Washington (CNN) Government officials from civil aviation authorities in nine countries, as well as members of the three US federal agencies, will investigate how the 737 Max airplane was initially certified, according to a release from the Federal Aviation Administration.

The group, called the Joint Authorities Technical Review, will begin work on April 29, and will review the initial certification of "the aircraft's automated flight control system," the release states. The review is expected to take 90 days, according to the release. The three American agencies involved in the investigation will be the FAA, National Transportation Safety Board and NASA.

The 737 Max was grounded in March after one of the planes flown by Ethiopian Airlines crashed, killing everyone on board. It was the second accident involving the jet model in less than six months, after another flown by Indonesia's Lion Air crashed last October. The crashes killed 346 people in total.

The group's review of the initial certification is separate from the ongoing certification process that Boeing, the company that makes the 737 Max planes, is undergoing with the FAA to re-certify the planes, according to an FAA spokesman.

Boeing has come under intense scrutiny since the Ethiopian airline crash in March. The company at first defended the planes and insisted they were safe to fly, but after intense public pressure, they grounded the planes and admitted that a software fix was needed.

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