As the topic title says, is this aircraft an Antonov An-28? Testing my spotting skills to the max, it's my best guess. Sorry for the quality of the photo, I was zoomed 4.0x on the digital lens and then enlarged it another 5x or so in PhotoEditor.

I was in COS last weekend, this little plane was doing touch and goes for the better part of 2 days, at least when I was paying attention. It had no obvious markings (airline or air force), and I was never close enough to see a registration. (I was 3 miles or so from the airport at best. It flew over the neighborhood numerous times. No, I couldn't peel away to look for it at the airport.)

My clues are the swept twin vertical stabilizers and tapered aft fuselage (therefore not a Shorts 330 -- also the nose was not as long as a Shorts 330, nor is it an An-14). If I had to guess, it seemed to sound like a similarly-sized Twin Otter, common at that airport, so I'd guess it was turboprop, too. I'm presuming that this is a civilian An-28 (hence this forum), for what would a Russian/Polish/Ukrainian Air Force transport be flying at a USAF Base? Am I missing any other look-alikes (apart from the obvious PZL Mielec M-28)?

If it is the An-28, what on earth is it doing in COS? Are civilian examples more common in the US than I assumed? Anyone with more info, either about the aircraft or why it might be in Colorado, I'd be happy for the input.

-Rampart