The Federal Aviation Administration said Thursday it is conducting an investigation into Boeing's 737 Max 9 aircraft following Friday's mid-air blowout of a door plug on an Alaska Airlines flight.

"This incident should have never happened and it cannot happen again," the FAA said in the statement.

The agency said the probe will examine whether Boeing "failed to ensure" whether the jet conformed to its design and whether its aircraft "were in a condition for safe operation in compliance with FAA regulations." It added that the investigation stems from the door plug's blowout and "additional discrepancies."

"We will cooperate fully and transparently with the FAA and the [National Transportation Safety Board] on their investigations," Boeing said in a statement.

Boeing President and CEO Dave Calhoun addressed the incident at a meeting with employees Tuesday. 

"We're going to approach this number one acknowledging our mistake," Calhoun said in the meeting, a Boeing spokesperson confirmed to CBS News. "We're going to approach it with 100% and complete transparency every step of the way. We are going to work with the NTSB who is investigating the accident itself to find out what the cause is. We have a long experience with this group. They're as good as it gets."

The blowout occurred just minutes after an Alaska Airlines flight left Portland, Oregon, forcing it to make an emergency landing Friday night, the agency said in a letter. 

Following the January 5 incident, Alaska Airlines and United Airlines  — the only U.S. carriers who operate the 737 Max 9 — said they found loose bolts on door plugs on several of their Max 9 aircraft. The FAA said Tuesday that every 737 Max 9 plane with a door plug will remain grounded until the agency determines that the jets can safely return to service. In total, 171 of the Boeing jets are equipped with plugs.

"Boeing's manufacturing practices need to comply with the high safety standards they're legally accountable to meet," the agency said Thursday, adding, "The safety of the flying public, not speed, will determine the timeline for returning the Boeing 737-9 Max to service."

In:
• Federal Aviation Administration
• Boeing
• Alaska Airlines