CASA, as a Government owned corporation, needs "a Board" to comply with the incorporation rules.
CASA isn’t a Government owned corporation.
CASA does not need a board to comply with any rules, incorporation or otherwise.
CASA is a statutory body corporate established by the Civil Aviation Act. CASA exists as body corporate because an Act says so.
Whether CASA ‘needs’ a board depends on whether the Civil Aviation Act says CASA has a board. The Civil Aviation Act currently says CASA has a board. As I noted above, there was a period during which the Civil Aviation Act did not say CASA has a board. As I also noted above, the period during which CASA had no board was no better or worse for aviation regulation than the periods during which CASA has had a board.