Project about Aeronautical Navigation Systems - Jan 2013

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Certificate
This is to certify that Michael Bseliss, student of B.Tech. in Engineering Department
has carried out the work presented in this Term paper entitled “Aeronautical
Navigation System.” as a part of 2013 year programme of Bachelor of Technology in
Aerospace Engineering from Amity University, Dubai, UAE under my supervision.
Name & signature of the Faculty Guide

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Acknowledgement
I would like to express my gratitude to my faculty guide Mr. Ved P
Mishra who was abundantly helpful and offered invaluable assistance,
support and guidance, also would thank Amity University to give me this
chance, to learn how to prepare and complete such reports.
Michael Bseliss

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Table of Contents
1- Certificate ………………………….…………………..………….. 3
2- Acknowledgement ………………….……………….……………. 4
3- Abstract …………………………….…………………….……….. 6
4- Introduction ………………………….…………………….…........ 6
5- Early Navigation Tools …………….…………………….……….. 8
6- Radio Navigation System ………….……………………………... 9
7- Celestial Navigation System ………….…………………………... 11
8- Dead-reckoning Navigation System …………………………….. 12
9- Map-Matching (Mapping) Navigation …………………………... 14
10- Global Navigation Satellite System …………………………….. 14
11- Area Navigation System …………………..………...………....... 15
12- Airborne Collision Avoidance Systems ……………………......... 17
13- Terrain Avoidance And Warning System ……………………… 21
14- Future Air Navigation System …………………………………... 22
15- Conclusion ....................................................................................... 23
16- References ………………………………………………………. 24

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3-Abstract
Navigation is an essential part of flying where crew keep track of the position of a
moving aircraft relative to the Earth. Early in aviation history the tools for this were
maps, compass, airspeed, indicator, clock, and astronavigation. Modern systems in the
craft, on the ground and in space, have to a large degree automated this task and provides
high accuracy and availability. There are now ground based navigation systems with area
coverage, specialized systems for landing procedures, radio beacons, distance measuring
equipment, radar and transponders, inertial navigation systems, and satellite navigation
receivers. Equally important as these technical aids are air traffic control, maps, and
procedures. Today the art of air navigation involves a working knowledge of all these
systems.
4- Introduction
In recent years, satellite navigation systems have revolutionized the concept of instrument
navigation.
Developed as a military system by the United States and the Soviet Union, coupled with
the computer systems which have developed at the same time, they allow much more
accurate and available position fixing for aircrew.
The type of navigation used by pilots depends on many factors. The navigation method
used depends on where the pilot is going, how long the flight will take, when the flight is
to take off, the type of aircraft being flown, the on-board navigation equipment, the
ratings and currency of the pilot and especially the expected weather.
As definition, Navigation is the determination of the position and velocity of the mass
center of a moving vehicle.

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Air navigation, the method of directing the flight of an airplane towards its destination,
has evolved into a mature science over last century. In the early days of aviation, the pilot
visually recognized landmarks on the ground and directed the airplane from one
landmark to another until he reached his destination. Mistakes in identifying landmarks
due to poor visibility led to unscheduled landings or accidents.
Accurate knowledge of the aircraft’s position in terms of its latitude/longitude
coordinates, ground speed and track angle, height and vertical velocity is also equally
essential for the navigation of the aircraft.
Navigation thus involves both control of the aircraft’s flight path and the guidance
for its mission.
The importance of high integrity navigation:
The need for accurate and high integrity navigation is briefly summarized below:
 For civil aircraft, the density of air traffic on major air routes requires the aircraft to fly in
a specified corridor or ‘tube in the sky’, these air routes being defined by the Air Traffic
Control authorities.
Not only must the aircraft follow the defined three dimensional flight path with high
accuracy, but there is also a fourth dimension namely that of time, as the aircraft’s arrival
time must correspond to a specified time slot.

