US regulator grounds Boeing MAX 9 indefinitely, flights canceled to Tuesday

WASHINGTON, Jan 12 (Reuters) - The U.S. aviation regulator on Friday extended the grounding of Boeing 737 MAX 9 airplanes indefinitely and announced it will tighten oversight of Boeing BA.N itself after a cabin panel broke off a new jet in mid-flight.

As United Airlines UAL.O and Alaska Airlines canceled flights through Tuesday, the Federal Aviation Administration also said it will require another round of inspections before it will consider putting the jets back in service.

Under more stringent supervision, the regulator will audit the Boeing 737 MAX 9 production line and suppliers and consider having an independent entity take over from Boeing certain aspects of certifying the safety of new aircraft that the FAA previously assigned to the planemaker.

The FAA said the continued grounding of 171 planes with the same configuration as the one in the incident was "for the safety of American travelers." The regulator said Monday the grounding would be lifted once they were inspected.

But on Friday, the FAA said 40 of the planes must be reinspected, then the agency will review the results and determine if safety is adequate to allow the MAX 9s to resume flying.

Alaska Airlines and United Airlines UAL.O, the two

U.S. airlines that use the aircraft involved, have had to cancel hundreds of flights in the last week due to the grounding as a widening crisis engulfed the U.S. planemaker.

Alaska and United on Friday both canceled all MAX 9 flights through Tuesday and United canceled some additional flights in the following days.

Boeing shares closed down 2.2% on Friday and are down nearly 12% since the Jan. 5 incident. Confidence in Boeing has been shaken since a pair of MAX 8 crashes in 2018 and 2019 killed 346 people and led Congress to pass sweeping reforms to certification of new airplanes.

On Thursday, the FAA announced a formal investigation into the MAX 9, which the FAA said had "significant problems" and noted Boeing's history of production issues.

The National Transportation Safety Board (NTSB) is investigating if the MAX 9 jet in the Alaska episode was missing or had improperly tightened bolts.

FAA Administrator Mike Whitaker told Reuters Friday he sees the MAX 9 problems as a manufacturing issue, not a design problem. Noting years of production problems at Boeing, he said: "Whatever's happening isn't fixing the problem and requires an extensive review. We are becoming increasingly focused on the manufacturing process."