Boeing is in the “endgame” of preparing its 737 Max to return to the commercial market after two deadly crashes prompted a global grounding more than six months ago, CEO Dennis Muilenburg said in an interview. The planemaker is fine-tuning a software upgrade for the Max’s flight-control computers in its simulation lab and girding for the evaluation of a final version by line pilots. The company is discussing the timing of the certification flight with US officials, although no date has been set. That’s the final hurdle before the Federal Aviation Administration determines whether the flying ban can be lifted, Muilenburg said Monday.