International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 2
Number 4
December 2008
GNSS for an Aviation
M. Grzegorzewski, J. Cwiklak & H. Jafernik
Air Force Academy, Deblin, Poland
A. Fellner
The State School of Higher Education, Chelm, Poland
ABSTRACT: In Polish aviation on-board GPS units are used for enroute procedures mainly. The use of
GNSS for approach and landing procedures requires overcoming a lot of obstructions, including both
organizational and technical ones. The paper presents information connecting with GNSS implementation in
The Global Air Navigation Plan for CNS/ATM
Systems (Doc 9750) recognizes the Global
Navigation Satellite System (GNSS) as a key
element of Communication, Navigation,
Surveillance and Air Traffic Management
(CNS/ATM) systems and a foundation upon which
States can deliver improved aeronautical navigation
services. Standards and Recommended Practices
(SARPs) for the Global Navigation Satellite System
(GNSS) were developed by the Global Navigation
Satellite System Panel and introduced in ICAO
Annex 10, Volume I in 2001 as a part of
Amendment 76 to Annex 10. Guidance material in
Attachment D to Volume I provides extensive
guidance on technical aspects and application of
GNSS SARPs that provided, at the publication date,
for satellite-based en-route through Category I
precision approach operations.
GNSS service can be introduced in stages as the
technology and operational procedures develop. The
staged implementation of GNSS service may be
affected by various factors, including:
the existing navigation services;
availability of GNSS procedures design criteria;
level of air traffic services supporting GNSS
aerodrome infrastructure;
extent of aircraft equipage;
completeness of relevant regulations.
Depending upon these factors, States may adopt
different implementation strategies and derive
different benefits from the various stages of
The introduction of augmentation systems
enhances service and eliminates most limitations.
Based on traffic volume and airspace structure,
States can choose their level of involvement in the
development and implementation of ABAS, SBAS
and/or GBAS. These implementation efforts require
a high level of cooperation among States to deliver
maximum operational advantages to aircraft
1.1 Operations using Aircraft-Based Augmentation
System (ABAS)
In the early 1990s, many aircraft operators were
quick to adopt GNSS because of the availability of
relatively inexpensive GPS receivers. Operators used
these early receivers as an aid to VFR and IFR
navigation. They quickly saw the benefits of having
a global area navigation (RNAV) capability, and
demanded avionics that could be used for IFR
navigation. The core satellite constellations were not
developed to satisfy the strict requirements of IFR
navigation. For that reason, GNSS avionics used in
IFR operations should augment the GNSS signal to
ensure, among other things, its integrity. The
aircraft-based augmentation system (ABAS)
augments and/or integrates GNSS information with
information available onboard the aircraft to enhance
the performance of the core satellite systems.
The most common ABAS technique is called
receiver autonomous integrity monitoring (RAIM).
RAIM requires redundant satellite range
measurements to detect faulty signals and alert the
pilot. The requirement for redundant signals means
that navigation guidance with integrity provided by
RAIM may not be available 100 per cent of the time.
RAIM availability depends on the type of operation;
it is lower for non-precision approach than for
terminal, and lower for terminal than for en-route. It
is for this reason that GPS/RAIM approvals usually
have operational restrictions. Another ABAS
technique involves integration of GNSS with other
airborne sensors such as inertial navigation systems.
Many States have taken advantage of GPS/ABAS to
improve service without any expenditure on
infrastructure. The exploitation of GPS/ABAS is a
worthwhile first stage in a phased transition to
GNSS guidance for all phases of flight. Initial
approvals covered en-route, terminal and non-
precision approach operations.
Many service providers have designed new GPS
stand-alone approaches that offer significant benefits
because they can be designed to provide the most
effective flight path to the runway, do not require a
course reversal and provide the pilot with precise
position information throughout the procedure. Most
GPS stand-alone approaches provide straight-in
guidance, so they are considerably safer than circling
approaches. In some States, pilots are authorized to
fly suitable VOR, VOR/DME, NDB and NDB/DME
non-precision approach procedures using GPS
guidance. These are termed “GPS overlay
approaches and allow operators to benefit from
better accuracy and situational awareness without the
need for the service provider to design a new
This is seen as an interim step to bring early
benefits to users. Using GPS guidance, pilots follow
the path defined by the traditional NAVAIDs, and
comply with the visibility and minimum descent
altitude associated with the traditional approach.
