Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of aircraft service company Air Transport Services Group (NASDAQ:ATSG) jumped 16% today after the company released earnings.

So what: Fourth-quarter revenue fell 7.2% from a year ago, to $154.6 million, and fell just short of the $159.0 million that analysts expected. But the bottom line is in focus today, and the company's earnings per share of $0.18 easily outpaced the $0.13 expectation.  

Now what: Beating estimates is always good, but I'm worried about falling revenue and profit this quarter. There seem to be a lot of "ifs" in the company's future, which could send the stock dramatically higher or lower next year. That's enough for me to steer clear, although the stock will be worth another look if it returns to consistent growth.

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Fool contributor Travis Hoium has no position in any stocks mentioned. 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.