“I think we need to know more about how the inspection is being done, who is doing it, and how the results will be made public,” Blumenthal said in an interview on Capitol Hill. “I think they’re rushing these planes into the sky without sufficient assurance to the American public.”

He added that the National Transportation Safety Board, which is investigating the Jan. 5 incident in which a door plug on an Alaska Airlines flight blew out midair, also should weigh in on whether it thinks the planes are safe to fly. The NTSB on Thursday responded to Blumenthal’s suggestion by observing that as the regulator, FAA controls that decision.

The two airlines’ combined 171 MAX 9 planes have been grounded since shortly after the blowout. No one was seriously injured, but the incident has revived concerns about production and quality control at the aerospace giant, along with regulatory probes and promised congressional hearings.

Republican Sen. J.D. Vance of Ohio, echoed Blumenthal’s concerns Thursday.

“I’m extremely skeptical that the MAX 9 should be brought back into service until we know a lot more about what happened,” said Vance, who along with Blumenthal had been among the first lawmakers to speak out about the door failure.

Boeing deferred questions on timing to the FAA and the airlines, but pointed to a previous statement that the company continues to “cooperate fully and transparently with the FAA and follow their direction as we take action to strengthen safety and quality at Boeing.”

When asked if the timing was too soon, the FAA on Thursday pointed to FAA administrator Mike Whitaker’s comments from the prior day. “We grounded the Boeing 737-9 MAX within hours of the incident over Portland and made clear this aircraft would not go back into service until it was safe,” Whitaker said in conjunction with the FAA’s issued inspection guidelines, released Wednesday.

Other senators said they trust the FAA’s proposed fix for the MAX 9.

The Democratic chair of the Senate Commerce aviation subcommittee, Sen. Tammy Duckworth (D-Ill.), said if the FAA clears them as safe to fly, “I don’t think it’s too soon.”

But she agreed that Boeing has “a quality control, cultural problem” and ripped what she called “their continued insistence on getting special exemptions in order to put aircraft into service.”

Duckworth was referencing Boeing’s ongoing request for the FAA to exempt from safety standards a de-icing system on its MAX 7 that is at risk of overheating. Boeing is working on a fix and has argued that the problem can be mitigated in the meantime by limiting the system’s use in certain conditions.

If the FAA grants that exemption, it would allow Boeing to deliver the Max 7 to airlines once certified. “That’s not going to happen,” Duckworth said.

Sen. Ted Cruz of Texas, the top Republican on the Senate Commerce Committee, on Thursday backed the FAA’s procedure for returning the planes to flight but demurred when asked if it may be too soon.

“We need to do everything necessary to prevent a similar accident from happening,” he said.

Cruz helped organize a briefing for Commerce members last week with leaders from FAA and NTSB to get an update on their investigations and “the factors that led to this accident in particular” and what can be done “to ensure that something similar cannot happen again,” he said.

Lee Moak, who helped lead a DOT investigation into two Boeing 737 MAX 8 crashes that killed 346 people in Ethiopia and Indonesia in 2018 and 2019, said the FAA and Boeing have “very good people” who are inspecting the planes and that the airlines appear to have resolved the issues with the door plug bolts at fault in the Alaska Airlines incident.

“It’s a very safe airplane and I think we should look forward to it continuing to fly for many years,” Moak, who is a former commercial airline pilot, said in an interview. “I’m very comfortable with the plane.” Moak is the former head of the Air Line Pilots Association, the largest pilots’ union, and now runs a strategic communications firm called Intrepid.

He added that though the incident was alarming, “the engineering of the airplane, when you have a failure like this, is remarkable because the plane came back safely,” he said.

Moak’s review of Boeing’s safety practices in 2020 — as well as the FAA’s process for allowing manufacturers to certify their planes as safe to fly with FAA oversight — concluded that the certification system was effective and should stay in place, as it has produced “the remarkable level of safety that has been attained in recent decades,” he said.

Sara Nelson, president of the Association of Flight Attendants, which represents flight attendants at Alaska, United and 17 other airlines, said she had faith in FAA administrator Mike Whitaker’s “stellar” leadership but added that it’s “clear that this isn’t where this issue ends.”

She said the union supports “increased oversight and investigations into the manufacturer’s quality control including limiting production lines.”

Syracuse University professor Kivanc Avrenli, whose research focuses on commercial aviation safety, said “the quality control problems at Boeing date back to the 1980s,” when a Japan Airlines crash killed 524 people. He said he believes the bolt issues with the MAX 9 have been fixed, but suggested it’s hard to know what other problems might be lurking undiscovered.

“Who knows? Maybe there is another issue with this aircraft and that’s going to come out of the blue someday” because at its root, Boeing’s safety culture is “deeply troubled,” Avrenli said.

Former NTSB Chair Robert Sumwalt, now executive director of the Boeing Center for Aviation & Aerospace Safety at Embry-Riddle Aeronautical University, said the FAA and Boeing “have every reason to get this right” and that as a result, he’s “confident” that the bolt issue will be rectified.

And he noted that Boeing needs to slow down production to ensure safety. The FAA on Wednesday also said it won’t allow Boeing to expand production of its 737 MAX models until the agency is satisfied that Boeing has rectified its quality control issues.

“To those [who] are saying they can fix the issues without drastic change, my question to Boeing would be, ‘How’s that working for you’?” Sumwalt said.

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