Design issue or isolated problem? What we know about the Boeing jet that blew open mid-air
Who flies the Boeing 737 MAX 9 plane and what's been the impact on the aviation giant after the Alaska Airlines blowout incident?

The door plug from Alaska Airlines Flight 1282 on Jan 8, 2024, in Portland, Oregon. (Photo: AP/National Transportation Safety Board)
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SINGAPORE: Alaska Airlines flight 1282 was about halfway to its cruising altitude on Jan 5 when passengers heard a loud boom and the roaring wind that filled the cabin.
“We knew something was wrong," passenger Kelly Bartlett told the Associated Press.
The door plug of the Boeing 737 MAX 9 had blown out mid-air, leaving a gaping hole through which items flew out, including an iPhone that managed to survive the drop.
The chief of the National Transportation Safety Board (NTSB) said it was "very, very fortunate" that the incident had not ended in tragedy.
But the incident has once again cast the spotlight on Boeing's safety record.
Here's what we know so far about investigations and what it means for the aviation giant.
WHICH AIRLINES FLY THE 737 MAX 9?
The Boeing 737 MAX 9 is mainly flown by US carriers Alaska Airlines and United Airlines. Together, the airlines' combined fleets represent about 70 per cent of 737 MAX 9 planes in service.
Other airlines that fly the model are Panama’s Copa Airlines, Aeromexico, Turkish Airlines, FlyDubai and Iceland Air. Indonesia's Lion Air flew a MAX 9 with a different configuration before they were temporarily grounded.
The US Federal Aviation Administration (FAA) said 171 planes worldwide would be affected by its call for some 737 MAX 9 to be grounded for inspections.
Airlines in the European Union do not currently operate the 737 MAX 9.
While Indian airlines do not operate the 737 MAX 9, checks were conducted on the Max 8 model to the satisfaction of the country's aviation regulator.
DO 737 MAX 9 PLANES FLY TO SINGAPORE?
Singapore Airlines, one of Asia's largest carriers, said it does not fly the 737 MAX 9.
In fact, no 737 MAX 9 aircraft operate to and from Singapore, said the Civil Aviation Authority of Singapore in response to CNA's queries.
"CAAS is in close contact with FAA and Boeing and monitoring the issue closely," said senior director of the CAAS safety regulation group Alan Foo.


WHAT IS A DOOR PLUG?
The piece of fuselage that was blown off the Alaska Airlines plane is known as a door plug, which is fitted to "plug" an emergency exit that the airline does not use.
Such plugs are on most of Boeing's 737 MAX 9 jets.
Planes with more than 200 seats will require more sets of emergency exits. In the case of Alaska Airlines and United Airlines, their 737 MAX 9s are configured to have fewer than 180 seats, so instead of side exits, permanent plugs the size of an exit door are installed.
To passengers, the panel would appear like a normal window.
Plugs are a type of self-sealing door that is typically used in aviation. As planes ascend, plug doors typically seal themselves by leveraging differential pressure.
They can only be opened usually once a plane has descended and its cabin is no longer pressurised.
The force of the Alaska Airlines 737 MAX 9 decompression was so strong it blew open the cockpit door, according to a person briefed on the investigation.
The plug door was eventually recovered in the backyard of a Portland school teacher.
WERE THERE PRIOR WARNINGS?
Pilots on the same Alaska Airlines aircraft reported that the auto pressurisation fail light had illuminated on three other occasions - Dec 7, Jan 3 and Jan 4.
The auto pressurisation fail light comes on when the pressure in the cabin changes at an unusually fast rate.
However, it is unclear if there are any connections between the three incidences and the one on Jan 5, said NTSB chair Jennifer Homendy.
She added that the airline had made a decision after the warnings to restrict the aircraft from making long flights over water to Hawaii so that it could return quickly to an airport if needed.
Alaska Airlines said earlier in a response to questions about the warning lights that aircraft pressurisation system write-ups were typical in commercial aviation operations with large planes.
