Home' RTCA Documents for Review : DO-253D_Change1_FRAC Contents Appendix E
DO-253D Change 1
© 2019, RTCA, Inc.
APPENDIX E: SERVICE VOLUME DEFINITIONS AND MAXIMUM USE DISTANCE
This appendix presents an overview of some requirements in ICAO Annex 10 concerning
GBAS coverage, approach service volumes, and maximum use distance (Dmax) as
harmonized in RTCA/DO-253D and ICAO Annex 10, that including Amendment 91. This
appendix discusses the Differentially Corrected Positioning Service (DCPS) service
volume and the approach service volume. It describes the options that are available for
service providers in establishing service volumes, including expanded service volumes, as
well as areas where GBAS can be used for advisory information. It also includes
operational considerations related to expanded service volumes and the use of GBAS
information outside of the approach service volume.
The maximum use distance, Dmax, is a parameter in the Type 2 message, Additional Data
Block 1. ICAO Annex 10 only requires broadcast of the Type 2 message, Additional Data
Block 1, when the GBAS station provides either the positioning service or GAST-D
service. When broadcast, Dmax values can be from 2 km to 510 km or set to “no distance
limitation.” When not broadcast, the equipment will operate the same as if Dmax were
broadcast set to “no distance limitation.”
Description of SARPs Service Volume Requirements Changes
In the GBAS SARPs the approach service volume is distinct from Dmax (maximum use
distance), if Dmax is broadcast by the ground subsystem. In previous SARPs requirements,
approach integrity, and, if DCPS was provided, DCPS integrity had to be met everywhere
within Dmax. In the current embodiment, only the DCPS integrity (when provided) has to
be met within Dmax.
The SARPs uses the phrase “service volume” in ICAO Annex 10 Section 22.214.171.124.3 in lieu
of the word “coverage.”
This differentiates the regions where a supported operation
requires use of GBAS from regions where the GBAS signal might be available for advisory
information and can aid the operation, but the operation is not predicated on use of GBAS.
ICAO Annex 10 defines three service volumes in Section 126.96.36.199.3: an approach service
volume, an autoland/guided takeoff service volume, and a positioning service volume. As
defined in Appendix A, the GBAS service volume is the region in which the system meets
all relevant SARPs requirements, including integrity, continuity, availability, and field
strength within which frequency protection is provided.
If a non-zero value of Dmax is broadcast by the ground subsystem, the airborne receiver is
required to only apply pseudorange corrections when the distance to the GBAS reference
point is less than Dmax. That is the requirement defined in the SARPs and this MOPS
Considerations for Setting Dmax for the Positioning Service
When providing Dmax for the positioning service, Dmax is set large enough to enclose the
desired positioning service volume and small enough that the GBAS meets all positioning
service integrity requirements within Dmax. The setting of Dmax for the positioning
service needs to be large enough to enable use of the intended approach service.
Considerations for Setting Dmax for the Approach Service Volume
Within the SARPs, there are three options for setting Dmax when providing approach
service. These options are (1) setting Dmax to just enclose the most distant approach
service volume, (2) setting Dmax to a value larger than the most distant approach service
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