Local Area Augmentation System
Encyclopedia
The Local Area Augmentation System (LAAS) is an all-weather aircraft landing system based on real-time differential correction of the GPS
signal. Local reference receiver
s located around the airport send data to a central location at the airport
. This data is used to formulate a correction message, which is then transmitted to users via a VHF Data Link
. A receiver on an aircraft
uses this information to correct GPS signals, which then provides a standard ILS
-style display to use while flying a precision approach. The International Civil Aviation Organization
(ICAO) calls this type of system a Ground Based Augmentation System (GBAS).
develops a clock problem, there is no way to rapidly warn the user not to use that satellite. WAAS, LAAS and other differential solutions fix this problem and provide GPS system integrity. Another problem is positional accuracy. Sources of error such as satellite clock drift
or ionospheric delays can introduce several meters of error in an aircraft's position. These errors must be corrected in real time for a precision approach where there is little or no visibility.
Honeywell has developed a Non-Federal CAT-1 LAAS which received System Design Approval (SDA) from the Federal Aviation Administration (FAA) in September 2009[1] Current proposed installations include: airports in Newark, NJ; Memphis, TN; Atlantic City, NJ; and Olathe, KS.
LAAS's VHF uplink signal is currently slated to share the frequency band from 108 MHz to 118 MHz with existing ILS localizer and VOR navigational aids. LAAS utilizes a Time Division Multiple Access (TDMA) technology in servicing the entire airport with a single frequency allocation. With future replacement of ILS, LAAS will reduce the congested VHF NAV band.
ends each with a separate ILS, all 12 ILS facilities can be replaced with a single LAAS system. This represents a significant cost savings in maintenance and upkeep of the existing ILS equipment.
Another benefit is the potential for approaches that are not straight- in. Aircraft equipped with LAAS technology can utilize curved or complex approaches such that they could be flown on to avoid obstacles or to decrease noise levels in areas surrounding an airport.
The FAA also contends that only a single set of navigational equipment will be needed on an aircraft for both LAAS and WAAS capability. This lowers initial cost and maintenance per aircraft since only one receiver is required instead of multiple receivers for NDB
's, DME
, VOR
, ILS
, MLS
and GPS
. The FAA hopes this will result in decreased cost to the airline
s and passengers as well as general aviation
.
In order to mitigate these problems, the resulting national system will likely have LAAS capability at major airports, WAAS capability for the rest of North America with a limited amount of conventional navaids as a national backup.
(JPALS) is a similar system for military usage.
(NAS) Enterprise Architecture (EA) is the blueprint for transforming the current NAS to the Next Generation Air Transportation System
(NextGen). The NAS Service Roadmaps lay out the strategic activities for service delivery to improve NAS operations and move towards the NextGen vision. They show the evolution of major FAA investments/programs in today's NAS services to meet the future demand. The GBAS Precision Approaches is one of the investment programs that provide solution to “Increase Flexibility in the Terminal Environment” in the NextGen Implementation Plan.
The FAA plans to replace legacy navigation systems with satellite based navigation technology. The FAA has determined that GBAS is the only cost effective alternative to the existing Instrument Landing Systems (ILS) by providing terminal, non-precision, and CAT I/II/III precision approach capabilities in the NAS. Some of these existing ILS systems will be phased out over time as GBAS are installed. A number of ILS facilities are expected to remain operational, to continue to provide precision approach service as a backup in the event of unavailability of GBAS services.
Global Positioning System
The 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...
signal. Local reference 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...
s located around the airport send data to a central location at the airport
Airport
An airport is a location where aircraft such as fixed-wing aircraft, helicopters, and blimps take off and land. Aircraft may be stored or maintained at an airport...
. This data is used to formulate a correction message, which is then transmitted to users via a VHF Data Link
VHF Data Link
The VHF Data Link or VHF Digital Link is a means of sending information between aircraft and ground stations . Aeronautical VHF data links use the band 117.975 - 137 MHz assigned by the International Telecommunication Union to Aeronautical Mobile Route Services...
. A receiver on an 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...
uses this information to correct GPS signals, which then provides a standard ILS
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...
