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Transcript of MLS
located 400 ft from the side of the runway between runway threshold and touchdown zone
elevation to at least 15°
An MLS elevation guidance station HISTORY System MLS ADVANTAGES Principle basic limitations:
site sensitivity and high installation costs;
single approach path;
multi path interference; and
channel limitations - 40 channels only. ILS LIMITATIONS Wide selection of channels to avoid interference with other nearby airports
Excellent performance in all weather
Small "footprint" at the airports OPERATIONAL ADVANTAGES Elimination of ILS/FM broadcast interference problems;
Provision of all-weather coverage up to ±60 degrees from runway centre line, from 0.9 degree to 15 degrees in elevation, and out of 20 nautical miles (NM);
Capability to provide precision guidance to small landing areas such as roof-top heliports;
Continuous availability of a wide range of glide paths to accommodate STOL and VTOL aircraft and helicopters;
In 1994, the US government issued a statement that no further
work would be done on MLS and that GPS would be used instead. can include both the basic and auxiliary data words
MLS data are transmitted throughout the azimuth (and back azimuth when provided) coverage sectors DATA COMMUNICATIONS It is used by aircraft to determine their distance from a land-based transponder by receiving pulse pairs- two pulses of fixed duration and separation.
The DME is composed of a UHF
In the aircraft and UHF receiver/
Transmitter (transponder) on the ground. OPERATION OF DME provided by the precision Distance Measuring Equipment (DME, DME/P)
provides continuous and highly accurate distance information
DME(Distance Measuring Equipment)
- is a transponder-based radio navigation technology that measures
slant range distance by timing the propagation delay of VHF or UHF
-it was developed in Australia and was invented by Edward George
“Taffy” Bowen. RANGE COMMUNICATIONS APPROACH ELEVATION Antennas were much smaller
Did not have to be placed at a specific point at the airport
Signals covered a very wide fan-shaped area off the end of the runway
Uses a single frequency, broadcasting the azimuth and altitude information one after the other ADVANTAGES over ILS Accommodation of both segments and curved approaches;
Availability of 200 channels - five times more than ILS;
Potential reduction of Category I (CAT l) minimums;
Improved guidance quality with fewer flight path corrections required;
Provision of back-azimuth for missed approaches and departure guidance;
Elimination of service interruptions caused by snow accumulation; and
Lower site preparation, repair, and maintenance costs. MLS employs 5GHz transmitters at the landing place which use passive electronically scanned rays 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. (MLS) Microwave LANDING In the mid 1970’s the US was running into ILS frequency
congestion problems in the North Eastern part of the country.
(the 40 channel problem) In an attempt to alleviate the situation, they proposed that ICAO has to specify a new type of landing aid that would use microwave frequencies (specifically about 15 GHz) In response, two techniques were proposed. The US and
Australia proposed a Time Referenced Scanning Beam (TRSB)
system and the British proposed a Doppler system. Because there was very little differencebetween the two
systems and because there was perceived to be a great deal of
economic benefit to the “winners”, the selection process became
almost entirely political. To no one’s surprise, the US/Australian system was adopted.
Unfortunately, the FAA, which was given the job of introducing
the MLS into the civil aviation system, failed completely. *http://microwave.landing-system.com/