Aviation Communication,
Navigation, and Surveillance
(CNS)
Instructor: Dr. George L. Donohue
Prepared by: Arash Yousefi
Spring 2002
Summary
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Chapter 1: Introduction to
CNS

Chapter 2: The

Chapter 3: Terrestrial RadioNavigation Systems
Chapter 4: Satellite Radio
Navigation
Chapter 5: Terrestrial
Integrated Radio
Communication-Navigation
Systems
Chapter 6: Air-Data Systems

Navigation Equations
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
Chapter 7: Attitude and
Heading References
Chapter 8: Doppler and
Altimeter Radars
Chapter 9: Mapping &
Multimode Radars
Chapter 10: Landing
Systems
Chapter 11: Data Links and
digital communication
Chapter One
Introduction
Definitions

Navigation: the determination of the position and velocity of a
moving vehicle. The process of measuring and calculating state
Vy
vector onboard
vx
X
Vx
Vz
Z


Y

V  vy
Six- component
vz
state vector
x
y
z
Surveillance or Position Reporting: the process of measuring and
calculating state vector out side the vehicle
Navigation sensor: may be located in the vehicle, in another
vehicle, on the ground , or in space
Definitions


Automatic Dependent Surveillance(ADS):
reporting of position, measured by sensors
in an aircraft, to a traffic control center.
Guidance: handling of the vehicle. Two
Meanings;
1.
2.
Steering toward a destination of known position
from the aircraft’s present position
Steering toward a destination without explicitly
measuring the state vector (mostly military
arcfts)
Categories of Navigation
1. Radio Systems: consist of a network of
transmitters(sometimes also receivers) on the
ground, satellite or on other vehicle.
2. Celestial Systems: compute position by
measuring the elevation and azimuth of celestial
bodies relative to the navigation coordinate frame
at precisely known times.
3. Mapping Navigation Systems: observe images
of the ground, profile of altitude, or other external
features.
Dead-reckoning navigation
systems
Derive their state vector fro, a continuous
series of measurements relative to an initial
position. Two kinds:

1.
Acft heading & either speed or acceleration.



2.
Gyroscopes or magnetic compassesheading
Air-data sensors or Doppler radar speed
Inertial sensorsvector acceleration
Emissions from continues-wave radio stations

Create ambiguous “lanes” that must be counted to
keep track of coarse position
The Vehicle (1)
1. Civil Aircraft: mostly operate in developed
areas(Ground-based radio aids are plentiful)


Air Carriers: large acft used on trunk
routes and small acft used in commuter
service.
General Aviation(GA): range from single-
place crop dusters to well-equipped fourengine corporate jets.
The Vehicle (2)
2. Military Aircraft
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Interceptors & combat air patrol: small, high-climb-rate
protecting the homeland
Close-air support: mid-size to deliver weapons in support
of land armies
Interdiction: mid-size and large acft to strike behind
enemy lines to attack ground targets
Cargo Carriers: same navigation requirements as civil acft
Reconnaissance acft: collect photograph
Helicopter & short take of and landing(STOL) vehicle
Unmanned air vehicle
The Vehicle (3)

Fig 1.1
Avionics Placement on multi-purpose transport
Phases of Flight
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Takeoff
Terminal Area
En-Route
Approach
Landing
Surface
Weather
Navigation Phases
Navigation Phases
Picture courtesy of MITRE Corporation
Takeoff Navigation



From taxiing into runway to climb out
Acft is guided along the runway centerline by
hand-flying or a coupled autopilot based on
steering signals
Two important speed measurements are
made on the runway


The highest ground speed at which an aborted takeoff is
possible pre-computed and compared, during the takeoff
run, to the actual ground speed as displayed by navigation
system
The airspeed at which the nose is lifted is pre-calculated and
compared to the actual airspeed as displayed by the air-data
system
Terminal Area Navigation
1.
Departure: begins from maneuvering out the

runway, ends when acft leaves the terminal-control
area
Approach: acft enters the terminal area, ends when
it intercepts the landing aid at an approach fix
Standard Instrument Departure (SIDs) & Standard
Terminal Approach Route (STARs)
Vertical navigation Barometric sensors

Heading vectors  Assigned by traffic controller
2.
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En Route Navigation
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Leads from the origin to the destination and alternate
destinations
Airways are defined by navaids over the land and by
lat/long over water fixes
The width of airways and their lateral separation
depends on the quality of the navigation system
From 1990s use of GPS has allowed precise
navigation
In the US en-route navigation error must be less than
2.8 nm over land & 12 nm over ocean
Approach Navigation


Begins at acquisition of the landing aid until the
airport is in sight or the acrft is on the runway,
depending on the capabilities of the landing aid
Decision height (DH): altitude above the runway at
which the approach must be aborted if the runway is
not in sight



The better the landing aids, the lower the the DH
DHs are published for each runway at each airport
An acrft executing a non precision approach must abort if
the runway is not visible at the minimum descent altitude
(typically=700 ft above the runway)
Landing Navigation
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Begins at the DH ends when the acrf exits the
runway
Navigation may be visual or navigational set’s
may be coupled to a autopilot
A radio altimeter measures the height of the
main landing gear above the runway for
guiding the flare
The rollout is guided by the landing aid (e.g.
the ILS localizer)
Missed Approach




Is initiated at the pilot’s option or at the
traffic controller’s request, typically because
of poor visibility. And alignment with the
runway
The flight path and altitude profile are
published
Consists of a climb to a predetermined
holding fix at which the acrf awaits further
instructions
Terminal area navaids are used
Surface Navigation


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Acrf movement from the runway to gates,
hanger
Is visual on the part of the crew, whereas the
ground controller observes acrf visually or
with surface surveillance radar
GPS reports from acrfs that concealed in
radar shadows reduce the risk of collision
Weather


Instrument meteorological conditions
(IMC) are weather conditions in which
visibility is restricted, typically less than
3 miles
Acft operating in IMC are supposed to
fly under IFR
Design Trade-Offs (1)
1.
Cost


2.
Construction & maintenance of transmitter
stations Government Concern
Purchase of on-board HW/SWUser Concern
Accuracy of Position & velocity



Specified in terms of statistically distribution of
errors as observed on a large # of flights
Civil air carrier Based on the risk of collision(10 9 )
Landing error depends on runway width, acft
handling characteristics, flying weather
Design Trade-Offs (2)
3.
Autonomy:The extent to which the vehicle
determines its own position & velocity without
external aids. Subdivided to;


Passive self-contained systems neither receive nor transmit
electromagnetic signals (dead-reckoning systems such as
inertial navigators
Active self-contained systems Radiate but do not receive
externally generated signals(radars, sensors). Not dependent
on existence of navigation stations
Design Trade-Offs(3)
(continue form previous
slide)



Natural radiation receivers  i.e. magnetic
compasses, star trackers, passive map
correlators
Artificial radiation receivers measure
electromagnetic radiation from navaids(earth or
space based) but do not transmit (VOR, GPS)
Active radio navaidsexchange signals with
navigation stations(i.e. DME, collision-avoidance
systems). The vehicle betrays its presence by
emitting & requires cooperative external
stations. The least autonomous of navigation
systems
Design Trade-Offs (4)

Latency
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

Time delay in calculating position & velocity,
caused by computational & sensor delays
Can be caused by computer-processing delays,
scanning by a radar beam, or gaps in satellite
coverage
Geographic coverage

Terrestrial radio systems operating below
approximately 100 KHz can be received beyond
line of sight on earth; those operating above 100
KHz are confirmed to line of sight
Design Trade-Offs (5)

Automations
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Availability
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The crew receive a direct reading of position, velocity, &
equipment status, without human intervention
The fraction of time the system is usable
Scheduled maintenance, equipment failure, radiopropagation problems
i.e 0.99 HRS Outage/YR for voice communication
System capacity
Reliability
Maintainability
Design Trade-Offs (6)
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Ambiguity
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The identification, by the navigation system, of
two or more possible positions of the acft, with no
indication of which is correct
Integrity

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Ability of the system to provide timely warning to
acft when its error are excessive
For en-route an alarm must be generated within
30sec of the time a computed position exceeds its
specified error
Evolution of Air Navigation
1922 ATC begins
1935, an airline consortium opened
the first Airway Traffic Control
Station
1930 Control Tower
Page 11-15 Katon, Fried
1940s Impact of
radar
Airway Centers
ADS-B GPS
1960s & 70s
Integrated Avionics
Subsystems (1)
1.
2.
Navigation
Communication

3.
Flight control
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

4.
intercom among the crew members & one or more external twoway voice & data links
Stability augmentation & autopilot
The former points the airframe & controls its oscillations
The latter provides such functions as attitude-hold, heading-hold,
altitude hold
Engine control

The electronic control of engine thrust(throttle management)
Integrated Avionics
Subsystems (2)
5. Flight management

Stores the coordinates of en-route waypoints
and calculates the steering signals to fly toward
them
6. Subsystem monitoring & control

Displays faults in all subsystems and
recommends actions to be taken
7. Collision-avoidance

Predicts impending collision with other acft or
the ground & recommends an avoidance
maneuver
Integrated Avionics
Subsystems (3)
Weather detection
8.


