In G 5/91 (OJ 1992, 617) the Enlarged Board stated that although Art. 24 EPC applied only to members of the boards of appeal and of the Enlarged Board of Appeal, it must be considered as a general principle of law that nobody should decide a case in respect of which a party may have good reasons to assume partiality. The basic requirement of impartiality therefore applies also to the members of the EPO's departments of first instance who take part in decision-making activities affecting the rights of any party (see also T 433/93, T 95/04, T 283/03, T 1193/02). The board noted, however, that Art. 24(1) EPC 1973 contained some provisions specifically aimed at safeguarding the impartiality of members of the boards of appeal and of the Enlarged Board of Appeal. For example, while no member of a board of appeal could take part in an appeal if he had participated in the decision under appeal (see in this chapter III.J.5.1.2), it was clearly permissible under Art. 19(2) EPC 1973 for one member of an opposition division to have taken part in the proceedings for grant of the patent to which the opposition related. In T 1674/12 the board observed that, whilst the rules applicable to board members were different, a member of an examining division which had granted a patent could take part in opposition proceedings concerning the same patent, provided he did not act as chairman (see Art. 19(2) EPC). In T 1647/15 the board, with reference to G 5/91 (OJ 1992, 617), stated that there was no legal basis for automatically applying Art. 24(3) and (4) EPC to an opposition division (as had been argued by the appellants).

T 990/06 concerned enlargement of the opposition division by the addition of a legally qualified examiner. The board stressed that the division's composition had to be clear at all times so that its compliance with Art. 19(2) EPC and its members' impartiality pursuant to G 5/91 could be verified.

See also chapter III.K.1. "Composition of the competent departments of first instance".