A rift between regulators over the Boeing Co. 737 Max could undermine a long-established system of mutual recognition and hold back new plane programs, the International Air Transport Association said.

Splits like those over the Max’s grounding and the approval process for its return could add years to the certification of future models and hundreds of millions of dollars in development costs, says Gilberto Lopez Meyer, senior vice president for safety and flight operations at the airline industry group.

The U.S. Federal Aviation Authority idled Boeing’s top-selling model in March after regulators elsewhere had taken the unprecedented step of unilaterally banning flights following two fatal crashes in five months. The FAA on Wednesday dropped plans to get the Max flying again this year, after European Union Aviation Safety Agency and its counterpart in the United Arab Emirates had indicated they would carry out independent reviews.

“What we’ve seen in the past six months is a fragmentation,” IATA Chief Executive Officer Alexandre de Juniac told Bloomberg TV from Geneva after briefings on industry issues. “We will have for the re-entry into service of the 737 Max several different certification processes in various parts of the world. We are advocating against that but unfortunately it will be the case.”

Concern about U.S. oversight of the Max has extended to China, the first nation to ground the plane, and Canada, where a safety official at the national regulator emailed the FAA to suggest that a software system blamed for the crashes be removed, according to a report last month in the New York Times.

Agencies from Australia, Brazil, Japan, Indonesia, Singapore are also involved via their participation in the Joint Authorities Technical Review panel, which in a 69-page report in October criticized U.S. authorities for failing to follow their own rules, using out-of-date procedures and lacking the resources and expertise to fully vet design changes implicated in two fatal crashes.

De Juniac said that IATA continues to favor the status quo, with a single authority responsible for a particular aircraft type “and the others following.” Where there are questions over the certification process the relevant agency should cooperate and collaborate to restore confidence, he added.

“We are not the safest industry by chance,” he said. “We’re the safest because we have strong, very reliable safety processes and programs.”

Lopez Meyer, the former head of Mexico’s aviation authority and also speaking in Geneva, said the existing system “is in jeopardy,” while expressing optimism that the limited number of authorities with the technical ability to certify aircraft might put a brake on the emerging schism.