Observes weather ahead of the acft so that the
route of flight can be alerted to avoid
thunderstorms & areas of high wind shears
Sensors are usually radar and laser
Emergency locator transmitter(ELT)
9.


Is triggered automatically on high-g impact or
manually
Emit distinctive tones on 121.5, 243, and 406
MHz
Architecture (1)

Displays;


Present information from avionics to the pilot
Information consists of vertical and horizontal navigation
data, flight-control data (e.g. speed and angle of attack),
and communication data (radio frequencies)
Architecture (2)

Flight controls;



The means of inputting information from the pilot to the avionics
Traditionally consists of rudder pedals and a control-column or stick
Switches are mounted on the control column, stick, throttle, and
hand-controllers
Architecture (3)
Computation;
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

The method of processing sensor data
Two extreme organizations exist:
1. Centralized; Data from all sensors are
collected in a bank of central computer in
which software from several subsystems are
intermingled
2. Decentralized; Each traditional subsystem
retains its integrity
Architecture (4)

Data buses
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Copper or fiber-optics paths among sensors,
computers, actuators, displays, and controls
Safety partitioning

Commercial acft sometimes divide the avionics
to;
1.
2.
3.

Highly redundant safety-critical flight-control system
Dually redundant ,mission-critical flight-management
system
Non-redundant maintenance system
Military acrft sometimes partition their avionics
for reason other than safety
Architecture (5)

Environment

Avionics equipment are subject to;



acft-generated electricity-power transient, whose effects
are reduced by filtering and batteries,
externally generated disturbances from radio
transmitters, lightening, and high-intensity radiated fields
The effect of external disturbances are reduced by


shielding metal wires and by using fiberoptic data buses
add a Faraday shielding to meal skin of the acft
Architecture (6)

Standards

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Navaid signals in space are standardized by ICAO
Interfaces among airborne subsystems, within the
acft, are standardized by Aeronautical Radio INC.
(ARINC), Annapolis Maryland, a nonprofit
organization owned by member airlines
Other Standards are set by:



Radio Technical Commissions for Aeronautics,
Washington DC
European Organization for Civil Aviation Equipment
(EUROCAE)
etc.
Human Navigator

Large acft often had (before 1970) a third
crew member, flight engineer:



To operate engines and acft subsystems e.g. air
conditioning and hydraulics)
Use celestial fixes for positioning
Production of cockpits with inertial, doppler,
and radio equipments facilitated the
automatically stations selection,
position/waypoint steering calculations and
eliminated the number of cockpit crew to two
or one.
Chapter Two
The Navigation Equations
Data resources

The navigation equations



describe how the sensor outputs are processed in
the on-board computer in order to calculate the
position, velocity, and attitude.
contain instructions & data and are part of the
airborne software. The data is stored in read-only
(ROM) at the time of manufacturing
Mission-dependent data (e.g. waypoints) are
either loaded from cockpit keyboard or a
cartridge (data-entry device)
Acrft navigation system

The system utilizes three types of sensor
information
1.
2.
3.

Absolute position data from radio aids, radar
checkpoints, and satellites
Dead-reckoning data, obtained from inertial,
Doppler, or air-data sensors, as a mean of
extrapolating present position
Line-of-sight directions to stars, which measure
a combination of position & attitude errors
The navigation computer combines the
sensor information to obtain an estimate of
acft’s position, velocity, and attitude.
System Hierarchy
Heading
attitude
•Inertial
air data
•Doppler
Star line
of sight
Deadreckoning
computations
Celestial
equations
To cockpit display
pointing sensor
Attitude
•Position
Way
points
•Velocity
•Attitude
Most probable
position
computation
Position
computations
•Satellite
(GPS)
•Radar
Range, bearing
to displays, FMS
Steering signals
to autopilot
•Positioning
sensors
•Radio(VOR,
DME, Loran,
Omega)
Time to go
Course
To map display
Positioning
computations
Position
data
Velocity
Block diagram of an
aircraft navigation system
To weapon computers
Geometry of The Earth (1)

Apparent gravity field g = the vector
sum of the gravitational and centrifugal
fields
g  G  Ω  (Ω  R )
G = Newtonian gravitational attraction of
the earth
Ω = inertial angular velocity of the
earth(15.04107 deg/hr
g = apparent gravity field
Geometry of The Earth (2)


For navigational purposes, the earth’s surface can be
represented by an ellipsoid of rotation around the
Earth’s spin axis
The size & shape of the best-fitting ellipsoid is chosen
to match the sea-level equipotential surface.
Geometry of The Earth (3)
Fig 2.2
Median section
of the earth,
showing the
reference
ellipsoid &
gravity field
Coordinate Frames (1)

The position, velocity and attitude of the aircraft
must be expressed in a coordinate frame.
Navigation
coordinate frame
Coordinate Frames (2)
1.
Earth-centered, Earth-fixed (ECEF): The basic coordinate
frame for navigation near the Earth




2.
Origin is at the mass center of earth
y1, y2  Lie in True equator
y2  Lies in the Greenwhich meridian
y3  Lies along the earth’s spin axis
Geodetic spherical coordinates: Spherical coordinates of the
normal to the reference ellipsoid.




Z1  longitude
Z2  geodetic latitude
Z3  altitude h above the reference ellipsoid
This system is used in maps and mechanization of deadreckoning and radio navigation systems.
Coordinate Frames (3)
3.
Geodetic wander azimuth: Locally level to the
reference ellipsoid




Z3 is vertical up
  , west of true north.
Z2 points at an angle
Z1 points at an angle  , north of true east
Most commonly used in inertial navigation
Dead-Reckoning Computation (1)



DR is the technique of calculating position
from measuring of velocity.
It is the means of navigation in the absence
of position fixes and consists in calculating
the position (the zi-coordinates) of a vehicle
by extrapolating (integrating) estimated or
measured ground speed.
Prior to GPS, DR computations were the heart
of every automatic navigator.
Dead-Reckoning Computation (2)

In simplest form, neglecting wind:
t
V north Vg cos wT , y  y0   Vnorthdt
0
t
V east Vg sin wT , x  x0   Veast dt
Where:
y  y0 , x  x0 0
east & north distances traveled
during the measurement interval
Vg
Ground speed
WT
True heading
T
Angle between acft heading and
true north
Dead-Reckoning Computation (3)

Fig 2.4
Dead-Reckoning Computation (4)


In the presence of a crosswind the groundspeed vector does not lie along the acft’s
center line but makes an angle  with it
The drift angle  can be measured with a
Doppler radar or a drift sight (a downwardpointing telescope whose reticle can be
rotated by the navigator to align with the
moving ground)
Dead-Reckoning Computation (5)

In the moving air mass:
V north VTAS cos(   ) cos( T   )  Vwind north
V east VTAS sin(    ) sin( T   )  Vwind east
Where:

The pitch angle
VTAS True airspeed

Then:
Sideslip angle
t
y  y0   Vnorthdt
0
t
x  x0   Veast dt
0
Positioning (1)

Radio Fixes: There are five basic airborne
radio measurements:
1.
2.
Bearing: The angle of arrival, relative to the
airframe, of a radio signal from an external
transmitter. It is measured by difference in
phase or time of arrival at multiple sensors
Phase: The airborne receiver measures the
phase difference between continuse-wave
signals emitted by two stations using a single
airborne antenna
Positioning (2)
3.
4.
5.
(Radio Fixes Cont.)
Time difference: The airborne receiver
measures the difference in time of arrival
between pulses sent from two stations.
Two-way range: The airborne receiver
measures the time delay between the
transmission of a pulse and its return from
an external transponder at a known location
One-way range: The airborne receiver
measures the time of arrival with respect to
its own clock
Positioning (3)