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 For military operations, very accurate navigation systems are essential to enable the
aircraft to fly low and take advantage of terrain screening from enemy radars, to avoid
known defenses and in particular to enable the target to be acquired in time.
The aircraft flies fast and very low so that the pilot cannot see the target until the aircraft
is very near to it. There may be then only about six to ten seconds in which to acquire the
target, aim and launch the weapons.
Clearly the integrity of the navigation system must be very high in both civil and military
aircraft as large navigation errors could jeopardize the safety of the aircraft.
5- Early Navigation Tools
Before the invention of accurate navigation tools, getting from place to place was very
inefficient. Travel could take several days or many months. This often stifled trade and
commerce.
New societies and resources were undiscovered for thousands of years without the
availability of good navigational tools.
Few Old Navigation Methods Used in Ships & Boats [2]
 Stars
The celestial heavens were used as tools to navigate, but that meant being limited to only
using them at night, which was dangerous. Also, some societies lacked vitamin A
nutrition and therefore did not have reliable night vision. Another factor limiting
accurate star navigation is the fact that stars moved across the night sky instead of
staying in one place due to the rotation of the earth.
That left Polaris (also called the North Star) as one of the few stars to get a fairly good
idea of direction. This could only occur on clear nights when the star was visible, and
only in the northern hemisphere.

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 Sun
The sun was one form of primary reference since it always rises in the east and sets in
the west. But using it as a reference without a gauge also has its disadvantages since the
earth changes its angle in relation to the sun due to its axial tilt during its orbit around
the sun. Later in time, several inventions enabled accuracy to navigate by the sun.
However, some of these favored devices often required staring into the sun and caused
blindness.
 Winds
Another form of navigation involved the use of the winds. Using the patterns of the
wind, they named the prevailing winds North wind, East wind, South wind, and West
wind.
 Time
Time is crucial with modern navigation as much as it was in the early days. The
employment of time in navigation came about from needing to determine location
through the use of the stars and sun which are constantly moving across the heavens (in
relation to how you see them from the ground). Using a point in the sky, knowing what
time it is and the latitude, it then became possible to reference a navigational almanac or
celestial chart and calculate a more precise location.
6- Radio Navigation System [1]
Radio navigation is the application of radio frequencies to determine a position on the
earth. As aviation began to expand in the 1930s, the first radio navigation systems were
developed.
Radio Systems consists of a network of transmitters (sometimes also receivers) on the
ground or in satellites. A vehicle detects the transmissions and computes its position
relative to the known positions of the stations in the navigation coordinate frame. The
vehicle’s velocity is measured from the Doppler shift of the transmissions or from a
sequence of position measurements.

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Measuring the Doppler Shift is a satellite tracking technique for determining the
distance between the satellite and the receiver at the time of closest approach as well as
the time itself.
Many of radio navigation aids have been invented and many of them have been widely
deployed.
Radio direction finding:
The first system of radio navigation was the Radio Direction Finder, or RDF. By tuning
in a radio station and then using a directional antenna, one could determine the direction
to the broadcasting antenna. A second measurement using another station was then taken.
Using triangulation, the two directions can be plotted on a map where their intersection
reveals the location of the navigator. Commercial AM radio stations can be used for this
task due to their long range and high power, but strings of low-power radio beacons were
also set up specifically for this task, especially near airports and harbors.
The main problem with RDF is that it required a special antenna on the vehicle, which
may not be easy to mount on smaller vehicles or single-crew aircraft.
A smaller problem is that the accuracy of the system is based to a degree on the size of
the antenna, but larger antennas would likewise make the installation more difficult.
 Global Positioning System [3]
Global Positioning System (GPS) is a complete navigational system based on radio
transmissions from satellites in medium earth orbits of about 20,000 km from earth’s
center. The system consists of over 24 satellites in six orbits. Each satellite completes
about two orbits in 24 hours. The navigational system is based on using the satellite as
sky marks. Each satellite transmits digital radio signals carrying information about the
current position of the satellite and time on the onboard precision clock. The accuracy of
the position and time information is monitored and maintained by ground stations in
USA, which owns and operates the system.

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There are three types of GPS receiver: sequential tracking, continuous tracking and
multiplex.
A vehicle derives its three-dimensional position and velocity from ranging signals at
1.575 GHz received from four or more satellites.
GPS offers better than 30-m ranging errors to civil users and 10-m ranging errors to
military users.
GPS provides continuous worldwide navigation for the first time in history.
 Differential GPS
(DGPS) employs one or more ground stations at
known locations, which receive GPS
signals and transmit measured errors on a radio link
to nearby ships and aircraft.
DGPS improves accuracy (centimeters for fixed observers)
and detects faults in GPS satellites.
Differential techniques involve the transmission of a corrected message derived from
users located on the ground. The correction information is sent to the user who can apply
the corrections and reduce the satellite ranging error.
Outside of DGPS cover user equipment usually reverts to working as a 'normal' GPS
receiver.
7- Celestial Navigation System [8]
Also known as astronavigation is a position fixing technique that has evolved over
several thousand years to help sailors cross oceans without having to rely on estimated
calculations to know their position.
Celestial navigation uses "sights", or angular measurements taken between a celestial
body (the sun, the moon, a planet or a star) and the visible horizon, but when an airplane
is above the clouds or flying at night, its navigator can’t see the horizon. The bubble
sextant solves this problem by providing an artificial horizon.

