DO-246D includes the earlier document revisions and
incorporates the standards for LAAS to support Cat. II and III
precision approaches.  DO-246C included changes to harmonize
the document with DO-245A, LAAS MASPS.  The three primary areas
of change were:  
1.   Definition of additional data for supporting Cat. II/III
     precision approach operations [Additional data blocks 
     3 and 4 for Message Type 2].
2.   Definition of LAAS uplinked Terminal Area Paths (TAP)
     data for supporting additional Terminal Area Procedures
     [Provisions for TAP data to be included in Message
     Type 4].
3.   All references to pseudolites / Ground Based Ranging
     Sources were removed.