Boeing shares tumble after panel blows out midflight, FAA grounds dozens of 737 Maxes

• Boeing shares tumbled 8% on Monday.
• The Federal Aviation Administration grounded dozens of Boeing Max 737 9 planes after a door plug blew out midair during an Alaska Airlines flight.
• Friday's accident occurred just as Boeing has been trying to ramp up output of the Max and brings fresh scrutiny of Boeing's quality assurances.

Shares of Boeing tumbled 8% on Monday as investors digested the news that the Federal Aviation Administration had ordered airlines to ground dozens of Boeing 737 Max 9 aircraft for urgent inspections.

The FAA issued the order on Saturday after a door plug blew out in the middle of an Alaska Airlines flight on Friday when the nearly brand-new aircraft was flying at around 16,000 feet.

Boeing stock recovered some of its losses midmorning after the aircraft manufacturer issued 737 Max 9 inspection instructions to airlines, a key step toward resuming flights. Shares were last down around 6%.

Shares of Alaska Air closed flat. Spirit AeroSystems, which makes fuselages for the 737 Max, fell 11%.

The incident again thrusts Boeing into the spotlight. CEO Dave Calhoun has been trying to assure investors that Boeing is getting back on better footing after a string of problems, including two crashes that killed 346 people, pandemic supply chain havoc and a series of quality defects.

Large-scale groundings by aviation authorities are rare, but the FAA has been scrutinizing Boeing and its bestselling 737 Max since the fatal crashes in 2018 and 2019. Boeing said it agrees with the FAA's decision to ground the Max 9 planes for inspections. It was working on drafting instructions with federal regulators for airlines to begin inspections.

Friday's accident occurred just as Boeing has been trying to ramp up output of the Max.

"An escape of this nature makes one question the quality control of the 737 delivery ramp and the impact of inexperienced labor on both Boeing and its supply chain," Bank of America aerospace analyst Ron Epstein wrote in an analyst note Monday, adding that the plane was delivered just months earlier. "This aircraft still had 'new airplane' smell and the sticker price in its window."

The FAA on Saturday said around 171 planes would be affected by its emergency airworthiness directive, which applies to U.S. airlines and carriers operating in U.S. territory. Alaska Airlines and United Airlines are the largest operators of the 737 Max 9 model, of which more than 200 are flying worldwide, according to Cirium.

United Airlines has the most with 79 and Alaska has 65, while the remainder are spread across other airlines.

Shares of United rose more than 2% Monday.

'Considerable pressure'

The National Transportation Safety Board over the weekend described a harrowing few minutes onboard the Alaska Airlines flight, starting with a loud bang and a force so violent it tore off headrests and seatbacks, and blew open the cockpit door.

A schoolteacher found the blown-out plane panel in his backyard, the NTSB said late Sunday.

Images shared on social media showed a hole in the side of the aircraft and passengers using oxygen masks. The flight — Alaska Airlines Flight 1282 — returned to Portland, Oregon, shortly after departing for Ontario, California.

Russ Mould, investment director at AJ Bell, noted that Friday's incident is the latest in a "string of problems for the company," and suggested airlines using 737 Max planes will be "thinking long and hard about their future aircraft requirements."

Shares of Boeing's European rival Airbus gained 2.5% in Paris as investors speculated that it could take market share from the U.S. powerhouse.

"There are naturally questions being asked about the quality checks and whether Boeing is trying to do too much too fast," Mould said.

"Boeing's management will be under considerable pressure from the regulators and customers to explain what's going on, which means considerable headwinds ahead for the business. It's no wonder investors have raced to sell the shares as the risks to the investment case have just shot up."

Don't miss these stories from CNBC PRO:

• There's one stock Wall Street loves so much for 2024 that five analysts in one day picked it as their favorite
• Morgan Stanley names its top stocks for 2024, including this streaming giant
• Investing tips from Warren Buffett to start the new year on the right foot
• Goldman sees a 50% gain ahead for this Chinese electric vehicle stock, initiates with buy rating
• 'Twice as cheap': These stocks' discount to the S&P 500 is double its average, Ritholtz's Brown says

Correction: This story has been updated to correct that there are more than 200 737 Max 9s in service, including 79 operated by United Airlines and 65 operated by Alaska Airlines.