In just over two years, Southwest Airlines landed a major chunk of the Charleston air travelers market.

The Dallas-based airline touched down in the Lowcountry in March 2011. Since then, the low-cost carrier has bumped United Airlines down a notch from the third-largest carrier at Charleston International Airport.

Southwest now accounts for about 20 percent of the local commercial air passenger market.

Atlanta-based Delta Air Lines is still No. 1, according to the Charleston County Aviation Authority. It commands 35.1 percent of the local market. Five years ago, it also was No. 1, carrying nearly 36 percent of Charleston’s travelers.

US Airways, which hopes to merge with American Airlines, maintains the second-place spot with 24.2 percent of local air travel. Five years ago it flew 28.3 percent. American carries less than 5 percent of local travelers.

Five years ago, United, which is merging with Continental, carried 10 percent of all travelers at the North Charleston-based airport. Continental held 7.6 percent of the market. This year, United, with Continental folded into it, came in with 13.8 percent of the local market.

Southwest has obviously nibbled into United a little, but where did the rest of its gain come from?

US Airways lost about 4 percent of its market share since 2008. Southwest filled the gap left by the 2009 departure of AirTran Airways, which held about 10 percent of the market. Southwest later bought AirTran. In 2008, Northwest Airlines, which carried about 5 percent of Charleston’s travelers, merged with Delta, but Delta’s share since then has not grown. In fact, it’s down slightly.

So it appears Southwest probably picked up some of Delta’s customers as well.

In short, it looks like Southwest gained shares from US Airways, United and Delta and cruised safely into the spot left vacant by AirTran.

Low-cost carrier JetBlue Airways entered the Charleston market Feb. 28 with three daily flights to the Northeast, so it’s too early to tell what share it will take. For the four months of March through June, it flew 2.5 percent of Charleston’s travelers.

And it appears there’s room for more growth.

The Aviation Authority projects the number of boarding passengers to grow from 1.35 million this year to 1.74 million by 2022, a 28.5 percent increase with growth averaging 2.9 percent a year. The projection is based on population growth of 2.3 percent each year through 2022.

Charleston’s airline seating capacity has also increased.

Bucking the trend of nearby airports, the number of seats has jumped 9.2 percent since 2007 while Columbia’s airport lost 23 percent of its seating capacity and Myrtle Beach decreased by 9 percent, according to the Aviation Authority.

Altogether, the number of seats at Charleston International grew 274,000 for the fiscal year that ended in June to 1.9 million. A majority of the new seats came from JetBlue, at about 115,000, but other airlines also added seating capacity, a sign the market is growing for almost all of the airlines serving Charleston.

The result of all of that growth can be seen with all the construction going on at the airport. The terminal is undergoing a $189 million overhaul over the next two years. To follow construction progress, go to www.chs-trip.com.

Reach Warren L. Wise at 937-5524 or twitter.com/warrenlancewise.