Boeing 737 Max 9 problems mount after incidents involving Alaska and United Airlines. Here’s what we know.

On Monday, United Airlines reported that loose bolts and other “installation issues” had been discovered in the door caps of some of the company’s Boeing 737 MAX 9 planes.

“Since we began preliminary inspections on Saturday, we have found instances that appear to be related to installation issues in the door plug, such as bolts that required additional tightening,” United said.

The mandatory inspections come after the Federal Aviation Administration grounded Boeing 737 MAX 9 planes. Alaska Airlines and United are the only two U.S. airlines that operate that particular model of Boeing 737.

“Boeing 737-9 aircraft will remain grounded until operators complete comprehensive inspections, including the left and right cabin door exit plugs, door components and fasteners,” the FAA said in a statement on Monday, adding that any issues found during the inspections must be corrected before the planes can return to service.

According to the Federal Aviation Administration, the disruption affected about 171 planes worldwide and led to the cancellation of hundreds of flights.

On Friday, Alaska Airlines Flight 1282 was forced to make an emergency landing shortly after takeoff after a door plug blew out, creating a large hole in the side of the plane as it climbed. The door plug has since been recovered, and the National Transportation Safety Board launched an investigation over the weekend into what it called an “accident.”

Boeing shares fell as much as 9% at the opening of trading on Monday morning, the first business day since the incident.

No serious injuries

Incredibly, none of the 171 passengers and six crew members on board the flight from Portland, Oregon, to Ontario, California, were injured.

The plane was climbing at an altitude of approximately 16,000 feet when a panel on the fuselage of the plane was blown off.

There was no one in 26A and 26B, where the door plug was located.

“We are very, very fortunate here that this didn’t end in something more tragic,” NTSB Chair Jennifer Homendy said over the weekend.

The plane had not yet reached cruising altitude and the ‘fasten seat belts’ sign was still on to discourage passengers and crew from walking around the cabin.

“Just talking to everybody who was in the interviews, it was described as chaos, very loud, between the air and everything that was going on around them,” Homendy said at a news conference Sunday. “And it was very violent when the rapid decompression and the door (plug) was thrown out of the plane.”

Some passengers were treated on board for minor injuries.

What the research has yielded so far

The lost door plug, which weighs 65 pounds and measures 26 by 48 inches, was found Sunday in the backyard of a Portland teacher.

NTSB investigators will examine the cap for evidence of how it came loose and compare it to the cap on the other side of the aircraft door.

The plane used for Flight 1282 had other problems. After a warning light came on during three previous flights indicating a pressurization problem, the plane was restricted from longer routes to Hawaii that went over open water. The restriction was in place in case the warning light came on again, so the plane could quickly return to an airport. The warning light had previously come on on Dec. 7, 2023, and on Jan. 3 and 4, just one day before the door plug blew off.

Alaska Airlines had ordered additional maintenance personnel to look at the pressurization warning light, Homendy added, but that had not been completed before Friday’s accident. Homendy acknowledged that the warning light issue may not be related.

An additional hurdle is that investigators cannot rely on the cockpit data recorder from Flight 1282.

“The cockpit voice recorder was completely overwritten… after two hours it is re-recorded, so we have nothing left of the CVR (cockpit voice recorder),” Homendy told reporters, adding that it is “critical” to extend that recording time to 25 hours, the standard currently used by Europe and many other countries.

While the Federal Aviation Administration has proposed a new rule to implement that increase, it would apply only to newer flights, so the Alaska Airlines flight would not have qualified, Homendy said.

Two cell phones that appeared to belong to passengers aboard Flight 1282 were later recovered. One was found in a yard, and the other by the side of the road.

What’s next

The NTSB is expected to work with officials from Alaska Airlines, Boeing, the FAA and pilot and flight attendant advocacy groups in the investigation.

“While we await the inspection criteria for the airworthiness directive from the FAA and Boeing, our maintenance teams are prepared and ready to perform the required inspections,” Alaska Airlines said in a statement. The airline said cancellations will continue through the first half of the week and that passengers should check alaskaair.com for updates.

United Airlines also issued a statement about X and said they are working with affected customers to find “alternative travel options” for them and advised them to check united.com or the United app for updates.

Meanwhile, Boeing CEO Dave Calhoun sent a companywide memo saying, in part, “When serious accidents like this occur, it is critical that we work transparently with our customers and regulators to understand and address the root causes of the occurrence and ensure they don’t happen again. That is and must be the focus of our team at this time.”

Calhoun plans to hold an all-worker safety meeting at the 737 plant in Renton, Washington, on Tuesday.