Fuel Cost, Low Fares Felt at Northwest  CHICAGO (Reuters) - Northwest Airlines Corp. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=NWAC.O target=/stocks/quickinfo/fullquote"&gt;NWAC.O&lt;/A&gt;, the  No. 4 U.S. air carrier, posted a quarterly loss on Wednesday as  high fuel prices and low fares weighed on the industry.