Outside investors have increased their ownership in a proposed merger of US Airways Group Inc. and America West Holdings Corp. to 49 percent from 41 percent, according to a proxy statement filed by US Airways with the Securities and Exchange Commission yesterday.

Wellington Management Co. LLP boosted its equity stake by $149 million, lifting total outside investment and reducing America West's share in the new airline to 39 percent from 45 percent and US Airways' stake to 12 percent from 14 percent when the deal was announced, according to the filing.

Separately, US Airways announced yesterday that it lost $39.7 million in May, due largely to higher fuel costs. Along with Wellington Management, outside investors, including Par Investment Partners, Air Canada's parent ACE Aviation Holdings Inc. and Eastshore Aviation LLC have pumped $500 million in equity into the proposed merger.

Although US Airways and America West shareholders would end up with less equity, the new carrier would have a large liquidity base, which would provide a stronger financial cushion, especially at a time of high fuel costs, said airline analyst Raymond E. Neidl of Calyon Securities Inc.

"In this uncertain environment, you can't have too much cash," Neidl said.

The $1.5 billion merger, which was cleared by the Justice Department last week, still needs approval from America West shareholders, US Airways creditors and the U.S. Bankruptcy Court. US Airways has been operating under Chapter 11 bankruptcy protection since September.

The airlines reiterated yesterday that they hope to have the merger completed by the fall.

The newly created airline would retain the US Airways name but be based in Tempe, Ariz., where America West is headquartered.

In the proxy, the airlines said the new carrier would save about $600 million a year. They also outlined possible challenges to the merger, including employees and union leaders who may seek to delay or block the deal.

The filing said key managers from both carriers were devoting large amounts of time to completing the deal.

"The managements of US Airways Group and America West Holdings will have to devote substantial effort to such integration that could otherwise be spent on operational matters or other strategic opportunities," the filing said.

US Airways is expected to submit its reorganization plan as early as tomorrow. In yesterday's filing, the airline said that the merger was "a key component of the plan of reorganization."

Outside investors' ownership in the proposed US Airways-America West merger has jumped to 49 percent.