Southwest Airlines (NYSE:LUV) saw small increases in several of its key metrics last month, and for the initial quarter of 2013. For the month, the company's revenue passenger miles grew by 4% over March 2012's number, to hit 9.4 billion. Available seat miles increased by 3.8% on a year-over-year basis, to 11.5 billion. Load factor -- i.e., airplane occupancy -- grew by 0.2 percentage points over the same time frame, coming in at 82%.

In terms of passenger figures, the total number of revenue passengers carried saw a 3.1% year-over-year rise last month, coming in at 9.9 million. Overall, slightly more than 12 million riders were enplaned, a 2.6% gain from March 2012.

On a quarterly basis, RPMs amounted to 23.8 billion, a 0.3% increase over March 2012's number. ASMs also saw an uptick, by 0.6%, to 30.8 billion. Load factor for the three months was slightly down on a comparative basis, however -- it was 77.1%, against 77.3% in the same quarter last year.

Fool contributor Eric Volkman has no position in Southwest Airlines. The Motley Fool recommends Southwest Airlines. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.