Some VOR and NDB-based procedures are not
suited to the overlay programme because certain
approach legs cannot be adapted to the RNAV data
coding system. GPS overlay approaches are not ideal
from the pilot’s perspective, because the original
procedure was not intended to be flown using an
RNAV system. An overlay approach should be
removed from State Aeronautical Information
Publication (AIP) when a GPS stand-alone approach
is designed for the same runway to avoid the
potential for confusion between two approaches to
the same runway. Certain operational restrictions
were deemed necessary for the implementation of
GPS-based NPA procedures. The reasons for and
nature of these restrictions varied by State including:
the effects of GPS outages in large regions; the
availability of traditional NAVAIDs as a backup;
traffic density; and regulations for avionics
A common operational restriction is that the pilot
shall not take credit for GPS approaches at an
alternate aerodrome when determining alternate
weather minima requirements. Some States have
also approved the use of GPS as the only navigation
service in oceanic and remote areas. In this case
avionics should not only have the ability to detect a
faulty satellite (RAIM), but should also exclude that
satellite and continue to provide guidance. This
feature is called fault detection and exclusion (FDE).
Under such approval, aircraft carry dual systems and
operators perform pre-flight predictions to ensure
that there will be enough satellites in view to support
the planned flight. This provides operators with a
cost-effective alternative to inertial navigation
systems in oceanic and remote airspace. Some
aircraft with existing inertial navigation systems
have used another ABAS technique which involves
integration of GNSS with the inertial data. The
combination of GNSS FD, or FDE, along with the
short term accuracy of modern inertial navigation
systems provides enhanced availability of GNSS
integrity for all phases of flight. As long as pilots
rely on map reading and visual contact with the
ground, this use of GPS can increase efficiency and
1.2 Operations using Satellite-based Augmentation
System (SBAS)
An SBAS augments core satellite systems by
providing ranging, integrity and correction
information via geostationary satellites. The system
a network of ground reference stations that
monitor satellite signals;
master stations that collect and process reference
station data and generate SBAS messages;
uplink stations that send the messages to
geostationary satellites; and transponders on these
satellites that broadcast the SBAS messages.
By providing differential corrections, extra
ranging signals via geostationary satellites and
integrity information for each navigation satellite,
SBAS delivers much higher availability of service
than the core satellite constellations with ABAS
alone. SBAS, in certain configurations can support
approaches with vertical guidance (APV). There are
two levels of APV: APV I and APV II. Both use the
same lateral obstacle surfaces as localizer, however
APV II may have lower minima due to better vertical
performance. There will be only one APV approach
to a runway end, based on the level of service that
SBAS can support at an aerodrome. The two APV
approach types are identical from the perspective of
avionics and pilot procedures. In many cases, SBAS
will support lower minima than that associated with
non-precision approaches, resulting in higher airport
usability. Almost all SBAS approaches will feature
vertical guidance, resulting in a significant increase
in safety. APV minima (down to 75 m (250 ft) DH
approximately) will be higher than Category I
minima, but APV approaches would not require the
same ground infrastructure, so this increase in safety
will be affordable at most airports. SBAS
availability levels will allow operators to take
advantage of SBAS instrument approach minima
when designating an alternate airport. An SBAS
approach does not require any SBAS infrastructure
at an airport. SBAS can support all en-route and
terminal RNAV operations. Significantly, SBAS
offers the promise of affordable RNAV capability
for a wide cross section of users. This will allow
States to reorganize airspace for maximum
efficiency and capacity, allowing aircraft to follow
the most efficient flight path between airports. High
availability of service will permit States to
decommission traditional NAVAIDs, resulting in
lower costs.
There are four SBASs being developed: the
European Geostationary Navigation Overlay Service
(EGNOS); the Indian GPS and GEO Augmented
Navigation (GAGAN) System; the Japanese Multi-
functional Transport Satellite (MTSAT) Satellite-
Based Augmentation System (MSAS); and the
United States Wide Area Augmentation System
(WAAS). Geostationary satellite footprints define
the coverage area of an SBAS. Within this coverage
area, States may establish service areas where SBAS
supports approved operations. Other States can take
advantage of the signals available in the coverage
area in two ways: by fielding SBAS components
integrated with an existing SBAS or, by authorizing
the use of SBAS signals. The first option offers
some degree of control and improved performance.
The second option lacks any degree of control, and
the degree of improved performance depends on the
proximity to the service area of the host SBAS.
