| Microwave Landing System |
Article Index for Microwave |
Website Links For Microwave |
Information AboutMicrowave Landing System |
| CATEGORIES ABOUT MICROWAVE LANDING SYSTEM | |
| aircraft instruments | |
| radio navigation | |
|
The Microwave Landing System (MLS) is an all-weather, precision landing system originally intended to replace or supplement the Instrument Landing System (ILS). HISTORY The MLS was a joint development between the FAA , NASA , and the U.S. Department Of Defense and 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. Similar to other precision landing systems, lateral and vertical guidance may be displayed on conventional course deviation indicators or incorporated into multipurpose cockpit displays. Range information can also be displayed by conventional DME indicators and also incorporated into multipurpose displays. The MLS supplements the Instrument Landing System (ILS) as the standard landing system in the U.S. for civil, military, and international civil aviation. At international airports, ILS service is protected to 2010. OPERATIONAL FUNCTIONS The system may be divided into five functions: Approach azimuth, Back azimuth, Approach elevation, Range and Data communications. Approach azimuth guidance The azimuth station transmits MLS angle and data on one of 200 channels within the frequency range of 5031 to 5091 MHz and is normally located about 1,000 feet (300 m) beyond the stop end of the runway, but there is considerable flexibility in selecting sites. For example, for heliport operations the azimuth transmitter can be collocated with the elevation transmitter. The azimuth coverage extends: Laterally, at least 40 degrees on either side of the runway centerline in a standard configuration. In elevation, up to an angle of 15 degrees and to at least 20,000 feet (6 km), and in range, to at least 20 nautical miles (37 km) (See FIG 1-1-8.) Elevation guidance The elevation station transmits signals on the same frequency as the azimuth station. A single frequency is time-shared between angle and data functions and is normally located about 400 feet from the side of the runway between runway threshold and the touchdown zone. Elevation coverage is provided in the same airspace as the azimuth guidance signals: In elevation, to at least +15 degrees; Laterally, to fill the Azimuth lateral coverage and in range, to at least 20 nautical miles (37 km) (See FIG 1-1-9.) Range guidance The MLS Precision Distance Measuring Equipment (DME/P) functions the same as the navigation DME, but there are some technical differences. The beacon transponder operates in the frequency band 962 to 1105 MHz and responds to an aircraft interrogator. The MLS DME/P accuracy is improved to be consistent with the accuracy provided by the MLS azimuth and elevation stations. A DME/P channel is paired with the azimuth and elevation channel. A complete listing of the 200 paired channels of the DME/P with the angle functions is contained in FAA Standard 022 (MLS Interoperability and Performance Requirements). The DME/N or DME/P is an integral part of the MLS and is installed at all MLS facilities unless a waiver is obtained. This occurs infrequently and only at outlying, low density airports where Marker Beacon s or Compass Locator s are already in place. Data communications The data transmission can include both the basic and auxiliary data words. All MLS facilities transmit basic data. Where needed, auxiliary data can be transmitted. MLS data are transmitted throughout the azimuth (and back azimuth when provided) coverage sectors. Representative data include: Station identification, Exact locations of azimuth, elevation and DME/P stations (for MLS receiver processing functions), Ground equipment performance level; and DME/P channel and status. Auxiliary data content: Representative data include: 3-D locations of MLS equipment, Waypoint coordinates, Runway conditions and Weather (e.g., RVR, ceiling, altimeter setting, wind, wake vortex, wind shear). SYSTEM CONFIGURATION The standard configuration of MLS ground equipment includes: An azimuth station to perform azimuth and data communication functions. In addition to providing azimuth navigation guidance, the station transmits basic data which consists of information associated directly with the operation of the landing system, as well as advisory data on the performance of the ground equipment. An elevation station to provide elevation guidance. Distance Measuring Equipment (DME) to perform range guidance, both standard DME (DME/N) and precision DME (DME/P). MLS Expansion Capabilities. The standard configuration can be expanded by adding one or more of the following functions or characteristics. Back azimuth which provides lateral guidance for missed approach and departure navigation. Auxiliary data transmissions, which provides additional data, including refined airborne positioning, meteorological information, runway status, and other supplementary information. Expanded Service Volume (ESV) proportional guidance to 60 degrees. MLS identification is a four-letter designation starting with the letter M. It is transmitted in International Morse Code at least six times per minute by the approach azimuth (and back azimuth) ground equipment. OPERATIONAL FLEXIBILITY The MLS has the capability to fulfill a variety of needs in the approach, landing, missed approach and departure phases of flight. For example, the system can support: Curved and segmented approaches, Selectable glide path angles, Accurate 3-D positioning of the aircraft in space and the establishment of boundaries to ensure clearance from obstructions in the terminal area. While many of these capabilities are available to any MLS-equipped aircraft, the more sophisticated capabilities (such as curved and segmented approaches) are dependent upon the particular capabilities of the airborne equipment. VARIATIONS NASA operates a similar system called the Microwave Scanning Beam Landing System to land the Space Shuttle . FUTURE The FAA suspended the MLS program in 1994 in favor of the GPS ( Wide Area Augmentation System {WAAS) system that may supplement or replace existing MLS systems. Many countries in Europe (particularly those known for low visibility conditions) have embraced the MLS system as a replacement to ILS. Phasing down of MLS systems in the U.S. is planned to begin in 2010. However, it is unclear whether all the systems will be replaced or taken out of service, but (like LORAN-C ) it is reasonable to speculate that if funding becomes unfeasible, they will be. SUMMARY The MLS provides precision three-dimensional navigation guidance accurate enough for all approach and landing maneuvers and accuracy is consistent throughout the coverage volumes. (See FIG 1-1-10.) The system has low susceptibility to interference from weather conditions and airport ground traffic. The MLS has 200 channels, theoretically enough for any foreseeable need. It also transmits ground-air data messages associated with the systems operation and provides continuous range information with an accuracy of about 100 feet. The FAA has halted support for the MLS program; countries in Europe are continuing development. SEE ALSO
References
EXTERNAL LINKS |
|
|