According to the established jurisprudence of the boards of appeal, if a party is to receive a fair hearing before a tribunal, such a party should have no reasonable ground (on an objective basis) to suspect that any member of the tribunal is partial or prejudiced in relation to deciding the case (cf. G 5/91, OJ 1992, 617, G 1/05, OJ 2007, 362, T 433/93, OJ 1997, 509, T 95/04, T 283/03, T 1193/02).
The Enlarged Board of Appeal stated in G 1/05 that, as the wording of the provision indicated, for an objection under Art. 24(3), first sentence, EPC to be justified, it was not necessary that the board member concerned actually be partial. It sufficed that there was a suspicion, i.e. an appearance, of partiality (in the jurisprudence of the European Court of Human Rights (ECHR) called the "objective test" since Piersack v. Belgium (1982) of 1 October 1982, Series A, 5 E.H.C.R. 169, Series A, No. 53, paragraph 30). There should be no risk that the courts would not ensure that justice was both done and perceived to have been done by the public. What was at stake was the confidence that the boards of appeal inspired in the public (T 190/03, OJ 2006, 502, point 9 of the Reasons; ECHR: Puolitaival and Pirttiaho v. Finland of 23 November 2004, No. 54857/00, paragraph 42).
The Enlarged Board noted that it was, however, also commonly recognised in the jurisprudence of the boards of appeal and elsewhere that the "suspicion" by the party had to be justified on an objective basis. Purely subjective impressions or vague suspicions were not enough (see also T 190/03, point 7 of the Reasons and the other decisions cited there). The standpoint of the person concerned was important but not decisive (ECHR: Puolitaival, paragraph 42; see also T 241/98 of 22 March 1999). The question was whether a reasonable, objective and informed person would on the correct facts reasonably apprehend that the judge had not or would not bring an impartial mind to bear on the adjudication of the case. It was thus necessary that a reasonable onlooker considering the circumstances of the case would conclude that the party might have good reasons to doubt the impartiality of the member objected to (see also T 954/98).
The boards of appeal have stressed that what matters is not just whether the member objected to is in fact partial, but solely whether "good reasons" or "reasonable grounds" objectively exist to suspect a member of partiality (T 190/03) (see e.g. T 261/88, OJ 1992, 627, T 433/93, OJ 1997, 509, T 1028/96). The requirement for "objective" and "reasonable" grounds means that, notwithstanding the strict observance of the requirement of impartiality set out in G 5/91, purely subjective impressions or vague suspicions are not enough (see T 954/98, T 261/88).