Marker beacon
Encyclopedia
A marker beacon is a particular type of VHF radio beacon used in aviation
, usually in conjunction with an instrument landing system
(ILS), to give pilot
s a means to determine position along an established route to a destination such as a runway
. From the 1930s until the 1950s, markers were used extensively along airways to provide an indication of an aircraft's specific position along the route, but from the 1960s they have become increasingly limited to ILS approach
installations. They are now very gradually being phased out of service, especially in more developed parts of the world, as GPS and other technologies have made marker beacons increasingly obsolete.
There are three types of marker beacons that may be installed as part of their most common application, an Instrument Landing System:
The Outer Marker, which normally identifies the final approach fix (FAF), is situated on the same line with the localizer
and the runway
centerline, 4 to 7 nautical mile
s before the runway threshold. It is typically located about 1 NM inside the point where the glideslope intercepts the intermediate altitude and transmits a 400 Hz tone signal on a low-powered (3 watts), 75 MHz
carrier frequency
. Its antenna
is highly directional, and is pointed straight up. The valid signal area is a 2400 ft (731.5 m) × 4200 ft (1,280 m) ellipse (as measured 1000 ft (304.8 m) above the antenna.) When the aircraft
passes over the outer marker antenna, its marker beacon receiver
detects the signal. The system gives the pilot a visual (blinking blue
outer marker light) and aural (continuous series of audio tone morse code
-like 'dashes') indication. Some countries, such as Canada
, have abandoned marker beacons completely, replacing the outer marker with a non-directional beacon
(NDB), and more recently with GPS fixes. In the United States
, the outer marker has often been combined with an NDB to make a Locator Outer Marker
(LOM). Some ILS approaches have no navigation aid at all situated at the final approach fix, but use other means, such as VOR
radial intersections, distance measuring equipment
(DME), GPS, or radar fixes, to identify the position.
A middle marker works on the same principle as an outer marker. It is normally positioned 0.5 to 0.8 nautical miles (1 km) before the runway threshold. When the aircraft is above the middle marker, the receiver’s amber
middle marker light starts blinking, and a repeating pattern of audible morse code-like dot-dashes at a frequency of 1,300 Hz in the headset. This alerts the pilot that the CAT I missed approach point
(typically 200 feet (61 m) above the ground level
on the glideslope) has been passed and should have already initiated the missed approach
if one of several visual cues has not been spotted.
Similar to the outer and middle markers; located at the beginning (threshold) of the runway on some ILS approach systems (usually Category II and III) having decision heights of less than 200 feet (61 m) AGL. Triggers a flashing white light on the same marker beacon receiver used for the outer and middle markers; also a series of audio tone 'dots' at a frequency of 3,000 Hz in the headset.
's AIM
publication don't mention fan markers the way older editions used to, and they appear to be an out-dated piece of technology, at least in the USA.
Aviation
Aviation is the design, development, production, operation, and use of aircraft, especially heavier-than-air aircraft. Aviation is derived from avis, the Latin word for bird.-History:...
, usually in conjunction with an instrument landing system
Instrument Landing System
An instrument landing system is a ground-based instrument approach system that provides precision guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument...
(ILS), to give pilot
Aviator
An aviator is a person who flies an aircraft. The first recorded use of the term was in 1887, as a variation of 'aviation', from the Latin avis , coined in 1863 by G. de la Landelle in Aviation Ou Navigation Aérienne...
s a means to determine position along an established route to a destination such as a runway
Runway
According to ICAO a runway is a "defined rectangular area on a land aerodrome prepared for the landing and take-off of aircraft." Runways may be a man-made surface or a natural surface .- Orientation and dimensions :Runways are named by a number between 01 and 36, which is generally one tenth...
. From the 1930s until the 1950s, markers were used extensively along airways to provide an indication of an aircraft's specific position along the route, but from the 1960s they have become increasingly limited to ILS approach
Instrument Landing System
An instrument landing system is a ground-based instrument approach system that provides precision guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument...
installations. They are now very gradually being phased out of service, especially in more developed parts of the world, as GPS and other technologies have made marker beacons increasingly obsolete.
There are three types of marker beacons that may be installed as part of their most common application, an Instrument Landing System:
Outer marker
Localizer
In aviation, a localizer is one of the components of an Instrument Landing System , and it provides runway centerline guidance to aircraft. In some cases, a course projected by localizer is at an angle to the runway . It is then called a Localizer Type Directional Aid...
and the runway
Runway
According to ICAO a runway is a "defined rectangular area on a land aerodrome prepared for the landing and take-off of aircraft." Runways may be a man-made surface or a natural surface .- Orientation and dimensions :Runways are named by a number between 01 and 36, which is generally one tenth...
centerline, 4 to 7 nautical mile
Nautical mile
The nautical mile is a unit of length that is about one minute of arc of latitude along any meridian, but is approximately one minute of arc of longitude only at the equator...
s before the runway threshold. It is typically located about 1 NM inside the point where the glideslope intercepts the intermediate altitude and transmits a 400 Hz tone signal on a low-powered (3 watts), 75 MHz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
carrier frequency
Carrier wave
In telecommunications, a carrier wave or carrier is a waveform that is modulated with an input signal for the purpose of conveying information. This carrier wave is usually a much higher frequency than the input signal...
