A global team of experts this week will begin reviewing how the Boeing 737 Max's flight control system was approved by the U.S. Federal Aviation Administration.
The FAA says experts from nine international civil aviation authorities have confirmed participation in a technical review promised by the agency.
Former National Transportation Safety Board Chairman Chris Hart will lead the group, which also will have experts from the FAA and NASA. They will look at the plane's automated system including the way it interacts with pilots. The group will meet Tuesday and is expected to finish in 90 days.
The Boeing jetliner has been grounded around the world since mid-March after two crashes killed 346 people. Investigators are focusing on anti-stall software that pushed the planes' noses down based on erroneous sensor readings.
In a statement Friday, the FAA said aviation authorities from Australia, Brazil, Canada, China, the European Union, Japan, Indonesia, Singapore and the United Arab Emirates have agreed to help with the work, called a Joint Authorities Technical Review.
The group will evaluate the automated flight control design and determine whether it complies with regulations. It also will decide if changes need to be made in the FAA's approval process.
Chicago-based Boeing is working on a software fix to the planes' anti-stall system, known by its acronym, MCAS. In both an October crash off the coast of Indonesia and a March crash in Ethiopia, a faulty sensor reading triggered MCAS and pushed the plane's nose down, and pilots were unable to recover.
Pilots at U.S. airlines complained that they didn't even know about MCAS until after the October crash. They then received computer training that described the system and how to respond when something goes wrong with it.
On Wednesday, Boeing CEO Dennis Muilenburg said the company completed its last test flight of updated flight-control software. Muilenburg said test pilots flew 120 flights totaling 203 hours with the new software. The company is expected to conduct a crucial certification flight with an FAA test pilot on board soon, possibly next week.
"We are making steady progress toward certification" and returning the Max to service, Muilenburg said as he stood in front of a Max jet at Boeing Field in Seattle.
Muilenburg said he went on a test flight that day and saw the updated software "operating as designed across a range of flight conditions."
In the U.S., United Airlines has removed its 14 Max jets from the schedule until early July, while American, with 24, and Southwest, with 34, are not counting on the planes until August.
It could take longer before foreign airlines can use their Max jets. Regulators outside the U.S. once relied on the FAA's judgment in such matters but have indicated plans to conduct their own reviews this time.
Foreign countries may impose additional requirements, delaying the use of the Max by their carriers.
For example, FAA experts concluded in a draft report that while pilots need training on the anti-stall system, they do not need additional time in flight simulators. Canada's transportation minister said this week, however, that he wants simulator training for Max pilots. Air Canada has 24 Max jets.