The Federal Aviation Administration said on Friday that it was expanding its scrutiny of Boeing, increasing oversight of the company with an audit of production of the 737 Max 9, a week after a panel in the body of one of those planes was blown out during flight.
Later Friday night, the F.A.A. said it was mandating an initial round of inspections of the panel — a plug where an exit door would go in a different configuration — on 40 Max 9 planes before it would approve Boeing’s proposed inspection and maintenance instructions for all grounded Max 9s. The agency said it needed more information on the inspection process before it could approve Boeing’s guidance for distribution.
The grounded planes, 171 in total in the United States, will be not be cleared to fly again until they are inspected, which could take several days, though possibly a lot longer, once the F.A.A. has approved an inspection process.
About 20 percent of Alaska Airlines’ fleet is made up of Max 9 jets, and the company has already had to cancel roughly that many of its flights in recent days as a result of the grounding. United Airlines is the biggest U.S. user of the plane, though the jet makes up just 8 percent of the larger company’s fleet.
“We are working to make sure nothing like this happens again,” the F.A.A.’s administrator, Mike Whitaker, said in a statement. “Our only concern is the safety of American travelers, and the Boeing 737-9 Max will not return to the skies until we are entirely satisfied it is safe.”
The audit will assess whether Boeing and its suppliers adhered to approved quality control practices. The F.A.A. also said it would more closely scrutinize problems on the Max 9 and investigate safety risks associated with the agency’s practice of outsourcing some oversight to authorized Boeing employees, which some lawmakers and safety experts criticized after two crashes of 737 Max 8 planes killed 346 people.
“It is time to re-examine the delegation of authority and assess any associated safety risks,” Mr. Whitaker, said in an earlier statement. “The grounding of the 737-9 and the multiple production-related issues identified in recent years require us to look at every option to reduce risk.”
There were no serious injuries from the accident last week, but the episode could have been far more catastrophic had it happened when the plane was at cruising altitude; the door plug blew out when the plane was at 16,000 feet and still ascending after taking off from Portland, Ore.
Alaska Airlines and United Airlines have both canceled Max 9 flights through Tuesday. Alaska said as many as 150 daily flights were affected, while United said it had about 200 daily flights, on average, planned aboard the Max 9. The airlines have swapped in new planes to carry out some flights and rebooked customers to minimize the disruption. Both said their technicians had begun inspecting the planes and would share their findings with the F.A.A.
“As we’ve said before, these aircraft won’t fly until they are approved and we are confident they are 100 percent safe,” United said in a statement.
Alaska Airlines also said specially trained crews would start moving some Max 9 planes to its maintenance bases on flights without passengers or flight attendants.
On Thursday, the F.A.A. announced an investigation into whether Boeing failed to ensure that the plane was up to standards and safe to operate.
Boeing said in a statement that it welcomed “the F.A.A.’s announcement and will cooperate fully and transparently with our regulator.”
“We support all actions that strengthen quality and safety,” the company added, “and we are taking actions across our production system.”
The F.A.A. has for years outsourced to corporate employees some oversight of the certification of airplanes and airplane parts. After a lengthy investigation into the design, development and certification of the Max, House Democrats criticized that practice, saying the agency had outsourced too much responsibility to Boeing employees, who may not be sufficiently independent.
On Friday, Mr. Whitaker, whom the Senate confirmed as F.A.A. administrator in October, said he would be willing to give the program another look. He also said the agency was exploring the use of an independent third party to oversee Boeing’s inspections and its quality system.
Some aviation experts say that the practice is necessary given the F.A.A.’s limited resources and that changing it would require Congress to give the agency more money and authority to hire more professionals.
Arjun Garg, a former chief counsel and acting deputy administrator of the F.A.A., said the agency did not have the resources to inspect every aspect of a plane. Bringing in-house all the work that has been delegated to Boeing and other manufacturers in the aviation industry would overwhelm the agency’s work force and budget, Mr. Garg said.
“I don’t think you can blame Congress for this or the F.A.A.,” he added. “This is just how the system has been designed given the need to have safety oversight and the practicality of resource constraints.”
Outsourcing of oversight is common among regulators, but a Government Accountability Office report in 2022 found that the F.A.A. did not audit the practice as closely as the European Union Aviation Safety Agency. That year, the F.A.A. said it had strengthened oversight of the practice by better protecting the deputized company employees from interference.
A day before the F.A.A.’s statement, Senator Maria Cantwell, the Washington State Democrat who leads the Senate Commerce, Science and Transportation Committee, called on the F.A.A. to increase its oversight of manufacturers, including contractors like Spirit AeroSystems, which produces the fuselage of the 737 Max for Boeing.
“The public deserves a comprehensive evaluation of Boeing and Spirit AeroSystems to strengthen production quality and aviation safety,” Ms. Cantwell said in a statement on Friday.