Ground-based augmentation systems (GBAS) provide localized precision GPS corrections to aircraft, enabling precision approaches. GBAS has benefits over instrument landing systems like supporting more runways with one system. GBAS also allows for flexible siting, steadier guidance, and less frequent inspections. While GBAS can increase efficiency and capacity, limitations remain such as the need for aircraft and ground infrastructure to support its full capabilities. Airports are working to certify GBAS for low-visibility operations and eventually replace ILS.

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Optimizing Precision Final Approach
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Introduction
Navigation is a very ancient science, which began with human travel. Literally,
navigation can be described as to determine the exact position, orientation and velocity of a
moving object based upon the previous position (which is also known as dead-reckoning) or
with the assistance of a map, celestial charts or any external information (termed as position-
fixing) at a specified given time. Nowadays, space technology has advanced to a stage where
humans can use a consumer satellite receiver to pinpoint his/her position at virtually any place in
the world. This is thanks to navigation satellites, and the advantages of this technology will be
extended even further as the modernization of the Global Positioning Systems (GPS) takes place
as scheduled and the full deployment of GLONASS and Galileo satellite constellations are
completed according to time and roadmap.
For civil aviation applications, more accurate and precise data are required. This is where
augmentation systems are essential. One common problem faced by navigation satellite users for
civil aviation purposes is availability. In order to increase the availability, this work proposes a
way to interoperate between several Navigation Satellites, i.e. GPS, GLONASS and GALILEO,
and possibly the Chinese COMPASS/Beidou and the Indian IRNSS (FAA 2013).
Ground-based Augmentation Systems (GBAS)
Ground-based augmentation systems (GBAS) is a localized reference system within 20
km that supports navigation satellite augmentation through the use of terrestrial radio messages
composed of an individual or a network of accurately surveyed ground stations, which take
measurements concerning the GNSS, and one or more radio frequency signals, which transmit

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the information directly to the user receiver., while DGPS is a differential system specifically
designed for GPS. Current requirements on-board an aircraft as well as on-ground for precision
approach in (ATC) for GBAS (FAA 2013).
In the past, the FAA referred to GBAS as the Local Area Augmentation System (LAAS).
Current GBAS systems approved by the FAA only monitor and augment the Global Positioning
System (GPS) L1 C/A broadcast. Compared to traditional ILS the GBAS have extended
advantages. Multiple runway ends can be supported by just one GBAS thus reducing a number
of systems in a single airport. Due to reduction in Very High Frequency (VHF) requirements.
This reduces the Very High Frequency (VHF) requirements and simplifies airport infrastructure.
Just one VHF assignment for 48 individual approach procedures is required by the GBAS, and
not like ILS which needs one frequency for each system. Besides flexible sitting criteris allows
the GBAS to manage runways, unlike the ILS which cannot support.
The GBAS, which is a generic term, has more flexible siting criteria, allowing the GBAS
to serve runways which ILS is unable to support. A GBAS is sited to minimize critical areas
which place fewer restrictions on aircraft movement during ground taxi and air operations. The
GBAS approach guidance is steadier than ILS approach guidance. Also,
GBAS requires less frequent flight inspections compared to those required of ILS systems.
GBAS implementations example is the United States Local Area Augmentation System (LAAS).
Air services is implementing the Honeywell Smartpath™ SLS-4000 GBAS into the National
Airways System (FAA 2013).

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GBAS working principles:
GBAS on Ground Facility consists of at least three antennas, a central processing system,
a VHF Data transmitter on ground near the airport. In the aircraft the GBAS avionics within the
multi-mode receiver system provides continuous GPS implementation, GBAS and ILS with the
help of antennas and hardware. On Ground GBAS Facility utilizes VHF radio link to provide
aircraft with GPS corrections and information about the approach path. Reference antennas of
GBAS gets signals through satellites, its receivers then measure the time of transmission between
the reference antenna and the GPS satellite subsequently determining the distance the signal has
travelled. GBAS Facility on ground compares the measured distance and the actual distance,
based on satellite position and GPS receiver position and then determines the error in the
measurement. If GBAS Ground Facility determines some potential problem with a GPS satellite,
it broadcast of corrections are stopped for that particular satellite, thus preventing the GBAS
avionics from using the satellite. The GBAS Ground Facility transmits correction messages
twice in two seconds by means of the VDB, or VHF data broadcast, and guidance to 48 approach
paths. Within a 23 nautical mile radius the GBAS provides its services, the volume of which
supports aircraft during its transition for en route airspace through the terminal airspace by
means of precision landing approach.

