Navigation Flashcards
What is true direction?
Direction measured with reference to true North
What is magnetic direction?
Direction measured with reference to magnetic North
What is magnetic variation?
The difference between magnetic north and true North. E + / W -
What is compass direction?
Direction measured with reference to compass North.
What is compass deviation?
The difference between compass north and magnetic North. E + / W -
What are the lines that run pole to pole on the earth called?
Meridians of longitude - They run from pole to pole and their units are degrees, minutes and seconds and are named east to wet depending on their position in relation to the Greenwich meridian.
How do you measure a change of latitude?
They are measured in North and South in terms of degrees, minutes and seconds (60 minutes = 1 degree).
What are the lines that run East to West on the earth called?
Parallels of latitude and are described by their angle above or below the equator. They are measured in degrees minutes and seconds and have a maximum value of 90.
How do you measure the change in longitude?
Ch. long = Departure / Cos Lat
What is a great circle track?
A great circle track is the shortest distance from one place to another on a sphere with a constantly changing track (convergence)
What is a Rhumb line?
A rhumb line is a straight line between 2 points on a sphere and therefore takes longer than a great circle track.
What is convergency?
Convergency is the angle of inclination between 2 meridians measured at a given latitude. As it’s a function of Sine, and therefore maximum at the poles and 0 at the equator. Convergency = Ch. Long x sine mean latitude
What is a conversion angle?
A conversion angle is the angle between a rhumb line and a great circle track. 1/2 x convergency = Conversion angle
What is chart scale?
Chart Scale or Representative Fraction is the ratio of chart length to earth distance. Therefore: 1/RF = CL/ED
Describe the doppler effect?
The doppler effect is the apparent change in frequency received caused by the relative motion of a transmitter (Doppler shift).
What is an airborne Doppler system?
An airborne Doppler system is a self contained radio / radar based system which is based on the Doppler effect which is used to mathematically calculate the ground speed of an aircraft.
What is an INS / IRS?
An INS, inertial navigation system is an on board self contained navigation system which mathematically provides continuous information on the aircrafts position without any external reference. In order to keep the accelerometers level they are mounted on a gimbal assembly platform which is kept level with the use of rate gyros and motors.
How does an INS / IRS work?
An INS / IRS works by measuring the aircrafts accelerations in order to mathematically provide continuous information on the aircrafts position by entering a known value (lat / long). It contains, Accelerometers, gyroscopes and a position computer.
How does an INS / IRS find true North?
By using its rate gyros it is aligned to true North.
How does an INS / IRS find magnetic north?
By using a stored magnetic variation and applying it to True North.
Advantages of an INS / IRS?
INS: Self contained and therefore free from external navigation aids. Very accurate Totally global system and can therefore allow travel where no ground based nav aids exists, such as Atlantic or Pacific. IRS: Quick warm up times No real wander No precession Extreme accracy
Describe GPS?
Global Positioning System (GPS0 / Global Navigation Satellite System (GNSS). USA: NAVSTAR SV: 6 Orbits: 4 Height: 20,180 Km Degrees to the EQ: 55 degrees Time to Orbit: 11hr 56 mins L1: 1575 MHz (All users) L2: 1227 MHz (Authorised users) Geodetic system: WGS84 2 Satellites give a lat and long, 3rd satellite will confirm the position and a 4th will give altitude information also. 5 provide basic RAIM and 6 give full RAIM (or 5SV + barometric height input). RAIM is Receiver Autonomous Integrity Monitoring and will identify and remove the SV causing the error from the satellite solution.
What are the advantages of GPS? (5)
Truly global
Ability to be very accurate
Higher capability with redundancy
Free
Global Landing System (GLS) - USA only
Disadvantages of GPS? (4 x system errors).
System errors:
Clock error - Corrected with Pseudo ranges
Ionospheric - Reduced by using 2 frequencies
Multi path - Relected signals from ground objects
Orbital Perturbations - Other satellites passing close by
What is included in the GPS navigation message? (6)
Clock data
Ephemeris data
Orbital
Ionospheric
Health
Almanac
How long does the GPS navigation message take to download?
12.5 minutes usually, but 15 to also get the first GPS fix.
What type of GPS receiver is used on aircraft?
Multichannel - tracks up to 12 SV’s - Best for dynamic environment.
What is SBAS?
SBAS: WAAS (Satellite Based Augmentation System: Wide Area Augmentation System) - continental range
This is a space based augmentation system which improves accuracy to CAT 1 Level. This is done by monitoring stations producing correction messages that are transmitted in real time to receivers from geostationary satellites.
