US FAA extends Boeing MAX 9 grounding for new safety checks

The US aviation regulator has extended the grounding of Boeing 737 MAX 9 airplanes indefinitely for new safety checks and announced it will tighten oversight of Boeing itself after a cabin panel broke off a new jet in mid-flight.

As United Airlines and Alaska Airlines cancelled flights through Tuesday, the Federal Aviation Administration (FAA) 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 had said Monday the grounding would be lifted once they were inspected before saying more work was needed on planned checks.

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, the two US 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 US planemaker.

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

The Alaska Airlines aircraft, which had been in service for just eight weeks, took off from Portland, Oregon last Friday and was flying at 16,000 feet when the panel tore off the plane. Pilots flew the jet back to Portland, with only minor injuries among passengers.

On Thursday, the FAA announced a formal investigation into the MAX 9. FAA Administrator Mike Whitaker said the Alaska Airlines MAX 9 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.