The Enlarged Board of Appeal stated in G 5/91 (OJ 1992, 617) that there was no legal basis under the EPC for any separate appeal against an order of a director of a department of the first instance such as an opposition division rejecting an objection to a member of the division on the ground of suspected partiality. However, the composition of the opposition division could be challenged on such a ground on appeal against the final decision of the division or against any interlocutory decision under Art. 106(3) EPC 1973 allowing separate appeal. If not all the members of an opposition division fulfilled the requirement of impartiality, there was a procedural violation as to the composition of the opposition division, which would normally render the decision void. The Enlarged Board of Appeal made it clear that it lay within the competence of the boards of appeal to consider and decide on whether the requirements concerning the composition of an opposition division had been fulfilled. This was also done in practice (cf. e.g. T 251/88, T 939/91, T 382/92, T 476/95, T 838/02, T 1349/10). Such consideration might take place of the boards' own motion or at the request of a party to the appeal proceedings.
In T 479/04, the board found that it could be inferred from G 5/91 that there was no principle prohibiting an opposition division from deciding itself on an allegation of partiality made against it. The board found that the order in G 5/91 had in fact left it open whether the decision on the opposition division's partiality necessarily had to be taken before its final or interlocutory decision on the substance. The board held in the case at issue that, although the Enlarged Board had considered it advantageous for the procedural matter to be settled before a decision on the substance was taken, it could not be inferred from the order in G 5/91 that it was forbidden in principle to decide on that matter together with the decision on the substance. The board therefore concluded that the opposition division had not committed any procedural error in the case in hand by deciding itself, as part of the contested decision.