The acting head of the Federal Aviation Administration says he does not have a specific timetable to approve Boeing's 737 MAX for flight after two fatal crashes since October prompted the plane to be grounded worldwide.
The FAA is meeting with more than 30 international air regulators including China, the European Union, Brazil and Canada on Thursday to discuss a software fix and new pilot training developed to ensure the jets are safe.
"It's a constant give and take until it is exactly right," Deputy FAA Administrator Dan Elwell told reporters of the discussions with Boeing.
"It's taking as long as it takes to be right."
The plane was grounded in March following a fatal Ethiopian Airlines crash, months after a similar Lion Air disaster in Indonesia.
The two crashes together killed 346 people.
Asked if it is realistic that the 737 MAX could be flying again by August, Elwell declined to be specific.
"If you said October I wouldn't even say that, only because we haven't finished determining exactly what the training requirements will be," Elwell said.
Elwell said he plans to share the FAA's "safety analysis that will form the basis for our return to service decision process" on Thursday.
But he said the agency is still waiting for Boeing to formally submit the software upgrade for approval, and emphasised the FAA has not decided on the revised training requirements, including whether to require simulator training.
Global airlines that had rushed to buy the fuel-efficient, longer-range aircraft have since cancelled flights and scrambled to cover routes.
Elwell rejected any idea he was trying to win consensus with international regulators over the path to re-approving the MAX at the meeting.
Foreign regulators have signalled disagreements over measures to end the grounding, with Canadian Transport Minister Marc Garneau calling for pilots to receive simulator training for the MAX, rather than just computer courses.
Canada and Europe said on Wednesday they would bring back the grounded aircraft on their own terms if their specific concerns are not addressed.
