Citing erosion in the core businesses of Tribune Co. and failure to invest aggressively in new business, the Chandler Family suggested in a filing with the Securities and Exchange Commission made public Wednesday that the company should spin off its newspaper business from the broadcast division. The 11-page letter also calls upon the Tribune Co. board to appoint an independent commission to review and evaluate management, business and strategic issues facing the company. “Given the risk of continued deterioration in the company’s primary businesses, if a separation of the newspaper and broadcast businesses or other strategic steps relative to the newspaper business cannot be accomplished by the end of the year, then the possibility of an acquisition of Tribune as a whole should take priority,” the letter said. The Chandler Family became the second largest shareholder in Tribune Co. following the 2000 acquisition by Tribune of the Times Mirror Co., parent of the Los Angeles Times and several other daily newspapers. The letter comes just weeks after Tribune Co. offered to buy back millions of shares of stock. The Chandler Family indicated it would not tender any of the shares it owns as part of the buyback.