Line-of-Sight distance measurements
Acft near the surface of the earth at R si and a radio station that
may be near the surface or in space, at R 0 The slant range,
|R si  R 0 |from the acft to the station could be measured by oneway or two-way ranging
Positioning (4)
Assume an
acft position
Ground-Wave One-Way Ranging: Loran and Omega waves
propagate along the curved surface of the earth. With a sensor, an
acft can measure the time of arrival of the navigation signal from
two or more two or more station & compute its own position
Calculate the exact distance and
azimuth to each radio transmitter
using ellipsoid Earth equation
Calculate the difference between
the measured and predicted time of
arrival to each station
Calculate the predicted propagation
time & time of arrival
The probable position is the
assumed position, offset by the
vector sum of the time difference,
each in the direction of its station,
converted to distance
Measure the time of arrival using
the acft’s own clock
Assume a new acft position and
iterate until the residual is within
the allowed error
Positioning (5)
Assume an
acft position
Ground wave Time-differencing: An acft can measure
the difference in time of arrival of Loran & Omega signals
from two or more station
Calculate the exact range and
azimuth from the assumed position
to each observed radio station
using ellipsoid Earth equation
Calculate the predicted propagation
time allowing fir the conductivity of
the intervening Earth’s surface and
the presence of the sunlight
terminate between the acft and the
station
Subtract the times to two station to
calculate the predicted difference in
propagation time
Measure the difference in time of
arrival of the signals from the two
stations
Subtract the measured and
predicted time differences to the
two stations
Calculate The time-difference
gradients from which is calculated
the most probable position of the
acft after the measurements
Iterate until the residual is smaller
than the allowed error
Positioning (6)

Terrain-Matching Navigation: These nav. sys.
obtain occasional updates when the acft over
flies a patch of a few square miles, chosen for
its unique profile.



A digital map of altitude above sea level, hsis
stored for several parallel tracks
The acft measures the height of the terrain above
sea level as the difference between barometric
altitude and radar altitude.
Each pair of height measurements & the deadreckoning position are recorded & time taged
Positioning (7)

(Terrain-Matching Navigation)
After passing over the patch, acft uses its measured
velocity to calculate the profile as a function of
distance along track hm (x) between the measured and
stored profile and calculates the cross-correlation
function between the measured and stored profiles
ms ( )
Terrain-Matching Navigation (1)
Fig 2.6
Parallel tracks
through
terrain patch
Terrain-Matching Navigation (2)

Fig 2.7
Measurement
of terrain
altitude
hs  hbaro  hradar
nA
ms ( )   hm ( x)hs ( x   )dx
0
Where: A= length of map patch, the integration is long enough
(n>1),
Course Computation (1)
Range & Bearing Calculation: is to
calculate range and bearing from an
acft to one or more desired waypoints,
targets, airports, checkpoints, or radio
beacons.
Best-estimate
of the present
position of acft
Course
computation
Computed range &
bearing to other
vehicle subsystems
Course Computation (2)

D
Fig 2.8
( x  x )
1
2
 ( y  y1 ) 2
x  xt
BT  arctan
y  yt

Course Computation (3)
Airway Steering: It calculates a great circle from the takeoff

point(or from a waypoint) to the destination (or another
waypoint).
The acft steered along this great circle by calculating the lateral
deviation L from the desired great circle and commanding a
bank angle:
 c  K1 L  K 2 L  K 3  Ldt


The bank angle is limited to prevent excessive control
commands when the acft is far of course. Near the destination,
the track is frozen to prevent erratic steering
As the acft passes each waypoint, a new waypoint is fetched,
thus selecting a new desired track. The acft can then fly along a
series of airways connecting checkpoints or navigation station
Course Computation (4)
Area Navigation:



Between 1950-1980, acft in developed countries flew
on airways, guided by VOR bearing signals
Position along the airway could be determined at
discrete intersections using cross-bearings to another
VOR( )
In 1970s DME, collocated with VOR, allowed acft to
determine their position along the airway 
continuously. Thereafter authorities allowed them to
fly anywhere with proper clearance a technique
called RNAV (random navigation) or area navigation
Course Computation (5)

Area Navigation
Plan view of
area-navigation fix
Measure
ρ1, ρ2
(distances
to DME
stations
V1, V2)
Triangle
P1V1V3
Position
P1
Course Computation (6)
Area Navigation


RNAV uses combinations of VORs and DMEs
to create artificial airways either by
connecting waypoints defined by lat/long or
by triangulation or tri-lateration to VORTAC
stations(doted lines to A1)
The on-board flight-management or
navigation computer calculates the lateral
displacement L from the artificial airway and
the distance D to the next waypoint A1 along
the airway
Course Computation (7)
Assume P1 based
on prior nav.
information
Calculate
Area Navigation: An artificial airway is defined
by the points A1 and A2. D and L are found
interatively:
End
ρ1, ρ2 using the range
equation
Correct the measures ranges for the
altitudes of acft and DME station
Subtract the measured &
calculated ranges
1  1 (measured )  1 (calculated )
3  3 (measured )  3 (calculated )
 i Is small
enough
Estimate ρ1 along the vector k
whose components along 1and
 3 are 1and 3
 i Is not
small enough
Digital Charts
1.
2.
3.
Visual charts: Showing terrain, airports, some
navaids and restricted areas.
En-route instrument chart: Showing airways,
navigation aids, intersections, restricted areas, and
legal boundaries of controlled airspace.
Approach plates, SIDs and STARs: Showing
horizontal and vertical profile of pre-selected paths
to and from the runway, beginning or ending at enroute fixes. High terrain and man-made obstacles
are indicated. Missed approach to a holding fix are
described visually
Chapter Three
Terrestrial Radio-Navigation
Systems
General Principles
1. Radio Transmission and Reception
If an antenna with length of L is placed in space and
excited with an alternating current with wave
length of λ and;
If L=λ /2 then almost all the applied AC power will be
radiated into space
Modular
Transmitter
Receiver
Elementary radio-navigation system
Processor
Display of
data bus
interface
Radio Frequencies
Name
Abbreviation
Frequency
Frequency
Wave length
VLF
3 to 30 kHz
100 to 10km
Low
LF
30 to 300 kHz
10 to 1km
Medium
MF
300 to 3000 kHz
1km to 100 m
High
HF
3 to 30 MHz
100 to 10m
Very high
VHF
30 to 300 MHz
10 to 1cm
Ultrahigh
UHF
300 to 3000 MHz
1m to 10cm
Super high
SHF
3 to 30 GHz
10 to 1cm
Extremely
high
EHF
30 to 300 GHz
10 to 1mm
Very low
Free Space Rules (1)
Regardless of frequency, the following
rules apply in free space.
1.
2.
The propagation speed of radio waves in a
vacuum=speed of light (300k km/sec)
The receiver energy is a function of the area of the
receiving antenna. R=the range between antenna
in the same units as for antenna area
Receiver power
Transmitte d power
 Receiver antenna area
4R 2
Free Space Rules (2)
Multiple antennas may be used at both ends of the path to
increase the effective antenna area. Increase in area produce
an increase in directivity or gain and result in more of the
transmitted power reaching the receiver.
3.



gain(G) in the direction of maximum response=directivity(D) *
efficiency
Maximum effective aperture=effective area of an antenna= D / 4
A transmitter of power P & antenna gain G has effective radiated
power (ERP) of PG along its axis of maximum gain
AA
Received power
 r2 2t
Transmitte d power R 
Ar effective area of receiving antenna
At effective area of transmitt ing antenna
R range between antennas
 wavele nght (the speed of light/freq uency)
Free Space Rules (3)
4.
The minimum power that a receiver can
detect is referred to as its sensitivity. Where
unlimited amplification is possible,
sensitivity is limited by the noise existing at
the input of receiver. Noise types;
1.
2.
External. Due to other unwanted transmitters,
electrical-machinery interference, atmospheric
noise
Internal. Depending on the state of the art and
approaching, as a lower limit, the thermal noise
across the input impedance of the receiver
Free Space Rules (4)
5.
The minimum bandwidth occupied by the
system is proportional to the information
rate.
1.
To assess the free-space range of a radio
system, it is necessary to have at least the
following facts:
1.
2.
3.
4.
Transmitter power and antenna gain
Receiver antenna gain and noise figure
The effective bandwidth of the system
The effect on the system performance of external or
internal noise
Free Space Rules (5)

Required radio transmitter power of a radio system as a function
of key system parameters
It is assumed that
the polarization of
the transmitting &
receiving antenna
are the same
P  S
10 log  T      LP  NF  GT  GR  FN
 PN   N  REQ
PT transm itter power
(dB)
PN noise power in receiver
( S / N ) REQ
required signal - to - noise ratio in receiver
NF receiver noise figure
FN
noise improvemen t factor due to modulation mehod
and bandwidth spreading (e.g. frequency modulation )
GT
trans mitter antenna gain
GR
receiver antenna gain
LP
propagatio n path antenna loss
Free Space Rules (6)