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A sextant is used to measure the altitude of a celestial body above a horizontal line of
reference. But acceleration of the aircraft and turbulence frequently deflect the true
vertical, therefore, a single reading may not be accurate. For that reason, the bubble
sextant also has a mechanical averager.
It takes 60 altitude readings over a two-minute period, using a little counter that looks
like a car’s speedometer to average and display the measurements.
8- Dead Reckoning Navigation System [3]
Dead reckoning, as applied to flying, is the navigation of an airplane solely by means of
computations based on airspeed, path, heading, wind direction and speed, groundspeed,
and elapsed time.
Dead reckoning is a system of determining where the airplane should be on the basis of
where it has been. The simplest kind of dead reckoning assumes that the air is calm. If
the wind were to remain calm, the airplane's track (path) over the ground would be the
same as the intended course and the groundspeed would be the same as the airplane's true
airspeed.

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As shown in the figure, an airplane flying eastward
at an airspeed of 120 knots in still air, will have
a groundspeed exactly the same - 120 knots.
If the mass of air is moving eastward at 20 knots,
the speed of the airplane (airspeed) through the air
will not be affected, but the progress of the airplane
as measured over the ground will be 120 plus 20,
or a groundspeed of 140 knots. On the other hand,
if the mass of air is moving westward at 20 knots,
the airspeed of the airplane still remains the same but
the groundspeed becomes 120 minus 20 or 100 knots.
In actual flight, winds may cause considerable deviation from the desired ground track
unless some sort of correction is made. An airplane flying within a moving mass of air
will move with the air in the same direction and speed that the air is moving over the
ground. Consequently, at the end of a given time period, the airplane will be in a position
which resulted from a combination of the two motions: the movement of the air mass in
reference to the ground, and the forward movement of the airplane through the air mass.
As shown in the figure, if the airplane
is flying eastward at an airspeed
of 120 knots, and the air mass is
moving southward at 20 knots, the airplane
at the end of 1 hour will be at a point that is approximately
120 miles eastward of its point of departure (due to its progress through the air) and 20
miles southward (due to the motion of the air). Under these circumstances the airspeed
remains 120 knots, but the groundspeed is determined by combining the movement of the
airplane with the movement of the air mass. Groundspeed can be measured as the
distance traveled in 1 hour from the point of departure.

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9- Map-Matching (Mapping) Navigation System [8]
A map matching navigation system for monitoring vehicle state characteristics including
the location of a vehicle on a map route. As computer power grows, map-matching
navigation is becoming more important. On aircraft, mapping radars and optical sensors
present a visual image of the terrain to the crew. Since the 1960s, automatic map-
matchers have been built that correlate the observed image to stored images, choosing the
closest match to update the dead-reckoned pictures. Aircraft and cruise missiles measure
the vertical profile of the terrain below the vehicle and match it to a stored profile. The
profile of the terrain is measured by subtracting the readings of a baro-inertial altimeter
(calibrated for altitude above sea level) and a radar altimeter (measuring terrain
clearance).
An on-board computer calculates the autocorrelation function between the measured
profile and each of many stored profiles. Hence the direction of flight through the stored
map is known, saving the considerable computation time that would be needed to
correlate for an unknown azimuth of the flight path.
The azimuth is the angle between the real north and the magnetic north that the compass
indicates to.
The most complex mapping systems observe their surroundings, by radar or digitized
video, and create their own map of the surrounding terrain. Guidance software then steers
the vehicle. Optical map matchers may be used for landings at fields that are not
equipped with electronic aids.
10- Global Navigation Satellite Systems (GNSS) [7]
Global Navigation Satellite Systems (GNSS), and their regional augmentations, are being
developed in a number of countries and users will soon be faced with a confusing array of
jargon and capabilities from “competing” systems.
There are currently two GNSS, the Global Positioning System (GPS), which is operated
by the United States military and the Global Navigation Satellite System (GLONASS),
which is operated by the Russian Federation military, but never reached Full Operational
Capability due to a withdrawal of funding.

