AUTOMATIC LANDING SYSTEM
A precision instrument approach to touchdown and, in some cases, through the landing roll
out performed by the aircraft autopilot. The autopilot receives position information and/or
steering commands from onboard navigation equipment and is not dependent on any ground-based aids. ALS approaches are flown in VFR (very high frequency) and IFR (instrument flight rules). These approaches are usually carried out when the weather conditions are less than approximately 600
meters RVR(runway visual range), provided the crews are certified for auto
land approaches.
Before landing, the pilot has to perform a
landing checklist to ensure that critical items such as fuel flow, landing gear
down. Flaps are used for most landings because they permit a lower- approach
speed and a steeper angle of descent.The airspeed and rate of descent are
stabilized, and the airplane is aligned with the runway centerline.
The
phases of ALS are as follows:
1. Capturing Beam :
The first stage is to capture the beams
coming from the Instrument Landing System that includes the Localizer and Glide
Slope.
- Localizer radiates the beams for Horizontal
Guidance.
- Glide Slope originates the beams for Vertical
Guidance.
2. Decision Height :
In this stage, the pilot has to decide
considering the weather and other conditions whether to land or not.
3. Flare :
The position of an aircraft in which the
nose of an aircraft is slightly downward and the tail is slightly upward. The purpose of this
"flare" is to reduce the energy of the aircraft such that it
"stops flying" and settles onto the runway.
4. Decrabbing :
Decrab is the phase of the landing with
xwind in which the airplane is vulnerable to the gustings and for this reason,
all aircraft have to apply cross-controls: left rudder, right aileron (if wind
is coming from starboard) meaning rudder and aileron in opposite directions. The nose points
into the wind so that the aircraft approaches the runway slightly skewed with
respect to the runway centerline (crabbing).
5.
Touch Down :
The point where the aircraft lands or
touch it's wheels on the runway is called Touch Down.
MARKER
BEACONS
A
marker beacon is a particular type of VHF radio beacon used in an Instrument
Landing System(ILS),to provide visual and audible cues to the crew
to determine position along an established route to a destination such as
Runway.Marker Beacons operate at 75 MHz and radiate approximately 3-4 W
of power.
OUTER MARKER:
- It is
located between four and seven miles from the runway.
- It
transmits Morse code dashes at tone frequency of 400 Hz and illuminates a
cyan light ('OM' icon for display).
- It
provides the approximate point at which an aircraft on the localizer will
intercept the glide slope.
MIDDLE MARKER:
- It
is located approximately 3500 feet from the runway.
- It
transmits Morse code of dots/dashes modulated at 1300 Hz frequency and
amber light ('MM' icon for display) is illuminated.
- It
coincides with the aircraft being 200 feet above the runway touchdown
point.
INNER MARKER:
- It is
located at a distance of 60 m from the runway.
- The
crew recieve Morse code dots modulated at 3000 Hz on the audio system and
a corresponding white light ('IM' icon for display) is illuminated.
RUNWAY
A
defined rectangular area on a land aerodrome prepared for the landing and
takeoff of aircraft is called Runway.
Runways may be a
man-made surface (often asphalt, concrete, or a mixture of both) or a natural
surface (grass,dirt, gravel, ice, or salt).
DIMENSIONS OF RUNWAY:
Runway dimensions vary
from as small as 245 m (804 ft) long and 8 m (26 ft) wide in smaller general
aviation airports, to 5,500 m (18,045 ft) long and 80 m (262 ft) wide at large
international airports.
TYPES OF RUNWAY:
There are three types of Runways.
Visual
Runways:
- These
runways are used at small air strips and are usually just a strip of
grass, gravel, ice, asphalt or concrete.
- Usually,
there are no markings on a visual runway, they may have Threshold
Markings, Designators and Centerline.
- They
donot provide an instrument-based landing procedure; pilots must be able
to see the runway to use it.
- Radio
communication may not be avaliable and pilots must be self-reliant.
Non-Precision
Instrument Runways:
- These
runways are often used at small to medium size airports.
- These
runways, depending on the surface, may be marked with Threshold Markings,
Designators, Centerline and sometimes a 1000 feet (305 m) mark known as an
Aiming Point, sometimes installed at 1500 feet (457 m).
- They
provide horizontal position guidance to planes on instrument approach via
NDB (Non-directional Beacon), VHF Omni directional Range (VOR), Global
Positioning System (GPS) etc.
Precision Instrument
Runways:
- These
runways are found at medium and large size airports.
- These
consist of a Blast Pad/ Stop-way (optional for airports handling jets,
Threshold, Designators, Centerline, Aiming Point and 500 feet (152 m),
1000 feet (305 m) / 1500 feet (457 m), 2000 feet (610 m), 2500 feet (762
m) and 3000 feet (914 m) Touch-down zone marks.
