Boeing Co. has said it is close to a significant milestone that's one of the last steps before it submits to U.S. regulators a patch for anti-stall software linked to two fatal 737 Max accidents.

The company has completed its engineering trial of the updated software, and its technical and engineering leaders were on board the final flight test earlier this week, Chief Executive Officer Dennis Muilenburg said in a video message late Wednesday.

Up next is the certification flight, he said, as Boeing prepares to submit the final paperwork to the Federal Aviation Administration.