Flights have been disrupted and thousands of passengers face cancellations after multiple US airlines grounded Boeing 737 Max 9s following an in-flight blowout over Oregon.

The US aviation regulator has mandated grounding 171 Boeing 737 Max 9s for immediate checks after part of a fuselage from an Alaska Airlines plane detached mid-flight on Friday.

Alaska Airlines has warned that flight disruptions are likely to persist into the next week, with United Airlines grounding 79 of its planes.

The cancellations are expected to primarily affect US flights after the Federal Aviation Administration (FAA) ordered instant inspections of the global 737 Max 9 fleet. Each required check is estimated to take around four to eight hours per aircraft.

The European Union Aviation Safety Agency (EASA) is adopting the FAA's approach, but expects minimal flight disturbances in Europe. EASA believes that no European airlines operate Max 9s with the configuration subject to the FAA order.

Notably, London Heathrow Airport, one of the world's busiest, reported no flight impacts due to the situation.

The majority of the impacted planes are owned by US airlines. United Airlines has grounded all 79 of its Max 9 planes, while Alaska Airlines disclosed the cancellation of 160 flights on Saturday, affecting around 23,000 passengers.

Boeing welcomed the FAA's decision and affirmed its ongoing close collaboration with the regulator.

During the recent incident involving Alaska Airlines Flight 1282 from Portland, Oregon, to Ontario, California, the aircraft reached 16,000ft (4,876m) when a substantial section of its outer shell detached soon after takeoff.

Passengers witnessed the night sky through the gaping hole in the fuselage as the plane made an emergency landing. Some described the gap as "as wide as a refrigerator," with insulation material and debris being visible.

Following the incident, Alaska Airlines' CEO Ben Minicucci expressed gratitude to the flight crew for their response, apologizing to those onboard for the harrowing experience. The airline grounded 65 of its 737 Max 9 planes voluntarily and carried out in-depth inspections on 18 of them. However, these have now been removed from service in compliance with the FAA order.

The affected section of the aircraft was a plug door, located near the rear and specific to certain configurations of the Max 9 planes.

The National Transportation Safety Board (NTSB) has initiated an investigation into the Alaska incident. Fortunately, no passenger was seated next to the affected area. Efforts are underway to locate the fallen door in the community of Cedar Hills, around seven miles west of downtown Portland.

Boeing's 737 Max faced extensive scrutiny after two fatal crashes in 2019 led to its grounding for 18 months. However, experts note that the recent Alaska Airlines incident is unrelated to the previously grounded issues and emphasize the aircraft's strong safety record since its return to service.

Boeing has been working on increasing the delivery pace of its 737 Max jets after resolving a supply error that prompted lengthy inspections. To date, approximately 1,300 737 Max aircraft have been delivered to customers.

Last month, the FAA urged airlines to inspect Max models for possible loose bolts in rudder control systems. Photo by Clemens Vasters, Wikimedia commons.