whichever requires less bank
What are the ACFT approach categories?
- CAT. A nominal Vat less than 91 kts IAS
- CAT. B nominal Vat 91 kts to 120 kts IAS
- CAT. C nominal Vat 121 kts to 140 kts IAS
- CAT. D nominal Vat 141 kts to 165 kts IAS
- CAT. E nominal Vat 166 kts to 210 kts IAS
Define Nominal Velocity at Threshold
1.3 x Stalling Speed in the landing configuration at Maximum Certificated Landing Mass
What is the INS?
Inertial Navigation System
A navigation device that uses a computer, motion sensors (accelerometers) and rotation sensors (gyroscopes) to continuously calculate by dead reckoning, position, orientation and velocity (direction and speed) of a moving object without the need for external references
Basic Principle
If you know where an ACFT starts, and how far it has subsequently moved in any given direction, then you will also know it’s current position
Put Simply
The INS is a stand-alone system using accelerometers on a gyroscopic platform to calculate movement in all 3 dimensions
Pilot Input
- Prior to taxi, pilot inputs precise lat/long then selects align. Platform levels itself. Together with compass system, it finds true North
- After alignment, the system is selected to Nav
- Any ACFT movement prior to selecting Nav will invalidate alignment and the above sequence would have to be repeated
- Cannot be restarted once in flight so triple systems for redundancy
Within the INS, how does the ACFT know how far it has moved and in which direction?
Amount of movement is obtained using accelerometers which measure the acceleration in each direction (Forwards (X-axis), Sideways (Y-axis), Vertically (Z-axis))
N.B. Acceleration is defined as change in velocity
What sort of points does the INS store?
Waypoints
- Beacon positions
- Airspace boundaries
- Airfield locations
- Reporting points
N.B. BAAR
INS instantly solves navigation problem using triangle of velocity. What instant readings/display options is the pilot then presented with? (8)
- ACFT track and groundspeed (TR/GS)
- Heading and drift angle (HDG/DA)
- Dist. off track and track angle error (XTR/TRE)
- Current position (POS)
- Waypoint insertion and viewing (WAY/PT)
- Distance and time to next waypoint (DIS/TIME)
- Current wind velocity (WIND)
- Desired track to next waypoint and system status (DSRTR/STS)
The mounting board for accelerometers in an INS also contains gyroscopes to ensure it remains level with regards to the surface of the Earth. What sort of gyroscopes do modern INS systems incorporate and why?
Laser ring gyroscopes as they eliminate the problem of drift
What is GNSS?
Global Navigation Satellite System
A constellation of satellites providing signals from space that transmit positioning and timing date to GNSS receivers. Receivers use this to determine location. WGS84 is the reference
Examples include
- Europe’s Galileo
- USA’s NAVSTAR GPS
- Russia’s GLONASS
- China’s BeiDou
How does GPS work?
- GPS satellites circle the Earth every 12 hours in a very precise orbit, transmitting signal info to Earth
- GPS receivers take this information and use triangulation to calculate users exact location
- Essentially GPS receiver compares the time a signal was transmitted with the time it was received. The difference tells the GPS receiver how far away the satellite is
How is the performance of GNSS assessed? (4)
- Accuracy: the difference between a receiver’s measured and real position, speed or time
- Integrity: a system’s capacity to provide a threshold of confidence and, in the event of an anomaly in the positioning data, an alarm
- Continuity: a system’s ability to function without interruption
- Availability: the percentage of time a signal fulfils the above accuracy, integrity and continuity criteria
What are the primary reasons that Civilian GPS suffer from position errors?
- Satellite Geometry/Shading- The wider the angle between satellites, the better the accuracy
- Ionosphere and Troposphere Delays - signal slows as it passed through atmosphere. System used a built in average delay
- Receiver Clock Errors - built in clock can have very slight timing errors
- Orbital Errors - AKA ephemera’s errors, these are inaccuracies of the satellites location
- Number of Satellites Visible - Line of sight needed from satellites
- Signal Multi-path - Occurs when GPS signal reflects off objects such as tall buildings or large rock surfaces before it reaches the receiver. Increases travel time of the signal thereby causing errors
N.B. S.I.R.O.N.S
How can GNSS errors be corrected? (3)
- ABAS - Airborne based Augmentation System. (RAIM)
- GBAS - Ground Based (Differential GPS)
- SBAS - Satellite Based (WAAS, EGNOS)
What is ABAS?
