NEW YORK, United States - The US Federal Aviation Administration (FAA) announced Thursday it is launching a safety probe into Boeing following last week's near-catastrophic incident on an Alaska Airlines-operated 737 MAX.

"This incident should have never happened and it cannot happen again," the FAA said in a statement, after a panel known as a "door plug" blew out of the plane over the western US state of Oregon.

There were no fatalities or serious injuries after Alaska Airlines safely executed an emergency landing in the January 5 incident, but investigators with the National Transportation Safety Board have said the episode could have resulted in serious harm.

The FAA probe -- which could result in a financial penalty on Boeing -- marks an escalation by the agency into the episode, the first major in-flight safety issue on a Boeing plane since the fatal 2018 and 2019 737 MAX crashes that led to a lengthy grounding of the aircraft.

Besides the incident itself, the FAA also said it was investigating "additional discrepancies on other Boeing 737-9 airplanes," according to a letter to the company that gave it 10 days to respond.

That is an allusion to reports from Alaska and United Airlines of "loose" hardware on delivered planes found in preliminary investigations of the jets.

"Boeing's manufacturing practices need to comply with the high safety standards they're legally accountable to meet," the FAA said in a statement.

The letter cited a statute requiring Boeing to ensure that "completed products" are "in a condition for safe operation."

The agency said Boeing's response to the FAA should include the "root cause" of the incident, actions to prevent a recurrence and any relevant mitigating circumstances.

Boeing said Thursday that it would "cooperate fully and transparently" with the investigations.

Aviation consultant Jeff Guzzetti, a former head of the FAA's investigation division who also worked at the NTSB, said the "sweeping" language in the FAA letter suggests the probe could be broadened to Boeing's production processes, including into other planes besides the MAX.

Boeing will need to spell out its investigative findings, even if it has not determined a root cause, said Guzzetti, adding that the probe could take months and result in fines.

Guzzetti said he is hoping that the Alaska Airlines problem was a "one off" but "if it turns out to be many aircraft, that will be disturbing to me."

- 'Quality escape' -

US regulators have grounded 171 737 MAX 9 planes with the same configuration as the jet involved in last Friday's incident.

Earlier this week, Boeing Chief Executive Dave Calhoun took responsibility for the incident, vowing "complete transparency" as the aviation giant tries to pivot from its latest crisis.

In an interview with CNBC on Wednesday, Calhoun described the incident as a "quality escape," and said the company was still in fact-finding mode.

"We're going to want to know what broke down in our gauntlet of inspections, what broke down in the original work that allowed for that escape to happen," Calhoun said.

The affected door plug panel is used to fill an unneeded emergency exit in planes, and NTSB investigators have suggested that the part was not affixed adequately.

The FAA has been working with Boeing on inspection instructions for the 737 MAX 9 planes before they can be returned to service.

Alaska has canceled flights on the aircraft through Saturday, January 13, resulting in between 110 and 150 flight cancellations per day, the company said Wednesday.

Shares of Boeing fell 1.8 percent in afternoon trading.