By Susan Carey 

The four largest U.S. airlines said Monday that they had canceled a combined 74,500 flights in the first two months of this year due to extreme winter weather, with Delta Air Lines Inc. saying it had taken a $90 million hit to revenue as a result.

Speaking at a J.P. Morgan aviation conference in New York on Monday, Ed Bastian, Delta's president, said the storms forced the airline to cancel 17,000 flights in the period, and the revenue hit translated to a pretax loss of $55 million. But he said Delta expects to post a net profit in the first quarter.

The Atlanta-based carrier, the nation's third-largest by traffic, expects its first-quarter unit revenue--the amount it takes in for each passenger flown a mile--to be up 3% to 4%, compared with the year-ago period, he said.

United Continental Holdings Inc. Vice Chairman Jim Compton, speaking at the same conference, said United canceled 23,000 flights in January and February due to the weather, 90% of them smaller aircraft flown by its regional partners. Weather-driven cancellations reduced the carrier's capacity in the two months by about two percentage points. United, based in Chicago, is the second-largest airline by traffic.

American Airlines Group Inc. said it scrubbed 28,000 flights in those two months, an increase of 164% from the year earlier. American said it expects to disclose the impact to its profitability in early April. On Monday, the company said the cancellations had a slightly positive impact on unit revenue, but had a large negative impact on unit cost and first-quarter profitability.

Unit revenue in the first quarter is expected to rise 2% to 4% compared with a year ago, said American, now the No. 1 airline by traffic since its December 2013 merger with US Airways.

Southwest Airlines Co. canceled 4,000 flights in January and 2,500 in February, Tammy Romo, the chief financial officer, said at the J.P. Morgan conference. Southwest, which is No. 4 by traffic, expects its first-quarter unit revenue to be up about 3% compared with a year ago, Ms. Romo said. The Dallas airline offered 2.2% less capacity in the first two months than a year ago.

Separately, American and JetBlue Airways Corp. said Monday that they intend to terminate a four-year-old agreement in which they shared passengers through one-stop bookings and check-in, known as "interline" agreements, on a limited number of flights out of Boston and New York.

In a joint news release, the companies said they would no longer accept interline sales for travel on the other carrier, effective Monday. And beginning April 1, their reciprocal frequent-flier program accrual agreement will end. All American AAdvantage miles and JetBlue TrueBlue points already accrued through the partnership will be credited to passengers' accounts and won't be affected, they said.

When the two airlines formed their partnership in April 2010, the move was seen as a way of shoring up American's diminished East Coast network by letting American offer its passengers travel on more than two dozen domestic routes from Boston and New York's John F. Kennedy Airport, which the larger airline didn't serve. JetBlue passengers could fly on more than a dozen American international routes from New York and Boston.

But the December 2013 merger with US Airways gave American a robust East Coast route network. A JetBlue spokesman said Monday that the company was informed by American that it intended to end the relationship. "While we are not surprised in light of the recent merger, we will work with American to minimize the customer impact," he said.

JetBlue has interline and code-sharing partnerships and some frequent-flier tie-ins with 31 other mostly international airlines that want access to its leading positions at New York's Kennedy Airport and Boston. Those carriers want access for their passengers to JetBlue's domestic and Caribbean network. And JetBlue customers get the opportunity to book seats to world-wide destinations on JetBlue's partners.

Write to Susan Carey at susan.carey@wsj.com

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