The radiation pattern from half-wave wires is
a maximum along their perpendicular
bisectors & a minimum along the axis of the
wirethe equisignal pattern forming a
“doughnut”
Propagation & noise
characteristics
In free space, all radio waves, regardless of
frequency, are propagated in straight lines at
the speed of light.
Along the surface of the earth:


About 3 MHz appreciable amount of energy follows the
curvature of the earth. Ground wave
Up to about 30 MHz, appreciable energy is reflected from the
ionosphere. Sky wave
Ground Wave


Normally received when listening to a
standard AM broadcast transmitter
Dependent on several factors:
1.
2.
3.
Conductivity and dielectric constant of the earth
At low frequencies, it is physically difficult to
construct a vertical transmitting antenna large
enough to be half a wavelength
In most parts of the world & at most times of
the years, atmospheric noise at low frequencies
is so much greater than receiver noise that
additional transmitter power must be used
Ground Wave
4.
5.
(continue from previous slide)
A characteristic of ground waves is that their
propagation velocity is not entirely constant
At low frequencies they offer the only long-range
radio communication means to vehicle that are
not dependent on the ionosphere or airborne or
satellite-borne relay station
Sky Wave (1)

Ionosphere:
between 50 & 500 km above the earth’s surface, radiation from the
sun produces a set of ionized layers

Acts as a refractive medium; when the refractive index is high

At A: the radio wave strikes the refractive layer at too steep angle
and continues to space

At B:the radio wave strikes at a oblique, is bent sufficiently and
travels somewhat parallel to the earth

At C: the wave arrives at the refractive layer with glancing
incidence & immediately returns to earth

At D: the refractive index is too low in relation
Ionosphere
to frequency to seriously deflect the radio wave.
A B C
D
Travels on out to space& happens at
F1 F2 F3
F4
frequencies above 30 MHz

Transmitter
Receiver
Skip distance at F1
Sky Wave (2)



Maximum usable frequency: maximum
frequency that for a given distance & degree
of ionization a signal returns to earth
Skip distance: The distance that a given
signals returns to earth
If more than one ionizing layer are present,
there may be various skip distances for the
same frequency
Sky wave vs. Ground wave


At those frequencies and distances where ionospheric
reflection occurs, the attenuation of the radio signals
is only that due to the spreading out of the power
over the surface of the earth and is, consequently,
proportional to distance.
Ground wave attenuation is very much greater,
except at the lowest frequencies
How the signal level produced at the receiver by
the two types of transmitter is look like, at the
frequencies around 1 MHz
Distance from transmitter
Line-of-Sight Waves (1)



Above approximately 30 MHz, propagation follows
the free-space laws. The transmission path is
predictable, and the wavelengths are so short as to
readily permit almost any desired antenna structure
From approximately 100 MHz to 3 GHz, the
transmission path is highly predictable and is
unaffected by the time of the day, season,
precipitation, or atmospherics.
Above 3 GHz, absorption & scattering be precipitation
& by the atmosphere begin to be noticed, and
become limiting factors above 10 GHz
Line-of-Sight Waves (2)



A receiver, at a point in space, receives a direct ray from transmitter
and a reflected ray from the ground
Because of the short wavelength, the path difference is sufficient to
cause addition or cancellation as the receiver moves up & down in
elevation.
Deep nulls, of vertically zero signal strength, are produced at those
vertical angles at which the direct wave path & the reflected wave path
differ by exactly an odd multiple of half-wavelength
With
counterpoise
Without
counterpoise
Vertical reflection path
Line-of-Sight Waves (3)




Maxima of signal strength occur where the two path
lengths produce in-phase signal
The number of nulls per vertical degree of elevation
increases with the height of the antenna & frequency
Line-of-sight systems on the earth are subject to the
limitations of the horizon
Beyond the line of of sight, signal strength at these
frequencies drops off almost as suddenly as does
visible light when passing from day to night. Very
large powers & antenna gains are needed and such
systems don’t have much value in aircraft CNS
systems
Line-of-Sight Waves (4)
Line-of-sight range
Position determination methods

Fig4.8
Common geometric
position fixing scheme
Direction finding (1)

Ground-based direction-finders: Take bearings on
airborne transmitter & then advise the acft of its
bearing from the ground station.


The operation is time cumbersome & time-consuming, and
requires an airborne transmitter & communication link
Airborne direction-finders & homing adaptors: Take
bearings on ground transmitter and typically can
afford only the simplest of systems and must tolerate
large errors.

Direction-finding continues to be used as a backup aid to
more accurate systems
Direction finding (2)

Loop antenna Direction-Finder Principles: No longer
in production but is principles still apply to the
current generation of equipments





Measures the differential distance to a transmitter from two
or more known points
Is a rectangular loop of wire whose inductance is resonated
by a variable capacitor to the frequency to be received
The signal is assumed to be vertically polarized & it induces
voltage in the arms AB & CD
Currents in AB&CD are equal in amplitude & phase when the
plan of the loop is 90deg to the direction of arrival of the
signal (null position)
Physically rotating the loop to the null position indicates the
direction to the transmitting station
Loop Antenna Direction
Finding

Fig 4.9-
Direction
finding loop
Airborne VHF/UHF DirectionFinder Systems

VHF equipment used by Coast Guard for air-sea
rescue on the 225 to 400 MHz communication band
on the distress frequency of 343 MHz



Equipment designed only for hominguse a fixed-antenna
system that generates two sequentially switched cardioid
patterns whose equisignal crossover direction is found by
turning the acft toward transmitting station
Equipment designed for both direction finding and
hominguses a rotating antenna that generates a similar
pair of cardioid patterns, whose equisignal crossover
direction is found
Civil-aviation communication118-156 MHz, Militaryaviation communication 225-400 MHz
Non directional Beacons



Aircraft use radio beacons to aid in finding the initial approach
point of an instrument landing system as well as for
nonprecision or precision approach systems
Operating in the 200 to 1600 kHz, they have output power
ranging from as low as 20 watts up to several kilowatts
They are connected to a single vertical antenna & produce a
vertical pattern
Cone of
silence
Nondirectional beacon, vertical pattern
Marker Beacons (1)



Each beacon generates a fan-shaped pattern, the
axis of the fan being at right angles to the airway
Operate at 75 MHz & radiate a narrow pattern
upward from the ground, with little horizontal
strength, so that interference between marker
beacons is negligible
Fig 4.12
Fan-marker
pattern
Marker Beacons (2)

Fig 4-13
Fan-marker
pattern
VHF Omnidirectional
Range(VOR) (1)



Adopted for voice communication & navigation
The VOR operates in 108 to 118 MHz band, with
channels spaced 100 kHz apart
The ground station radiates a cardioids pattern that
rotates at 30rps, generating a 30 Hz sine wave at the
airborne receiver. Ground station also radiates an
omnidirectional signal, which is frequency modulated
with a fixed 30 Hz reference tone. There is no skywave contamination at very high frequency & no
interference from stations beyond the horizon,
performance is relatively consistent
VHF Omnidirectional
Range(VOR) (2)

Transmitter Characteristics


VOR adapted horizontal polarization, even though acft VHF
communication uses vertical polarization. Each radiator in
the ground station transmitter is an Alford loop. The Alford
loop generates a horizontally polarized signal having the
same field pattern as a vertical dipole
Fig 4.14
Alford loop
VOR Block Diagram

Fig 4.15
VHF Omnidirectional
Range(VOR)

Receiver characteristics

The airborne equipment comprises a horizontally polarized
receiving antenna & a receiver. This receiver detects the 30
Hz amplitude modulation produced by the rotating pattern &
compares it with the 30 Hz frequency-modulated reference.

Fig 4.16
Doppler VOR






Doppler VOR applies the principles of wide antenna aperture to
the reduction of site error
The solution used in US by FAA involves a 44-ft diameter circle
of 52 Alford loops, together with a single Alfrod loop in the
center
Reference phaseThe central Alford loop radiates an
omnidirectional continuous wave that is amplitude modulated at
30 Hz
The circle of 52 Alford loops is fed by a capacitive commutator
so as to simulate the rotation of a single antenna at a radius of
22ft
Rotation is at 30rps, & a carrier frequency 9960 Hz higher than
that in the centeral antenna is fed to the commutator
With 44-ft diameter & a rotation speed of 30 rps, the peripheral
speed is on the order of 1400 meters per second, or 480
wavelengths per second at VOR radio frequencies
Distance-Measuring
Equipment (DME) (1)

DME is a internationally
standard pulse-ranging
system for acft,
operating in the 960 to
1215 MHz band. In the
US in 1996, there were
over 4600 sets in use
by scheduled airlines
and about 90,000 sets
by GA
DME Operation
Distance-Measuring
Equipment (DME) (2)

The acft interrogator transmits pulses on one of 126
frequencies, spaced 1 MHz apart, in the 1025 to 1150
MHz band. Paired pulses are used in order to reduce
interference from other pulse systems. The ground
beacon(transponder) receives these pulses & after a
50 sec fixed delay, retransmits them back to the
acft. The airborne automatically compares the
elapsed time between transmission and reception,
subtracts out the fixed 50 sec delay, & displays the
result ona meter calibrated in nautical miles.
Hyperbolic Systems

Named after the hyperbolic lines of
position (LOP) that they produce rather
than the circles




Loran-C
Omega
Decca
Chayka
Measure the time-difference
between the signal from two or
more transmitting station
Measure the phase-difference
between the signal transmitted
from pairs of stations
Long-Range Navigation(Loran)

A hyperbolic radio-navigation system beginning
before outbreak of WW II
1.
2.
3.
4.

