On Tuesday morning, United Continental (UAL) - Get Report is scheduled to report earnings. So what should investors expect?

According to TheStreet's Jim Cramer, co-manager of the Action Alerts PLUS portfolio, investors could be impressed with the continuously improving situation.

The airline's CEO Oscar Munoz is doing a great job in turning United around, Cramer said. UAL had been very poorly run, Cramer said -- nothing like the exceptionally well-run Southwest Airlines (LUV) - Get Report .

In fact, Cramer wishes he would have "pulled the trigger" and bought Southwest for the Action Alerts PLUS portfolio, he remarked.

"The airlines are back," he said. Capacity has not grown as much as previously expected, which means the airline companies will not have to reduce fares by as much as investors had thought, he said. That's good for the bottom line.

Given this new outlook, earnings for 2017 should be stronger than previously expected, and because of the low valuations on these stocks, the airlines are again becoming attractive, Cramer said.

Analysts expect United to earn $2.88 per share on $9.89 billion in revenue for the quarter.

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At the time of publication, Cramer's Action Alerts PLUS had no position in companies mentioned.