Nuts About Southwest

If you were to ask me how we write the Southwest Airlines flight schedule, my answer would be much different today than it was just a few years ago.  When I joined Southwest in 1990, we had just over 100 airplanes, a little over 1,000 flights a day, and about eight to nine weeks to analyze and re-write our airlines schedule by hand;which we did five times a year.
 

Fast forward to 1999.  By that point, we had grown to nearly 300 airplanes, over 2,400 flights a day, and we still had no more than eight to nine weeks to analyze and re-write our airline's schedule, which we still did five times a year by hand.  Clearly, the size of the job we had to do in the time allotted had grown enormously, the complexity of the job had increased, and our system had grown exponentially, but given our process, we had no more time nor available manpower to apply.  It became clear to the Company that we had to find a way to bring computer technology into the mix to help us work quicker and work better.  We had to be able to look at more scenarios and produce a more effective schedule that was more convenient for our Customers QUICK!

Unfortunately, in talking to experts in optimization theory across the industry (believe it or not, airline schedule optimization is quite the science!), we found that our network had become too dense and large to solve, given the limitations of the science and technology at the time.  The roadblock turned out to be our basic business model!  In a previous blog post, I explained the difference between our point-to-point network and a hub-and-spoke airline network (click here to read that post).  For a variety of reasons (which I won't bore you with!) hub-and-spoke networks are relatively easy to schedule.  Point-to-point networks are very hard to schedule because there are vastly more options in departure times, ways to "hook together" flights, and many other factors.  One optimization scientist said that, based on the size of our network at the time, there were 10²³ (that's the number ten followed by 23 zeros!) of different possible combinations of our set of flights, departure times and "hook-ups" that could comprise a valid, flyable Southwest Airlines schedule.  Looking back at my years of writing ever-increasingly more complex schedules, I suddenly realized why my hair had gone gray.  To think, I had been blaming the "snow on my roof" on my son!
 

As we continued to research optimization shops, one of the Southwest Airlines Employees on the Schedule Optimization Team came back to the office after Christmas break and showed us an optimized schedule output that was unlike anything we'd seen before.  It still needed work, but it had conquered the major hurdle, treating every single flight's departure time and hook-up in the network as a variable.  We were amazed and VERY excited.  Which of the optimization companies had produced this, we asked?
 

None of them, he replied.  He had cracked the problem on his own and produced the solution himself, over Christmas break, on his home PC, metaphorically, in his garage.  He had done what was actually thought to be mathematically and technologically impossible at the time.  THE
''GARAGE-O-MIZER" WAS BORN!
 

The rest of the story is the stuff of Southwest legend.  We continued to refine the process and calibrate the over 2,300 parameters in the optimization process for what seemed like forever, but we began flying our first, fully optimized schedule in October 2004 (which we dubbed the "Optober" schedule).  The magnitude of change we were able to incorporate into the schedule was staggering.   

We continued to refine the optimization process, and by February 2006, we began flying our second reoptimized schedule, which, ultimately, generated millions of dollars in added revenue for the Company and our Shareholders.
 

Going forward, we plan to take maximum advantage of weather changes from winter, into summer, and back into winter.  Flights typically take less time in the warm weather months than they do in cold months, and optimization technology will allow us to take advantage of shorter flying times by putting even more flights into our schedule without investing in more aircraft.
 

We hope you like our new schedules, and we hope that you appreciate the time and effort we've spent in making our network even more convenient for you.  Now get out there; fly somewhere on Southwest;and exercise your freedom to move about our Country!