This is interesting. They followed their flight plan, albeit a little below their planned altitude, and suddenly descended and crashed just a few miles from their destination airport.  Plane was twin engine, so if one engine failed, they had a second engine.  No MayDay signal reported.  Very odd. The plane had a range of flying 1100 miles.  I just checked the distance (driving by car) and it is only 700 miles between Grand Rapids, Mich and Sioux Falls, South Dakota, so flight distance would have been much less as the crow flies.    I was wondering if they had a depressurization, which might have caused them both to pass out.  But if their fuel tanks were full, the plane should have flown further before crashing.  If they were on auto pilot and full tanks, if depressurization occurred killing them en-route, the plane would have continued on and come down when it ran out of fuel in Wyoming or something. No MayDay signal has been reported.  If they were having trouble, they would have put out a mayday signal. Any reports of seeing an explosion in the air right before crash landing???