Uses ground waves at low frequencies, thereby securing an
operating range of over 1000 mi, independent of line of
sight
Uses pulse technique to avoid sky-wave contamination
A hyperbolic systemit is not subject to the site errors of
point-source systems
Uses a form of cycle (phase) measurements to improve
precision
All modern systems are of the Loran-C variety
Long-Range Navigation(LoranC) (1)




Is a low-frequency radio-navigation aid operating in the
radio spectrum of 90 to 110 kHz
Consists of at least three transmitting stations in groups
forming chains
Using a Loran-C receiver, a user gets location information
by measuring the very small difference in arrival times of
the pulses for each Master -Secondary pair
Each Master-Secondary pair measurement is a time
difference. One time difference is a set of points that are,
mathematically, a hyperbola. Therefore, position is the
intersection of two hyperbolas. Knowing the exact location
of the transmitters and the pulse spacing, it is possible to
convert Loran time difference information into latitude and
longitude
Loran-C (2)
Signal shape
Position determination
Loran-C (2)
Omega (1)

Eight VLF radio navigation transmitting stations trough out the
world
1.
2.

Sub-ionosphere



Continuous-wave (CW) signals transmitted on four common
frequencies, and
One station unique frequency
They are propagated between the earth’s surface and the
ionosphere
VLF signal attenuation is low Omega signals propagate to
great ranges (typically 5000 to 15,000 nmi
Primary interest to navigation users is the signal phase which
provides a measure of transmitter-receiver distance
Omega (2)

Omega receiver provides an accuracy of 2 to 4 nmi
95% of the time for navigation purposes



When a receiver utilizes Omega signal phase corrections
transmitted from nearby monitor stationposition accuracy
comes down to 500 meters
Thus the resulting system has an accuracy that is
comparable to the high-accuracy navigation aid
Commonly used in oceanic civil airline configurations,
combined with an inertial navigation system, so that
the Omega system error effectively ‘bounds” the
error of the inertial system
Omega (3)

Fig. 4.34
Omega station configuration
Omega (4)

Important features of omega signals
1.
2.
3.
4.
Four common transmitted signal frequencies:
10.2, 11 1/3, 13.6, and 11.05 kHz
One unique signal frequency for each station
A separate interval of 0.2 sec between each of
the eight transmissions
Variable-length transmission periods
Omega (5)

Fig. 4.35
Omega
system signal
transmission
format
Omega (6)

Position determination

Fig 4.37
Hybrid geometry
for phase-difference
measurements
Decca



Developed by British and used during World War II.
Based on the measurment of differential arrival time(at the vehicular
receiver) of transmissions from two or more synchronized stations
(typicaly 70 mi apart)
i.e two stations (A,B) 10 mi apart and each radiating synchronized
radio-frequency carries of 100 kHz




Wave length=3000 m, ~2 mi
On a line between the stations the movement of a vehicle D one mile from
the other station will cause the vehicle to traverse one cycle of differential
radio-frequency phase
10 places along the line AB where the signals from the twp stations will be
in phase one
As the vehicle moves laterally away from this line, isophase LOPs can be
formed with the stations and BD-AD as a constatnt for each LOP
Chayka




A pulse-phase radio-navigation system similar
to the Loran-C system
Used in Russia and surrounding territories
By using ground waves at low frequencies,
the operating range is over 1000 mi; by using
pulse techniques, sky-wave contamination
can be avoided
Designed to provide both a means of
determining an accurate user position and
source of high-accuracy time signals
Chapter Four
Satellite Radio Navigation
Introduction (1)



Since the 1960s, the use of satellites was established
as an important means of navigation on earth
Equipped acft receiving satellite transmitted signals
can derive their 3D position and velocity.
There are two main satellite navigation systems


The U.S. Department of Defense’s NAVSTAR Global
Positioning System (GPS) and
The Russian Federation’s Global Orbiting Navigation Satellite
System(GLONASS)
Introduction (2)



ICAO & RTCA have defined a more global system that includes
these two systems , geostationary overlay satellite, along with
any future satellite navigation systems
The advantage of satellite navigation is that they
provide an accurate all-weather worldwide navigation
capability
The major disadvantages are that they can be
vulnerable to international or uninternational
interference and temporary unavailability due to the
signal masking or lack of visibility coverage
System Configuration

Consists of three segments



Space segment
Control segment
User segment
Space Segment



The space segment is comprised of the satellite constellation
made up of multiple satellites. The satellite provides the basic
navigation frame of reference and transmit the radio signals
from which the user can collect measurements required for his
navigation solution
Knowledge of the satellites’ position and time history
(ephemeris and time) is also required for the user’s solutions.
The satellite also transmit that information via data modulation
of the signals
•CDMA @ 1.2 to 1.5 GHz
•LB and “P” “C”
•Very accurate atomic clocks ~< nanosecond
Control Segment

Consists of three major elements



Monitor stations that track the satellites’
transmitted signals & collect measurements similar
to those that the user collect for their navigation
A master control station that uses these
measurements to determine & predict the
satellites’ ephemeris & time history and
subsequently to upload parameters that the
satellite modulate on the transmitted signals
Ground station antennas that perform the upload
control of the satellite
User Segment


Is comprised of the receiving equipment
and processors that perform the
navigation solution
These equipments come in a variety of
forms and functions, depending upon
the navigation application
Basics of Satellite Radio
Navigation (1)


Different types of user equipments solve a basic set of
equations for their solutions, using the ranging and/or range
rate (or change in range) measurements as input to a leastsquares, or a Kalman filter algorithm.
Fig 5.2
Ranging satellite
radio-navigation
solution
Basics of Satellite Radio
Navigation (2)

The measurements are not range & range rate (or change in range),
but quantities described as pseudorange & pseudorange rate (or
change in pseudorange). This is because they consisits of errors,
dominated by timing errors, that are part of the solution. For example,
if only ranging type measurments are made, the actual measurement is
of the form
PRi  Ri  ct si  ctu   PRi
PRi is the measured peseudorange from satellite i
Ri is the geometric range to that satellite, t si is the clock error in
satellite i, tu is the user’s clock error, c is the speed of light
and  PRi is the sum of various correctable or uncorrectable
measurements error
Basics of Satellite Radio
Navigation (3)

Neglecting for the moment the clock and
other measurement errors, the range to
satellite i is given as
Ri 
 X si  X u   Ysi  Yu   Z si  Zu 
X si , Ysi andZ si are
2
2
2
the earth-centered, earth fixed
(ECEF) position components of the satellite at
the time of transmission and X u , Yu andZ u are the
ECEF user position components at that time
Atmospheric Effects on
Satellite Communication

Ionosphere:






Shell of electrons and electrically charged atoms &
molecules that surrounds the earth
Stretching from 50km to more than 1000km
Result of ultraviolet radiation from sun
Free electrons affect the propagation of radio
waves
At frequency below about 30 MHz acts like a
mirror bending the radio wave to the earth
thereby allowing long distance communication
At higher frequencies (satellite radio navigation)
radio waves pass through the ionosphere
NAVSTAR Global Positioning
System

GPS was conceived as a U.S. Department of Defense
(DoD) multi-service program in 1973, bearing some
resemblance to & consisting of the best elements of
two predecessor development programs:



The U.S. Navy’s TIMATION program
The U.S. Air Force’s program
GPS is a passive, survivable, continuous, space-based
system that provides any suitably equipped user with
highly accurate three-dimensional position, velocity,
and time information anywhere on or near the earth
Principles of GPS & System
Operation


GPS is basically a ranging system, although precise Doppler
measurements are also available
To provide accurate ranging measurements, which are time-ofarrival measurements, very accurate timing is required in the
satellite. (t<3 nsec)



