Swift Air LLC, a Phoenix-based aviation company that provides worldwide charter services, has signed a five-year agreement with the Piedmont Triad International Airport in Greensboro to lease a vacant site that will provide it with about 100,000 square feet. Company officials could not be reached for comment about when operations would begin, but PTI Executive Director Kevin Baker said Swift Air plans to lease the space within an existing aircraft hangar. According to airport documents, Swift Air's…