Home' RTCA Documents for Review : DO-253D_Change1_FRAC Contents Appendix I
DO-253D Change 1
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touchdown performance requirements. Hence no unique standard, position domain NSE
level accuracy is specified for this Service Type. The same holds true for Integrity and
Continuity. For GAST D, monitoring performance requirements are specified in the
pseudorange domain. The acceptable airplane level performance is determined by the end-
user and the service provider is only responsible for ensuring that the signals provided by
the ground station meets the pseudorange domain monitoring requirements and performs
all other functional requirements necessary so that the user can determine the appropriate
NSE characteristics in the position domain under faulted and fault free conditions.
Similarly, Continuity is defined in terms of the continuity of the service actually provided
by the ground station and not at the output of a ‘fault free’ receiver. The determination of
position domain NSE continuity and the assessment of the suitability of that continuity for
the operational intent is the responsibility of the end user.
GBAS Facility Classifications
A GBAS Facility Classification (GFC) is composed of the following elements:
Facility Approach Service Type (FAST) – This is a collection of letters from A to D
indicating the Service Types that are supported by the ground facility. For example, FAST
C denotes a ground station that meets all the performance and functional requirements
necessary to support Service Type C. As another example, a FAST CD ground station
supports approaches with service types C and D.
Ranging Source Types – Indicates what ranging sources are augmented by the ground
facility. The coding for this parameter is as follows:
G2 - SBAS
G3 - GLONASS
G4 - Reserved for Galileo
G5+ - Reserved for future Ranging Sources
Facility Coverage – Defines coverage of the positioning service. (Note that coverage for
specific approaches is covered below as part of the Approach Facility Designations). The
facility coverage is coded as 0 for Ground facilities that do not support the Positioning
Service. For other cases, the facility coverage indicates the radius of Dma x expressed in
Polarization – Defines the polarization of the VHF Data Broadcast (VDB) signal. E
indicates elliptical polarization and H indicates horizontal polarization.
Facility Approach Service Type (FAST)
The facility classification scheme for GBAS includes an indication of which Service Types
the ground station can support. What this means is, the ground station meets all the
performance requirements and functional requirements such that a compatible airborne
user can apply the information from the ground station and have quantifiable performance
at the output of the processing. It does not necessarily mean that the ground facility
supports all service types on every runway end. Which Service Types are supported for
each approach on a given runway end is indicated as part of the Approach Facility
Designation and in the Type 4 message (Approach Performance Designator).
GBAS Facility Classification Examples
The facility classification for a specific facility would be specified by a concatenated series
of codes for the elements described in Section I.4 . In general:
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