In either case, the State, which established an
SBAS service area, should assume responsibility for
the SBAS signals within that service area. This
requires the provision of NOTAM information, as
described in Section. If ABAS-only operations are
approved within the coverage area of SBAS, SBAS
avionics will also support ABAS operations and in
fact better meet availability-of-service requirements.
Although the architectures of the various SBASs are
different, they broadcast the standard message
format on the same frequency (GPS L1) and so are
interoperable from the user perspective. It is
anticipated that these SBAS networks will expand
beyond their initial service areas. Other SBAS
networks may also be developed. When SBAS
coverage areas overlap, it is possible for an SBAS
operator to monitor and send integrity and correction
messages for geostationary satellites of another
SBAS, thus improving availability by adding ranging
sources. This system enhancement should be
accomplished by all SBAS operators.
1.3 Operations using Ground-Based Augmentation
System (GBAS)
GBAS ground sub-systems are intended to provide a
precision approach service and optionally may
provide a GBAS positioning service. The precision
approach service is intended to provide deviation
guidance for final approach segments, while the
GBAS positioning service provides horizontal
position information to support 2D RNAV
operations in terminal areas. A ground station at the
airport broadcasts locally relevant corrections,
integrity parameters and approach data to aircraft in
the terminal area in the 108 MHz - 117 MHz band.
A GBAS installation will typically provide
corrections that support approaches to multiple
runways at a single airport. In some cases, the data
may be used for nearby airports and heliports as
GBAS infrastructure includes electronic
equipment, which can be installed in any suitable
airport building, and antennas to broadcast data
broadcast and to receive the satellite signals.
Antenna location is independent of the runway
configuration, but requires the careful evaluation of
local sources of interference, signal blockage, and
multipath. Sitting of the VHF data broadcast antenna
should ensure that the coverage area is sufficient for
the intended operations. The complexity and
redundancy of GBAS ground station installation
depends on the service provided. The cost and
flexibility of GBAS will result in more runway-ends
having qualified electronic precision approach
guidance, resulting in significant safety and
efficiency benefits. Such runways, however, should
meet standards for physical characteristics and
The implementation of GNSS operations requires
that Polish aviation authority consider a number of
elements including the following:
planning and organization;
procedure development;
air traffic management (airspace and ATC
aeronautical information services;
system safety analysis;
certification and operational approvals;
anomaly/interference reporting;
transition planning.
Considering the complexity and diversity of the
global airspace system, planning can best be
achieved if organized regionally and/or in wide areas
of common requirements and interest, taking into
account traffic density and level(s) of service
required. Planning and implementation is a State’s
responsibility within FIRs where it provides air
traffic services, unless States have agreed to jointly
plan services in an area covering more than one
State. Owing to the global nature of GNSS signals, it
is important to coordinate the planning and
implementation of GNSS services to the greatest
extent possible.
While this objective is normally pursued through
ICAO and its regional bodies, it should be
supplemented by bilateral and multilateral
coordination where necessary. The latter
coordination should address detailed aspects not
covered within the ICAO framework. Experience
has shown that the decision to implement GNSS
within States should be made at the highest level and
coordinated regionally within the ICAO Regional
Implementation Planning Groups. Successful
implementation programmes usually involve
cooperative efforts that include all departments
and/or individuals who are affected by the possible
outcomes, who will have the authority for
committing resources to ensure completion of the
There is a need for users, including air carriers,
general aviation, and the military, to be included in
the GNSS implementation team to allow them to
communicate their specific requirements. Users will
then be able to assist State authorities to develop an
effective and efficient GNSS implementation
strategy. A technical committee could be formed and
given the responsibility for defining requirements
and executing the implementation plan. Team
composition may vary by State, but the core group
responsible for the GNSS programme should include
members with operational expertise in aviation, and
could include:
Operations (persons responsible for operational
approvals, pilot training, and flight procedures);
Airworthiness standards (persons responsible for
approving avionics and installations);
Aviation standards (persons responsible for
developing instrument approach procedures and
developing obstacle clearance criteria, etc);
Aeronautical information service (persons who
are involved in NOTAM, procedure
design, databases etc);
Air traffic services (persons responsible for
developing ATC procedures and controller
Aerodrome operator (persons responsible for
developing aerodrome infrastructure to
support approach operations);
Engineering (engineers responsible for the design
of systems and equipment);
Airline representatives (personnel from flight
operations and flight crew training);
Other user groups (representatives of general,
business, commercial aviation, unions, as well as
other modes of transport that may use GNSS;
surveyors, GNSS receiver manufacturing
representatives etc);
Military representatives;
Other foreign civil aviation or ICAO officials (for
educational purposes).
