Radio Navigation Flashcards
Speed of light
300,000 km/s
Relationship between frequency and wavelength
c = f x lambda
c = speed of light
f = frequency
lambda = wavelength
Radio frequency spectrum
Attenuation
Reduction in power of a radio wave.
Atmospheric attenuation is due to dust and items in the atmosphere, surface attenuation changes over different surfaces (ice caps and poles worst, sea the best).
Space waves
- Frequencies that use it
Line of Sight waves
Used in VHF (and higher freq)
Surface waves (aka ground waves)
Waves following curvature of the earth due to diffraction and attenuation.
Strongest for low frequencies (MF and above)
Skywaves
- time of day
Waves that are reflected back from the ionosphere, strongest in day (due to solar radiation).
Fading
Interference of ground and sky waves
Skip zone
HF skywaves bounce back around 600NM to 1200NM away, whilst ground waves (space & surface) only 150NM, so there is a gap in the middle where no signal is received, called the skip zone or dead zone.
Skip DISTANCE is distance from transmitter to skywave landing point.
Ionospheric refraction of different frequencies
- VHF
- HF
- LF/MF
VHF - Not refracted
HF - Refracted a bit so get a skip zone, thus used for long distance comms
LF/MF - Refracted a lot so ground waves interfere with sky waves
Propagation of:
VHF
MF
VHF: Space waves
MF: Ground & Sky waves (thus subject to fading)
Civilian VHF range
118MHz to 137 MHz
Q codes
QDM: Magnetic TO
QTE: True FROM
QDR: Magnetic FROM
QUJ: True TO
Relative Bearing Indicator (RBI)
AKA radio compass
Simply shows relative direction of an NDB signal.
Radio Magnetic Indicator (RMI)
Similar to moving card ADF but with compass card automatically turned (usually by remote compass). This is what we have on modern aircraft, possible as part of EFIS (on the ND).
Often have two arrows for two signals and can feed from ADF or VOR.
VOR Frequencies
108MHz to 117.975MHz (VHF)
108 to 112 MHz shared with ILS so 0.2MHz spacing (108.0, 108.2) and terminal VORs only (generally)
112 to 117.975 MHz at 0.05 MHz spacing more likely for en-route VORs.
Omni-bearing indicator (OBI)
AKA CDI
VOR indicator which you dial in to a radial and see deviation marks and TO/FROM indicator.
Full scale deviation is 10 degrees (can have 5 dots of 2 dots).
Can have glidescope info which gives vertical and horizontal deviation lines.
Instrument has no concept of heading or direction (i.e. compass card)!
Horizontal Situation Indicator (HSI)
Similar to RMI, both have rotating cards driven by remote compass.
Where RMI simply points to VOR, HSI has a selected radial and then deviation marks (and to/from).
Procedure turn (2)
Head out from NDB/VOR for fixed time period or until a fix position.
Turn off 45 degrees and straight for a period of time (about 1 min) then commence turning circle (in opposite direction) to regain radial.
OR turn off 80 degrees then immediate 260 degree turn in opposite direction to regain radial.
ILS localiser frequencies
108MHz to 111.95MHz
Odd 0.1MHz, and 0.05MHz above
e.g. 108.1, 108.15, 108.3, 108.35
[108.2 is VOR, 108.25 not allocated]
AMPLITUDE modulated (otherwise the two frequencies on each side wouldn’t work!)
ILS Ident
1020 Hz tone amplitude modulated onto the carrier wave.
Usually 3 letter code, can have “I” infront to identify as ILS
Deviation markings for ILS
Displayed on OBI or HSI
Localiser deviation is 2.5 deg each side (a quarter of VOR deviation).
Glidescope deviation is 0.75deg each side (so 0.15deg per dot) [0.7?]
ILS functionality
- Beam modulation
- How centreline is identified
ILS sends out 2 beams, a 90Hz AMPLITUDE modulated “yellow” beam to left of track, a 150Hz modulated “blue” beam to the right.
Indicator measures “Depth of modulation” to assess which it gets more of, with DDM = 0 (or equal DDM) being the “green” centre line.
[Glidepath uses yellow 90Hz above and blue 150Hz below glidepath]
[Change in depth of modulation linear with angular displacement]
ILS coverage
Up to 25NM away - 10 degrees either side
Up to 17NM away - 35 degrees either side
ILS categories and minima
Cat I: 200ft minima (Baro) [100ft accuracy]
Cat II: 100ft minima (Radalt) [50ft accuracy]
Cat IIIA: 0ft, RVR 200m
Cat IIIB: 0ft, RVR 75m
Cat IIIC: 0ft, RVR 0m
Type A and B approach minima
Type A: >= 250ft
Type B: < 250ft
MLS functionality
Sends out 2 sets of signals, one in azimuth, one in elevation and a precision DME (DME/P).
Sweeps signals from left to right so timing of when “to” and “fro” signals pass tells you where you are in the wave.
FMS/APFDS can be programmed to follow a route.
MLS vs ILS
MLS allows curved flight paths.
Both affected by shadowing but MLS can interrupt signals to take into account stationary object, so LESS sensitive to geographic location.
In reality MLS was rarely implemented and is being replaced with GPS.
Weather radar reflection
Water better reflection than ice, so tops of thunderstorms not very visible.
