Speaking at an investor conference, Mr Muilenburg said what other players in the industry have been suggesting for some time, namely that the past practice of regulators of the aviation of other countries, following the FAA's opinion regarding the decision to certify an aircraft, might not be the case this time around.
"I think that a gradual decomposition of the aircraft among regulators around the world is a possibility," he said.
Muilenburg said that he thought there was "broad convergence" between different regulators and that "the FAA is working very hard to build this collaboration between regulators and bring everyone together".
The plane was grounded after two fatal crashes that killed the 346 people on board. Second crash, of an Ethiopian Airlines jet just minutes after takeoff on March 10, quick action around the world to anchor the 737. By the time the FAA also decided to land the aircraft on March 13, the only US aircraft was still flying.
In the past, like the case of Boeing's 787 Dreamliner, which had been grounded for several months in 2013 due to concerns about battery fires, all the world's aviation authorities The whole thing acted almost simultaneously to allow it to fly again.
A gradual recertification will cause problems, as most of the nearly 400 aircraft in service at the time of the grounding flight of non-US carriers. Southwest Airlines, American Airlines and United have less than 70 aircraft at their disposal.
Muilenburg said Boeing still hoped to get the plane to fly early in the fourth quarter, starting October 1st. He added that the issue of "regulator alignment around the world" posed the greatest risk of meeting this timetable.
