Spirit Airlines, an impish upstart that shook the industry with its irreverent ads and deep discount fares, announced Saturday that it has gone out of business after 34 years. U.S. Transportation Secretary Sean Duffy said Saturday that Spirit had a reserve fund set up for customers who bought directly from the airline to get refunds. Duffy also said other airlines would help with Spirit employees who might be stranded as well as offering them a preferential application process as they look for work.