We’ve talked about the possibility of Southwest Airlines coming to Charlotte before. The airline released its year-end financial numbers today, which support the notion that CLT’s short-term window of opportunity to attract the airline is closing.

Sample quote:

While we will continue our disciplined route strategy, and currently do not have plans to grow capacity in 2010, we were still able to expand our cities served in 2009 without adding aircraft due to our successful route optimization efforts.

Southwest can only optimize its route structure so much before it’ll need additional planes to add new cities. Southwest had 537 in service at the end of 2009, the same number as at he end of 2008. While they took delivery of 13 new 737s in 2009, they retired an equal number of older planes. Southwest is due to take 10 new 737s this year, but not growing capacity means that about 10 older planes will go away during 2010 as well.

In 2011, the airline also is scheduled to take 10 new planes. It also holds seven options for additional 737s. Don’t get excited about that though, as the airline has already allowed three other 2011 delivery options to expire. The odds that they’ll execute the others seem rather low.

So essentially, Southwest comes to CLT soon — late this year, early 2011 — or probably not until mid-decade.