Returns with strongest at top:
Wet hail
Rain
Wet snow
Dry hail
Dry snow
Drizzle
NOT clouds, turbulence, lightning, fog, sandstorms.
Predictive Wind Shear (PWS)
Can be activated and works below 2300ft even when weather radar is off.
Scans for wind shear ahead and provides a “WIND SHEAR AHEAD” warning if detected.
Distinct from TAWS windshear which is based on IRS.
Detects doppler shift in precipitation only (doesn’t work if zero precipitation).
DME functionality
Pairs of pulses sent out with 12 (X) or 36 (Y) microsecond gap, timing is unique to each transmission though for identification.
After 50 microsecond display the ground transponder responds.
Time delay (less 50 microseconds) converted to a slant distance.
SSR frequencies
Ground station sends out pulses at 1030 MHz.
Aircraft responds with a longer set of pulses on 1090 MHz.
GPSS
Satellites for
- 2D fix
- 3D fix
2d fix needs 3 satellites
3d fix needs 4 satellites (or 3 + altitude info)
2 purposes of satellite augmentation systems
- Differential GPS, i.e. increasing accuracy
- Provision of integrity monitoring
Note that systems like RAIM and AAIM provide integrity monitoring but do NOT increase accuracy
Airborne Based Augmentation Systems (ABAS)
- RAIM
With 1 redundant satellite (so 4 for 2d fix, 5 for 3d fix) RAIM can provide Fault Detection (FD) which means it can tell a satellite is faulty, but not which one.
With 2 redundant satellites (5 for 2d, 6 for 3d) can provide Fault Detection and Exclusion (FDE).
Look for “redundant range measurements”
Airborne Based Augmentation Systems (ABAS)
- Aircraft Autonomous Integrity Monitoring (AAIM)
This is where the aircraft uses position data from several sources (IRS & barometric altimeter - NOT VOR/DME in questions) to carry out integrity monitoring.
Ground Based Augmentation Systems (GBAS)
- description
- frequencies
- range
A ground station monitors GPS and identifies errors (satellite clock, ephemeris and ionospheric propagation, NOT receiver, multipath or some atmospheric propagation errors).
Data broadcast over VOR range (108 to 118 MHz) up to 20NM from station.
GBAS
- 2 services provided
GBAS positioning service is just for added accuracy. Can have multiple connected (Ground Regional AS - GRAS) together.
Precision Approach Service (GLS approach) works like ILS down to 200ft, needs to be selected via 5 digit channel number.
Satellite Based Augmentation Systems (SBAS)
Use a separate satellite system with space segment (geostationary satellites) and ground segment.
Errors detected at all reference stations, calculated at master station and transmitted at ground earth station to satellites.
PBN definition
NON sensor specific navigation specification system based on ability to meet performance requirements, regardless of sensors or tools used to achieve it.
RNP vs RNAV
RNP specifications include requirement for on-board performance monitoring and alerting.
RNAV do not.
3 elements of RNP/RNAV Total System Error
Path Definition Error (PDE) - desired path to defined path
Flight Technical Error (FTE) - defined path to estimated position
Navigation System Error (NSE) - estimated path to actual position
Approval for PBN
Pilots must have PBN endorsement on Instrument Rating.
EASA only require specific operational approval for some procedures (e.g. RNP AR APCH and RNP 0.3)
Advanced RNP (A-RNP) specification
A new RNP specification, the only one covering ALL phases of flight.
Incorporates specs of:
RNAV 5, 2, 1
RNP 2, 1, APCH
BRNAV
System used in Europe, which is same as RNP-5
PRNAV
Precision RNAV
Equivalent to RNP-1
RNP APCH
RNP AP APCH
ONLY for approach phases and they are the ONLY specifications (other than advanced RNP) including Final approach.
AP stands for approval/authorisation required.
RNAV spec flight phases
RNP spec flight phases
Types of approach (diagram)
RNP approaches
Use GPS primarily.
DO NOT include precision approaches, which are based on ground aids.
Are either:
i) non-precision (LNAV only); or
ii) approaches with vertical guidance (APV) - either barometric (LNAV/VNAV) or SBAS (LPV).
Note: Without vertical guidance need to fly to a MDA, which is higher than the published DA
Approaches with Vertical Guidance (APV)
PBN/RNAV approaches with one of two forms of vertical guidance:
i) LNAV/VNAV or APV Baro - FMS constructs a glide slope and uses barometric data to provide guidance along it
ii) LPV (Localiser Performance with Vertical Guidance) or APV SBAS - Use SBAS to give enough GNSS data to construct geometric vertical approach. Needs an enhanced Final Approach Segment (FAS) data block in the ND.
Approach minima:
- Non-precision GPS (LNAV)
- APV Baro (LNAV/VNAV)
- APV SBAS (LPV)
- Precision (ILS or GLS [GBAS])
LNAV: 400-600ft MDA
LNAV/VNAV: 350 - 400ft DA
LPV: 200 - 300ft DA
ILS/GLS: 0 - 200ft DA
Rate of descent calculation from groundspeed
Descent rate (fpm) = 5 x groundspeed (kt)
NANU
Notice Advisory to Navstar Users
Informs of GPS constellation and planned maintenance (missed 72 hours in advance)
Examples of non-precision approaches
NDB, Loc/DME, VOR
Examples of precision approaches
ILS, MLS, GLS
FANS
Future Air Navigation System
Datalink ATC, “communications”