- Precision
runways provide both Horizontal and Vertical guuidance insrument
approaches.
SECTIONS OF RUNWAY:
There
are runway markings.
- Runway Threshold: markings across
runway denoting the space designated for normal Landing and Take-off
conditions.
- Runway Safety Area: cleared, smoothed and graded
area around the paved runway which is kept away from obstacles.
- Runway: surface from threshold to tthreshold
features threshold markings, centerline and numbers.
- Blast Pads: stopways overrun areas at
the end of runways as emergency space to stop the planes when landing or
takeoff goes wrong. They are marked with yellow chevrons, not allowing
takeoff or land on it except emergency situations.
AIR
FIELD LIGHTING:
Approach
Lights: A
sequence of high-intensity lighting at length of 900 m before the runway
actually begins.The pilot can see from these lights whether his aircraft is
centered correctly.
Runway
Edge Lights: are
used to outline the edges of runway during periods of darkness or restricted
visibility conditions.
Runway
End Identifier Lights: are used to provide rapid and positive
identification of the approach end of a particular runway.The system consists
of a pair of a pair of synchronized flashing lights located laterally on each
side of the runway threshold.
Runway
Center Lights: are
located along the centerline of the runway.The lights are located from the
threshold to the end of longitudinal spacing of approximately 15 m.
Touchdown
Zone Lights: define
the landing portion of the runway.Touchdown Zone Lights are white in color
& shall extend from the threshold for a longitudinal distance of 900 m.
Taxiway
Edge Lights: blue
colored lights define the outline of taxiway during low visibility conditions.
Taxiway
Center Light: green
colored lights define the centerline of the taxiway during low visibility
conditions.
PAPI & VASI LIGHTS
Precision
Approach Path Indicator: is a visual aid that provides
guidance information to help a pilot acquire and maintain the correct approach
(in the vertical plane) to an airport or an aerodrome. It is generally located
beside the runway approximately 300 meters beyond the landing threshold of the
runway.
Visual
Approach Slope Indicator: is a system
of lights on the side of an airport runway threshold that
provides visual descent guidance information during
approach. These lights may be visible from up to 8 kilometres (5.0 mi)
during the day and up to 32 kilometres (20 mi) or more at night.
AUTOMATIC LANDING SYSTEM
A precision instrument approach to touchdown and, in some cases, through the landing roll
out performed by the aircraft autopilot. The autopilot receives position information and/or
steering commands from onboard navigation equipment and is not dependent on any ground-based aids. ALS approaches are flown in VFR (very high frequency) and IFR (instrument flight rules). These approaches are usually carried out when the weather conditions are less than approximately 600
meters RVR(runway visual range), provided the crews are certified for auto
land approaches.
Before landing, the pilot has to perform a
landing checklist to ensure that critical items such as fuel flow, landing gear
down. Flaps are used for most landings because they permit a lower- approach
speed and a steeper angle of descent.The airspeed and rate of descent are
stabilized, and the airplane is aligned with the runway centerline.
The
phases of ALS are as follows:
1. Capturing Beam :
The first stage is to capture the beams
coming from the Instrument Landing System that includes the Localizer and Glide
Slope.
- Localizer radiates the beams for Horizontal
Guidance.
- Glide Slope originates the beams for Vertical
Guidance.
2. Decision Height :
In this stage, the pilot has to decide
considering the weather and other conditions whether to land or not.
3. Flare :
The position of an aircraft in which the
nose of an aircraft is slightly downward and the tail is slightly upward. The purpose of this
"flare" is to reduce the energy of the aircraft such that it
"stops flying" and settles onto the runway.
4. Decrabbing :
Decrab is the phase of the landing with
xwind in which the airplane is vulnerable to the gustings and for this reason,
all aircraft have to apply cross-controls: left rudder, right aileron (if wind
is coming from starboard) meaning rudder and aileron in opposite directions. The nose points
into the wind so that the aircraft approaches the runway slightly skewed with
respect to the runway centerline (crabbing).
5.
Touch Down :
The point where the aircraft lands or
touch it's wheels on the runway is called Touch Down.
MARKER
BEACONS
A
marker beacon is a particular type of VHF radio beacon used in an Instrument
Landing System(ILS),to provide visual and audible cues to the crew
to determine position along an established route to a destination such as
Runway.Marker Beacons operate at 75 MHz and radiate approximately 3-4 W
of power.
OUTER MARKER:
- It is
located between four and seven miles from the runway.
- It
transmits Morse code dashes at tone frequency of 400 Hz and illuminates a
cyan light ('OM' icon for display).
