Alaska Airlines has canceled all scheduled Boeing 737 Max 9 flights through Saturday, continuing to await official instructions from Boeing and the FAA that will allow it to begin inspections.
The cancellations will amount to between 110 and 150 flights per day.
"We hope this action provides guests with a little more certainty, and we are working around the clock to re-accommodate impacted guests on other flights," the carrier said Wednesday.
Meanwhile, United said that would cancel 167 Max 9 flights on Wednesday while preventing approximately 45 cancellations by using other aircraft.
"We expect significant cancellations on Thursday, as well," the airline said.
The FAA grounded approximately 171 Max 9 aircraft, most of them operated by Alaska or United, after the Jan. 5 incident in which a rearward exit door plug on an Alaska Max 9 blew out after takeoff from Portland, Ore. Such plugs are used by some Max 9 operators in place of exit doors that would be required if the plane were configured with a larger number of seats.
Alaska Airlines Flight 1282 was able to descend from its altitude of about 16,000 feet and land back in Portland without casualties.
During the early stages of its investigation into the incident, the National Transportation Safety Board (NTSB) had zeroed in on four bolts that were missing from the Alaska door plug, which was recovered from the garden of a Portland-area schoolteacher on Monday morning.
United has also reported that preliminary inspections of grounded Max 9 aircraft turned up what appear to be loose bolts on some emergency exit door plugs. And Alaska said that its technicians have noted visible "loose hardware" on some of its Max 9 planes.
Speaking to Boeing staff during a Tuesday meeting, CEO Dave Calhoun said the company will work closely with NTSB investigators.
"We are going to approach this, number one, acknowledging our mistake," Calhoun said. "We are going to approach it 100% in complete transparency every step of the way."