WASHINGTON (AP) — Federal regulators have approved an inspection process that will let airlines resume flying their Boeing 737 Max 9 jetliners, which have been grounded since a side panel blew out of a plane in midflight earlier this month.

The head of the Federal Aviation Administration said Wednesday that his agency’s review of the scary incident on board an Alaska Airlines Boeing jet gives him confidence to clear a path for the planes to return to flying.

The official, Mike Whitaker, said the FAA would not agree to any Boeing request to expand production of Max planes until the agency is satisfied that quality-control concerns have been addressed.

The move came on the same day that a key senator indicated that Congress will join the scrutiny of Boeing.

Sen. Maria Cantwell, D-Wash., met with Boeing CEO David Calhoun to discuss incidents, including one this month in which a panel called a door plug blew off a Boeing 737 Max 9 jetliner as it flew 3 miles (5 kilometers) above Oregon.

Cantwell said she told Calhoun that quality engineering and safety must be the company’s top priorities.

“The American flying public and Boeing line workers deserve a culture of leadership at Boeing that puts safety ahead of profits,” said Cantwell, who represents the state where Boeing assembles 737s.

Cantwell said the Senate Commerce, Science & Transportation Committee, which she chairs, will hold hearings “to investigate the root causes of these safety lapses.” No dates were announced.

Boeing did not respond immediately to a request for comment.

The National Transportation Safety Board is investigating the accident on an Alaska Airlines Max 9. NTSB officials have said they are looking into whether bolts that help secure a panel called a door plug were missing before the plane took off from Portland, Oregon, on Jan. 5. The blowout left a hole in the side of the plane, but pilots were able to land safely.

An NTSB investigator will return to Boeing’s 737 assembly factory in Renton, Washington, on Friday as the probe continues, a spokesman for the board said. Investigators are building a timeline of the door plug that failed, from the early stages of its production to the flight on which it blew off the plane.

The Federal Aviation Administration is looking into whether Boeing and its suppliers followed proper safety procedures during manufacturing.