Some Boeing jets to remain grounded as investigators search for part that blew off plane

(Reuters) - U.S. regulators on Sunday said certain Boeing-made jets would remain grounded until deemed safe to fly again, as authorities conduct a search near Portland, Oregon for a missing panel that blew off a new Boeing (BA.N) 737 MAX 9 jet during a flight on Friday.

The U.S. Federal Aviation Administration (FAA) on Saturday grounded 171 Boeing jets installed with the same panel after the emergency landing of the plane that had been in service for just eight weeks. “They will remain grounded until the FAA is satisfied that they are safe,” the agency said in a statement on Sunday.

The so-called door plug tore off the left side of an Alaska Airlines (ALK.N) jet following takeoff from Portland en route to Ontario, California, forcing pilots to turn back and land safely with all 171 passengers and six crew on board, with only a few minor injuries reported.

The panel, put in place on some planes in lieu of an additional emergency exit, is likely to have landed somewhere in the western suburbs of Portland, but has not yet been found. Authorities have asked the public for help finding the panel.

The accident has put Boeing back under scrutiny as it awaits certification of its smaller MAX 7 as well as the larger MAX 10, which is needed to compete with a hot-selling Airbus (AIR.PA) model.

The vast majority of the MAX 9 jet model used in the United States are operated by United Airlines (UAL.O) and Alaska Airlines (ALK.N), while Turkish Airlines, Panama’s Copa Airlines and Aeromexico also grounded jets for inspections.

Airlines must inspect the panel and carry out any necessary repairs. Before U.S. airlines can start flying the planes, the FAA must additionally agree to detailed inspection criteria proposed by Boeing. It was unclear if it would do so on Sunday.

Alaska Airlines halted the use of 18 MAX 9 planes on Saturday that it had resumed using following earlier maintenance checks on the FAA’s order.

On Sunday, it canceled 163 flights, or 21%, and said travel disruptions from the grounding are expected to last through at least midweek. United canceled 230 flights on Sunday, or 8% of scheduled departures.

“I imagine this was a pretty terrifying event. We don’t often talk about psychological injuries but I am sure that occurred here,” National Transportation Safety Board (NTSB) Chair Jennifer Homendy told reporters on Saturday, adding that it was too early to say what caused the event.