Volkswacht Bodensee - US opens safety probe into Boeing after Alaska Airlines incident

"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.

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 mitigating circumstances which you believe may be relevant to this case."

Boeing said Thursday that it would "cooperate fully and transparently with the FAA and the NTSB on their investigations."

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 National Transportation Safety Board investigators have suggested that the part was not affixed adequately.

Shares of Boeing fell 1.4 percent in afternoon trading.

F.Wagner--VB