very quick and dirty, Frank or Kolusu might come up with something better
000004 //S1 EXEC PGM=SORT
000005 //SYSPRINT DD SYSOUT=*
000006 //SYSOUT DD SYSOUT=*
000007 //SORTIN DD *
000008 AAA
000009 BBB
000010 CCC
000011 XXX
000012 EEE
000013 FFF
000014 GGG
000015 HHH
000016 III
000017 //SORTOUT DD SYSOUT=*,
000018 // DCB=(RECFM=FB,LRECL=80)
000019 //SYSIN DD *
000020 SORT FIELDS=COPY
000021 INREC IFTHEN=(WHEN=GROUP,BEGIN(1,3,CH,EQ,C'XXX'),
000022 PUSH=(81:ID=1))
000023 OUTFIL INCLUDE=(81,1,CH,EQ,C'1',AND,1,3,CH,NE,C'XXX'),BUILD=(1,80)
000024 //*