The U-28 is a single propeller engine plane that can conduct a variety of missions for special operations forces. The U-28 can be outfitted to carry a suite of sensors and cameras to observe activity on the ground. It is also a STOL aircraft which allows it to land on short dirt or grass strips. The U-28A is a variant of the Pilatus PC-12 (see WikipediA for more info). You can view pictures of the PC-12 on the Pilatus Aircraft Ltd. website here and on americanspecialops.com here.
"Hurlburt’s 319th SOS, which flies the U-28A, a variant of the single-engine Pilatus PC-12, is a pioneer in the field. Air Force Special Operations Command is tight-lipped, as are the U-28A’s small crews, about the aircraft. Its ability to operate on short and unimproved surfaces, and suite of advanced radar, communications, and navigation tools make the U-28 ideal for small, secretive missions.News Articles about the U-28 plane crash in Africa:
In 2008, a second nonstandard aviation unit stood up—the 318th SOS at Cannon. It is home to the PC-12 and will soon add additional light and medium twin-engine aircraft. By Feb. 10, the squadron had one of 10 planned M-28 Skytrucks—a Polish light twin-engine transport based on the Antonov An-28 design." (Source: "The SOF Makeover", AirForce-Magazine.com", Vol. 93, No.6, June 2010.)
The four airmen were assigned to special operations squadrons at Hurlbert Field, Florida. The flyers were identified as belonging to the 34th, 319th, and 25th Squadrons. See "DoD Identifies Air Force Casualties", U.S. Department of Defense News Release, February 20, 2012.