Southwest is waiting for Boeing Co.'s decision about the fate of the workhorse jet. The aircraft maker is deciding whether to update the plane with a more fuel-efficient engine or start over by building a new aircraft that might be quite different. It could take years to develop a new plane, which might also increase the complexity of training and scheduling pilots and performing maintenance.

On a Southwest conference call with analysts on Thursday, analyst Ray Neidl of Maxim Group asked Southwest CEO Gary Kelly whether his airline might consider buying Airbus jets if Boeing decides against "re-engining" the 737.

QUESTION: Will Boeing re-engine the 737, and if not, does that change your thinking about which planes to buy in the future?

ANSWER: "Boeing hasn't given us an answer," Kelly said. "If they told us that we're not going to see a more fuel-efficient 737 for another 20 years, that probably would cause us to do something. We love the 737. We would love for it to be more fuel-efficient."

Southwest expects to break the 737-only model when it completes its pending acquisition of AirTran Airways and takes on AirTran's smaller Boeing 717 jets. Kelly said that experience will teach Southwest about operating a fleet with more than one type of plane.