This removes position errors and selective availability as well as reducing propagation errors.
What is GBAS?
GBAS : LAAS (Ground Based Augmentation System / Local Area Augmentation System) - 20 nm range
This is a ground based augmentation system which improves accuracy to CAT 3 Level. This is done by monitoring stations on airfields producing correction messages that are transmitted in real time by ground based VHF transmitters to.
Pseudolites may also be used to enhance the accuracy and are usually located in pairs either side of the approach path.
This removes position errors and selective availability as well as reducing propagation errors.
What do you know about FANS?
FANS - Future Air Navigation Systems is the operational concepts for the future of air traffic management such as:
CPDLC (Controller Pilot Data Link Communications)
ACARS (Aircraft Communications Addressing and Reporting System)
TCAS (Traffic Collision and Avoidance Systems)
What is RNAV?
RNAV is area navigation is any system that allows the aircraft to fly within a required level of accuracy, without the requirementtofly directly over ground based facilities.
What are the two different types of RNAV?
Basic RNAV (B-RNAV) - within 5 nm accuracy at least 95% of the time. RNP5
Precision RNAV (P-RNAV) - within 1 nm accuracy at least 95% of the time. This is used FMS. RNP1
What are the 3 different levels of RNAV (for both P and B)?
1D = Just horizontal plane
2D = Horizontal and Vertical plane
3D = Horizontal, Vertical and Timing
What are the 1st, 2nd and 3rd choice of system for the FMS?
1) DME/DME (theta/theta)
2) VOR/DME (rho/theta)
3) DR (only for limited time though - uses last computer data)
What are the components of an RNAV system?
Navigation Computer Unit
CDI / HSI
Control Display Unit (CDU)
Describe VHF direction finding?
VDF is used in order to triangulate an aircrafts position with certain stations which are capable (listed in AIP). These positions are then passed to the pilot in the following format:
QDM - Magnetic bearing to station
QDR - Magnetic bearing from a station
QUJ - True bearing to station
QTE - Tr;ue bearing from a station
Request example:
“True bearing, true bearing, Oxford approach, G-ABCD request true bearing G-ABCD”
All no wind.
What are the 4 accuracies of VDF?
A = 2 degrees
B = 5 degrees
C = 10 degrees
D = <10 degrees
Usually will only get Bravo.
What is the line of sight formula?
Line of sight range (mtrs) = 1.23 x (√Height Tx + √Height Rx)
Describe the principle of operation on an NDB / ADF.
NDB (Nondirectional Beacon) is ground based.
ADF (Automatic Direction Finding) is aircraft based.
Bearing by switched Cardioid
NDB’s are a medium range ground based navigation aid and transmit in the MF / LF band (190 KHz - 1750 KHz).
The ADF inside the aircraft is either displayed a relative bearing (RBI) or as a QDM on an RMI)
What is the range of an NDB (formulas for it)? (2)
Rang in nm = 3 x √ Power in Watts (land)
Rang in nm = 9 x √ Power in Watts (sea)
What are the errors of NDB / ADF?
Static (thunderstorms) - large discharges of static electricity will cause large bearing errors in the ADF and will point towards the CB.
Night effect - At night the D region in the ionosphere disappears and allows skywave contamination.
Coastal Refraction - As the speed of a wave speeds up over water, it can refract (be pulled) twards the coast. This is minimal when 90 degrees to the coast but increases as the angle of incidence increases. This is why coastal NDB’s are positioned very close to the coast.
Station interferrence - due to congestion of stations in the LF / MF bands.
Outside the DOC - The DOC of an NDB is based upon a daytime signal / noise ratio of 3:1.
Quadrantial error - This is caused by the interferrence of the aircraft itself and is worst when at 45, 135, 225 and 335 degrees to the beacon.
What accuracy does ICAO say an NDB must maintain accuracy within?
5 degrees
What is ADF BFO?
ADF Beat frequency oscilator (BFO)
NDB’s have 2 different types of emmission:
A1A or A2A:
- A1A is for tuning and ID
- A2A is for tuning only
The BFO circuit imposes a tone onto the carrier wave to make the NDB’s ident audible.
What are the types VOR and how do they work? (3)
Reference
Variphase
Clockwise / Anti-clockwise
A VOR is a VHF Omnidirectional Range that provides a magnetic bearing from the beacon by phase comparison.
There are 3 main different types of VOR, a CVOR (Conventional VOR), a DVOR, (Doppler VOR) and a TVOR (Terminal VOR).
