14.4 Functional Supplement to Global Satellite Radio Navigation Systems
269
Fig. 14.15 Final approach flight control (FAS) implementation
The ground-based regional augmentation system GRAS is designed to support
AV operations using GNSS en route, in the terminal area, non-precision approaches,
departures and approaches with vertical guidance in a certain area of airspace
(region).
GRAS is the result of a combination of SBAS and GBAS principles to improve
the performance and enhancement of GNSS navigation capabilities to users. GRAS,
like SBAS, uses a distributed network of reference stations to monitor the GNSS
satellite constellation signals and a processing center to calculate GNSS integrity and
differential correction information. The difference is that GRAS does not transmit
this information via a geostationary satellite, but reformats it and transmits it via a
network of ground stations in the VHF band, similar to GBAS.
When performing a precision approach using GBAS, keep in mind the following.
The flight trajectory by GBAS is defined differently from the ILS approach trajectory.
Trajectory data, including glide path, horizontal sector width, horizontal sensitivity,
and other guidance sector characteristics, are transmitted by GBAS ground stations
(LCCS) to GNSS (multi-mode receiver, MMR) avionics via a high-integrity digital
data link. The digital message defines the FAS trajectory and guidance characteristics. Onboard GNSS equipment, based on geometric relationships, calculates the
trajectory parameters and determines the guidance characteristics indicated in the
transmitted digital data. The same equipment generates guidance parameters with
characteristics similar to other precision approach systems, such as ILS.
The decision to perform a precision approach using GLS is made by the crew after
listening to the automatic terminal information service (ATIS) report before passing
the starting point of the selected procedure for the landing aerodrome and the lack
of information from the air traffic controller about the impossibility of performing
this operation due to the presence of any anomaly.
269
Fig. 14.15 Final approach flight control (FAS) implementation
The ground-based regional augmentation system GRAS is designed to support
AV operations using GNSS en route, in the terminal area, non-precision approaches,
departures and approaches with vertical guidance in a certain area of airspace
(region).
GRAS is the result of a combination of SBAS and GBAS principles to improve
the performance and enhancement of GNSS navigation capabilities to users. GRAS,
like SBAS, uses a distributed network of reference stations to monitor the GNSS
satellite constellation signals and a processing center to calculate GNSS integrity and
differential correction information. The difference is that GRAS does not transmit
this information via a geostationary satellite, but reformats it and transmits it via a
network of ground stations in the VHF band, similar to GBAS.
When performing a precision approach using GBAS, keep in mind the following.
The flight trajectory by GBAS is defined differently from the ILS approach trajectory.
Trajectory data, including glide path, horizontal sector width, horizontal sensitivity,
and other guidance sector characteristics, are transmitted by GBAS ground stations
(LCCS) to GNSS (multi-mode receiver, MMR) avionics via a high-integrity digital
data link. The digital message defines the FAS trajectory and guidance characteristics. Onboard GNSS equipment, based on geometric relationships, calculates the
trajectory parameters and determines the guidance characteristics indicated in the
transmitted digital data. The same equipment generates guidance parameters with
characteristics similar to other precision approach systems, such as ILS.
The decision to perform a precision approach using GLS is made by the crew after
listening to the automatic terminal information service (ATIS) report before passing
the starting point of the selected procedure for the landing aerodrome and the lack
of information from the air traffic controller about the impossibility of performing
this operation due to the presence of any anomaly.