By David Shepardson
WASHINGTON (Reuters) - The Federal Aviation Administration (FAA) said on Wednesday that inspections of an initial group of 40 Boeing 737 MAX 9 airplanes have been completed, a key hurdle to eventually ungrounding the planes after a Jan. 5 cabin panel broke off in mid-flight on a new Alaska Airlines jet.
On Friday, the FAA had said 40 of 171 grounded planes needed to be re-inspected before the agency would review the results and determine if it is safe to allow the Boeing MAX 9s to resume flying. The FAA agency on Wednesday it will "thoroughly review the data" before deciding if the planes can resume flights.
The incident has shaken confidence in Boeing's planes a few years after a pair of crashes killed 346 people and sparked investigations into the company's production processes. On Wednesday, the heads of Boeing and supplier Spirit AeroSystems, which made the panel, met with Spirit employees in Kansas, while regulators answered questions from U.S. senators in a closed-door hearing in Washington.
Boeing shares have lost roughly 20% of their value since the beginning of the year.
The National Transportation Safety Board (NTSB) and FAA briefed senators on the Commerce Committee for more than an hour on the investigation into why the MAX 9 cabin panel - a door plug for an unused emergency exit on those planes - blew out, leaving a gaping hole.
NTSB Chair Jennifer Homendy said the board still did not know what went wrong, but was casting a wide net for potential issues, and said the NTSB will be looking at numerous records related to the door plug.
Homendy said the door plug on the MAX 9 was produced by a Spirit AeroSystems facility in Malaysia. She said the NTSB is looking at the door plug transfer from Malaysia to Wichita and then onto the fuselage, along with the shipment by rail to Boeing's Renton, Washington facility and then work by Boeing "to ensure quality assurance."
Ohio Senator J.D. Vance said the door plug "gets put on and taken off a lot and it is not really clear at what step of the process there was a failure here."
Other senators said there remained many unanswered questions.
"Who's screwed up? We don't know, but it's obvious somebody screwed up," said Senator Ted Cruz, the top Republican on the panel. "This investigation needs to find out where the mistake was, what caused this accident, and critically what needs to be done to make sure it doesn't happen again."
Senate Commerce Committee chair Maria Cantwell said she plans to hold a hearing on the issue and wants to make sure the FAA is ensuring strong oversight of Boeing.
Alaska Airlines and United Airlines, the two U.S. carriers that use the aircraft and completed the inspections, have had to cancel hundreds of flights since last week and have canceled all MAX 9 flights through Wednesday.
United declined to comment.
Alaska CEO Ben Minicucci said in a video Wednesday the grounding impacted 20% of its fleet, adding that the airline "will return these aircraft to service only when all findings have been fully resolved and meet the stringent standards of Boeing, the FAA and Alaska Airlines."
Boeing did not immediately comment.
Spirit AeroSystems said it was "supporting Boeing's efforts with the FAA and the affected airlines as they inspect the 737-9 fleet and work to safely return those airplanes to service."
Boeing on Tuesday named retired U.S. Navy admiral Kirkland H. Donald to advise the planemaker's CEO on improving quality control. He and a team will evaluate quality practices at Boeing Commercial Airplanes and its supply chain, and provide recommendations to Boeing CEO David Calhoun and the board of directors.
Calhoun was visiting Spirit AeroSystems' production facilities in Wichita, Kansas, on Wednesday to speak with employees alongside that company's CEO, Pat Shanahan.
(Reporting by David Shepardson and Valerie Insinna; editing by Bill Berkrot and Nick Zieminski)