AMR to advance with merger review, source says five airlines eyed NEW YORK (Reuters) - The bankrupt parent of American Airlines said on Tuesday it will press ahead with evaluating potential mergers and will reach out to interested parties, a move set to satisfy some creditors less than impressed with its stand-alone restructuring plan. A source familiar with the situation said AMR sees itself as an acquirer in potential mergers and at least five airlines -- US Airways Group Inc (LCC.N), JetBlue Airways Corp (JBLU.O), Alaska Air Group (ALK.N), Republic Airways' (RJET.O) Frontier Airlines, and Virgin America -- will be considered. Any merger proposals would be weighed against the standalone restructuring plan being developed, the source added. American has faced mounting pressure from vocal members of its creditors committee, led by its largest labor unions, who have argued that a merger with US Airways would give the combined carrier a strong network to compete with rivals beefed up by their own mergers. US Airways has expressed interest in a merger and has been courting AMR's creditors. Executives at American, the No.3 U.S. airline, mentioned the five carriers as potential merger candidates at a meeting with its unsecured creditors committee on Tuesday and discussed the merits and challenges of each combination, said the source, who asked not to be identified because the matter is not public. Chief Executive Tom Horton said in a letter to employees that greater clarity on revenue and the company's cost structure was allowing a review of potential mergers. "It now makes sense to carefully evaluate a range of strategic options, including potential mergers, which could make the new American even stronger," he wrote. The letter comes two months after American said it would explore merger options while still in bankruptcy. US Airways said in a statement it was pleased with the development. "All we have asked for is a fair and balanced opportunity to present our plan versus others, and we are hopeful this is the beginning of such a process," US Airways said. The source also said private equity firms, other legacy U.S. carriers and even foreign airlines may show interest in a potential deal or investment once American starts the evaluation work. American, which sought bankruptcy protection in November, citing high labor costs, is also taking new steps to stabilize its court restructuring with progress on labor negotiations aimed at achieving more than $1 billion in annual cost reductions, mainly from unions. The carrier has struck a tentative deal with pilots for cost savings and on Tuesday reached a similar agreement with the final two groups of unionized mechanics and other ground workers. Talks continue with flight attendants. Horton said American, working together with the creditors committee, would analyze synergies, costs and tax and capital structure implications when looking at potential mergers. The source said American plans to send out non-disclosure agreements to interested parties in the coming weeks after sharing the documents first with its creditors committee. He added that the process could continue through the fall. Horton said he has been a proponent of industry consolidation for many years and the company has assessed many possible combinations in the past, including an acquisition of US Airways. But since American's slide into Chapter 11, Horton's view has been that American should first straighten out its own business before considering a "complex and challenging airline acquisition," he said. But it is also a prudent merger strategy, should we take that path, to assure that we begin from a position of greatest strength and stability. Delta Air Lines Inc (DAL.N) and Northwest Airlines both emerged from bankruptcies several years ago as stand-alone companies before striking a merger deal with each other. United Airlines also stepped out of Chapter 11 on its own before tying up with Continental Airlines. American has sought court permission to extend until the end of the year the time it can take to develop a business plan without interference from outside parties. The current exclusivity period expires at the end of September. Additional reporting by John Crawley in Washington; Editing by Gunna Dickson, Andre Grenon and Edwina Gibbs