U.S. regulators on Saturday temporarily grounded 171 Boeing 737 MAX 9 jetliners for safety checks following a cabin panel blowout that forced a new Alaska Airlines jet carrying passengers to make an emergency landing.

A piece of fuselage tore off the left side of the jet as it climbed following takeoff from Portland, Oregon, en route to Ontario, California, on Friday, forcing pilots to turn back and land safely with all 171 passengers and six crew on board.

Several passengers suffered injuries. The plane had been in service for just eight weeks.

Late on Saturday, both Alaska Air and United Airlines (UAL.O) said they would halt use of some MAX 9 planes they had resumed using that day after inspections they believed would answer the Federal Aviation Administration (FAA)'s concerns.

Alaska said it was in talks "to determine what, if any, further work is required before these aircraft are returned to service."

The FAA decision is well short of the global grounding of Boeing (BA.N) MAX jets almost five years ago after two crashes that killed nearly 350 people.

Still, it is a blow to Boeing as it tries to recover from back-to-back crises over safety and the pandemic under heavy debt.

The FAA did not rule out further action as a probe began into the apparent structural failure, which left a rectangular hole in an area of fuselage reserved for an optional extra door but which is deactivated on Alaska's aircraft.