Spirit Airlines (SAVE 0.25%) saw notable increases in several of its key metrics last month and for the year-to-date period. For March, the company's revenue passenger miles grew by 19.1% over March 2012's number, to hit almost 1 billion. Available seat miles increased by 16.5% on a year-over-year basis, to 1.1 billion. Load factor -- i.e., airplane occupancy -- grew by 2.0 percentage points over the same time frame, coming in at 87.9%.

On a year-to-date basis, RPMs amounted to 2.7 billion, a 21.3% increase over the same period of 2012. ASMs advanced at nearly the same rate, by 20.8%, to 3.1 billion. Load factor for the three months saw a slight uptick on a comparative basis, to 85.1%, against 84.8% in the same period last year.