U.S. regulators have now ordered the temporary grounding of 171 of the jets.

The decision came after a piece of fuselage tore off the left side of the aircraft late Friday, forcing pilots to turn back and safely land a plane that was en route to Ontario, California with 171 passengers and six crew on board.

"...yeah, I'm sleeping and I just feel the plane drop. And it wasn't like any other turbulence just because the masks came down too. So that's when I knew, like, oh, gosh, this is something way different. And yeah, I started freaking out."

Emma Vu was a passenger on the plane

"In the moment...a lot of tears. I just didn't know what was going on. But I think I will say that I feel that a lot of people around me were a lot calmer than I would have thought for a situation like this."

The Federal Aviation Administration's decision falls well short of a full indefinite safety ban comparable to the grounding of all MAX-family jets almost five years ago following major crashes in 2018 and 2019.

Alaska Airlines CEO Ben Minicucci said in a statement that its fleet of 65 similar planes would be returned to service only after precautionary maintenance and safety inspections, which he expected to be completed in the "next few days."

There were no immediate indications of the cause of the apparent structural failure Friday, nor any reports of injuries.

The National Transportation Safety Board said on Saturday that a team of experts in structures, operations and systems would arrive on the scene later that day.

Boeing also said it was looking into the incident.

According to FAA data, the new MAX 9 was delivered to Alaska Airlines in late October and certified in early November.