US Air, Pilots to Reopen Concession Talks  WASHINGTON (Reuters) - US Airways Group Inc.  &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=UAIR.O target=/stocks/quickinfo/fullquote"&gt;UAIR.O&lt;/A&gt; and  its pilots union agreed late on Friday to reopen concession  talks after leaders of the labor group declined to endorse a  plan proposed by management for nearly \$300 million in  givebacks, both sides said.