Order unanimously reversed, without costs of this appeal to any party and proceeding dismissed, without costs, without prejudice to a proceeding under section 1450 of the Civil Practice Act. Memorandum: An article 78 proceeding based upon affidavits was instituted for a determination that a notice of intent to file a claim under the MVAIC clause of the petitioner's policy had been timely given. The court undertook to decide the question of the timeliness of the notice on the basis of the affidavits. The resulting order was improper for two reasons: (1) The question should not have been decided on affidavits in this action but a plenary hearing should have been held; (2) the proceeding under article 78 of the Civil Practice Act was unauthorized. The proper procedure is that authorized under section 1450 of the Civil Practice Act. A plenary hearing of substantial preliminary questions should be had under that section ( Matter of Rosenbaum [ Amer. Sur. Co. of N.Y.], 11 N.Y.2d 310).