Note: The greatest passenger transportation success story of the past half century has been the advent of Southwest Airlines. Starting in June 1971 with three planes flying between Dallas and Houston, and Dallas and San Antonio, Southwest has grown to a fleet of more than 550 737s, operating more than 3,400 flights daily, and employing 45,000. The following describes how Southwest is having to retool its business model because of market forces and changing times. If a behemoth like Southwest can change and adapt . . .

By Gary Kelly

This month, we celebrate the 43rd anniversary of Southwest Airlines.

When Southwest first took to the skies, there was nothing like it; flying was for the rich and elite.

Fares were high and service was low. But Southwest had a vision to offer low fares, friendly customer service, and a convenient flight schedule.

We offered short-haul, high-frequency service and carved out a niche that has served us well.

We launched the low-fare revolution, and weve since grown to carry more passengers within the domestic U.S. than any other airline.

But the world has changed greatly since 1971. For example, record-high energy prices have impacted demand; despite the fact that our short-haul market share increased during the timeframe, we served six million fewer customers on short-haul routes in 2013 than in 2000.

Thats significant, especially for an airline like Southwest.

Weve responded accordingly, evolving our business model to meet our customers changing needs.

Weve refreshed our cabin interiors, installing Wi-Fi and offering free live TV onboard, thanks to DISH.

Were bringing on larger airplanes that are better suited for longer fights. Weve expanded our service in big markets like New York and Washington, D.C.

Weve revamped our Rapid Rewards Frequent Flyer program.

Weve acquired AirTran Airways, and were in the final stages of integrating our airlines to become one by the end of this year.

That has set the stage for launching Southwests first flights to international destinations. (Service to Aruba, the Bahamas and Jamaica began in July.)

By years end, well offer Southwest service to all of AirTrans current international destinations . . . with an eye toward expanding even further.

What started as a revolution is now undergoing an evolution.

But we havent changed what we stand for: low fares, a convenient flight schedule, and the friendliest employees in the world.

Our purpose is to connect you, our valued customer, to the moments that are most important in your life through friendly, reliable and low-cost air travel.

That was true in 1971, and its just as true today. Thank you for allowing us to share the LUV for the past 43 years. Heres to many more!

Gary Kelly is chairman, president and CEO of Southwest. This column is reprinted from the June issue of Southwests Spirit magazine.