Frontier Airlines last Friday became the fourth US carrier to file for bankruptcy protection, although unlike recent predecessors Aloha Airlines, ATA Airlines and Skybus Airlines it intends to continue flying while undergoing reorganization. Founded in 1994, the Denver-based carrier blamed "an unexpected attempt by its principal credit card processor to substantially increase a holdback of customer receipts" for its situation, and said it will operate a full schedule, meet its obligations and maintain employment levels and benefits during reorganization. "To be clear, we filed for very different reasons than those of other recent carriers," President and CEO Sean Menke said. "We felt that Frontier would be able to withstand the challenges confronting the US airline industry. . .[We] have continued to perform relatively well in this difficult environment, and contrary to the trend, we have not seen a decrease in consumer demand." However, Menke said the processor's decision "would have represented a material change our cash forecasts and business plan. Unchecked, it would have put severe restraints on [our] liquidity and would have made it impossible for us to continue normal operations." Bankruptcy prohibits the processor, identified in press reports as Colorado-based First Data Corp., from increasing the holdback. FDC reportedly told Frontier that it would increase required collateral to $130 million from $54.5 million while retaining half its credit card sales.