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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This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.