Alaska, United Airlines identify issues with multiple grounded Boeing 737 MAX 9 jets

Inspections of grounded Boeing 737 MAX 9 aircraft are already underway at some airlines. But it seems the Alaska Airlines jet that lost a door plug Friday night was just the canary in the coal mine for issues with the plane’s finishes.

United Airlines, the largest operator of the MAX 9 in the U.S., with 79 of the aircraft in its fleet, confirmed in a statement to USA TODAY that its preliminary inspections have identified problems on multiple jets.

“Since we began preliminary inspections on Saturday, we have found instances that appear to relate to installation issues in the door plug – for example, bolts that needed additional tightening. These findings will be remedied by our Tech Ops team to safely return the aircraft to service,” the statement said.

Alaska Airlines also said in a statement Monday night that it had begun preliminary inspections on its MAX 9 aircraft and found problems on multiple planes.

"As our maintenance technicians began preparing our 737-9 MAX fleet for inspections, they accessed the area in question. Initial reports from our technicians indicate some loose hardware was visible on some aircraft," the statement said.

Just after 8 a.m. ET Tuesday, both Alaska and United were reporting significant cancelations for the day. United had 191 canceled flights, or about 7% of its schedule, while Alaska had 106 cancelations, about 16% of its schedule, according to FlightAware.

Both airlines are offering flexible rebooking policies for passengers affected by the grounding. Alaska's systemwide policy can be seen by clicking here, and United's various waivers for today by clicking here.

United said it expects each inspection to be performed by a team of five technicians and will take several hours per aircraft. The process will include removing two rows of seats near the door plug, inspecting and verifying that the plug was installed properly, opening the door to check the area and its seal, and then resecuring the plug.

Alaska said it will be reporting the findings of its inspections to the FAA, per regulatory requirements.

"The safety of these aircraft is our priority and we will take the time and steps necessary to ensure their airworthiness, in close partnership with the FAA," the airline's statement said.

Zach Wichter is a travel reporter for USA TODAY based in New York. You can reach him at zwichter@usatoday.com

This article originally appeared on USA TODAY: Alaska and United confirm finding defects in multiple 737 MAX 9 jets