NEW YORK (TheStreet) -- Billionaire investor Warren Buffett's Berkshire Hathaway (BRK.A, BRK.B) bought a stake in four major airlines, according to an SEC filing Monday. The four stocks are rising this morning, including American Airlines (AAL), Delta Air Lines (DAL), United Continental (UAL), and Southwest Air (LUV).

This move is in stark contrast to Buffett's comment at a company meeting in 2013 that the airline sector was a "death trap" for investors. He has been sour on airline stocks ever since losing money on a U.S. Airways investment in 1989.

The airline companies are a lot different now than they were in the late 80s and they're now all "huge earners" with "huge capital being returned to shareholders," TheStreet's Jim Cramer said on CNBC's "Squawk Box" Tuesday morning.  

"The fact is that what Buffett hated about them was that they were losing money and there was a de-regulated world that they couldn't handle," Cramer noted. "Well we got re-regulated by a lot of mergers so to speak, not a lot of competition, not a capacity coming on."

In addition, a lot of people haven't yet realized that all four companies have "very strong" CEOs now, Cramer noted. "That also is different from what Warren Buffet felt back in '89 when he felt there really wasn't the leadership."

United Airlines has looked good since Oscar Munos took it over in 2015 and Gary Kelly of Southwest Airlines still has Cramer's support, he said. "I would trust any one of those people with any company in America. I think they'd do a good job."

If you're looking to invest in airlines, "be careful" because "you might be coming in a little bit late here," Cramer cautioned, noting the dramatic move the stocks have seen in the last few weeks.

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