Thirteen months after entering chapter 11 protection, the Philadelphia Orchestra Association yesterday filed its plan for exiting bankruptcy, the Philadelphia Enquirer reported today. With consent now in place from key creditors, the orchestra's blueprint for recovery will be considered by the bankruptcy court in the coming months. If the plan draws support and no objections from creditors, and Bankruptcy Judge Eric L. Frank approves it, the orchestra expects to be out of bankruptcy by July 31. Orchestra leaders say the reorganization allows them to unload about $100 million in obligations. The burden of the larger chunk of those pension obligations, a claim of about $60 million, now falls to the Pension Benefit Guaranty Corp.