SINGAPORE, Jan 9 — A type of aircraft grounded in the United States after a piece of fuselage broke off mid-flight does not fly to and from Singapore, the authorities here said today in response to TODAY’s queries.

The Civil Aviation Authority of Singapore (CAAS) made the statement after a door plug, or panel, broke off a Boeing 737 MAX 9 aircraft operated by Alaska Airlines on Friday.

This incident prompted the US Federal Aviation Authority (FAA) to ground 171 Boeing 737 MAX 9s operated by US airlines or in US territory for safety checks.

"CAAS is in close contact with the FAA and Boeing and monitoring the issue closely,” said Mr Alan Foo, senior director for safety regulation group at CAAS, today.

A spokesperson for Singapore Airlines (SIA) said SIA and its budget carrier Scoot do not operate any Boeing 737 MAX 9 aircraft, and the airlines are unaffected by FAA’s directive.

Seven minutes after taking off from Oregon in the US, a door plug on the fuselage of Alaska Airlines aircraft blew out.

This depressurised the plane, causing oxygen masks to drop from the ceiling. A gaping hole was also left on the side of the plane.

A door plug seals unused emergency exits on planes, and looks similar to a normal window. The two seats next to the door plug which tore off on the Alaska Airlines plane were empty at the time.

None of the 171 passengers, including four unaccompanied minors, three babies seated in their caregivers’ laps and six crew members, were seriously injured during the incident.

The troubled history of Boeing’s 737 max

This is not the first time Boeing’s 737 planes have been under the spotlight.

An earlier iteration of the 737 MAX 9, the 737 MAX 8, was involved in two deadly crashes which sparked a crisis for the US aircraft maker and the grounding of all 737 MAX planes worldwide for nearly two years from March 2019.

While Singapore Airlines operates 16 Boeing 737 MAX 8 aircraft, this model is not the subject of the FAA’s latest directive, which relates only to the 737 MAX 9.

Transport analyst Terence Fan of the Singapore Management University (SMU) said that the door plug that flew off the Boeing 737 Max 9 is "not ordinarily offered” in the 737 Max 8.

All Boeing 737 MAX planes were grounded globally in March 2019 for nearly two years after two crashes involving the Boeing 737 MAX 8 within five months.

In October 2018, all 189 passengers and crew onboard a Lion Air 737 MAX 8 died after the plane crashed into the Java Sea minutes after take-off. Five months later in March 2019, an Ethiopian Airlines plane crashed, killing all 157 on board.

US investigations found that Boeing had failed in the design and development of its 737 MAX planes.

The aviation company eventually agreed on a US$2.5 billion (RM15 billion) settlement with the US Justice Department in 2021, which included a penalty of US$243.6 million for not being transparent with FAA’s aircraft evaluation group.

Other Boeing planes have also been involved in blowout cases, though most were the result of metal fatigue in the plane’s aluminium skin.

For example, a Boeing 737-300 passenger jet operated by Southwest Airlines rapidly depressurised while cruising in Arizona in the US, resulting in a roughly 150cm long hole in the plane’s fuselage.

Differences in the Boeing 737 MAX 8, 9 and 10

The Boeing 737 MAX 9 had its maiden flight in April 2017 and has a longer fuselage than the 737 MAX 8, which had its first flight in 2016.

Professor Fan of SMU said that this incident highlights some potential concerns about Boeing 737 MAX 10s, which feature a longer fuselage than both the Boeing 737 MAX 9 and MAX 8.

Boeing said in October 2023 that the FAA had cleared it to begin certification flight testing of the 737 MAX 10. It also said then that the first aircraft will be delivered in 2024.

"The same ‘door’ is on the MAX 10, but because of its longer fuselage and higher passenger capacity, airlines likely have to use the ‘door’ as a regular emergency door, rather than disable it as in Alaska Airlines’ MAX 9,” said Prof Fan.

Alaska Airlines had disabled its MAX 9’s emergency door by installing a door plug as it had configured its plane with fewer seats and could meet FAA’s safety requirements without the door, he added.

"For now, it is very likely that there is a possibility of either a manufacturer’s fault or some missed procedures upon the aeroplane being handed to its operator,” he said.

"As we understand, the Boeing 737 MAX 9 was only delivered to Alaska Airlines a few months ago, in late 2023.”

News outlet Reuters reported that Spirit AeroSystems, Boeing’s largest supplier of commercial planes that builds fuselage and other parts for Boeing MAX jets, manufactured the door plug but fits them semi-completed.

Boeing then removes the plug as part of the production process in its factory in Washington.

Since inspections started, Alaska Airlines and United Airlines have reported loose parts on multiple grounded Boeing 737 MAX 9 aircraft.

The Alaska Airlines plane had also some issues as its auto pressurisation fail light turned on during three flights before the blowout last Friday — though several experts warn that there is no clear correlation between the two incidents.

Due to these alerts, the airline had temporarily restricted the plane from being flown over water to Hawaii. It had also asked maintenance crews to examine the light, though this had not been done before the door plug came off.

What are airlines doing following this incident?

According to aviation analytics firm Cirium, eight airlines use Boeing 737 MAX 9 planes: Alaska Airlines, United Airlines, Panama’s Copa Airlines, Aeromexico, Turkish Airlines, Icelandair, FlyDubai, and SCAT Airlines in Kazakhstan.

A spokesperson for FlyDubai told the New York Times that three 737 MAX 9 aircraft in its fleet have completed necessary safety checks in the past two years. The firm said it is waiting for direction from Boeing before carrying out any further inspections.

Alaska Airlines has cancelled 60 flights yesterday and said that disruptions to its flights are expected to continue at least until the middle of this week.

In response to the Alaska Airlines incident, a Boeing spokesperson said that the firm is "working to gather more information and are in contact with our airline customer”.

The company also said that it fully supports the FAA’s decision to require inspections of its 737 MAX 9 airplanes with the same configuration as the affected airplane. It is also supporting investigations into the incident. — TODAY