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GPS and GLONASS are currently being modified to make them more useful for civilian
applications.
GNSS is becoming an international endeavor with many countries contributing to the
global systems using their own local augmentations and navigation satellites.
 There is also one Chinese Regional Satellite System called Beidou, it is part of a
positioning system that will cover China and some of the surrounding areas.
 A new GNSS is being developed by the European Union (EU), called Galileo.
That will also be designed to accommodate the more varied needs of these civilian users.
 Japan is planning a Quasi-Zenith Satellite System (QZSS) that will increase the integrity
of the current systems.
11- Area Navigation System (ANS) [5]
Area navigation (ANS) is a method of instrument flight rules navigation that allows an
aircraft to choose any path within a network of navigation beacons, rather than navigating
directly to and from the beacons.
A beacon is an intentionally conspicuous device designed to attract attention to a specific
location.
The Area Navigation System (ANS) offers an advanced technology, worldwide area
navigation system with automatic radio updating capability.

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There are several potential advantages of ANS routes and procedures:
1. Time and fuel savings.
2. Reduced dependence on radar vectoring, altitude, and speed assignments.
3. More efficient use of airspace.
4. This can conserve flight distance & reduce congestion.

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Bulk storage of navigation data:
The ANS provides prestored data for use in the flight plan as waypoints and for
automatic selection of stations for radio updating the inertially derived position.
In addition, custom routes and waypoints may be stored for later recall and use.
Requirements for navigation applications on specific routes or within a specific airspace
must be defined in a clear and concise manner. This is to ensure that the flight crew and
the air traffic controllers are aware of the on-board ANS system capabilities in order to
determine if the performance of the ANS system is appropriate for the specific airspace
requirements.
 ANS specifications include requirements for certain navigation functions.
These functional requirements include:
1. Continuous indication of aircraft position relative to track to be displayed to the
pilot flying on a navigation display situated in his primary field of view.
2. Display of distance and bearing to the active waypoint.
3. Display of ground speed or time to the active waypoint.
4. Navigation data storage function.
5. Appropriate failure indication of the RNAV system including its sensors.
12- Airborne Collision Avoidance Systems (ACAS) [6]
A collision avoidance system is an aircraft safety system designed to reduce the severity
of an accident. Also known as pre-crash system, use radar and sometimes laser and
camera sensors to detect an imminent crash, warning pilots of the presence of other
aircraft that may present a threat of collision.
A distinction is increasingly being made between ACAS and ASAS (Airborne
Separation Assurance System).
ACAS is being used to describe short-range systems intended to prevent actual metal-on-
metal collisions.

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In contrast, ASAS is being used to describe longer-range systems used to maintain
standard en route separation between aircrafts (9.25 km horizontal / 305 m vertical).
The collision avoidance logic must distinguish a genuine collision threat from routine
safe passages.
The collision avoidance logic must distinguish a genuine collision threat from routine
safe passages. The relative range rate is derived from successive range reports. Likewise,
an altitude rate is estimated from the other aircraft's altitude.
An estimate of the time of closest approach (τ) can be calculated from the equation:
𝝉 =
− 𝒓𝒂𝒏𝒈𝒆
𝒓𝒂𝒏𝒈𝒆 𝒓𝒂𝒕𝒆
Each nearby aircraft is evaluated once per second, and is deemed a threat if the range is
already small or if τ is small.
Each nearby aircraft is evaluated once per second, and is deemed a threat if the range is
already small or if τ is small, and if the relative altitude is predicted to be small.
When a threat is declared, the effects of potential climb and descent maneuvers are
estimated. The maneuver sense that gives the greater separation is chosen, except that a
vertical crossing is not selected if the noncrossing sense gives adequate separation.

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Advisories:
 Traffic Advisory (TA): Help the pilots in the visual search for the intruder
aircraft, and alert them to be ready for a potential advisory decision.
 Decision Advisory (DA): Avoidance maneuvers recommended to the pilot

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Types of ACAS:
There are three main types of ACAS in different stages of use or development:
1. ACAS 1: will provide a warning (TA traffic advisory) of proximate traffic
without guidance to avoid potential collisions.
2. ACAS 11: will provide warning (TA traffic advisory) and vertical plane guidance
(DA decision advisories) to avoid potential collisions.
3. ACAS 111: the next generation of ACAS still under development will provide
TA’s and DA’s which include vertical plane and horizontal plane guidance.