ACFT Based Augmentation System
- Augments and/or integrates info obtained from GNSS with other information available on board the ACFT (INS)
- Aim is to enhance overall performance of GPS system in terms of integrity, availability and accuracy
Two Techniques
- Receiver Autonomous Integrity Monitoring (RAIM) - Integrity of GNSS systems checked without reference to other sensors or integrity systems other than the receiver itself. Achieved with a consistency check amount redundant pseudo-range measurements
- Airborne Autonomous Integrity Monitoring (AAIM) - GNSS info complemented with onboard sensors and other components
What is GBAS?
Ground Based Augmentation System
- ICAO definition of GBAS for satellite navigation is Local Area Augmentation System (LAAS)
- An example of LAAS is differential GPS (DGPS) - accuracy of GNSS improved by combining GPS and DGPS receivers
How does DPGS work?
- Placing a GPS receiver at a known location called a reference station
- Since exact location of above is known, it can determine errors in satellite signals
- Difference between measured and calculated range becomes a differential correction
- Corrections applied to GPS receivers calculations, removing many common errors of GNSS and improving accuracy
What is SBAS?
Satellite Based Augmentation System
- Geostationary satellites to broadcast information to users over a large geographical area
- Europeans version is called EGNOS(European Geostationary Navigation Overlay Service)
- Similar to DGPS but uses 2 satellites to further correct readings together with ground stations
What is GPS Jamming?
Military use GPS for tactical reasons and will occasionally require to practice jamming these signals. GPS jamming NOTAM will be issued
What errors are associate with the ASI?
- Instrument Error - small imperfections in instrument
- Pressure Error - Subdivided into Position and Manoeuvre Error - error when pitot tube is not pointing directly into the airflow
- Density Error - less air pressure at altitude
- Compressibility Error - If TAS exceeds about 300kts, air entering pitot tube compressed over the pitot hole causing the ASI to over-read - can be corrected
ASI errors should not exceed 3% or
N.B. DICP(PM)
What are the different types of airspeed used? (5)
- Indicated Airspeed (IAS) - Speed of ACFT read directly from ASI. Used by ATC for speed control
- Rectified Airspeed (RAS) - We do not need to know what this is
- True Airspeed (TAS) - The actual speed of the ACFT through the air
- Ground Speed (GS) - The actual speed of the ACFT over the surface of the Earth - corrects TAS for wind
- Mach Number - TAS expressed as a fraction of the local speed of sound. Depends on temperature - the cold the slower
How is Mach number calculated?
TAS divided by local speed of sound (approx 660kts at sea level). Given as a decimal point of 1
When do subsonic conditions exist?
When Mach Number is less than Mach 1
When do transonic conditions exist?
When some part of an ACFT is above Mach 1
When do supersonic conditions exist?
When all of the airframe is above Mach 1
Define Critical Mach Number (Mcrit)
The speed at which the shock waves ahead of the airframe attach themselves to the airframe causing buffeting, loss of lift and control problems. Dependent on the aerodynamic shape of the airframe
Classification of speeds:
1. Subsonic Flight: __________
2. Transonic Flight: __________
3. Supersonic Flight: __________
4. Hypersonic Flight: __________
- Less than M 0.8
- M0.8 to M1.2
- M1.2 to M5.0
- Above M5.0
What are the EU regulations for supersonic flight?
- All medium and high level supersonic flights must be made over the sea
Why would a pilot fly just below Mcrit?
- Optimum performance
- Minimum discomfort and fatigue
How does TAS relate to IAS?
How is wind expressed?
In degrees as a 3 figure number with reference to true north
N.B. Shown in magnetic when displayed in ATC
Which 3 vectors is the behavior of an ACFT in flight a result of?
- Heading and True Airspeed
- Wind Velocity
- Track and Ground Speed
What is drift angle?
- When there is wind, the angle between heading and track is known as drift angle (measured in degrees port or starboard of the ACFT heading)
- If there is no wind, Heading/TAS would be the same as Track/GS
What is Required Track?
An appropriate heading which takes into account the prevailing wind
What is Track Made Good?
- The track that the ACFT actually traces over the ground once airborne
- Could differ from required track if the forecast wind was not the same as the actual wind encountered
What is Track Error?
The angle between required track and track made good
What is plotting?
The physical calculation of an ACFTs flight progress
N.B. A vector has magnitude and direction. Knowing 2 vectors, the 3rd can be calculated
Things to remember when plotting ACFTs flight progress
- Achieved using a Triangle of Velocity
- Wind blows from heading to track
- Wind is normally in ºT
- Heading and Track could be in ºT, ºM, ºC(ompass)
- Use uniform units of distance i.e. Knots with nautical miles
- TAS is always measured along heading vector
- GS is always measured along the ground vector
What is a CRP-5 Computer?
