Alaska Airlines and United Airlines grounded all 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, according to the Associated Press.

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 in the air above Oregon. The return did not last long. The airline said Sunday that it had received a notice from the Federal Aviation Administration that additional work might be needed on those 18 planes.

Alaska said 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 said it had scrapped about 180 flights Sunday while maintaining others by finding other planes not covered by the grounding. The airline said it was waiting for Boeing to issue a multi-operator message, which is a service bulletin used when multiple airlines need to perform similar work on a particular type of plane.
Alaska and United are the only US airlines that fly the Max 9.

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