The Federal Aviation Administration says the initial round of inspections of the 737 MAX has ended

The Federal Aviation Administration said Wednesday that an initial round of inspections on 40 Boeing 737 Max 9 planes has been completed, but those and dozens of other Max 9 planes will remain grounded until the agency completes its inspection process.

The Federal Aviation Administration announced Friday that it is requiring 40 inspections before approving new inspection and maintenance instructions developed by Boeing. The agency grounded 171 Max 9 planes this month after the door panel of an Alaska Airlines plane exploded during boarding after taking off from Portland, Oregon, forcing it to make an emergency landing.

The FAA said in its statement Wednesday that it would review data from the 40 inspections, and that 737 Max 9 planes with door panels would remain on the ground until the agency signed off on instructions for airlines to inspect planes. The door panels go where the emergency exit door would be in a different aircraft configuration.

“The safety of the public, not speed, will determine the timeline for returning these aircraft to service,” the agency said in the statement.

Last week, the Federal Aviation Administration announced it was investigating whether Boeing failed to ensure the 737 MAX 9 was safe and compliant with the design approved by the agency. The accident involving the Alaska Airlines flight did not result in any serious injuries, but it could have been more serious if it had occurred when the plane was at cruising altitude.

The FAA said in its statement on Wednesday that it is “investigating Boeing's manufacturing practices and production lines, including those involving subcontractor Spirit AeroSystems,” which produces the 737 MAX fuselage.

Boeing declined to comment on the FAA statement. The aircraft manufacturer said it would cooperate with the agency's investigation, and announced Monday that it would make changes to its quality control processes. The company's CEO, Dave Calhoun, also visited Spirit AeroSystems in Wichita, Kansas, on Wednesday and participated in a town hall meeting with employees there.

Spirit spokesman Joe Buccino said the company “supports Boeing's efforts with the FAA and affected airlines as they inspect the 737-9 fleet and work to safely return those aircraft to service.”

After a closed briefing to members of the Senate Commerce Committee on Wednesday, Jennifer Homendy, chair of the National Transportation Safety Board, said the door panel that came off the plane was manufactured by Spirit in Malaysia.

The panel, also known as a door stopper, was transported to Spirit's factory in Wichita, where the fuselage was built, Ms. Homendy said. Homendy said the fuselage was then transported by rail to the Boeing factory in Renton, Washington state.

The safety board is investigating why the door plug became disconnected, and Ms Homendy said the board's investigation would look at the plug's entire journey.