Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of discount travel airline Allegiant Travel Company (NASDAQ:ALGT) throttled as much as 4.8% higher yesterday following the release of its March traffic data.

So what: Within the March traffic data report, Allegiant Travel Company also released some first-quarter total system growth as follows: a 10.2% increase in passengers, a 9.1% pop in revenue passenger miles, a 10% jump in available seat miles, a 9.4% leap in number of departures, but a 0.8% slip in load factor or percentage of seats filled (or tickets sold). The press release left it up to the reader to figure out the rest. 

Now what: The key is growth in revenue miles, the total miles traveled with seats filled with revenue-generating passengers; this one metric multiplied by revenue per mile gives you close to the total revenue for the quarter.

Analysts had been expecting only 7.9% growth in revenue for the first quarter, less than the 9.1% pop in revenue passenger miles. Allegiant Travel Company generates sales in two main ways: from actual ticket sales and prices, and from additional add-on fees, which together make up the revenue per mile. 

Revenue per mile has been going up for years, due somewhat to rising ticket prices, but mostly due to fees. Allegiant Travel Company has become known for its mastery of skyway robbery by luring in passengers with cheap ticket prices then coming up with creative ways to charge them for all sorts of things, such as $10 for printing a boarding pass, $3 for a water, and a staggering $50 for a simple carry-on bag.

Last year, the average amount of fees per passenger soared 13.4% to $40.52. Considering that increase, it's reasonable to expect the first quarter of 2014 to show at least some year-over-year gain, just like each quarter in 2013 did. Watch for analysts to either raise these estimates or look for a big "surprise" beat come earnings day later this month.