United Airlines said Monday that it found loose screws in the panels of its Boeing 737 Max 9 jets that resembled the part of an Alaska Airlines plane that exploded during a flight on Friday, raising growing safety concerns about the Max 9 even strengthened.
The disclosure followed reports that Alaska Airlines had been warned three times about problems with cabin pressure on its plane. These warnings were so serious that the airline decided that the aircraft could no longer be used on flights to Hawaii.
United found the loose screws in the panels, known in the industry as plugs, after it began removing seats and side panel panels this weekend to inspect the part, the airline said Monday. The plugs are placed where an emergency exit door would be if a jet had more seats.
About 10 minutes after takeoff from Portland, Oregon, on Friday, a door plug suddenly flew out of the Alaska Airlines plane as cabin pressure dropped, exposing passengers to howling winds and forcing pilots to quickly return to the airport. The door plug, phones, toys and other personal items poured out of the hole in the side of the plane and fell over the city.
Airlines have canceled hundreds of flights as they prepare to inspect nearly 200 planes that will remain grounded until regulators and company officials decide they are safe. Alaska Airlines used 65 Max 9 planes, about 20 percent of its fleet, and United used 79, more than any other airline and about 8 percent of its fleet, according to Cirium, an aviation data provider. Some passengers' travel plans could be disrupted for days.
The Federal Aviation Administration sent instructions to airlines Monday on how to conduct the inspections, although Alaska and United said they were waiting for additional approval from the FAA to begin.
Officials led by the National Transportation Safety Board are focusing on installing and inspecting the connector, among other things.
“I think investigators will focus on the manufacturing process of this particular aircraft,” said Jeff Guzzetti, a former NTSB and FAA investigator. “How was this door stopper installed or who installed it?”
The door was originally installed by Spirit AeroSystems, which makes the bodywork for the 737 Max and other aircraft. Investigators said they were looking into whether any work had been done on or near the door since the plane entered service in November.
Jennifer Homendy, the chairwoman of the NTSB, said investigators still have much work to do, including inspecting the plug, which was recovered in a backyard near Portland. The board will also examine a connector that remained intact on the other side of the plane, interview flight crews and passengers, review maintenance records and repair logs, and conduct laboratory analysis of parts of the plane.
Investigators may also examine whether the installation of wireless Internet devices on the aircraft by a contractor, AAR, between Nov. 27 and Dec. 7 played any role in the printing problems that occurred after that work was completed. In a statement Monday, AAR said that “no work was performed on or near a mid-cabin door plug on this particular aircraft.”
Although no serious injuries were reported, the accident could have been far more catastrophic, especially if the plane had been at a higher altitude, experts said. Ms Homendy said on Sunday evening that the passengers included three babies and four unaccompanied children aged between 5 and 17.
Ms. Homendy said in a brief interview on Monday that her team was checking the plane's flight data recorder to determine whether the pressure warning light may be connected to the door plug. The aircraft has several backup systems in case one of the pressure systems fails.
“There may have been something wrong with either the light or that one other unit, but there are redundancies in the system,” Ms Homendy said.
Kathleen Bangs, an aviation expert and former airline pilot, said she believed the investigation would reveal a door plug defect because of the plane's condition. Typically, explosive decompression incidents occur on older aircraft that exhibit metal corrosion and fatigue, Ms. Bangs said. In this case, she said, the plane was nearly new, indicating there was most likely a problem with the door plug.
Anthony Brickhouse, a professor of aerospace safety at Embry-Riddle Aeronautical University, said an explosion at a cruising altitude of more than 30,000 feet could have had catastrophic consequences. “We could have imagined a situation where more parts of the structure could have come loose, and we could have imagined a situation where passengers who were not properly restrained would have been ejected because the forces would have been so enormous .” he said.
Most commercial aircraft begin to experience pressurization at an altitude of about 8,000 feet, said Mr. Brickhouse, who previously investigated aviation accidents for the Safety Board. Failure to properly control the air entering and exiting the cabin can cause altitude sickness or hypoxia to passengers and crew.
Hypoxia, a condition that occurs when the brain is deprived of oxygen, can occur in aircraft without adequate pressure when flying above 10,000 feet or undergoing rapid decompression, the FAA says. For this reason, flight attendants are advising passengers to use drop-down masks in the event of rapid decompression, Brickhouse said.
In a statement, the FAA said required inspections would focus on the plugs, door components and fasteners.
“Our teams have worked diligently – with thorough FAA review – to provide operators with comprehensive technical guidance for the required inspections,” Stan Deal, the general manager of Boeing's commercial aircraft division, and Mike Delaney, the chief aerospace safety officer, said in a statement Message to staff at this unit on Monday.
Other airlines with Max 9 aircraft are located outside the United States, such as Copa Airlines of Panama, Turkish Airlines and Icelandair. The European Union's aviation safety agency announced Monday that Max 9 jets operating in Europe were not grounded because of a different configuration.
The FAA had previously said inspecting each aircraft would take four to eight hours. According to the aviation authority, the inspection of the almost 200 Max 9 aircraft in the USA could take a few days.
Aviation regulators and Boeing said the inspections covered only the Max 9 and not other versions of the Max jet. The Max 9, along with the more popular Max 8, was forced out of action for nearly two years after two Max 8 crashes in 2018 and 2019 killed 346 people.
Federal authorities investigating the incident are also investigating what led to pressure warnings on the damaged plane during three recent flights. Alaska Airlines officials reset the system and the plane returned to service, although the airline limited its use on flights to destinations such as Hawaii, Ms. Homendy said. She added that it was not yet clear whether the warnings were related to Friday's accident.
In a statement, Alaska said it could not answer many outstanding questions about the plane and what led to the explosion without approval from the safety board. The airline said it has asked the NTSB to share more information and will do so if permitted. In such investigations, the parties are typically limited in what they can share publicly.
Boeing CEO Dave Calhoun planned to host a company-wide safety meeting on Tuesday to discuss the company's response to the incident and reiterate its commitment to safety. Boeing is still working on approval of the smaller Max 7 and larger Max 10.
Boeing shares closed Monday down about 8 percent and shares of Spirit AeroSystems closed down 11 percent.
J. Edward Moreno contributed reporting.