GPS satellite contain redundant atomic frequency standards
To provide continues 3D navigation solutions to dynamic users,
a sufficient number of satellite are required to provide
geometrically spaced simultaneous measurements.
To provide those geometrically spaced simultaneous
measurements on a worldwide continues basis, relatively highaltitude satellite orbits are required
GPS System Configuration

Fig 5.8
General System Characteristics



The GPS satellites are in approximately 12
hour orbits(11 hours, 57 minutes, and 57.27
seconds) at an altitude of approximately
11,000 nmi
The total number of satellite in the
constellation has changed over the years ~24
Each satellite transmits signals at two
frequencies at L-Band to permit ionosphere
refraction corrections by properly equipped
users
System Accuracy



GPS provides two positioning services, the Precise Positioning
Service (PPS) & the Standard Positioning Service (SPS)
The PPS can be denied to unauthorized users, but SPS is
available free of charge to any user worldwide
Users that are crypto capable are authorized to use crypto keys
to always have access to the PPS. These users are normally
military users, including NATO and other friendly countries.
These keys allow the authorized user to acquire & track the
encrypted precise (P) code on both frequencies & to correct for
international degradation of the signal


WAAS < 3 m horizontal
< 7.5 m vertical
GPS 15m
The GPS segments
Segments
Input
Space

Control

User

Satellite
commands
Navigation
messages
PRN RF
signals
Telemetry
Universal
coordinated
Time(UTC)
PRN RF
signals
Navigation
messages
Function
Provide atomic time scale
Generate PRN RF signals
Store & forward navigation
message

Estimate time & ephemeris
Predict time & ephemeris
Manage space assets

Solve navigation equations

Product
PRN RF signals
Navigation message
Telemetry

Navigation message
Satellite commands

Position, velocity, & time

Wide Area Augmentation
System(WAAS)



Developed by the FAA in parallel with European Geostationary
Navigation Overlay Service (EGNOS) & Japan MTSAT SatelliteBased Augmentation System
A safety-critical system consisting of a signal-in-space & a
ground network to support en-route through precision
approach air navigation
The WAAS augments GPS with three services all phases of
flight down to category I precision approach
1.
2.
3.
A ground integrity broadcast that will meet the Required
Navigation Performance (RNP)
Wide area differential GPS (WADGPS) corrections that will provide
accuracy for GPS users so as to meet RNP accuracy requirements
A ranging function that will provide additional availability &
reliability that will help satisfy the RNP availability requirements
WAAS Concept (1)

Fig 5.34
WAAS Concept (2)

Fig 5.35
Inmarsat-3 four ocean-region deployment
showing 5deg elevation contours
WAAS Concept (3)



Uses geostationary satellite to broadcast the
integrity & correction data to users for all of
the GPS satellites visible to the WAAS
network
A slightly modified GPS avionics receiver can
receive these broadcasts
Since the codes will be synchronized to the
WAAS network time, which is the reference
time of the WADGPS corrections, the signals
can also be used for ranging
WAAS Concept (4)



A sufficient number of GEOs provides enough
augmentation to satisfy RNP availability &
reliability requirements
In the WAAS concept, a network of
monitoring stations (wide area reference
stations, WRSs) continuously track the GPS
(&GEO) satellite & rely the tracking
information to a central processing facility
# Geo  2 minimum & 4 desired
WAAS Concept (5)


The central processing facility (wide area
master station, WMS)m in turn, determines
the health & WADGPS corrections for each
signal in space & relays this information, via
the broadcast messages, to the ground earth
station (GESs) for uplink to the GEOs
The WMS also determines & relays the GEO
ephemeris & clock state messages to the
GEOs
Chapter Five
Terrestrial Integrated Radio
Communication-Navigation
Systems
Introduction (1)


Since 1970s, same portion of the frequency spectrum
& common technology has been use for
communication & navigation
Integrated relative & absolute communicationnavigation systems provide both digital
communication & navigation functions using same
wave form
1. Digital Communication
Content of the digital 2.
data & time of
arrival of the
message measured
by receiver
Navigation functions
Introduction (2)

Integrated relative & absolute communicationnavigation systems
1.
2.
Decentralized (node-less): The operation is not dependent
on any central site or node. Each user determines its own
position
Centralize: The operation is dependent on a central site
(node)


3.
Frequently it is desired to have the position of large number
of users known & tracked at a central site (i.g. military/civil
command & control system)
Users may obtain their positions by automatic, periodic, or
occasional requests from the central nodenodal system
Hybrid: Contain both nodal and node-less systems
Joint Tactical Information Distribution System
Relative Navigation (JTIDS Rel Nav)

Decentralized position location &
navigation system




Mostly military used
Each user determines its position, velocity,
and altitude from data received from other
users
~900-~1200 MHz
Spread spectrum
Chapter Six
Air-Data Systems
Introduction (1)


An air-data system consists of aerodynamic &
thermodynamic sensor & associated electronics
The sensors measure characteristics of the air
surrounding the vehicle and convert this information
into electrical signals that are subsequently processed
to derive flight parameters including

Calibrated airspeed,true airspeed, mach number, free-stream
static pressure, pressure altitude Baro-corrected altitude,
free-stream static pressure, pressure altitude, baro-corrected
altitude, free-stream outside air temperature, air density,
angle of attack, angle of sideslip
Introduction (2)



Measured information is used for flight displays,
autopilots, weapon-system fire-control computation,
and for the control of cabin-air pressurization
systems
Since 1990s, all computations & data management
are digital & based on microprocessor technology.
New avionics architectures are incorporating air-data
functions into other subsystems such as inertial/GPS
navigation units or are packaging the air-data
transducers into the flight-control computers
Each type pf acft has unique challenges, primarily in
regard to the accuracy of measuring the basic
aerodynamic phenomena
Air-data Measurements (1)


All of the air-data parameters that are relevant to
flight performance are derived by sensing the
pressure, temperatures, and flow direction
surrounding the vehicle
Because air is moving past the acft, the pressure at
various places on the acft’s skin may be slightly
higher or lower than free stream
Airborne
Sensors
•Pressure
•Temperature
•Flow direction
Air-data parameters
relevant to flight
performance
Air-data Measurements (2)


The probes deployed around the skin of acft,
sample the static pressure (via static ports),
total pressure (via the pitot tube), total
temperature (via the temperature probe), and
local flow direction (via the angle-of-attack &
sideslip vanes)
All of these sensing elements, except for the
flush-mounted static port, are intrusive
because they disturb the local airflow
Air-data System
Probes & vanes in
acft body
Typical nosemounted air-data
boom with pressure
probes & flowdirection vanes
Air-data (1)

Static pressure is the absolute pressure of the still air
surrounding the acft.


To obtain a sample of static air in a moving acft, a hole (static port)
or series of holes are drilled in a plate on the side of the fuselage
or on the side of the pilot tube probe which extends into the free
air stream
Total pressure refer to the pressure sensed in a tube that is
open at the front & closed at the rear
PT  PS  1 / 2 V 2
 f T
m V /C
C  f (T ,  ,  )
Air-data (2)


Outside air temperature, referred to as static
air temperature and is required for the
computation of true airspeed, air density
(which is required for some types of firecontrol aiming solutions)
Angle of attack is the angle, in the normally
vertical plane of symmetry of the acft, at
which the relative wind meets an arbitrary
longitudinal datum line in the fuselage
Chapter Seven
Attitude and Heading References
Introduction (1)

Heading references is required for steering &
navigation



Simplegravity-leveled magnetic compass
Elaborateinertial navigator
Attitude references




Simplevisible horizon
Elaborateattitude reference instruments in poor weather
An automatic pilot requires measurements of body rates &
attitude
Attitude & rate instruments stabilize other avionic
sensors(I.e. doppler radar, navigation radars, weapon
delivery systems)
Introduction (2)

Cockpit displays


Inexpensive acftself-contained vertical &
directional gyroscope that are viewed directly by
the crew
Complex acft



attitude driven from remotely located sensors & are
displayed on glass instruments
Vertical situation driven by the level-axis outputs of an
inertial navigator
Complex acft usually carry at least one set of selfcontained vertical & directional gyroscopes for
emergencies
Electronic display

Fig 9.1 a,b
Basic Instruments

Gyroscope


A spinning wheel(source of angular
momentum) that will retain its direction in
inertial space in the absence of applied
torques section 7.3.4.
Gravity Sensors

Simple pendulums with electromagnetic
pickoffs
Vertical References (1)

Basic reference is the earth’s gravitational
field that


stationary platformcan be sensed with great
accuracy by a simple pendulum, spirit level, or
accelerometer
Moving platformall the devises indicate the
vector sum of vehicle acceleration & local gravity.
δ=angle between the true & apparent vertical is
tan  
aH
g  aV
aH , aV : horizontal , vertical accelerati on of acft
g : accelarati on due to gravity (32.2 ft/sec 2 )
Vertical References (2)

