name  n/s  distfromc
BH    n    2
FV    n    1
C     c    0
RS    s    1
MTN   s    2

SELECT tablename.*
FROM tablename
ORDER BY
  `n/s` = 'n' DESC,
  CASE WHEN `n/s` = 'n' THEN distfromc END DESC,
  CASE WHEN `n/s` != 'n' THEN distfromc END ASC