FORT WORTH — Boeing and the Federal Aviation Administration want global consensus to get the 737 Max flying again. They may have to wait awhile.
Aviation regulators from around the world, who met in Fort Worth on Thursday, are continuing to press the F.A.A. for details on the fix to the anti-stall system blamed for two deadly crashes involving the Max, as well as the process for assessing the software, according to an F.A.A. official. One big sticking point: whether to require that pilots undergo additional training on a flight simulator.
If regulators did require training, the condition would mean that the plane would be out of service for months longer than expected. Boeing had recently outlined a target of late June to airlines. But the F.A.A. has been more circumspect.
“We can’t be driven by some arbitrary timeline,” Daniel Elwell, the acting F.A.A. administrator, said on Thursday. “I don’t have September as a target, I don’t have June as a target.”
For Boeing, the uncertainty is another blow to its efforts to return the Max to service, which has weighed on its stock and its profit. The company has finished a software fix in recent weeks and has been answering questions from regulators over the changes and the design.
For the F.A.A., consensus is important. The agency has long been regarded as the world’s most influential aviation regulator. But it has faced sharp criticism for moving too slowly to ground the Max after the second crash and for underestimating the potential risks of the new software.
Approving the fix is complex balancing act. The F.A.A. is trying to appear thorough and independent, while at the same time working efficiently to get the Max flying again. And it is making an effort to get other countries on the same page, while allowing foreign regulators to dictate their own terms needed to lift the grounding.
“If they unground relatively close to when we unground, I think it would help with public confidence,” said Mr. Elwell, the F.A.A. administrator. “We will not let the 737 Max fly again in the U.S. until it is safe to do so.”
Requiring additional training on a flight simulator would be a significant change.
The F.A.A. suggested last month that it would not require pilots in the United States to spend more time on a simulator. But that matter is not yet settled. There are some within the agency who are still advocating it, according to a person briefed on the discussions.
Other global regulators are also undecided. The European and Canadian aviation regulators were expected to work in tandem with the F.A.A. But recently, the European Union Aviation Safety Agency has suggested it may act independently.
The regulator said in a statement that it had a list of conditions before allowing the Max to fly again, including “the completion of the additional independent design review” and “adequate training of Boeing Max flight crews.”
The Canadian transport minister, after initially insisting on simulator experience, has backed away from that position, according to people familiar with his thinking. But the Canadians would also prefer to act in conjunction with the European Union.
“Transport Canada aims to move in collaboration globally with our aviation partners, including EASA,” the agency said in a statement on Thursday. “The Department prioritizes global confirmation that the aircraft is safe to fly.”
The Chinese aviation authorities and regulators from other emerging markets could be holdouts. They appear more likely to insist that their pilots — many of whom have less experience than their American, European and Canadian counterparts — train on simulators, according to a person briefed on the discussions.
Boeing has told its airline customers that the Chinese regulator is the biggest wild card. China was the first nation to ground the Max after the Ethiopian Airlines crash in March, citing concerns over whether pilots could manually control the plane if it ran into problems.
Delaying its approval for the Max could also provide China leverage in the trade war with the United States. Boeing aircraft are one of the largest American exports to China by dollar value, and an obvious target for officials in Beijing if they want to further retaliate.
The divergent views about the need for simulator training point to a growing debate within the global aviation community over the capabilities of pilots from various countries.
The F.A.A. tends to make decisions based on the experience of the average pilot in the United States, many of whom have more flight time than those in emerging markets. Unions representing pilots at Southwest and American Airlines, which fly the Max, have said that they do not believe that the agency should mandate time in a simulator.
But there is broader pressure on the F.A.A. to reconsider whether it needs to modify its standards to account for less-experienced pilots. Boeing is selling more and more aircraft in emerging markets as global air travel continues to expand.
“We have been working closely with the F.A.A. and other global regulators on the process they have laid out for certifying the updated Max software, along with the associated enhanced pilot training and education that will help prevent accidents like these from happening again,” Boeing said in a statement on Wednesday.
On Tuesday in Miami, Boeing executives briefed pilots and operations personnel from airlines and leasing companies in the United States on its efforts to return the plane to service.
The meeting, at the Marriott Hotel in downtown Miami, was led by Linda Mills, vice president of communications for Boeing Commercial Airplanes, according to two people briefed on the meeting. Mike Sinnett, Boeing’s vice president of product strategy, also addressed the group, as did a representative from CFM, the company that makes the Max engines.
The conversation centered on what operators would need to do to reactivate the Max planes that have been sitting idle for months, once the F.A.A. says they are clear to fly.
The people briefed on the meeting said that those in attendance were in general agreement that each plane could require at least 100 hours or more of work. Southwest, American and United, the three carriers in the United States that fly the Max, have more than 60 of the planes between them.
Representatives from the airlines also raised what would happen the first time a Max made an unscheduled landing for whatever reason, according to the people briefed on the meeting. Such a situation could happen, with so many of the planes that had been idled for months coming back into service at the same time. Even if the incident had nothing to do with the software tied to the two crashes, there will be a flurry of concern and there was a recognition that airlines and Boeing will have to prepare for the attention.
Ms. Mills was asked whether Boeing was considering rebranding the Max, a move suggested by President Trump in a tweet last month. Ms. Mills said that was not happening, and that Boeing was focused instead on rebuilding trust in the plane.
Toward the end of the meeting, an attendee pointed out that Boeing’s reputation was damaged in the wake of its response to the two crashes. Ms. Mills acknowledged that was the case and said that Boeing was working on rebuilding trust in the company, too.