INSTALLATION MANUAL
CMA-5024 GLSSU
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Page G.1
November 21, 2008
APPENDIX G
EXAMPLE OF FAS BLOCK DATA GENERATION
This Appendix contains an annotated example of encoding a FAA approach description into a stream of ARINC
429 data labels 45 and 46. The purpose is to help users to check their own implementation of the FAS
message formatting and encoding, including the CRC generation. Refer to ARINC 755 and DO-229D Appendix
D for the description and the specifications of the data format and encoding. The format of the FASDM is
summarized in Table G-1.
The FASDM Block has a Message Block Identifier of “1111000”’ to distinguish this message from a LAAS
message block. The GBAS ID field is set to “XLS1” for this message block. The FASDM Block has a Message
Type of 4 and the message format is identical to the FAS data described in DO-229D, Appendix D.
Table G-1. Final Approach Segment Data Message Block format
PARAMETER UNITS RANGE # BITS COMMENTS
Message Block
Identifier
N/A Value =
1111 0000 binary
8 240 decimal; 1010 1010 Normal GBAS ID
Reference
Station ID
ISO #5 Value = XLS1 24
Message Type BNR Value = 4 8
Message
Length
Bytes 9-256 8
The length in bytes of the FASDM Block including
the Message Block Identifier, GBAS ID, Message
Type, Message Length, Message, and CRC
Message N/A N/A 320 Refer to DO-229D, Appendix D, Table D-1
32-bit CRC N/A N/A 32 Refer to DO-229D, Appendix D, Section D.5
The following table shows on the left side the set of parameters from a typical FAA approach description, and on
the right side their hexadecimal values (Leftmost digit is most significant) after encoding. It shows also the two
CRC values computed in hexadecimal (Leftmost digit is most significant). The numerical scale factors and
offsets are defined in DO-229D. The hexadecimal output will be encoded in a stream of 26 ARINC 429 data
labels 45 and 46.
The document reference is online, please check the correspondence between the online documentation and the printed version.
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