Activist hedge fund Elliott Investment Management has launched a battle to seize control of the board at Southwest Airlines as it pushes to oust the airline’s chief executive and improve performance, the firm said.Elliot seeks to replace 10 of 15 directors, escalating a proxy fight over who should lead the airline and how it should change. The board nominees by the firm include transportation and airline bigwigs like Michael Cawley, a former Ryanair executive; David Cush, Virgin Air’s former CEO; Robert Mil ...