-style display to use while flying a precision approach. The International Civil Aviation Organization
International Civil Aviation Organization
The International Civil Aviation Organization , pronounced , , is a specialized agency of the United Nations. It codifies the principles and techniques of international air navigation and fosters the planning and development of international air transport to ensure safe and orderly growth...
(ICAO) calls this type of system a Ground Based Augmentation System (GBAS).
History
The Local Area Augmentation System (LAAS) is designed to correct some of the errors inherent to GPS. One problem is the lack of a real-time, rapid-response monitoring system. Category I equipment will normally alert the user of the problem within ten seconds of detecting a problem. GPS has no such rapid-warning system. For example, if a satelliteSatellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
develops a clock problem, there is no way to rapidly warn the user not to use that satellite. WAAS, LAAS and other differential solutions fix this problem and provide GPS system integrity. Another problem is positional accuracy. Sources of error such as satellite clock drift
Clock drift
Clock drift refers to several related phenomena where a clock does not run at the exact right speed compared to another clock. That is, after some time the clock "drifts apart" from the other clock. This phenomenon is also used for instance in computers to build random number generators...
or ionospheric delays can introduce several meters of error in an aircraft's position. These errors must be corrected in real time for a precision approach where there is little or no visibility.
Honeywell has developed a Non-Federal CAT-1 LAAS which received System Design Approval (SDA) from the Federal Aviation Administration (FAA) in September 2009[1] Current proposed installations include: airports in Newark, NJ; Memphis, TN; Atlantic City, NJ; and Olathe, KS.
Operation
Local reference receivers are located around an airport at precisely surveyed locations. The signal received from the GPS constellation is used to calculate the position of the LAAS ground station, which is then compared to its precisely surveyed position. This data is used to formulate a correction message which is transmitted to users via a VHF data link. A receiver on the aircraft uses this information to correct the GPS signals it receives. This information is used to create an ILS-type display for aircraft approach and landing purposes. Honeywell’s CAT I system provides precision approach service within a radius of 23 NM surrounding a single airport. LAAS mitigates GPS threats in the Local Area to a much greater accuracy than WAAS and therefore provides a higher level of service not attainable by WAAS.LAAS's VHF uplink signal is currently slated to share the frequency band from 108 MHz to 118 MHz with existing ILS localizer and VOR navigational aids. LAAS utilizes a Time Division Multiple Access (TDMA) technology in servicing the entire airport with a single frequency allocation. With future replacement of ILS, LAAS will reduce the congested VHF NAV band.
Accuracy
The current Non-Fed LAAS is capable of achieving a Category I ILS accuracy of 16 m laterally and 4 m vertically. The goal of the LAAS program is to provide Category III ILS capability. The minimum accuracy for lateral and vertical errors of a Category III system are specified in RTCA DO-245A, Minimum Aviation System Performance Standards for Local Area Augmentation System (LAAS). Category III GBAS will allow aircraft to land with zero visibility utilizing 'autoland' systems.Benefits
One of the primary benefits of LAAS is that a single installation at a major airport can be used for multiple precision approaches within the local area. For example, if Chicago O'Hare has 12 runwayRunway
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...
ends each with a separate ILS, all 12 ILS facilities can be replaced with a single LAAS system. This represents a significant cost savings in maintenance and upkeep of the existing ILS equipment.
Another benefit is the potential for approaches that are not straight- in. Aircraft equipped with LAAS technology can utilize curved or complex approaches such that they could be flown on to avoid obstacles or to decrease noise levels in areas surrounding an airport.
The FAA also contends that only a single set of navigational equipment will be needed on an aircraft for both LAAS and WAAS capability. This lowers initial cost and maintenance per aircraft since only one receiver is required instead of multiple receivers for NDB
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...
's, DME
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....
, 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...
, ILS
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...
, MLS
Microwave landing system
A microwave landing system is an all-weather, precision landing system originally intended to replace or supplement instrument landing systems...
and GPS
Global Positioning System
The 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...
