UPDATE 2-American Airlines raises estimate for key revenue metric

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July 12 (Reuters) - American Airlines Group Inc on Wednesday raised its estimate for a closely watched performance metric for the second time this year, citing higher average fares.

The No.1 U.S. airline's shares rose as much as 3.1 percent in morning trading, lifting stocks of other large carriers.

Unit revenue - which compares sales to flight capacity - is expected to increase by about 5 percent to 6 percent in the second quarter, compared with a 3.5 percent to 5.5 percent rise estimated earlier, American Airlines said.

The company also raised the lower end of its adjusted pre-tax margin forecast to a range of 13 percent to 14 percent from a range of 12 percent to 14 percent.

American Airlines is the latest carrier to lift its unit revenue estimate as an improving U.S. economy spurs demand for air travel.

United Continental Holdings Inc, the No. 3 U.S. airline by passenger traffic, said on Tuesday it expected a 2 percent rise in passenger unit revenue for the second quarter, compared with its previous forecast of 1-3 percent rise.

JPMorgan analyst Jamie Baker said United's forecast was healthy, while American's was less profound on a margin basis, but American's revised estimate could be viewed as higher quality due to "materially stronger" unit revenue.

Last week, smaller rival Delta Air Lines Inc also said it expected passenger unit revenue to be near the upper end of its second-quarter forecast.

Shares of Delta, American, United, Alaska Air Group Inc , Spirit Airlines Inc and JetBlue Airways Corp were all up between 1 percent and 3 percent.

Up to Tuesday's close, American Airlines' stock had risen 10.5 percent this year, compared with a 12.4 percent increase in the Dow Jones US Airlines index. (Reporting by Ankit Ajmera and Arunima Banerjee in Bengaluru; Editing by Arun Koyyur and Anil D'Silva)