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Illustration of GBAS System on ground and air-borne
Benefits of Capacity
GBAS supports intricate procedures and paths of terminal area and does not impacts the
safety. By reducing aircraft separation needs, it de-conflicts airspace by means of extended PTV
ranges. It also empowers the creation of approach procedures change with no infrastructure
changes, and offers the ease of implementation of multiple and variable glide slopes.
Benefits of Efficiency

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GBAS helps reduce the workload of air traffic controller by means of less
communication clutter and radar vectoring. It also helps shrink the time and distance in terminal
area which ultimately leads to fuel saving, which remains the most important benefit in terms of
cost and expenses to operators. IFR availability is increased through GBAS, including rollouts,
and arrival time procedures (ERCD 2012)
Benefits to the User
The in-aircraft procedure database is not required because the GBAS terminal area path
procedures are uplinked to the aircraft. It not only supports low powered descent touch downs
but also the TAP procedures up linking provides additional time to the aircrew for touchdowns.
Locations of aircraft and time or landing at key points along the TAP are necessary in order to
improve operations in the terminal.
Nose
Airports the world over are expanding rapidly with the increase in air traffic, similarly
those living as communities near the airports also are expanding, the vacant lands in the vicinity
of the airports get filled with human habitats. Due to this the concern for aviation related noise,
the ear shattering take-off and take-down nose of huge double decker aircrafts has a great impact
to the communities. Although the new era aircrafts with noise suppressed airframes have been
introduced, but it still remains a problem for airports around the world. Restricting the aircrafts
to a pre-defined three dimensional routes designed to suppress noise, the navigation provided by
GBAS offers an opportunity to reduce noise levels. GBAS offers flexibility to construct highly

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repeatable flight course for all weather, hence the costs related with noise mitigation may be
reduced to a considerable level. It was identified by Ray et al (2001) that code-range, carrier
phase and signal-to-noise ratio (SNR) measurements are impacted by multipath. These three
measurements can be parameterized and developed as state variables for the Kalman filters.
Potential areas of improvement and the necessary technical (GBAS) and operational changes.
GBAS, with all its benefits, is taken as a local and not a regional solution to providing
APV (Approach procedures with Vertical Guidance), because of its cost, more than $1.5 million
per aerodrome establishment cost. Besides GBAS avionics are neither feasible no available for
smaller aircrafts, hence practically it offers no solution for lower traffic volume or regional
airports. Heathrow is actively working with NATS and the airlines to assess the safety case
associated with LVP operations and the triggers (in particular cloud ceiling). LVP is safety
critical and so progress in this area has to be measured. We are also conducting research and
development as part of the SESAR programme, looking to certify Ground Based
Augmentation Systems (GBAS) to CATII/CATIII standards which will eventually replace the
use of ILS in low visibility and improve the landing rate so that LVPs cause less disruption to
airlines‟ schedules. For approach and landing operations down to Cat I, it is expected that
conventional non precision approaches (NPA) will be progressively replaced by standalone
RNAV approach operations. These RNAV approaches will also be implemented as a backup of
ILS Cat I. Depending on local business case and coordination with users, some ILS Cat I (small
airfields) are also expected to be replaced by SBAS or GBAS based approaches.
Many airports are working in tandem with airlines to evaluate the safety case related to
LVP operations. Heathrow has conducted R&D program as part of SESAR program in order to

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certify (GBAS) to CATII/CATIII standards which will ultimately replace the use of ILS in low
visibility. The Boeing Company has a private use GBAS installed and approved at its research
and development (R&D) facility at Moses Lake Airport (MWH) in Washington State. While
Japan is also investing in GBAS at Kansai International Airport and has already adopted Baro-
VNAV enabled APV at selected airports.
Case Study
Modifying approaches with the use of Ground-Based Augmentation System and
Required Navigation Performance Newark-Liberty International Airport (the Airport) is a critical
transportation hub for the New York-New Jersey metropolitan area and the nation. The port
authority has carried out various projects and actions over the last few years, like Sutainable
Infrastructure Guidelines in all port Authority and installation of GBAS system for flight
operations (SMP, 2013). It has also implemented full airside ground management program by
modifying course using GBAS and RNP (Required Navigation Performance). It is also
supporting other activities like new procedures to support environmental goals. Newark-Liberty
International Airport also installed GBAS as one of the first commissioned systems in the United
States and it is collaborating with FAA for its full implementation. In order to enhance safety in
US airports, the FAA program will help the port authority for the implementation of the Next
Gen air traffic control technologies, this will go a long way into making air travel more
convenient and safe. Besides for getting solutions to problems the Port Authority consults
regularly with external stakeholders on all issues, these stakeholders are:
- New Jersey Department of Environmental Protection (NJDEP)
- Federal Aviation Administration Eastern Region

