A major airline has closed down and cancelled all flights after plunging into financial difficulty. Spirit Airlines , an ultra-low cost airline that once operated hundreds of daily flights on its bright yellow planes and employed about 17,000 people said it had “started an orderly wind-down of our operations, effective immediately.” The carrier emerged from a trucking company founded in the 1960s, with air operations commencing after it was founded as an airline in 1983 and it moved its base to