Southwest Airlines is beginning to run up against reliability, parts obsolescence and supply challenges with the attitude display indicator (ADI) on the 737 Classic fleet, says Kent Horton, Southwest’s director of engineering.

“Right now, the situation is manageable, but we are monitoring it closely as unit availability on the open market shrinks and repair capacity also diminishes,” he says. “At this juncture, we are looking at whether we will need to change suppliers, or purchase additional spares to ensure a ready supply on hand. However, we are always looking for alternative sources of supply, as well as repairs in the supply chain.”

Despite reliability and spare parts issues, Southwest does not have any plans—at least for now—to replace the electro-mechanical cockpits on the 130 Boeing 737-300s and -500s it still flies, Horton says: “We are always evaluating the future of our 737-300s and -500s, which includes possible cockpit modifications as fleet planning warrants.”

Any such evaluation would have to factor in the new equipment’s capabilities, certification costs and the projected period the airplanes would remain in service. “Then, you have to consider the reliability of the components already in your cockpit, and how would that compare with new equipment?,” Horton asks. “Also, what residual value would be added to the aircraft?”

Horton adds that change can come quickly with respect to evolving air navigation requirements, and potential equipment reliability problems. “We are staying on top of any potential for change that can come about,” he says.