Motley Fool Stock Advisor recommendation JetBlue (NASDAQ:JBLU) reported mixed results for the second quarter. As expected, passenger revenue rose 32%. That news was offset by available seat miles skyrocketing 42%, with a resulting 0.8% decrease in the load factor -- which is still an enviable 84.5%. The bottom line: Net income fell 34%.

One factor sending operating margins down 4.5% was a 22% increase in average fuel cost. Fuel costs grew 2.7% to 17.5% of the total operating cost. But consider what Brain Gorman reported recently. Airlines such as JetBlue and ATA Holdings (NASDAQ:ATAH) operate new planes, so their fuel use is the most miserly. Ah, when being miserly is a virtue.

Also spiking was maintenance cost. It grew from 1.9% of total operating costs to 3.4%. As Whitney Tilson warned last year, these costs would increase as the company's planes aged.

More disturbing than the number of shares outstanding ballooning by 9% was the bulging total debt. While Southwest (NYSE:LUV) has more cash than debt, JetBlue has $514 million in cash and a total debt of $1.3 billion. While there is an advantage to expanding in a low-interest environment, interest payments are still an operating cost. The growth of debt, and its impact on operating costs, bears watching.

With the mixed news leading to lower earnings, why is JetBlue a Motley Fool Stock Advisor recommendation? First, there is customer satisfaction that continues to produce extremely high load factors. Then there are the operating efficiencies that allow the company to offer rock-bottom pricing with top-quality service. That's how to run an airline.

Of course, a Motley Fool Stock Advisor recommendation is expected to excel at earning money. Notice that, even with rapid expansion and higher fuel costs, JetBlue's lower operating margins were 14%. Prime rival Southwest has trailing 12-month margins of 8.6%. And get ready to shake your head. American parent AMR (NYSE:AMR) earns 0.4%, while Delta (NYSE:DAL) and Northwest (NASDAQ:NWAC) have negative margins.

JetBlue is a recommendation because it is a well-run airline that is delivering excellent returns in its industry. Sure, results are down. But, even with the rapid growth, the company continues to be profitable. At 28 times 2004 earnings, the stock is priced to reflect continued rapid growth and excellent operating results.

Discuss JetBlue and Southwest with other investors at the Fool .

Fool contributor W.D. Crotty likes flying JetBlue but does not own stock in it or the other airlines mentioned.