The plan should identify capabilities that should
be in place in order to meet various requirements for
each approval stage and steps needed for
implementation, and should consider regional and
global planning for CNS/ATM systems. The GNSS
plan should include the development of a business
case. The adoption of CNS/ATM systems has major
economic and financial implications for service
providers and airspace users. Business case
development at the State level is essential in
determining the effect of GNSS and also to choose
the most cost-effective implementation strategy.
It is important to note that there are not regulation
and certification concerning the utility of GNSS in
Polish aviation. The transition to GNSS represents a
significant change for aviation, so it requires new
approaches to regulations, providing service and
operating aircraft. A successful transition to GNSS
requires a comprehensive orientation and training
programme aimed at all involved parties. This
program should keep pace as GNSS evolves. It is
most important that the decision-makers in aviation
organizations receive a broad appreciation of the
capabilities and potential of GNSS to deliver service.
The GNSS transition path and timetable depends
on a variety of factors, so the information provided
to decision-makers should evolve accordingly. Staffs
in regulatory and service provider organizations
require background training to be able to appreciate
how GNSS could affect their area of responsibility.
This should include: the basic theory of GNSS
operations; GNSS capabilities and limitations;
avionics performance and integration; current
regulations; and concepts of operation. This should
be followed by job-specific training to prepare staff
to plan, manage, operate and maintain the system.
For many pilots, GNSS represents the first
exposure to avionics that require programming
instead of simply the selection of a frequency. The
wide variety of pilot interfaces dictates a new
approach to training and the certification of pilots.
Aircraft operators should develop manuals and other
documents aimed at assisting pilots to use GNSS
properly and safely. ATC training should include the
application of GNSS to RNAV to ensure maximum
use of this technology.
Polish trainer jet called TS11 Iskra equipped with
GPS hardware was used for the flight tests. The GPS
observations were carried out with Ashtech GPS
receivers (Ashtech Z-Surveyor, Ashtech Z-XII), for
EGNOS corrections Javad Legacy receiver was used.
Four GPS reference stations were taking part in the
experiment, located along the aircraft route. The
reliable - reference positions of the aircraft trajectory
were determined as an average of four positions
calculated independently on the basis of every
reference station.
Fig. 1. Vertical plot of the TS-11 Iskra aircraft as a function of
ellipsoidal height and GPS time
Fig. 2. Plot of mean geodesic co-ordinate errors during descent
The plot illustrates mean geodesic co-ordinate
errors during descent as well, but it is important to
note, that these errors rose, when the aircraft
executed approach descent flight with changing
flight parameters, such as G-force, the angle of pitch,
banking and the value of angle acceleration.
The analyse of ICAO documents concerning GNSS
implementation for aviation and experiences gained
during the experiment allow to draw the following
differential real time positioning methods (SBAS,
GBAS) are applicable during the approach and
landing phase;
mean geodesic co-ordinate errors obtained during
the experiment, when corrections based on
EGNOS were available, were only 0.5 m;
ellipsoidal height parameter was stable and
equalled 2 m, which is also favourable.
non-precision landing procedures based on
VOR/DME, NDB could be replaced with
procedures based on GNSS, particularly with
implementation of GNSS will enhance flight
safety and airspace capacity in area and terminal
the use of Polish part of the project EUPOS for
Polish aviation is advisable.
Galotti W.P., The Future Air Navigation System (FANS),
England 1997.
MANUAL, ICAO Version 1.0 AN-Conf/11.
Gunnar Frisk: Gate-to Gate Seamless Aviation, Galleo’s
World, Spring 2000).
Grzegorzewski M., Ćwiklak J., Oszczak S, Ciecko A.,
Popielarczyk D. Determination of Aircraft Flight
Wysokość elipsoidalna samolotu TS 11 Iskra w czasie zniżania
1 101 201 301 401 501 601
czas [s]
Trajectory with Radar, GPS OTF and EGNOS Positioning,
The GNSS Conference, Rotterdam 2004.
Oszczak S., Grzegorzewski M., Jaruszewski W., Fellner A.,
Wasilewski A. Preliminary Results of DGPS, DGLONASS
Su-22 and TS-11 “Iskra” Aircraft trajectory
Determinations, The GNSS Conference, Edynburg 2000.
Śledziński J., EUPOS - European network of multifunctional
reference stations, Seminar in The State School of Higher
Education, Chełm 2005.