Used for plotting in the cockpit where drawing vectors is impractical. On civil airliners, an onboard electrical computers undertake this task
What does surface wind at aerodrome dictate?
- The direction of TKOF and landing
- The time and distance it takes to get airborne
Calculation of headwind and crosswind components can be done by __________
Drawing Vectors
What is the simple mental method of calculating crosswind component?
Main method of calculating crosswind component in control tower?
Using a table such as below
Label the following diagram
What is Area Navigation (RNAV)
- Permits ACFT operation on any desired flight path within the coverage of navigation aids
or
- Within the limits of the capability of self-contained navigation aids (INS)
or
- A combination of both of the above
How does area navigation work?
- FMS will fly a series of pre-loaded waypoints and position ACFT on a computed track between the individual waypoints
- LNAV (Lateral) and VNAV (Vertical) functions used to ensure accuracy with WGS84 system
What is B-RNAV and what ACFT track-keeping accuracy is required?
Basic Area Navigation
- Forerunner of RNAV program
- Enables capacity gains through modifications to en-route structure
- ACFT track keeping accuracy of +/- 5nm for at least 95% flight time
- All IFR ACFT must be B-RNAV compliant
- Due to limitations of B-RNAV, RNAV becoming standard in ECAC airspace. It was not intended for use in TMA operations
What is RNP?
Required Navigation Performance
- Enables implementation of new routes and flight paths
- A statement of the navigation performance specification necessary for operation within a defined airspace
- System must monitor achieved performance and alert when failing to meet above specification
- Equipment must be sufficiently capable and accurate as denoted by regulatory body
- Based on GNSS (GPS)
- Part of broader concept called Performance Based Navigation (PBN)
N.B. Used to be based on INS
What are the main types of RNP accuracy?
There can be multiple types of RNP accuracy dependent on phase of flight
- RNP 0.3: +/-0.3nm
- RNP 1: +/- 1nm
- RNP 2: +/- 2nm
- RNP 4: +/ 4nm
Above deviation from desired track for 95% of the time i.e TSE: Total System Error
What happens if it becomes impossible for an ACFT to maintain its RNP accuracy appropriate to RNP airspace being used? i.e. if it fails…
ATC should be made aware so they can take appropriate action to provide increased separation and coordinate with other ATC units as appropriate
What is a fixed RNP route?
- Published ATS route which can be flight planned for use by ACFT approved for a specific RNP type
- They should begin and end at notified reporting points and waypoints are established along them
What is a contingency RNP route?
- Can be made available to ACFT approved for a specific RNP type during limited time periods (hours, days, seasons)
- May also be established to meet unusual temporary requirements at short notice
Where can RNP apply?
- To an area or volume of airspace or any airspace of defined dimensions
- Authorities can specify certain RNP types within these areas
- Unpublished tracks may also be flight-planned within designated published RNP areas
WHAT IS P-RNAV?
Precision Area Navigation
- Allows for en-route and/or TMA operations
- ACFT equipped and certified with P-RNAV systems (+/- 1nm accurate track) may operate P-RNAV SIDs/STARs
N.B. P-RNAV is specific to Europe only
What are RNP-RNAV monitoring requirements and accuracy?
- No requirement for airborne monitoring of achieved RNP type accuracy. Greater accuracy is ensured operationally
- Allows for approaches to +/- 0.3nm accuracy
- Can be used in terminal areas
What accuracy does an RNP APCH require?
- +/- 1nm in initial, intermediate and missed segments
- +/- 0.3nm in final segment
What is an RNP (AR) APCH?
RNP APCH with authorisation required or RNP AR build upon PBN concept
- RNP approach procedure that requires lateral TSE lower than standard RNP value on any segment of the approach procedure, down to 0.1nm
- Requires crew training in the same way as ILS CAT II/II procedures
What are the 3 components of the PBN concept?
- Navigation Specification
- Navaid infrastructure
- Navigation Application
What is the PBN concept component Navigation Specification?
- Performance requirements in terms of accuracy, integrity, continuity and availability for proposed operations in a particular airspace
- Describes how above can be achieved
- Either an RNP or RNAV specification
- RNP specifications includes requirements for onboard self contained performance monitoring while RNAV specifications do not
What is the PBN concept component Navaid Infrastructure?
Relates to ground or space based navigation aids that are called up in each navigation specification
What is the PBN concept component Navigation Application?