The CVOR works by using phase difference between AM and FM, whereby the FM is the reference signal and that AM is the variphase which moves clockwise.
The DVOR works by using phase difference between AM and FM, whereby the AM is the reference signal and that FM is the variphase which moves anti-clockwise.
The radial = Phase difference (FM to aM)
What frequencies do VOR’s transmit?
TVOR = 108 - 112 MHz (First decimal is even)
C/DVOR = 112 - 118 (Odd and even decimal)
What is that forumal for the range of a VOR?
1.23 x (√Htx + √Hrx)
What are the errors of a VOR?
Site error due to rough ground
Scalloping due to the removal of the D-layer at night
Co station interferrence (DOC)
Receiver error (+/- 3 degrees)
What is full scale deflection on a CDI of a VOR?
10 degrees
What accuracy of a VOR must be maintained within?
+/- 5 degrees within the DOC at ALL times
How many chnnels are available on a VOR?
160 channels
What has the further range out of an NDB or a VOR?
Technically an NDB has the furthest range due to its surface wave propogation path, and not line of sight propogation path i.e:
Range over land = 3 x √power in watts
Range over sea = 9 x √power in watts
Describe an ILS and how it works?
An ILS (Instrument Landing System) has 2 separate ground transmitters, the localiser and the glidpath. Its method of operation is bearing by lobe comparison and their depth of modulation.
The localiser has a 90Hz lobe (left) and a 150 Hz lobe (right) which depth of modulation increases away from the centreline. For example an aircraft with more 150Hz is more right of the centreline.
The glidepath has an upper (90Hz) and lower (150Hz) lobe which works on the same principle as the localiser. False glidepaths can occur and are only found above the actual glidepath.
What are the ILS LOC / GP frequency bands and where are they positioned?
LOC
VHF (108-112 with odd decimal)
Positioned approximately 300 metres from the up-wind end of the runway.
GP
UHF (330-335 MHz)
Positioned approximately 300 metres from the threshold and 200 metres from runway edge (abeam).
Markers:
Outer: Colour, Modulation Freq, Morse ID and Distance
Middle: Colour, Modulation Freq, Morse ID and Distance
Inner: Colour, Modulation Freq, Morse ID and Distance
Outer: Blue, 400Hz, - - - - and 6000m
Middle: Orange, 1300Hz, - . - . - . and 1000m
Inner: White, 3000Hz, . . . . and 300m
What is full scale deflection for both the ILS LOC and GS?
Localiser: 2.5 degrees
Glideslope: 0.7 degrees
What are the errors for an ILS?
Back beam
False glide path
Scalloping
FM interference (counteracted by FM immune filter)
Backcourse ILS (prohibited in most of EU including UK)
What is a primary radar?
Primary Surveillance Radar (PSR) transmits a high power signal, some of which is reflected by the aircraft back to the radar.
The radar determines the aircraft’s position in range from the elapsed time between transmission and reception of the reflection.
PSR does not require any specific equipment on the aircraft.
Primary radar uses 1 frequency to transmit and receive on.
What is secondary radar?
Secondary Surveillance Radar (SSR) systems consist of two main elements, a ground based interrogator/receiver and an aircraft transponder. The aircraft’s transponder responds to interrogations from the ground station, enabling the aircraft’s range and bearing from the ground station to be determined.
Describe PRI and PRF?
The PRI (pulse recurrence interval) is the time between two pulses
The PRF (pulse recurruence frequency) is the number of pulses transmitted per second.
1/PRI = PRF
1/PRF = PRI
What is the formula to work out the range (nm)?
Max range (nm) = 81,000 / PRF
NB:
1/PRI = PRF
How is transmission power proportional to the range? What do we need to do to the power in order to double the range?
In order to double the range we would need to multiple the power by 16.
P ∝ Range4
What is super refraction and how is it caused?
Certain atmospheric conditions can actually increase the range of radar pulses by refracting the waves that would usually travel in straight lines.
Predominantly these are caused by temperature inversions.
How does a radar receiver on MTI overcome false second trace returns?
MTI radars remove second trace returns by changing the PRI between onsecutive pulses with a technique known as “jittering the PRF”
In order to have a small point and not a large rectangle, the radar should have short pulses and narrow width. How do we achieve this?
We achieve this by increasing the size of the antenna
What radar (microwave horn, parabolic reflector or slotted planar aray) is best for producing smaller side lobes and improving resolution?
Slotted planar array reduces side lobes which reduces the power required and therefore improves the resolution
What does RADAR stand for?
