US Air to Keep Flying Most of Its Planes  NEW YORK (Reuters) - US Airways Group Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=UAIRQ.OB target=/stocks/quickinfo/fullquote"&gt;UAIRQ.OB&lt;/A&gt;,  which filed for bankruptcy protection in September, on Thursday  said it reached agreements with its lenders and lessors that  will let it keep flying most of its planes.