Factbox - What needs to happen before Boeing's 737 MAX can fly again

CHICAGO (Reuters) - Boeing Co's best-selling jet, the 737 MAX, was grounded globally in March, days after the crash of an Ethiopian Airlines flight that followed a similar Lion Air disaster in Indonesia in October. A total of 346 people died in the two crashes.Boeing has spent months working on updating critical flight control software at the centre of both crashes, with the hope of winning Federal Aviation Administration approval for the planes to fly again in the United States between October..