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What: Shares of aircraft products and service provider AAR (NYSE: AIR) are off by as much as 11% today on heavy volume after reporting mixed first-quarter earnings last night.

So what: It was a mixed announcement as the company beat analysts' estimates on revenue but fell short on earnings per share. Revenue rose 19% to $479.3 million, compared to the estimate of $453.2 million, while earnings per share of $0.41 didn’t quite meet the $0.45 consensus. Meanwhile, gross margin ticked down to 15.6% from 17.3%.

Now what: The company, which competes with larger rival Goodrich (NYSE: GR), said sales to commercial customers increased 40% on strength in spare parts support and the sale of two aircraft. Excluding the aircraft sales, commercial sales grew 21%, while defense sales rose 2%. AAR also announced that it won a contract valued at $77 million, besting four competing bids, to provide airlift support for Navy ships. Clearly investors were expecting more, but with net income rising 22% on a 19% revenue increase, I’m not sure what shareholders are so upset about.

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Fool contributor Evan Niu holds no position in any company mentioned. Click here to see his holdings and a short bio. 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.