KUWAIT (Reuters) - Regulators should work together in recertifying the grounded Boeing BA.N 737 MAX airliner instead of pursuing separate approval processes, the head of the International Air Transport Association (IATA) said on Tuesday.

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“For us, it’s a big, big, big mistake. Because we have built the safety of this industry on the single certification decision and the mutual recognition and it has worked very well,” IATA boss Alexandre de Juniac told Reuters in an interview in Kuwait.

Some international regulators have said they plan to conduct they own checks and not simply follow the U.S. Federal Aviation Administration (FAA) should it recertify the plane.

The U.S. FAA has traditionally taken the lead in certifying Boeing aircraft, but two fatal crashes in Indonesia and Ethiopia involving the Boeing 737 MAX have sparked criticism of the FAA’s oversight and its close links with the U.S. planemaker.

“If you want to restore the confidence ... we need to come back to this single, mutual recognition which has been so efficient,” de Juniac.

Any changes to the certification process should be made jointly and transparently by regulators, he said.

Otherwise, he said there was a risk that discrepancies could emerge if regulators followed different procedures, making the process more complex, increasing costs, and potentially less safe because of the lack of unanimity.

Boeing’s top-selling jet was grounded in March following the two crashes which killed all 346 people aboard.

Boeing is updating flight control software at the center of both crashes. This must be approved by regulators before the plane can fly commercially again.

The planemaker has said it aims to return the 737 MAX to service by the end of 2019 after making software changes.

The MAX could return to service in Europe during the first quarter of 2020, the European Union Aviation Safety Agency (EASA) said on Monday.