November was a month of transition for the U.S. airline industry. During the month, the Department of Justice finally settled its antitrust lawsuit with AMR and US Airways, allowing them to merge to become the new American Airlines (NASDAQ:AAL). American has started posting strong revenue results recently, and appears ready to hit the ground running now that it has merged with US Airways.

In November, American Airlines posted by far the best unit revenue results in the industry for the second-straight month. Here's how it stacked up against competitors in the last full month before the merger with US Airways:

Airline

Unit Revenue Change

Capacity Change

American Airlines

Up 1.0%

Up 1.8%

Delta Air Lines (NYSE:DAL)

Down 3.0%

Up 1.4%

Southwest Airlines (NYSE:LUV)

Down 6.0%

Up 0.8%

United Continental (NYSE:UAL)

Down 1.5%-2.5%

Up 3.0%

US Airways

Down 4.0%

Up 5.3%

Source: Airline press releases 

All in the timing
American Airlines was the only one of the five top U.S. carriers to report a unit revenue increase last month. In doing so, it overcame a strong calendar-related headwind. Since Thanksgiving fell on Nov. 28 this year, the Sunday and Monday following the holiday weekend moved into December.

These are two of the busiest -- and most lucrative -- travel days of the year, as many people are returning from their Thanksgiving trips then. This calendar shift weakened airlines' November results, with a corresponding benefit to December.

The airlines have been quick to reassure investors that they will offset the weak November with a very strong December. Delta projected a 7%-9% unit revenue gain for December, putting it on target for a 2%-3% gain for the combined November-December period. US Airways reiterated its forecast for the combined period, implying a roughly 2% total unit revenue gain. Lastly, Southwest is projecting a 2% unit revenue gain for the full fourth quarter.

American ends strong
By contrast, American Airlines didn't have to reassure investors with a December unit revenue forecast. For the second-consecutive month, it dominated the competition, exceeding the nearest competitor's gain by about three percentage points.

American's strong result implies that it is bringing a lot of momentum into its merger with US Airways. One of the key rationales for the merger was that with a broader network, the new American Airlines would be better able to compete for high-value corporate contracts. It appears that some customers may have already moved flying to American.

The company is also benefiting from its fleet renewal plan, which has allowed American to better match capacity to demand. This initiative will continue to provide unit revenue benefits for the next several years.

Foolish final thoughts
American's strong performance in the past two months is a harbinger of things to come. Now that its merger has been completed, American is likely to continue gaining corporate share, particularly at the expense of United Continental, with which it has significant route overlap. This is one of the key trends to watch for in the U.S. airline industry next year.

The longer-term success of the new American Airlines will depend on how smoothly the integration process goes. United Continental also enjoyed a "honeymoon" period in 2011, before its performance plummeted in 2012 and 2013. To make long-term investors happy, American will need to avoid similar integration mistakes.

Adam Levine-Weinberg is short shares of United Continental Holdings. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.