. Its antenna
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
is highly directional, and is pointed straight up. The valid signal area is a 2400 ft (731.5 m) × 4200 ft (1,280 m) ellipse (as measured 1000 ft (304.8 m) above the antenna.) When the aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
passes over the outer marker antenna, its marker beacon receiver
Receiver (radio)
A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...
detects the signal. The system gives the pilot a visual (blinking blue
Blue
Blue is a colour, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 440–490 nm. It is considered one of the additive primary colours. On the HSV Colour Wheel, the complement of blue is yellow; that is, a colour corresponding to an equal...
outer marker light) and aural (continuous series of audio tone morse code
Morse code
Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment...
-like 'dashes') indication. Some countries, such as Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, have abandoned marker beacons completely, replacing the outer marker with a non-directional beacon
Non-directional beacon
A non-directional beacon is a radio transmitter at a known location, used as an aviation or marine navigational aid. As the name implies, the signal transmitted does not include inherent directional information, in contrast to other navigational aids such as low frequency radio range, VHF...
(NDB), and more recently with GPS fixes. In the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, the outer marker has often been combined with an NDB to make a Locator Outer Marker
Locator Outer Marker
A locator outer marker, or LOM, is a navigation aid used as part of an instrument landing system instrument approach for aircraft in the United States and other countries...
(LOM). Some ILS approaches have no navigation aid at all situated at the final approach fix, but use other means, such as VOR
VHF omnidirectional range
VOR, short for VHF omnidirectional radio range, is a type of radio navigation system for aircraft. A VOR ground station broadcasts a VHF radio composite signal including the station's identifier, voice , and navigation signal. The identifier is typically a two- or three-letter string in Morse code...
radial intersections, distance measuring equipment
Distance Measuring Equipment
Distance measuring equipment is a transponder-based radio navigation technology that measures distance by timing the propagation delay of VHF or UHF radio signals....
(DME), GPS, or radar fixes, to identify the position.
Middle marker
Amber (color)
Amber is an orange-yellow color that got its name from the material known as amber. Due to this, amber can refer not to one but to a series of shades of orange, since the natural material varies from nearly yellow when newer to orange or reddish-orange when older.-Amber:Amber is a pure chroma color...
middle marker light starts blinking, and a repeating pattern of audible morse code-like dot-dashes at a frequency of 1,300 Hz in the headset. This alerts the pilot that the CAT I missed approach point
Missed approach point
Missed approach point is the "point prescribed in each instrument approach at which a missed approach procedure shall be executed if the required visual reference does not exist." It defines the point for precision and non-precision approaches when the missed approach segment of a flight begins...
(typically 200 feet (61 m) above the ground level
Above ground level
In aviation and atmospheric sciences, an altitude is said to be above ground level when it is measured with respect to the underlying ground surface. This is as opposed to above mean sea level , or in broadcast engineering, height above average terrain...
on the glideslope) has been passed and should have already initiated the missed approach
Missed approach
Missed approach is an instrument flight rules procedure which is a standard component segment of an instrument approach. Generally, if the pilot flying or the pilot in command determines by the time the aircraft is at the decision height or missed approach point , that the runway or its...
if one of several visual cues has not been spotted.
Inner marker
Back course marker
A back course marker (BC) normally indicates the ILS back course final approach fix where approach descent is commenced. Its cockpit audio and visual indications are the same as for an inner marker (IM), but its location on the approach course is very different (final approach fix for BC vs. runway threshold for IM).Fan marker
The term fan marker refers to the older type of beacons used mostly for en-route navigation. Recent editions of FAAFederal Aviation Administration
The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...
's AIM
Aeronautical Information Manual
In United States aviation, the Aeronautical Information Manual is the Federal Aviation Administration's official guide to basic flight information and ATC procedures....
publication don't mention fan markers the way older editions used to, and they appear to be an out-dated piece of technology, at least in the USA.
See also
- AN/MRN-3AN/MRN-3The AN/MRN-3 was a marker beacon set used by the Army Air Force during and after World War II, it was standardized 23 October 1943, and replaced SCR-241.-Use:...
- Distance Measuring EquipmentDistance Measuring EquipmentDistance measuring equipment is a transponder-based radio navigation technology that measures distance by timing the propagation delay of VHF or UHF radio signals....
(DME) - Global Positioning SystemGlobal Positioning SystemThe Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...
(GPS) - Instrument Landing SystemInstrument Landing SystemAn instrument landing system is a ground-based instrument approach system that provides precision guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument...
- Non-Directional BeaconNon-directional beaconA non-directional beacon is a radio transmitter at a known location, used as an aviation or marine navigational aid. As the name implies, the signal transmitted does not include inherent directional information, in contrast to other navigational aids such as low frequency radio range, VHF...
(NDB) - Transponder Landing SystemTransponder Landing SystemA transponder landing system is an all-weather, precision landing system that uses existing airborne transponder and instrument landing system equipment to create a precision approach at a location where an ILS would normally not be available....
(TLS) - VHF Omni-directional RangeVHF omnidirectional rangeVOR, short for VHF omnidirectional radio range, is a type of radio navigation system for aircraft. A VOR ground station broadcasts a VHF radio composite signal including the station's identifier, voice , and navigation signal. The identifier is typically a two- or three-letter string in Morse code...
(VOR)
External links
- 2008 Federal Radionavigation Plan This FRS publication has detailed description of ILS and other navigational systems
- ILS - Marker beacons Describes the marker beacons used for discontinuous measuring of the distance to the runway’s threshold.