- It
provides the approximate point at which an aircraft on the localizer will
intercept the glide slope.
MIDDLE MARKER:
- It
is located approximately 3500 feet from the runway.
- It
transmits Morse code of dots/dashes modulated at 1300 Hz frequency and
amber light ('MM' icon for display) is illuminated.
- It
coincides with the aircraft being 200 feet above the runway touchdown
point.
INNER MARKER:
- It is
located at a distance of 60 m from the runway.
- The crew recieve Morse code dots modulated at 3000 Hz on the audio system and a corresponding white light ('IM' icon for display) is illuminated.
RUNWAY
A
defined rectangular area on a land aerodrome prepared for the landing and
takeoff of aircraft is called Runway.
Runways may be a
man-made surface (often asphalt, concrete, or a mixture of both) or a natural
surface (grass,dirt, gravel, ice, or salt).
DIMENSIONS OF RUNWAY:
Runway dimensions vary
from as small as 245 m (804 ft) long and 8 m (26 ft) wide in smaller general
aviation airports, to 5,500 m (18,045 ft) long and 80 m (262 ft) wide at large
international airports.
TYPES OF RUNWAY:
There are three types of Runways.
Visual
Runways:
- These
runways are used at small air strips and are usually just a strip of
grass, gravel, ice, asphalt or concrete.
- Usually,
there are no markings on a visual runway, they may have Threshold
Markings, Designators and Centerline.
- They
donot provide an instrument-based landing procedure; pilots must be able
to see the runway to use it.
- Radio
communication may not be avaliable and pilots must be self-reliant.
Non-Precision
Instrument Runways:
- These
runways are often used at small to medium size airports.
- These
runways, depending on the surface, may be marked with Threshold Markings,
Designators, Centerline and sometimes a 1000 feet (305 m) mark known as an
Aiming Point, sometimes installed at 1500 feet (457 m).
- They
provide horizontal position guidance to planes on instrument approach via
NDB (Non-directional Beacon), VHF Omni directional Range (VOR), Global
Positioning System (GPS) etc.
Precision Instrument
Runways:
- These
runways are found at medium and large size airports.
- These
consist of a Blast Pad/ Stop-way (optional for airports handling jets,
Threshold, Designators, Centerline, Aiming Point and 500 feet (152 m),
1000 feet (305 m) / 1500 feet (457 m), 2000 feet (610 m), 2500 feet (762
m) and 3000 feet (914 m) Touch-down zone marks.
- Precision
runways provide both Horizontal and Vertical guuidance insrument
approaches.
SECTIONS OF RUNWAY:
There
are runway markings.
- Runway Threshold: markings across
runway denoting the space designated for normal Landing and Take-off
conditions.
- Runway Safety Area: cleared, smoothed and graded
area around the paved runway which is kept away from obstacles.
- Runway: surface from threshold to tthreshold
features threshold markings, centerline and numbers.
- Blast Pads: stopways overrun areas at
the end of runways as emergency space to stop the planes when landing or
takeoff goes wrong. They are marked with yellow chevrons, not allowing
takeoff or land on it except emergency situations.
AIR
FIELD LIGHTING:
Approach
Lights: A
sequence of high-intensity lighting at length of 900 m before the runway
actually begins.The pilot can see from these lights whether his aircraft is
centered correctly.
Runway
Edge Lights: are
used to outline the edges of runway during periods of darkness or restricted
visibility conditions.
Runway
End Identifier Lights: are used to provide rapid and positive
identification of the approach end of a particular runway.The system consists
of a pair of a pair of synchronized flashing lights located laterally on each
side of the runway threshold.
Runway
Center Lights: are
located along the centerline of the runway.The lights are located from the
threshold to the end of longitudinal spacing of approximately 15 m.
Touchdown
Zone Lights: define
the landing portion of the runway.Touchdown Zone Lights are white in color
& shall extend from the threshold for a longitudinal distance of 900 m.
Taxiway
Edge Lights: blue
colored lights define the outline of taxiway during low visibility conditions.
Taxiway
Center Light: green
colored lights define the centerline of the taxiway during low visibility
conditions.
PAPI & VASI LIGHTS
Precision
Approach Path Indicator: is a visual aid that provides
guidance information to help a pilot acquire and maintain the correct approach
(in the vertical plane) to an airport or an aerodrome. It is generally located
beside the runway approximately 300 meters beyond the landing threshold of the
runway.
Visual
Approach Slope Indicator: is a system
of lights on the side of an airport runway threshold that
provides visual descent guidance information during
approach. These lights may be visible from up to 8 kilometres (5.0 mi)
during the day and up to 32 kilometres (20 mi) or more at night.