Canceled flights are piling up as Alaska and United are stuck without their grounded Boeing jets

PORTLAND, Ore. — Alaska Airlines and United Airlines grounded all of their Boeing 737 Max 9 jetliners again on Sunday while they waited to be told how to inspect the planes to prevent another inflight blowout like the one that damaged an Alaska jet.

Alaska Airlines had returned 18 of its 65 737 Max 9 aircraft to service Saturday, less than 24 hours after part of the fuselage on another plane blew out three miles (4.8 kilometers) above Oregon.

The reprieve was short-lived.

The airline said Sunday that it received a notice from the Federal Aviation Administration that additional work might be needed on those 18 planes.

Alaska said that it had canceled 170 flights — more than one-fifth of its schedule — by mid-afternoon on the West Coast because of the groundings.

“These aircraft have now also been pulled from service until details about possible additional maintenance work are confirmed with the FAA,” the airline said in a statement.

“We are in touch with the FAA to determine what, if any, further work is required.”

United Airlines said it had scrapped about 180 flights Sunday while salvaging others by finding other planes not covered by the grounding.

Alaska and United are the only U.S. airlines that fly the Max 9.

United said it was waiting for Boeing to issue what is called a multi-operator message, which is a service bulletin used when multiple airlines need to perform similar work on a particular type of plane.

Boeing is working on a bulletin but had not yet submitted it to the FAA, according to a person familiar with the situation.

A panel used to plug an area reserved for an exit door on the Max 9 blew out Friday night shortly after Alaska Airlines flight 1282 took off from Portland, Oregon. The depressurized plane, carrying 171 passengers and six crew members, returned safely to Portland International Airport with no serious injuries.

Hours after the incident, the FAA ordered the grounding of 171 Max 9s including all those operated by Alaska and United until they could be inspected. The FAA said inspections will take four to eight hours.

Boeing has delivered 218 Max 9s worldwide, but not all of them are covered by the FAA order.

They are among more than 1,300 Max jetliners sold by the aircraft maker. The Max 8 and other versions of the Boeing 737 are not affected by the grounding.

U.S. Sen. Maria Cantwell, D-Wash., chair of the Senate’s Commerce, Science and Transportation Committee, said she agreed with the decision to ground the Max 9s.

“Safety is paramount. Aviation production has to meet a gold standard, including quality control inspections and strong FAA oversight,” she said in a statement.

Investigators from the National Transportation Safety Board searched Sunday for the paneled-over exit door that blew out from flight 1282. They have a good idea of where it landed, near Oregon Route 217 and Barnes Road in the Cedar Hills area west of Portland, NTSB Chair Jennifer Homendy said.

“If you find that, please, please contact local law enforcement,” she said.