Boeing chief executive Dave Calhoun is to step down at the end of the year as the US aircraft manufacturer struggles to contain a crisis over its safety standards following the mid-flight blowout of a door panel. Boeing said on Monday that its chair Larry Kellner would also leave the board after the company’s annual shareholders’ meeting in May. He will be replaced by former Qualcomm chief executive Steve Mollenkopf‚ who will lead the search for Calhoun’s successor. Stan Deal‚ head of the...