Geometry of vertical determination
Heading References


The best heading references are inertial
navigators
Less expensive, smaller, & less accurate
heading references are



Those that depend on the earth’s magnetic
field”magnetic compass”
Those that depend on the use of gyroscope to
retain a preset azimuth”directional gyroscope”
Those that use sub-inertial gyroscopes to maintain
a three-axis reference
Chapter Eight
Doppler and Altimeter Radars
Doppler Radars
(Functions & Applications)

The primary function is to continuously
determine the velocity vector of an acft
with respect to the ground
Doppler Radars

(Advantages)
Advantages over other methods of velocity
measurements

Velocity is measured with respect to the earth’s
surface. Unlike;




Air data systemwith respect to the air mass
Terrestrial radio navigation systemmeasurements are
based on differencing of successive position
measurements
Self-contained; it requires no ground-based
stations or satellite transmitters
Extremely small airborne transmitter power
requirements
Doppler Radars






(Advantages)
Narrow radar beams pointed toward the
ground at steep anglelow detect ability
All-weather system
Operates over both land terrain & water
Extremely accurate average velocity
information
No required international agreement
No required pre-flight alignment & warmup
Doppler Radars





(Disadvantages)
Requires an external airborne source of heading
information (I.e. gyro-magnetic compass, attitudeheading reference for autonomous dead-reckoning
navigation
Requires either internal or external vertical reference
for conversion of velocity info to earth referenced
Position info derived from
Short term velocity info is not as accurate as the
average velocity
For over-water operation, accuracy is degraded due
to backscattering characteristics
Functionalities

Fig 10.1
Doppler
navigation
system
Principles & Design Approach

Doppler effect: change (Doppler shift) in
observed frequency when there is relative
motion between a transmitter & a receiver

If the value of
λ is known & v
is measured,
the relative
velocity can be
calculated
If the relative velocity is much smaller than speed
of light:
VR f VR
v

c

v Doppler shift
f frequency of the transmiss ion
c speed of light
VR relative velocity between tr ansmitter & receiver
  c f waveleng th of transmiss ion
Doppler Radar Beam
Geometry
Basic Doppler
Radar beam
geometry
VR  2V cos   2Vb
or
2Vf
2V
cos  
cos 
c

 angle between th e velocity vector V and
v
the beam centeroid b unit vecto r along the
beam centroid
•Also used for ground proximity warning system.
• Combine with GPS digital terrain database for
enhanced ground proximity monitoring
Three beam Doppler Radar

To measure all three orthogonal components of
velocity
Three-beam lambda
Doppler radar
configuration
The Doppler Spectrum

Fig 10.6
Chapter Nine
Mapping & Multimode Radars
Introduction


Developed in World War II for bombing
through clouds at night
Perform two navigation functions


Permitted acft to find its way over enemy
terrain, without ground navigation aids or
sight of the ground
Provide precise navigation during the
bombing run by use of cursors set on the
target point in a display
Chapter Ten
Landing Systems
Introduction



Every successful flight culminates in a landing.
Although the majority of landings are conducted
solely with visual cues, acft must frequently land in
weather that requires electronic assistance to the
pilot or the autopilot
On the vicinity of the destination the acft begins its
decent & intercepts the projected runway center line,
then makes a final approach & landing with position
errors of a few feet in each axis at touchdown
The catastrophic accidents occur during these flights
phases of which two-thirds are attributed to errors
made by the flight crew
Low-Visibility Operations (1)


Considerable interference to civil & military
operations result due to reduced visibility in
terminal areas
i.e the visibility at London’s Gatwick Airport
requires Category II operational capabilities
for 115 hours per year & Category III
capabilities for 73 hours per year during
primary operating hours
Low-Visibility Operations (2)




While the successful landing of acft depends on many factors
other than ceiling & visibility, such as crosswinds & storm
activity, the term all-weather operations often refers only to
operations in condition of reduced visibility
Instrument meteorological conditions (IMC) are times in which
visibility is restricted to various degrees defined by regulations
in certain countries
Acft operating in IMC are supposed to fly under Instrument
Flight Rules also defined by regulations
During a landing, the decision height (DH) is the height above
the runway at which the landing must be aborted if the runway
is not in sight. The better the electronic aids, the lower is the
DH
Visibility Categories (by ICAO)
(1)

Category I




Decision height not lower than 200 ft; visibility not
less than 2600 ft, or Runway Visual Range (RVR)
not less than 1800 ft with appropriate runway
lighting.
The pilot must have visual reference to the
runway at the 200ft DH above the runway or abort
the landing.
Acft require ILS and marker-beacon receiver
beyond other requirements for flights under IFR.
Category I approaches are performed routinely by
pilots with instrument ratings
Visibility Categories (by ICAO)
(2)

Category II



DH not lower than 100 ft & RVR not less than
1200 ft (350m)
The pilot must see the runway above the DH or
abort the landing
Additional equipment that acft must carry include
dual ILS receivers, either a radar altimeter or an
inner-marker receiver to measure the DH, an
autopilot coupler or dual flight directors, two
pilots, rain-removal equipment (wipers or
chemicals), and missed-approach attitude
guidance. An auto-throttle system also may be
required
Visibility Categories (by ICAO)
(3)

Category III subdivided into



IIIA. DH lower than 100 ft and RVR not less than
700 ft (200m)-sometimes called see to land: it
requires a fail-passive autopilot or a head-up
display
IIIB. DH low than 50 ft & RVR not less than 150 ft
(50m)-sometimes called see to taxi; it requires a
fail-operational autopilot & an automatic rollout to
taxing speed
IIIC. Zero visibility. No DH or RVR limits. It has
not been approved anywhere in the world
Decision Height




Acfts are certified for decision heights, as are
crews
When a crew lands an acft at an airport, the
highest of the three DHs applies.
An abort at the DH is based on visibility
Alert height is the altitude below which
landing may continue in case of equipment
failure

Typical Alert height is 100 ft
Standard lighting Pattern

Airports at which Category II landings are permitted must be
equipped with the standard lighting pattern
Category III
runway
configuration
The Mechanics of Landing (1)
1. The approach

Day & night landings are permitted under visual
flight rules (VFR) when the ceiling exceeds 1000 ft
& the horizontal visibility exceeds 3 mi, as juged by
the airport control tower

In deteriorated weather, operations must be
conducted ubder Instrument Flight Rules (IFR)

An IFR approach is procedure is either non-precision
(lateral guidance only) or precision (both lateral & vertical
guidance signals)

Category I, II, and III operations are precision-approach
procedures
The Mechanics of Landing (2)



An afct landing under IFR must transition
from cruising flight to the final approach
along the extended runway center line by
using the standard approach procedures
published for each airport
Approach altitudes are measured
barometrically, and the transition flight path is
defined by initial & final approach fixes (IAF &
FAF) using VOR, VOR/DME
Radar vectors may be given to the crew by
approach control
The Mechanics of Landing (3)



From approximately 1500 ft above runway, a
precision approach is guided by radio beams
generated by ILS. Large acft maintain a speed of
100 to 150 knots during descent along the glide path
beginning at the FAF (outer marker)
The glide-path angle is set by obstacle-clearance and
noise-abatement considerations with 3 deg as the
international civil standard
The sink rate is 6 to 16 ft/sec, depending on the
acft’s speed & on headwinds
The Mechanics of Landing (4)
The ICAO standard: glide path will cross the runway
threshold at a height between 50 & 60 ft. Thus, the
projected glide path intercepts the runway surface
about 1000 ft from the threshold.
Fig 13.3

Wheel path
for instrument
landing of a
jet acft
The Mechanics of Landing (5)
2.
The flare Maneuver

Land-based acft are not designed to touch down
routinely at the 6 to 16 ft/sec sink rate that exits
along the glide path. Thus a flare maneuver must
be executed to reduce the decent rate to less than
3 ft/sec at touchdown
During the approach, the angle of attack is
maintained at a value that causes a lift force equal
to the acft’s weight, & the speed is adjusted for a
specified stall margin, typically 1.3 times the stall
speed plus a margin based on reported wind speed
& shear

The Mechanics of Landing
(Decrab Maneuver)
The Decrab Maneuver & Touchdown
In a crosswind Vcw, an acft will approach with a
cab angle b such that its ground-speed vector lies
along the runway’s centerline. At an approach
airspeed Va & a headwind Vhw,
1.

sin b  Vcw /(Va  Vhw )


b is usually less than 5 deg & is always less than 15 deg
After the decarb, the wind causes the acft to begin
drifting across the runway.
The Decrab Maneuver &
Touchdown

Table 13.2
The Mechanics of Landing
(Rollout & Taxi) (1)
3.
Rollout & Taxi

Approximately 600ft after main-gera
touchdown, a large jet acft lowers its noise
wheel & subsequently behaves like a
ground vehicle
Some methods for guiding acft on taxiways

1.
2.
3.
Measuring runway stopping-distance by DME
Guide the acft along a specific taxi route by
taxiway lights
Surface radars that aid in avoiding taxiway &
runway-incursion accidents
The Mechanics of Landing
(Rollout & Taxi) (2)
4.
5.
6.
Transponder-based systems
Radio broadcast of on-board derived position &
velocity
Milliwatt marker-beacon transmitter placed at all
runway thresholds would give a visual & audible
alarm on the flight deck of any acft that taxied
onto an active runway
Automatic Landing Systems (1)
Air carrier acft that are authorized for
precision-approach below category II must
have automatic landing (auto-land) system.
Guidance & control requirements by FAA

1.


