A missing UAB student was last seen in the vicinity of the Huntsville airport, police said.  20-year old Elizabeth Koury of Homewood left her parents' home for class on Friday.  But Koury apparently left her car in Birmingham and took a taxi cab to Huntsville, where she was last seen about 1:15 p.m. Friday near the airport.  Detectives are trying to determine whether Koury boarded a flight.  Koury was last seen wearing a red T-shirt, blue jeans and blue glasses, but police say she may have switched to contact lenses.