(a) For the purpose of carrying out its functions under the Acts, whenever action is taken by the entire permanent Board sitting en banc, three permanent members of the Board shall constitute a quorum, and official action of the permanent Board can be taken only on the concurring vote of at least three permanent members.

(b) The Board may delegate any or all of its powers except en banc review to panels of three members. Each panel shall consist of at least two permanent members. Two members of the panel shall constitute a quorum and official panel action can be taken only on the concurring vote of two members of the panel.

(c) A panel decision shall stand unless vacated or modified by the concurring vote of at least three permanent members sitting en banc.

(d) En banc action is not available in cases arising under the District of Columbia Workmen's Compensation Act.