Boeing Max 9 Depressurization Emergency Prompts Grounding

The Federal Aviation Administration grounded more than 170 Boeing 737 Max 9 aircraft over the weekend when it introduced an emergency airworthiness directive (AD) requiring immediate inspection of mid-exit plug doors. This followed the January 5 incident in which an Alaska Airlines aircraft depressurized soon after takeoff from Portland International Airport in Oregon. NTSB officials are investigating the incident, which involved Flight 1262 landing safely with 174 passengers and six crew members on board after the door detached from the fuselage at around 16,000 feet.

According to a fleet analysis by IBA, a UK-based aviation consultancy, the grounding could disrupt operations for around 85 percent of the 216 Max 9s delivered to date, with most of these being operated by Alaska Airlines and United Airlines. IBA said that the Max 9 BBJ large-cabin business jet also has the mid-exit plug door, while indicating that its records show just one example of this variant in service.

Following initial inspections of some aircraft, both Alaska Airlines and United Airlines indicated that technicians had found "loose hardware," apparently referring to bolts used to keep the plug doors in place. During a media briefing late on Monday, NTSB chair Jennifer Homendy acknowledged but did not explicitly confirm these reports, and told reporters the scope of the investigation and follow-up action could be expanded. "We won't be shy about going broader than this aircraft [the Max 9]," she said. "We first and foremost need to find out what happened here, and if we have a bigger system-wide or fleet issue, we will issue an urgent safety recommendation to push for change."

The European Union Aviation Safety Agency immediately adopted the FAA’s AD, while stating that no Max 9 aircraft with the mid-exit plug door currently operate in its jurisdiction. Late on Sunday, NTSB confirmed that the door had been found in a school teacher's backyard in the Portland area and will now be evaluated by the agency’s structures team.

Boeing is convening a company-wide meeting on safety issues to be webcasted on Tuesday from its production line in Renton, Washington. On Saturday, the company said it fully supports the FAA’s decision to require immediate aircraft inspections.

“We will spend time together Tuesday talking about our company’s response to this incident and reinforcing our focus on and our commitment to safety, quality, integrity, and transparency,” said Boeing president and CEO Dave Calhoun. “While we’ve made progress in strengthening our safety management and quality control systems and processes in the last few years, situations like this are a reminder that we must remain focused on continuing to improve every day.”

According to IBA, Boeing has 104 of the Max 9 aircraft on order, with the smaller Max 8 model having significantly more units in service and awaiting delivery. The airframer is working to complete type certification of the Max 7 and Max 10 members of its new-generation 737 family. The Max 10 will have the mid-exit door, but the smaller Max 7 model will not.

IBA explained that the mid-exit door is a requirement for larger versions of the Max aircraft configured with around 200 seats, rather than the standard Max 8 configuration of 189 seats. Operators have the option to plug this exit door if it is not required to carry higher numbers of passengers. The plug effectively blanks off the area of the fuselage where the door would be and seats can be installed as they would be in any area of the cabin without an emergency exit.

“It is unlikely there will be any meaningful impact [from the January 5 incident] to Max 9 deliveries and IBA also does not expect the recent events to impact the backlog for the Max 9,” the consultancy commented in a statement issued on Sunday. “Customers will remain committed to the type in IBA’s opinion.”

The mid-exit plug door incident marks the latest in a series of disparate safety and manufacturing issues for the Max airliners involving both Boeing and its aerostructures supplier Spirit AeroSystems. In December, Boeing instructed airlines to inspect the aircraft for a possible loose bolt in the rudder control system. Previously, Max 8 and 9 aircraft were grounded for almost two years after a pair of fatal accidents in 2018 and 2019 that forced changes to the automated flight control system.

In November, the FAA published a request it received from Boeing for an exemption to limitations imposed on the use of the current Max family’s engine anti-ice system. The exemption request could clear the way for type certification of the Max 7 by giving the manufacturer until May 31, 2026, to remedy issues raised by an AD issued in August. This would address the FAA’s concern about overheating from prolonged use of the anti-ice system causing debris to break away from the nacelle inlet, causing damage to the fuselage, wing, or tail.

The temporary solution required by the AD is that pilots must remember to deactivate the anti-icing system when it is not required to avoid overheating the nacelle. According to reports in the Seattle Times, the Allied Pilots Association and the Foundation for Aviation Safety have opposed the exemption, arguing that it would put an unreasonable onus on pilots and that instead Boeing should be required to resolve the defect before the Max 7 is certified.

This story was updated on January 9 to add details about reports of loose bolts found during initial inspections, and comments made during an NTSB media briefing.