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13- Terrain Avoidance And Warning System (TAWS) [4]
The advent of navigation systems which could provide great accuracy, coupled with
powerful computers which process large amounts of information, allowed the
development of systems which could provide such a predictive terrain hazard warning
function (warning of terrain ahead of the aircraft).
The first TAWS on the market, called the enhanced ground proximity warning system
(EGPWS).
TAWS is a system which provides the pilot or
navigator of an aircraft with a situation display
of the ground or obstacles which project above
either a horizontal plane through the aircraft or
a plane parallel to it, so that the pilot can maneuver
the aircraft to avoid the obstruction.
A TAWS works by using digital elevation data and airplane instrumental values to
predict if a likely future position of the aircraft intersects with the ground.
The flight crew is thus provided with "earlier aural and visual warning of impending
terrain, forward looking capability, and continued operation in the landing configuration.
Controlled flight into terrain (CFIT) describes an accident in which an airworthy aircraft,
under pilot control, is unintentionally flown into the ground, a mountain, water, or an
obstacle. The term was coined by engineers at Boeing in the late 1970s.
The pilots are generally unaware of the danger until it is too late.
While there are many reasons why a plane might crash into terrain, including bad weather
and navigation equipment problems, it is claimed that pilot error is the single biggest
factor leading to a CFIT incident.
Even highly experienced professionals may commit CFIT due to fatigue, loss of
situational awareness, or disorientation. CFIT is considered to be caused by spatial

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disorientation, where the pilot(s) do not correctly perceive their position and orientation
with respect to the Earth's surface.
The incidents often involve a collision with terrain such as hills or mountains, and may
occur in conditions of clouds or otherwise reduced visibility. CFIT often occurs during
aircraft descent to landing near an airport. CFIT may be associated with subtle equipment
malfunctions. If the malfunction occurs in a piece of navigational equipment and it is not
detected by the crew, it may mislead the crew into improperly guiding the aircraft despite
other information received from all properly functioning equipment, or despite clear sky
visibility that should have allowed the crew to easily notice ground proximity.
14- Future Air Navigation System [5]
In view of the increase in air traffic, there has been a great deal of work by the nations of
the world, toward developing the concept for a future air navigation infrastructure to
serve worldwide civil aviation efficiency.
The current air traffic management system is experiencing growing difficulty as air traffic
around the world continues to increase. With air traffic predicted to grow at the rate of
five percent annually, the industry must find a new air traffic management system that
provides greater capacity.
One potential solution is a concept called Future Air Navigation System, or FANS.
FANS offers a space-based method for handling increased air traffic, allowing operators
to obtain maximum revenue from their operations while ensuring safe conditions for their
passengers.
Operator benefits offered by FANS include reduced fuel burn and flight time through
direct routing, and increased payload capability for takeoff-weight-limited flights. If

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FANS were implemented, operators would be able to take advantage of several needed
improvements:
1. Reduced separation between airplanes.
2. More efficient route changes.
3. Satellite communication.
4. No altitude loss when crossing tracks.
5. More direct routings.
15- Conclusion
As we found in this report, there are several navigation systems used in aircrafts, starting
from most common system, GPS, that can be used in all moving vehicles.
We talked about Radio, Celestial, Dead-reckoning, Mapping, Global and Area
Navigation Systems that are being developed day by day around the world, finding new
methods and techniques in positioning domain.
Also Collision & Terrain Avoidance Systems are acquiring scientists’ attention because
of their importance in safeness of passengers.
Navigation has been an ever-present component of humankind’s exploitation of the
capability of flight. While the principles of navigation have not changed since the early
days of sail, the increased speed of flight, particularly with the advent of the jet age, has
placed an increased emphasis upon accurate navigation. The increasingly busy skies,
together with rapid technology developments, have emphasized the need for higher-
accuracy navigation and the means to accomplish it.

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16- References
[1] NASA website.
[2] The Compass Rose Geocoin ® website.
[3] R.P.G. Collinson, Introduction to Avionics Systems, © Springer
Science+Business Media B.V., 2011
[4] Bethesda, Md., The American Practical Navigator : An Epitome Of Navigation.
[5] Bernhard Hofmann-Wellenhof, Klaus Legat, M. Wieser, Navigation.
[6] Flying Instructors’ School, Avionics Systems.
[7] S P Govinda Raju, Aerobasics, An Introduction to Aeronautics.
[8] Cary R.Spitzer, The Avionics Handbook.
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