Alaska Airlines emergency: Fittings at the top of the door plug fractured, NTSB chair says

A door plug fell out of an Alaska Airlines flight Friday, National Transportation Safety Officials said.

The focus of the investigation into Friday's midair emergency on an Alaska Airlines flight is focused on the single aircraft, but could be broadened as the National Transportation Safety Board learns more, board Chief Jennifer Homendy said.

"However, at some point we may need to go broader. But right now we have to figure out how this occurred with this aircraft," Homendy said Tuesday on ABC News' "Good Morning America."

The door plug fell off the plane, a Boeing 737 Max 9, around 5:11 p.m. local time Friday as the aircraft with 171 passengers, including three babies and four unaccompanied minors, had climbed to 16,000 feet after taking off from Portland International Airport, according to the NTSB.

The Federal Aviation Administration said Tuesday, "Every Boeing 737-9 Max with a plug door will remain grounded until the FAA finds each can safely return to operation."

"The safety of the flying public, not speed, will determine the timeline for returning the Boeing 737-9 Max to service," the FAA said.