The Federal Aviation Administration on Saturday ordered the grounding and immediate inspection of about 171 Boeing 737 Max 9 aircraft worldwide after a mid-flight emergency late Friday involving one of the planes operated by Alaska Airlines.

"The FAA is requiring immediate inspections of certain Boeing 737 MAX 9 planes before they can return to flight," FAA Administrator Mike Whitaker said in a statement.

The decision comes after an Alaska Airlines flight was forced to abruptly land in Portland, Ore., on Friday night.

Hours later, Alaska Airlines grounded and ordered a fleet-wide inspection of its Boeing 737 Max 9 aircraft. On Saturday, the airline said there were "no concerning findings" after inspecting more than a quarter of its planes so far.

Alaska Airlines added that it will return planes to service after their inspections are completed "with our full confidence." The airline expects inspections on all 65 of its Boeing 737 Max 9s to be completed in the next few days.

Southwest Airlines and American Airlines told NPR they do not carry Boeing 737 Max 9s. While they do carry Boeing 737 Max 8s, both airlines said the model does not raise any concerns.

Meanwhile, India's aviation regulator ordered the immediate inspections of all Boeing Max 737 aircraft owned by domestic operators, Reuters reported. None of India's air operators are believed to carry the model that abruptly landed in Portland on Friday.

The incident comes less than four years after Boeing Max aircraft were allowed to fly passengers in the U.S. All Boeing Max planes were grounded worldwide in 2019 after two deadly crashes involving Max 8 jets.

Last week, Boeing urged the FAA to check its 737 Max jets for loose bolts after the discovery of at least two planes with improperly tightened nuts.

What happened Friday night

Alaska Airlines Flight 1282 took off from Portland, Ore., shortly after 5 p.m. PST Friday, bound for Ontario, Calif. According to social media posts, it appeared that a window and piece of fuselage had broke off midair — leaving a gaping hole on the plane's left side.

Oxygen masks were deployed as the aircraft quickly returned to Portland International Airport at 5:26 p.m. PST, according to FlightAware.com. The flight had 171 passengers and six crew members on board. No casualties or serious injuries were reported.

KPTV reported that the local fire department arrived on scene and treated minor injuries. At least one person needed further medical attention.

Following the emergency landing, Alaska Airlines said it was grounding all of its Boeing 737 Max 9 aircraft until it could inspect each plane. The National Transportation Safety Board and FAA are investigating the incident.

"We are working with Boeing and regulators to understand what occurred tonight, and will share updates as more information is available," Alaska Airlines CEO Ben Minicucci said in a statement.

Boeing 737 Max' troubled history

The aircraft's safety problems were under global scrutiny after deadly crashes in Indonesia in 2018 and Ethiopia in 2019 — which killed a total of 346 people. After a worldwide halt in 2019, Boeing 737 Max completed its first U.S. commercial flight in December 2020.

Investigators determined that the company's newly rolled-out flight control system was partly to blame. In both incidents, the system known as MCAS acted on a faulty sensor and forced both planes to erroneously nosedive even as the pilots attempted to regain control.

But it wasn't just manufacturing flaws. A report by the Department of Transportation's inspector general found that the company failed to tell regulators about critical changes it made to its flight control system. The report concluded that Boeing did this in order to expedite the plane's certification process.

In 2021, Boeing agreed to pay more than $2.5 billion to settle a criminal charge related to the crashes. Under the deal, Boeing was ordered to pay a criminal penalty of $243.6 million while $500 million went toward a fund for the families whose loved ones were killed in the crashes. Much of the rest of the settlement was marked off for airlines that had purchased the troubled 737 Max planes.