Radio Detection and Ranging
Where is the interrogator for SSR?
At a ground station
What frequencies do the ground station and aircraft transmit and receive on for SSR?
Ground system:
Transmits 1030 MHz
Receives 1090 MHz
Aircraft:
Transmits 1090 MHz
Receives 1030 MHz
UHF BAND
What does Mode A, C and S replies give?
Mode A:
Identification (12 replies give 4096 combinations)
Mode C:
Pressure Altitude
- Accuracy at aircraft = 300’
- Increments = 100’
- Accuracy at ATC = 50’
Mode S:
Selective addressing with:
- Nearly 17,000,000 discrete codes (24-bit)
- Data link
- Height readout in 25’ increments
What are the advantages and disadvantages of SSR?
Advantages:
- Callsign
- Pressure altitude or FL
- Groundspeed
- Destination
Disadvantages:
Requires transponder in the aircraft
Garbling (interference when aircraft is <1.7nm from eachother)
Fruiting (interferrence caused by replies to other interrogators on the ground)
Limited codes (4096)
What are the advantages of Mode S?
Unambiguous aircraft ID
No garble
Improved SA for controller
More codes
Reduced R/T (datalink)
Improved short term conflict alert
What type of Radar is a DME?
Secondary Radar
What band does DME operate and what frequencies?
UHF
Between 962 MHz and 1213 MHz.
1030 MHz and 1090 MHz is not available for DME.
What frequency difference is there between interrogation and transmitted frequencies for DME?
+/- 63 MHz
How does a DME operate?
The aircraft interrogator and receiver transmits pairs of pulses at random intervals omnidirectionally.
The ground station transponder re-transmits all pulses at +/- 63 MHz after a 50 micro second delay.
The aircraft receiver identifies its own pulses and determines the range from the time taken minus 50 microseconds.
How many aircraft can interrogate a DME at once?
100 aircraft
Describe the range search for a DME?
Rapid lock on: DME interrogator transmits 150 pulse-pairs per second for 15000 pulse-pairs.
If lock on is not achieved that it will go to 60 pulse per second.
At lock on it will go to 25 pulse pairs per second.
In modern equipment this takes around 5 seconds.
Describe the DME beacon saturation?
It is assumed that an aircraft will require 27 pulse pairs for lock on and the output of a modern ground beacon is a constant 2700 pulse pairs per second. Therefore it becomes saturated at 100 aircraft and excludes transmissions from aircraft whose pulses are weaker.
If DME is paired with an ILS where is zero range given?
On the threshold of the ILS runway
What is the only error DME experiences?
Slant range
Describe the functions of a transponder?
Code selection: 4 digit code should be changed when Tx is on STBY to avoid inadvertant distress signal.
Transmission functions:
STBY: Usually warmed up in the STBY position
ON: Provides mode A (ID only)
ALT: Additionally provides aircraft pressure alt or FL
TST: Provides a self check of its operation, if ok reply / monitor light will illuminate.
IDENT SWITCH: Causes a special symbol to bloom around the aircraft for 20 seconds on the controllers display
How does an isoecho / airborne weather radar work and what are its functions?
AWR is a primary radar and uses the echo principle to detect range and the searchlight principle to depict relative bearing.
The main functions of the AWR is:
- To detect the size of water droplets
- Determine the height of cloud tops
- Map the terrain
- Provide position fixes from prominent features.
What are the two types of beams and what are their uses / distances?
Pensil (conical) beam for ranges >60nm
Fan (Cosecant2) beam for ground mapping and shorter distances <60 nm
How is beam width reduced?
By increasing the size of the antenna
What frequency and band does the AWR operate in?
9375 MHz (9.375 GHZ) in the SHF band
What indicates turbulence on AWR?
Steep colour gradient
What could falsely indicate water on AWR?
Hill shadows or mountain shadows
What axis (2) is the AWR stabilised in?
Pitch and roll axis
What is the tilt of an AWR? (up/down and left/right)?
Up/down: +/- 15 degrees
Left/right: +/- 90 degrees
What is AGC (auto gain control) on AWR?
AGC makes the system less sensitive to short range returns so that an overall even picture is produced.
Without the AGC you would expect closer targets to be brighter on the screen.
What are the associated colours shown on AWR in respect to reflective levels in wx mode?
- Black
- Green
- Yellow
- Red
- Magenta
What are the associated colours shown on AWR in respect to reflective levels in navigation mode (terrain)?
Green (light returns)
Yellow (medium returns)
Red (heavy ground returns)
