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Microwave landing system
The microwave landing system (MLS) is an all-weather, precision radio guidance system intended to be installed at large airports to assist aircraft in landing, including 'blind landings'. MLS enables an approaching aircraft to determine when it is aligned with the destination runway and on the correct glidepath for a safe landing. MLS was intended to replace or supplement the instrument landing systems (ILS). MLS has a number of operational advantages over ILS, including a wider selection of channels to avoid interference with nearby installations, excellent performance in all weather, a small "footprint" at the airports, and wide vertical and horizontal "capture" angles that allowed approaches from wider areas around the airport.
Although some MLS systems became operational in the 1990s, the widespread deployment envisioned by some aviation agencies never became a reality. There were two reasons: (economic) while technically superior to ILS, MLS did not offer sufficiently greater capabilities to justify adding MLS receivers to aircraft equipage; and (potentially superior third system) GPS-based systems, notably WAAS, allowed the expectation of a similar level of positioning with no equipment needed at the airport. GPS/WAAS dramatically lowers an airport's cost of implementing precision "like" landing approaches, which is particularly important at small airports. For these reasons, most existing MLS systems in North America have been turned off. GPS/WAAS-based LPV 'Localizer Performance with Vertical guidance' approaches provide vertical guidance comparable to ILS Category I and FAA-published LPV approaches currently outnumber ILS approaches at US airports.
Though initially MLS appeared to be of interest in Europe, where concerns over the availability of GPS in Europe were an issue, widespread installation never occurred. Further deployment of the system is not likely. Rather, several European airports have implemented LPV approaches based on the EGNOS (WAAS-compatible) satellite system.
MLS employs 5 GHz transmitters at the landing place which use passive electronically scanned arrays to send scanning beams towards approaching aircraft. An aircraft that enters the scanned volume uses a special receiver that calculates its position by measuring the arrival times of the beams.
The US version of MLS, a joint development between the FAA, NASA, and the United States Department of Defense, was designed to provide precision navigation guidance for exact alignment and descent of aircraft on approach to a runway. It provides azimuth, elevation, and distance, as well as "back azimuth" for navigating away from an aborted landing or missed approach. MLS channels were also used for short-range communications with airport controllers, allowing long-distance frequencies to be handed over to other aircraft.
In Australia, design work commenced on a version of MLS in 1972. Most of this work was done jointly by the Federal Department of Civil Aviation (DCA), and the Radio Physics Division of the CSIRO. The project was called Interscan, one of several microwave landing systems under consideration internationally. Interscan was chosen by the FAA in 1975 and by the International Civil Aviation Organization in 1978 as the format to be adopted. An engineered version of the system, called MITAN, was developed by industry (AWA and Hawker de Havilland) under a contract with DCA's successor, the Department of Transport, and successfully demonstrated at Melbourne Airport in the late 1970s. The white antenna dishes could still be seen at Melbourne Airport until 2003 when they were dismantled.
This initial research was followed by the formation of Interscan International limited in Sydney, Australia in 1979 which manufactured MLS systems that were subsequently deployed in the US, EU, Taiwan, China and Australia. The Civil Aviation Authority (United Kingdom) developed a version of MLS, which is installed at Heathrow Airport and other airports, because of the greater incidence of instrument approaches with Cat II/III weather.
Compared with the existing instrument landing system (ILS), MLS had significant advantages. The antennas were much smaller, using a higher frequency signal. They also did not have to be placed at a specific location at the airport, and could "offset" their signals electronically. This made placement easier compared with the physically larger ILS systems, which had to be placed at the ends of the runways and along the approach path.
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Microwave landing system
The microwave landing system (MLS) is an all-weather, precision radio guidance system intended to be installed at large airports to assist aircraft in landing, including 'blind landings'. MLS enables an approaching aircraft to determine when it is aligned with the destination runway and on the correct glidepath for a safe landing. MLS was intended to replace or supplement the instrument landing systems (ILS). MLS has a number of operational advantages over ILS, including a wider selection of channels to avoid interference with nearby installations, excellent performance in all weather, a small "footprint" at the airports, and wide vertical and horizontal "capture" angles that allowed approaches from wider areas around the airport.
Although some MLS systems became operational in the 1990s, the widespread deployment envisioned by some aviation agencies never became a reality. There were two reasons: (economic) while technically superior to ILS, MLS did not offer sufficiently greater capabilities to justify adding MLS receivers to aircraft equipage; and (potentially superior third system) GPS-based systems, notably WAAS, allowed the expectation of a similar level of positioning with no equipment needed at the airport. GPS/WAAS dramatically lowers an airport's cost of implementing precision "like" landing approaches, which is particularly important at small airports. For these reasons, most existing MLS systems in North America have been turned off. GPS/WAAS-based LPV 'Localizer Performance with Vertical guidance' approaches provide vertical guidance comparable to ILS Category I and FAA-published LPV approaches currently outnumber ILS approaches at US airports.
Though initially MLS appeared to be of interest in Europe, where concerns over the availability of GPS in Europe were an issue, widespread installation never occurred. Further deployment of the system is not likely. Rather, several European airports have implemented LPV approaches based on the EGNOS (WAAS-compatible) satellite system.
MLS employs 5 GHz transmitters at the landing place which use passive electronically scanned arrays to send scanning beams towards approaching aircraft. An aircraft that enters the scanned volume uses a special receiver that calculates its position by measuring the arrival times of the beams.
The US version of MLS, a joint development between the FAA, NASA, and the United States Department of Defense, was designed to provide precision navigation guidance for exact alignment and descent of aircraft on approach to a runway. It provides azimuth, elevation, and distance, as well as "back azimuth" for navigating away from an aborted landing or missed approach. MLS channels were also used for short-range communications with airport controllers, allowing long-distance frequencies to be handed over to other aircraft.
In Australia, design work commenced on a version of MLS in 1972. Most of this work was done jointly by the Federal Department of Civil Aviation (DCA), and the Radio Physics Division of the CSIRO. The project was called Interscan, one of several microwave landing systems under consideration internationally. Interscan was chosen by the FAA in 1975 and by the International Civil Aviation Organization in 1978 as the format to be adopted. An engineered version of the system, called MITAN, was developed by industry (AWA and Hawker de Havilland) under a contract with DCA's successor, the Department of Transport, and successfully demonstrated at Melbourne Airport in the late 1970s. The white antenna dishes could still be seen at Melbourne Airport until 2003 when they were dismantled.
This initial research was followed by the formation of Interscan International limited in Sydney, Australia in 1979 which manufactured MLS systems that were subsequently deployed in the US, EU, Taiwan, China and Australia. The Civil Aviation Authority (United Kingdom) developed a version of MLS, which is installed at Heathrow Airport and other airports, because of the greater incidence of instrument approaches with Cat II/III weather.
Compared with the existing instrument landing system (ILS), MLS had significant advantages. The antennas were much smaller, using a higher frequency signal. They also did not have to be placed at a specific location at the airport, and could "offset" their signals electronically. This made placement easier compared with the physically larger ILS systems, which had to be placed at the ends of the runways and along the approach path.
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