WASHINGTON (AP) — A federal safety board planned on Wednesday to probe the Federal Aviation Administration’s oversight of Boeing and how it has changed since a door plug blew off a Boeing 737 Max in midflight.

The National Transportation Safety Board is holding a two-day hearing on the blowout during an Alaska Airlines flight in January.

Door plugs are installed on some 737s to seal a cutout left for an extra exit that was not required on the Alaska jet. The plug on the Alaska plane was opened at a Boeing factory to let workers fix damaged rivets, but bolts that help secure the panel were not replaced when the plug was closed.

A Boeing official said Tuesday that the company is redesigning door plugs so they cannot be closed until they are properly secured. Elizabeth Lund, who was named Boeing’s senior vice president of quality shortly after the blowout, said the company hopes to complete the fix within about a year, and that 737s already in service will be retrofitted.

On Wednesday, safety board members were scheduled to question representatives from Boeing and key supplier Spirit AeroSystems on their safety systems. They also plan to ask FAA officials about the agency’s monitoring of Boeing. including “changes in oversight methods.”

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FAA Administrator Mike Whitaker told Congress in June that the agency’s oversight was “too hands-off” before the blowout but has since put more inspectors inside Boeing and Spirit factories. Whitaker is not scheduled to testify.

The accident on Alaska Airlines flight 1282 occurred minutes after takeoff from Portland, Oregon, on Jan. 5. The blowout left a hole in the plane, oxygen masks dropped and the cockpit door flew open. Miraculously there were no major injuries, and pilots were able to return to Portland and land the plane safely.