Application of navigation specification and Navaid infrastructure in the context of an airspace concept to ATS routes and instrument flight procedures
What does future of air navigation look like?
- 4D - A move to gate to gate operations - requires accurate timings, possibly as strict as 2-5 seconds. 4D FMS with data link along with ATCO appropriate tools requires
- Business trajectories - Above and developing on from free route airspace
What are TSE, PDE, NSE and FTE?
- Total System Error
- Combination of PDE, NSE and FTE
- TSE is difference between physical true position of ACFT and desired path
- When an ACFT has demonstrated that with all errors combined, the ACFT is able to fly within the required performance 95% of the flight time with lateral track accuracy of +/- 1 nm or better
- Path Definition Error
- Defined path may not exactly match the desired path, caused by the resolution of the computer and irregular Earth’s surface.
- This is a small error managed in the data chain
- Navigation Sensor Error
- ACFTs actual position may not coincide with its estimated position, minimised by using more accurate position sensors
- Represents the difference between the true position and estimated position
- Flight Technical Error
- Ability of pilot or avionics to fly from estimated position onto the defined path
- Can be minimised by use of flight director or autopilot
What is LNAV/VNAV?
Lateral and Vertical guidance from the estimated position onto the defined path is called LNAV, VNAV respectively
What is a waypoint?
A geographic coordinate (in WGS84) identified by either
- 5 letter unique name code e.g. XILAN
- If located with a ground based NAVAID, by the 3 letter ICAO identifier for that station, e.g. TEB
- For Terminal Airspace only, by an alphanumeric name code, e.g. SA541
What are transitions (FRT)?
Fixed Radius Transition
- En-route functionality
- FRTs used for other ATS routes, usually at higher altitudes
Recommended turn radii of
- 22.5nm for airways above FL200
- 15nm for airways below FL190
What is a path terminator?
- Instrument Flight Procedures each ‘leg’ is associated with a ‘Path Terminator’, which defines how the path will be flown and how the ‘leg’ will be terminated
- RF (Radius to Fix), used for consistent turn performance on IFPs, is one example of a path terminator
- With RF the ‘leg’ is to be flown as a fixed radius around a defined arc centre and terminating at the next fix (which is a waypoint)
What is meant by parallel offset?
- Parallel track to the left or right of the designated or established airway/route
- Normally associated with RNAV
- Only used during the en-route phase and can be used to achieve lateral separation or to avoid wake turbulence etc as an alternative to radar vectoring etc
What is a fly-by waypoint?
- ACFTs RNAV system anticipates the turn
- The turn starts at some distance before the waypoint to allow tangential interception of the next leg of the ATS route or procedure
- Majority of ACFT capable of area navigation have this functionality
- Earliest the turn can be initiated is 20NM prior to the waypoint
What is a fly-over waypoint?
- ACFT starts to turn onto the next leg of the ATS route as it passes over the waypoint
- All ACFT capable of area navigation can perform a flyover turn
- Causes ACFT to overfly route which may conflict with parallel routes/ACFT
What is the 1 in 60 rule?
An angle of 1º will subtend a distance of 1nm over a range of 60nm. Reliable up to 20º. If 2 values are known, the thrips can be calculated
N.B. For example: An ACFT is known to be 1nm off track after having flown 60nm, then the track error is 1°
With flight plan concepts, along with route and altitude selection, what else is considered? (4)
- Safety - Terrain, recommended MSA, forecast MET en-route, locality of danger areas, availability of SAR, Alternate terminal and en-route airfields. ACFT safety equipment
- Legality - All flight must comply with: ATC requirements when flying in controlled airspace, SIDs, Airways, Advisory routes, STARs, Vertical limits applicable on the airways, separation rules
- Feasibility- ACFT range with load carried, ACFT altitude limit, type and extend of navigation equipment carried, preferred operating level relative to the line of sight range of available ground navigation beacons
- Costs - route distance, selected altitude, favourable winds, economical engine performance
After deciding on the route and altitude, the pilot must then submit a Flight Plan to obtain an ATC clearance. What is the submitted information based on?
- Cruising speed (TAS)
- Required Flight Level
- Route (including each reporting point)
- Destination
- Total estimated flight time
- Destination alternate
In a flight plan, what are estimated flight times based on? (3)
- Calculated ground speeds using forecast winds
- Required tracks
- Distances involved
In a flight plan, what does supplementary information include? (5)
- ACFT endurance
- Number of persons on board
- Radio and survival equipment carried
- Aircraft colour and markings
- Name of pilot