. The FAA hopes this will result in decreased cost to the airline
Airline
An airline provides air transport services for traveling passengers and freight. Airlines lease or own their aircraft with which to supply these services and may form partnerships or alliances with other airlines for mutual benefit...
s and passengers as well as general aviation
General aviation
General aviation is one of the two categories of civil aviation. It refers to all flights other than military and scheduled airline and regular cargo flights, both private and commercial. General aviation flights range from gliders and powered parachutes to large, non-scheduled cargo jet flights...
.
Drawbacks
LAAS shares in some of the same threats as all RF based landing systems; that being unintentional jamming, signal derogation due to multipath causing loss of accuracy or signal fading.In order to mitigate these problems, the resulting national system will likely have LAAS capability at major airports, WAAS capability for the rest of North America with a limited amount of conventional navaids as a national backup.
Variations
The Joint Precision Approach and Landing SystemJoint Precision Approach and Landing System
The Joint Precision Approach and Landing System is a military, all-weather landing system based on real-time differential correction of the GPS signal, augmented with a local area correction message, and transmitted to the user via secure means...
(JPALS) is a similar system for military usage.
Future
The FAA’s National Airspace SystemNational Airspace System
The National Airspace System of the United States is one of the most complex aviation systems in the world — consisting of thousands of people, procedures, facilities, and pieces of equipment — that enables safe and expeditious air travel in the United States and over large portions of the world's...
(NAS) Enterprise Architecture (EA) is the blueprint for transforming the current NAS to the Next Generation Air Transportation System
Next Generation Air Transportation System
The Next Generation Air Transportation System is the name given to a new National Airspace System due for implementation across the United States in stages between 2012 and 2025. The...
(NextGen). The NAS Service Roadmaps lay out the strategic activities for service delivery to improve NAS operations and move towards the NextGen vision. They show the evolution of major FAA investments/programs in today's NAS services to meet the future demand. The GBAS Precision Approaches is one of the investment programs that provide solution to “Increase Flexibility in the Terminal Environment” in the NextGen Implementation Plan.
The FAA plans to replace legacy navigation systems with satellite based navigation technology. The FAA has determined that GBAS is the only cost effective alternative to the existing Instrument Landing Systems (ILS) by providing terminal, non-precision, and CAT I/II/III precision approach capabilities in the NAS. Some of these existing ILS systems will be phased out over time as GBAS are installed. A number of ILS facilities are expected to remain operational, to continue to provide precision approach service as a backup in the event of unavailability of GBAS services.
See also
- Acronyms and abbreviations in avionicsAcronyms and abbreviations in avionics-A:*ACARS: Aircraft Communications Addressing and Reporting System.*ACAS: Airborne Collision Avoidance System.*ACP: Audio Control Panel.*ACS: Audio Control System.*ADAHRS: Air Data and Attitude Heading Reference System.*ADC: Air Data Computer....
- Differential GPSDifferential GPSDifferential Global Positioning System is an enhancement to Global Positioning System that provides improved location accuracy, from the 15-meter nominal GPS accuracy to about 10 cm in case of the best implementations....
- 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 and Geo Augmented Navigation
- 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...
: ILS - Joint Precision Approach and Landing SystemJoint Precision Approach and Landing SystemThe Joint Precision Approach and Landing System is a military, all-weather landing system based on real-time differential correction of the GPS signal, augmented with a local area correction message, and transmitted to the user via secure means...
is a similar system for military usage. - Precision approach
- WAASWide Area Augmentation SystemThe Wide Area Augmentation System is an air navigation aid developed by the Federal Aviation Administration to augment the Global Positioning System , with the goal of improving its accuracy, integrity, and availability...
- EGNOSEuropean Geostationary Navigation Overlay ServiceThe European Geostationary Navigation Overlay Service is a satellite based augmentation system developed by the European Space Agency, the European Commission and EUROCONTROL. It supplements the GPS, GLONASS and Galileo systems by reporting on the reliability and accuracy of the signals...
- AutolandAutolandIn aviation, autoland describes a system that fully automates the landing phase of an aircraft's flight, with the human crew merely supervising the process.-Description:...