Spirit Airlines has pushed full-year profit up by 71 per cent to $178m thanks in part to a successful final quarter in which the US ultra-low-cost carrier more than doubled year-on-year net income. The improved result was also partly down to the negative impact of Hurricane Sandy in 4Q 2012. Spirit’s business model hinges on ancillary sales, which it defines as ‘non-ticket revenue’, and this remained stable from year to year at 40 per cent of total revenue. However, the airline did manage to shift its cost metrics, recording almost a five per cent drop in cost per available seat kilometre. Another highlight was a one point increase in load factor to 86.2 per cent. Spirit ended 2013 with 54 aircraft in its fleet after receiving three new A320s in the final quarter.