UPDATE 3-Boeing CEO says 737 MAX software update working as designed

Boeing Co's chief executive said on Thursday that a software update designed to prevent disasters like two recent fatal crashes involving its 737 MAX is working, with about two-thirds of the fast-selling jetliner's customers having seen the fix in simulator sessions. In his first public speech since an Ethiopian Airlines 737 MAX crash that killed all 157 aboard on March 10, Boeing CEO Dennis Muilenburg said additional tests are expected in the coming weeks as the planemaker works to regain the confidence of its customers and the flying public. Boeing, fighting its biggest crisis in years, has been developing an upgrade to software that is under scrutiny in the Ethiopian Airlines accident and a Lion Air 737 MAX crash that killed all 189 on board on Oct. 29.