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Four days after a section of the fuselage suddenly detached as an Alaska Airlines plane was taking off, United Airlines reported Monday that its inspectors discovered several “instances that appear to relate to installation issues in the door plug,” including bolts needing additional tightening.
United Airlines said it has been inspecting its fleet of Boeing 737 Max 9 planes to make sure they are safe to fly as federal investigators continued to investigate Friday’s near-disaster aboard an Alaska Airlines plane.
Hours later, Alaska said in a statement that reports from its technicians, who had “accessed the area in question” while preparing the fleet for formal inspections, “indicate some loose hardware was visible on some aircraft.”
The announcements came a day after National Transportation Safety Board Chair Jennifer Homendy reported they had found a missing door plug that could be key to the investigation of the midair accident in the backyard of a home of a Portland, Oregon, teacher identified only as “Bob.”
The Federal Aviation Administration on Saturday grounded 171 of the Boeing 737 Max 9 planes worldwide so they could be inspected. On Monday, the agency said the aircraft would remain grounded “until operators complete enhanced inspections” and complete any necessary corrective action.
United Airlines said in its announcement that grounding its fleet of 79 737 Max 9 aircraft led to about 200 flight cancellations Monday, with “significant cancellations” expected Tuesday.
It said switching some flights dependent on the 737 Max 9 to other models will help preserve 30 flights that could have been canceled.
Inspection process
United said it began preparing for inspections Saturday by removing inner panels that lead to the door plugs and then doing visual checks ahead of more formal examination. Five United technicians will be assigned to each inspection, it said.
“To access each door plug, we remove two rows of seats and the sidewall liner,” United said in the statement. “This has already been done on most Max 9s.”
The airline said it will consider installation, hardware, and the structure around the door plugs.
“We’ll then resecure the door, ensuring proper fit and security,” United said. “We’ll document and correct any discrepancies before returning that aircraft to service.”
Alaska Airlines said Monday that it is waiting for final documentation before it can begin the formal inspection process, which will include logging and addressing all findings.
“No aircraft will be returned to service until all of these steps are complete,” the airline said in a statement. “The safety of these aircraft is our priority and we will take the time and steps necessary to ensure their airworthiness, in close partnership with the FAA.”
Early Friday evening, Alaska Airlines Flight 1282 from Portland, Oregon, to Ontario, California, experienced rapid depressurization when a door plug detached violently.
The plane was at about 16,000 feet when an explosive sound was heard, the NTSB has said.
The aircraft was only 10 minutes into the flight and still over the Portland area as its pilots scrambled back to the Oregon airport.
Homendy said the flight narrowly avoided tragedy, in part, because the plane was not yet at cruising altitude of 35,000 feet and no one was sitting in the seats next to the door plug. Passengers were still buckled into their seats, two of which experienced such violent force that their frames were torqued and they lost headrests. They were unoccupied.
The NTSB chair said Sunday night that investigators want to take a very close look at the door plug that that blew out, its fasteners, and the aircraft structure around it.
Door plug scrutinized
In an interview with NBC News, Homendy said NTSB investigators looked at the door plug on the right or starboard side of the aircraft Monday, seeking to answer major questions.
“How was it put together?” she said. “And how did it perform even when we put some pressure on it? And we really wanted to look at all the components there and see how it related to what we were seeing on the other side.”
To the chair’s eyes, the door plug that remained intact looked ship-shape, but the one that blew out was being sent to the NTSB’s laboratory, where it will be put under a high-resolution microscope and checked out by a metallurgist, she said.
Investigators will check threads on any fasteners, any possible metal-on-metal contact, the state of any sealant used, and any possible deformations or flaws in material, Homendy said during the interview Monday.
“Their whole goal is to really tell a story,” the chair said of NTSB investigators. “And that’s what the evidence provides — a story of what happened in those moments where the door was expelled.”
Pressurization alerts
The 737 Max 9’s pressurization system and alerts would also be examined, Homendy said earlier.
On Sunday, the NTSB reported that Alaska Airlines had previously restricted this particular plane from long flights over water, specifically to Hawaii, because an air pressurization alert light that had illuminated during three prior flights, twice in the days leading up to Friday.
But aviation experts told NBC News on Monday that based on the information provided thus far by federal authorities the light was going off as the result of a computer glitch of some kind and not indicating there was a mechanical problem on the plane.
“It’s not unusual in the aviation world for there to be issues with warning lights and most of the time the issue is with the warning light itself,” Jeff Guzzetti, a former NTSB investigator. “It’s not like Alaska Airlines ignored it. The fact that it restricted this plane from making flights over water while they were looking into this warning lights issue points to a robust safety culture.”
John Cox, who weighs-in regularly on aviation issues for NBC News, agreed.
“The pressurization system, from what I’ve read, was acting normally,” said Cox, who said he flew Boeing 737’s for 15 years. “This appears to be more a sensor problem. But Alaska Airlines, being a conservative airline, said this has happened a couple times now and we need to look into, but let’s not do that over the Pacific Ocean.”
The NTSB has said those alerts will be part of its investigation into what caused the door plug to blow off midflight.
Manufacturer Boeing said in a statement Monday that it was in touch with domestic airlines that operate 737 Max 9 aircraft and would “help address any and all findings” related to the FAA-mandated inspections.
“We are committed to ensuring every Boeing airplane meets design specifications and the highest safety and quality standards,” it said. “We regret the impact this has had on our customers and their passengers.”
