CHARLOTTE, N.C. -- The merger between US Airways ( LCC) and America West two years ago was in many ways among the most successful airline deals in history, but it hasn't done much for long-term shareholders. In fact, US Airways shares recently dipped below $20, their price when the airline emerged from bankruptcy in September 2005. The shares traded as high as $63.27 in November 2006. On Friday, they closed at $20.77. To be sure, some investors made money. Most prominent among them is Boston hedge fund PAR Investment Partners, an early investor during the US Airways bankruptcy and at one time the combined airline's largest shareholder. PAR sold 6.75 million shares in May at around $36 and 6.5 million in February at about $58. It had bought about 11 million shares at $15 and another 2.75 million at around $40. But in general, the recent story of US Airways is a cautionary chapter in the long saga of how airlines have destroyed investment value throughout the industry's history. The US Airways and America West combination "shows that mergers work, but they work in the short term," says Morningstar airline analyst Brian Nelson. "This transaction enabled the company to extract several hundred million dollars in network synergies, but I don't think it was enough to ultimately fix the carrier or to stimulate widespread consolidation." It is easily forgotten today, but giddiness abounded in the merger's early days. The transaction combined an airline in bankruptcy with a smaller airline closing in on bankruptcy to produce astonishing second-quarter 2006 growth in revenue per available seat mile: 28.8% at the former carrier and 18.6% at the latter. In the spring of 2006, shares surged, and JP Morgan analyst Jamie Baker set a target price of $100. Flush with success -- or perhaps aware that it could not possibly continue -- CEO Doug Parker mounted a hostile bid to acquire Delta ( DAL). That merger would have enabled the eighth-biggest airline, measured by 2004 revenue passenger miles, to take over the seventh- and third-largest airlines in less than two years.