Aircraft navigation system

VHF OMNIRANGE SYSTEM
Electronic navigation system.
 It produces 360 usable radials or courses ,any one
of which is radial path connected to the station.
 Operation is in the vhf portion of the radio
spectrum.
 Frequency range 108 MHz-117.95 MHz

 BENEFITES
 More accurate and precise flying

 Reliable
 Voice capable

 Reduces interference from atmosphere
and precipitation
 Navigation info is visually displayed on an

instrument in cockpit called the CDI (course
deviation indicator.)

VOR RECEIVING SYSTEMS CONSIST OF
 A RECEIVER
 VISUAL INDICATOR
 ANTENNAS
 A POWER SUPPLY
 FREQUENCY SELECTOR: USED TO TUNE RECEIVER
TO SELECTED VOR GROUND STATION
INFO FROM THE VOR RECEIVER IS DISPLAYED ON THE
CDI (COURSE DEVIATION INDICATOR).

WORKING OF VOR
 Info from the VOR receiver is displayed on the CDI
(Course Deviation Indicator).

The vertical needle is used as the course indicator.
 Vertical needle also indicates when the aircraft
deviates from the course and
 The direction of the aircraft must be turned to attain
the desired course.

WORKING OF VOR THROUGH CDI
 To-from indicator presents the direction to or from
the station along the omni radial.
 When the localizer signals are selected on the
receiver ,the indicator shows the position of the
localizer beam relative to the aircraft and the
direction the aircraft must be turned to intercept the
localizer.
 During VOR operation the VOR radial to be used is
selected by rotating the OBS (omni-bearing selector).
 OBS is graduated in degrees from 0 to 360.

INSTRUMENT LANDING SYSTEM (ILS)
Operates in the VHF portion of the electromagnetic
spectrum
System consists of a runaway localizer, a glide slope
signal, and marker beacons for position location

Localizer equipment produces a radio course aligned
with the centre of an airport runaway. The on course
signals result from the equal reception of two signals;
Blue sector(150 Hz) and yellow sector(90 Hz)

The glide slope : assists pilot in making the correct
angle of descent
Glide slope signals are radiated from two antennas
located adjacent to the touchdown point of the
runway.
Info from both localizer and glide slope receivers is
presented to the CDI;

THE COURSE DEVIATION INDICATOR
The vertical needle: localizer information
Horizontal needle : Glide slope information
When both needles are centered, the aircraft is on
course and descending at the proper rate

MARKER BEACONS
In connection with the instrument landing system.

signals which indicate the position of the aircraft
along the approach to the runway
Three markers are used in each installation:
Outer marker - the beginning of the approach path
is modulated by a 400 HZ signal, a tone keyed in
long dashes
Middle marker: 3500 ft from the end of the runway
is modulated at 1300 Hz, a higher-pitched tone

DISTANCE MEASURING EQUIPMENT(DME)
Constant visual indication of the distance the aircraft
is from a ground station
NOT a true indication of point to point distance as
measured over the ground
Indicates the slant range between the aircraft and
the ground station

WORKING OF DME
Transceiver transmits a pair of spaced pulses to the
ground station
Ground station responds with a pulse transmission
on a separate frequency to send a reply to the aircraft
Time elapsed is time between the challenges and
are measured;

Time travel is the distance separating plane and
station.
Distance is indicated in ‘nautical miles’ by a cockpit
instrument

 Transmitting frequencies are in 2 groups
 962 MHz to 1024 MHz
 1151 MHz to 1212 MHz
 Receiving frequency is between 1025 to 1149 MHz

Aircraft’s DME transceiver is tuned to the selected DME
ground station

AUTOMATIC DIRECTION FINDERS
Radio receivers equipped with directional antennas
Used to determine the direction from which signal
are received
Provide controls for manual operation in addition to
automatic direction finding.

Provide a means of fixing the position with
reasonable accuracy.
Operates in low and medium frequency spectra 190
kHz through 1750 kHz.

Consists of
 Receiver, Loop antenna,
 Sense or non-directional antenna,
 Indicator and control unit.
Loop antenna rotates through 360 degrees
Receives Max signal strength:
In parallel position with the direction of the
transmitted signal
Reaches the Min when perpendicular to the
transmitted signal position of the loop, is called the
null position

Null position of the loop is used for direction finding

Two null positions exist (180 degrees apart)
Loop antenna cannot differentiate, require sense
antenna
Signal strength of the sense antenna is superimposed
with the null antenna
Only one null position of the loop

DOPPLER NAVIGATION SYSTEM
Automatically and continuously computes and
displays ground speed and drift angle of an aircraft
without the aid of ground stations, wind estimates
or true air speed data
Does not sense direction as search radar does
Uses continuous carrier wave transmission energy
and determines the forward and lateral velocity
component of the air craft by utilizing the principle
known as DOPPLER EFFECT

INERTIAL NAVIGATION SYSTEM
Used on large aircraft as a long range navigation aid

Self-contained system; DOES NOT require any signal
inputs from ground navigational facilities
Derives altitude, velocity, and heading information
from measurement of the aircraft’s accelerations
Two accelerometers are required,
one referenced towards east and other towards north.
The accelerometers are mounted on a gyro stabilized
unit, called the stable platform
Averts the introduction of errors resulting from the
acceleration due to gravity.

An inertial navigation system is a complex containing
four basic components :A stable platform which is oriented to maintain
accelerometers horizontal to the earth’s surface.
Accelerometers arranged on the platform to
supply specific components of acceleration
Integrators which receive the output from the
accelerometers and furnish velocity and distance.

A computer which receives signals from the
integrators and changes distance travelled to
position in selected coordinates.

RADIO ALTIMETER
Measures the distance from the aircraft to the
ground
Accomplished by transmitting radio frequency
energy to the ground and receiving the reflected
energy at the aircraft
Modern Day: Pulse Type
Altitude determined by measuring time required
for transmitted pulse to hit ground and return.
Indicating instrument gives true altitude of aircraft
Used during landing to determine decision
whether to continue to land or execute climb-out

Aircraft navigation system

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Aircraft navigation system