For category II: the coupled autopilot or crew
hold the acft within the vertical error of +or- 12
ft at the 100ft height on a 3deg glide path
For category III: the demonstrated touchdown
dispersions should be limited to 1500ft
longtudinally & -or+ 27ft laterally
Automatic Landing Systems (2)
Flare Guidance
2.

During the final approach the glide-slope gain in
the auto-land system is reduced in a
programmed fashion. Supplementary sensors
must supply the vertical guidance below 100ft
Lateral Guidance
3.

Tracking of the localizer is aided by heading (or
integral-of-roll), roll, or roll-rate signals supplied
to the autopilot and by rate & acceleration data
from on-board inertial system
Instrument Landing
System(ILS) (1)




Is a collection of radio transmitting stations
used to guide acft to a specific runway.
In 1996 nearly 100 airports worldwide had at
least one runway certified to Category III
with ILS
More than one ILS in high density airports
About 1500 ILSs are in use at airports
throughout the US
Instrument Landing
System(ILS) (2)

ILS typically includes:




The localizer antenna is centered on the runway
beyond the stop end to provide lateral guidance
The glide slope antenna, located beside the
runway near the threshold to provide vertical
guidance
Marker beacons located at discrete positions along
the approach path; to alert pilots of their progress
along the glide-path
Radiation monitors that, in case of ILS failure
alarm the control tower, may shut-down a
Category I or II ILS, or switch a Category III ILS
to backup transmitters
ILS Guidance Signals (1)


The localizer, glide slope, and marker beacons
radiate continues wave, horizontally
polarized, radio frequency, energy
The frequency bands of operation are



Localizer, 40 channels from 108-112 MHz
Glide slop, 40 channels from 329-335 MHz
Marker beacons, all on a signal frequency of 75
MHz
ILS Guidance Signals (2)



The localizer establishes a radiation pattern in space
that provides a deviation signal in the acft when it is
displaced laterally from the vertical plane containing
the runway centerline
The deviation signal drives the left-right needle of the
pilot’s cross-pointer display & may be wired to the
autopilot/flight-control system for coupled
approaches
The deviation signal is proportional to azimuth angle
usually out to 5 deg or more either side of the center
line
ILS Guidance Signals (3)

Fig13.4
Sum & difference
radiation patterns
for the course
(CRS) &
clearance (CLR)
signals of a
directional
localizer array
The Localizer (1)


The typical localizer is an array usually located 600 to 1000 ft
beyond the stop end antenna of the runway
The array axis is perpendicular to the runway center line
Log-periodic
dipole antenna
used in many
localizer arrays
The Localizer (2)

Fig13.7
Category IIIB localizer
The Glide Slope (1)


There are five different of glide-slope arrays in
common use; three are image systems & two are not
Image arrays depend on reflections from level ground
in the direction of approaching acft to form the
radiation pattern



The three image systems are null-referenced system, with
two antennas supported on a vertical mast 14 & 28 ft above
the ground plane
The sideband-reference system, with two antennas 7 and
22ft above the ground plane
The capture-effect system, with 3 antennas 14, 28, and 42 ft
above the ground plane
The Glide Slope(2)

Fig 13.8
Category IIIB
capture-effect
glideslope & Tasker
transmissometer
The Glide Slope (3)

Fig 13.9
Glide-slope pattern
near the runway. DDM
counters are
symmetrical around
the vertical, but signal
strength drops rapidly
off course
The Glide Slope (4)



The cable radiators of the end-fire array are installed on stands
40 in. high & are site alongside the runway near desired
touchdown point
Fig 13.10
Fig 13.11
Standard end-fire glide-slope
system layout
Front slotted-cable radiator
of an end-fire glide slope
ILS Marker Beacons (1)


Marker beacons provide pilot alerts along the
approach path
Each beacon radiates a fan-shaped vertical
beam that is approximately +or- 40deg wide
along the glide path by +-85deg wide
perpendicular to the path

The outer marker(OM) is placed under the
approach course near the point of glide-path
intercept & it is modulated with two 400 Hz
Morse-code dashed per second
ILS Marker Beacons (2)
The middle marker(MM) is placed near the point
where missed-approach decision would need to be
made for Category I. MM is modulated with one
1300 Hz dash-dot pair second
 The inner marker (IM) may be required at runway
certified for Category II & III operations & is
placed near the point where the glide path is 100ft
above the runway. IM has six dots per second at
3000 Hz
Because of the real state problems the use of marker
beacons is decreasing
The increase use of DME & ILS has diminished the
pilot’s dependence on the markers



Receivers

Filter the detector separate the 90 &
150 Hz tones which in the most basic
circuit, are rectified & feed to a dc
micrometer
ILS Limitations (1)



Major limitation is its sensitivity to the
environment
At ILS frequencies, the very narrow beam
widths, necessary to avoid significant
illumination of the environment surrounding
the approach course, require array structure
which are too large to be practical
Accuracy degradations (beam bends) due to
reflections from buildings, terrain, airborne
acft, taxiing acft, and ground vehicles
ILS Limitations (2)

Fig 13.12
Formation of bends in the glide path
Microwave-Landing System
(MLS) (1)



Developed by U.S. military services to address the
ILS limitations
Designs were sought that retained the desirable
features of the ILS while mitigating its weaknesses
Same runway-residence of ILS because as the
landing acft approaches the runway, linear offset(due
to the errors in the angular guidance) continually
decreases, while the signal-to-noise ratio generally
increases.


Thus, in the most demanding phase of the flight close to the
ground, the positional accuracy is constantly improving &
the noise content is generally decreasing
freq~ 5MHz
Microwave-Landing System
(MLS) (2)


ILS sensitivity to environment is
eliminated by narrow beam-width
antennas that are physically small at
microwave frequencies
The lack of available channels, which
limits multiple ILS deployments in metro
areas, would no longer be a problem
Microwave-Landing System
(MLS) (3)


Never fully developed
Being replaced by WAAS and GPS
Satellite Landing Systems (1)



Before GPS become operational efforts had
been underway to use it for approach &
landing
An operational concept called Special
Category I Precision Approach Operations
Using DGPS, based on the differential GPS
(DGPS) technique, was developed, tested,
and certified for specific airports
The test results have been very promising
Satellite Landing Systems (2)

Augmentation Concepts
The basic GPS, without differential correction, cannot
be used for precision approach & landing
operations because;
1.
2.
3.

Accuracy: The nominal error is +- 15m, compared with
requirements (+-1.3m to +-8m for different Cats)
Integrity: The GPS design lacks a monitoring system
which can provide timely warning of guidance-data faults
within 10sec for Cat I, or less than 2sec for Cat III
Availability: The number of satellite in view in certain time
periods may not be adequate
GPS has been improved but still not operable for
landing systems
Future Trends (1)

Pilot aids

Use several technologies to



reduce pilot work load during approach &
landing
improve the pilot’s ability to monitor an
automatic landing
Future Trends (2)

Satellite landing aids


Solution to provide low-cost, non-precision
& near Cat I procedures at low-density
airports
Airport surface navigation

Spread the use of differential satellitebased systems for guidance & surveillance
of rollout, taxi & departure operations
under low-visibility conditions
Accuracy Allocation

Fig 13.1
Chapter Eleven
Data Links
Automatic Dependent
Surveillance - Broadcast (ADS-B)




A technology designed to address both airspace and
ground-based movement needs.
Collaborative decision making is possible through
ADS-B surveillance information available to both ATC
and aircrews.
ADS-B combined with predictable, repeatable flight
paths allow for increased airspace efficiencies in high
density terminal areas or when weather conditions
preclude visual operations.
Additionally, ADS-B allow for enhanced ground
movement management (aircraft and vehicles) and
improved airside safety
ADS-B