38 CFR §20.106

1. (a)Assignment. The Chairman may assign a proceeding instituted before the Board, including any motion, to an individual Member or to a panel of three or more Members for adjudication or other appropriate action. The Chairman may participate in a proceeding assigned to a panel of Members.
2. (b)Inability to serve. If a Member is unable to participate in the disposition of a proceeding or motion to which the Member has been assigned, the Chairman may assign the proceeding or motion to another Member or substitute another Member (in the case of a proceeding or motion assigned to a panel).