In an action, inter alia, to recover damages for legal malpractice, the plaintiff appeals from so much of an order of the Supreme Court, Suffolk County (Baisley, J.), entered July 5, 1989, as granted that branch of the defendant’s motion which was for summary judgment dismissing the plaintiffs first cause of action.
Ordered that the order is affirmed insofar as appealed from, without costs or disbursements.
The plaintiff commenced this action, inter alia, to recover damages for legal malpractice, alleging in relevant part that the defendant Raymond J. Aab was liable for negligently failing to perfect an appeal from a judgment of the Supreme Court, New York County, which denied his petition pursuant to CPLR article 78 and dismissed the proceeding.
In order to hold the defendant liable, the plaintiff must establish that he would have prevailed in the underlying proceeding if the defendant had exercised reasonable care (see, Kerson Co. v Shayne, Dachs, Weiss, Kolbrenner, Levy & Levine, 45 NY2d 730; Mahoney v Manfredi, 166 AD2d 557; Parksville Mobile Modular v Fabricant, 73 AD2d 595). The plaintiff has failed to meet his burden of proving that but for the negligence of the defendant, his appeal to the Appellate Division, First Department, would have been successful.
With regard to the merits of the underlying proceeding, we note that ordinarily, the decision of the Board of Trustees as to the cause of an officer’s disability will not be disturbed unless its factual findings are not supported by the evidence or its final determination and is arbitrary and capricious (Matter of Canfora v Board of Trustees, 60 NY2d 347, 351; Matter of Drayson v Board of Trustees, 37 AD2d 378, 380, affd 32 NY2d 852). Where, however, the Board of Trustees denies accidental disability benefits but grants ordinary disability benefits in consequence of a 6 to 6 tie vote, the petitioner is entitled to ordinary disability benefits based on a procedural