late on Thursday that it expects consolidated passenger revenue per available seat mile, an important measure called unit revenue, to rise 8.5 percent to 9.5 percent in the fourth quarter.

Helane Becker, an analyst with Dahlman Rose & Co, said her firm had estimated 10 percent growth in quarterly unit revenue.

"We think there are concerns about a recession in Europe," Becker said in an email. Dahlman Rose cut its fourth-quarter profit estimate for United Continental to 25 cents a share from 50 cents a share to account for lower capacity and traffic.

Becker said United would likely benefit in Chicago, Los Angeles and the Atlantic from the restructuring of AMR Corp's (NYSE:AMR - News) American Airlines, which filed for Chapter 11 protection last month.

James Higgins, an analyst with Ticonderoga Securities, reduced his fourth-quarter profit estimate on United Continental to 16 cents a share from 43 cents a share. Analysts on average, currently expect 46 cents a share, according to Thomson Reuters I/B/E/S.

In a note to clients, Higgins said exposure to mainland Asia revenue could be creating more revenue uncertainty for United than for other airlines.

"We like the carrier's longer-term prospects but are a bit wary of near-term revenue trends," Higgins wrote.

Most U.S. airlines have posted profits this year, aided by service cuts, higher fares and retirement of less fuel-efficient planes. Still, economic woes loom as a threat to overall demand for air travel.

Last week, Delta Air Lines Inc (NYSE:DAL - News) said it expects recessionary effects from the euro-zone crisis to weigh on 2012 and said it would cut capacity in Europe by 7 percent.

Shares of United Continental were off 6.7 percent at $18.91 in morning trading as Delta and US Airways Group (NYSE:LCC - News) also fell. The Arca Airline index (NYSE:^XAL - News) was down 2 percent. AMR Corp was up 4.3 percent to about 60 cents and Southwest Airlines (NYSE:LUV - News) rose 0.4 percent to $8.43.

(Reporting by Karen Jacobs, editing by Dave Zimmerman)