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- Federal Aviation Administration-New York Airports District Office
- City of Newark, NJ
- City of Elizabeth, NJ
- Tenant Airlines
- Concessionaires
- Air Services Development Office
- Council for Airport Opportunity
- Rental Car Companies
- Hotel Operators
- Cargo Operators
- Flight Kitchens
The stakeholders are consulted by the Port authority on major issues pertaining to community
engagement, aircraft noise issues, greenhouse effect and leasehold. The authority is also
connected with various organizations and industrial groups in this regard, they are:
- Airports Council International
- National Alliance to Advance NextGen (co-founder)
- American Association of Airport Executives
- US Green Building Council
- Transportation Research Board
- And others
The port Authority is also engaged in various community engagement activities which are:

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The authority ensures that the communities around the Airport have an open dialogue with a
representative of the region’s aviation industry on all important subjects, like aircraft noise
abatement, air traffic congestion, construction projects, besides other important quality of life
issues. The staff at the authority also prepares sustainability report card which shows all the
achievements and other EWR programs like noise abatement to keep the stakeholders and the
community apprised of the developments (SMP, 2013).
Recommendations
The FAA’s National Airspace System (NAS) Enterprise Architecture 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 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.
This plan has been also envisaged by Eurocontrol’s Single European Sky ATM Research
Programme as a critical enabler for improving air traffic capacity. Eurocontrol's GBAS activities
are managed by Eurocontrol GBAS Project.

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Limitations
But GBAS has not been used to its full potential because it is necessary for airplanes to
be equipped and the ground facilities installed. Besides all aircrafts do not have the capability to
use GBAS and the ones using it are the Airbus A380 and Boeing 747-8 only. Although the
navigation capabilities today have greater sophistication, the fact is the navigation professionals
are busy primarily aound positioning and steering (horizontally, vertically and in the 4th
dimension, time). So far as the PBN and landing application are related, the focus is to navigate
via various phases of flight as well as on the requirement of an increase in levels of trust in
navigational performance.
GBAS should have a major impact on noise pollution around Frankfurt. “There is a big
debate around the airport about noise levels,” according to DFS Chairman and CEO Klaus-Dieter
Scheurle. It is expected by the FAA that ICAO will approve by 2015, the GAST-D Standards
and Recommended Practices. Regarding GBAS system capable of providing CAT-I precision
approach, the FAA has given GBAS System Design Approval.
Conclusion
As GBAS is being used by major global airports in their daily aircrafts operations, it is
vital for the aviation managers, operational supervisors and navigation service providers to know
the capabilities and the improved potential enabled by GBAS, including the cost reduction
potential for present infrastructure of air space system. A major improvement can be available by

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the GBAS for the enhanced performance. A major contribution towards greater reliability as
provided by the GBAS can be vital for advanced air traffic operations.

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References
EUROCONTROL (2015) . Accessed on 17th March, 2015, from
http://www.eurocontrol.int/navigation-activities
ERCD data compared the CACI population databases from 1991 and 2011 for the 201057dBA
and 2011/12 48dBA 6.5hr noise contours ii. Hounslow Council. Accessed 17th March,
2015 from
http://search.hounslow.gov.uk/highlight.aspx?aid=418946&pckid=68946230&rn=1&sp_
id=1916497123&lid=144628766&highlight=census+#firsthighligh
Precision landing softens noise impact. Airport Focus (August 6, 2013). Accessed on 17th March
2015 from http://airportfocusinternational.com/precision-landing-softens-noise-impact/
Sustainable Management Plan. The Port Authority of NY and NJ, Newark Liberty International
Airport. Accessed on 17th March, 2015, from http://www.panynj.gov/airports/newark-
liberty.html
United States Federal Aviation Administration Journal. Satellite Navigation - GBAS benefits.
Accessed on 17th March, 2015 from
http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navse
rvices/gnss/laas/benefits/

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