"In every case, the write-up was fully evaluated and resolved per approved maintenance procedures and in full compliance with all applicable FAA regulations," said the airline.
A POSSIBLE DESIGN FLAW?
The latest mishap could stem from the manufacturing of the door plug that came loose, or bolts that were supposed to secure it, or from a quality control issue, said Scott Hamilton from aviation news outlet Leeham News.
"If it's indeed a quality assurance issue, whether it's in Spirit or at Boeing, I would say it's more than likely a narrow, quality assurance issue," he said, referring to Spirit Aerosystems, Boeing's main subcontractor.
"I think this is more of a one-off anomaly than I would a systemic issue," he said.
"For me, it is a very isolated problem," added Michel Merluzeau, an aeronautics specialist with consulting firm AIR. "I do not at all think it is a design problem."
He said evidence for this is the fact that the FAA ordered inspections that take just four to eight hours.
"We should be back to normal in about a week," said Merluzeau.
He said that the latest incident could be a result of supply chain and production problems that are currently affecting the commercial aviation sector.
For instance in 2020, as the pandemic raged and the US economy largely went into lockdown, Boeing stopped making planes for nearly a month.
As air travel fell off dramatically, Boeing laid off around 30,000 workers.
Boeing started hiring en masse again in 2022 but many experienced workers did not return to the company.
Related:
HAVE THERE BEEN SIMILAR BLOWOUT CASES?
There have been rare instances of holes opening in the fuselages of airliners. In most cases, they have been the result of metal fatigue in the plane's aluminium skin.
In the most horrific case, a flight attendant for Aloha Airlines was blown out of the cabin of a Boeing 737 over the Pacific Ocean in 1988 after an 18-foot-long chunk of the roof peeled away. Her body was never found.
The tragedy led to tougher rules for airlines to inspect and repair microscopic fuselage cracks before they tear open in flight.
In 2009, a hole opened in the roof of a Southwest Boeing 737 flying 35,000 feet over West Virginia. And in 2011, a five-foot-long gash unfurled in another Southwest Boeing 737, forcing pilots to make an emergency landing at a military base in Arizona. No one was injured in either of those cases, both of which were blamed on metal fatigue.
WHAT IS THE IMPACT ON BOEING?
The latest incident is yet another hit to Boeing's safety record.
The worst of Boeing's recent past came in the form of two crashes - of a Lion Air flight in October 2018, and an Ethiopian Airlines flight in March 2019 - that caused the deaths of 346 people in total and triggered the grounding of all 737 MAX planes for nearly two years.
Both tragedies occurred on 737 MAX 8 planes, the slightly smaller predecessor of the 737 MAX 9.
After protracted discussions with China's aviation regulator that involved design changes and test flights, the model returned to Chinese passenger service in January 2023.
Boeing's shares tumbled 8 per cent on Monday.
But even if the direct financial impact is contained, analysts said Boeing could face slower government approvals for new jets or on proposed repairs.
"The gravest injury in the most recent commercial jet accident is to Boeing's reputation," read the headline of a note from Morningstar.
Related:
IS THE 737 MAX 9 SAFE TO FLY?
Federal officials and airline executives in the US regularly tout the safety of air travel.
"We have the safest aviation system in the world. It is incredibly safe," said Homendy. "But we have to maintain that standard."
There has not been a fatal crash of a US airliner since 2009 when a Colgan Air plane operated for Continental crashed near Buffalo, New York, killing all 49 people on board and one on the ground.
The blowout is exceedingly rare in air travel, said Anthony Brickhouse, a professor of aerospace safety at Embry-Riddle Aeronautical University.
Brickhouse said fuselage panels sometimes tear off planes but he could not recall a previous incident that blew a gaping hole like the one that forced Friday's emergency landing.
Boeing chief executive Dave Calhoun said in a message to employees that "situations like this are a reminder that we must remain focused on continuing to improve every day".
"As operators conduct the required inspections, we are staying in close contact with them and will help address any and all findings," Boeing said late Monday.
"We are committed to ensuring every Boeing airplane meets design specifications and the highest safety and quality standards."