Thousands of passengers face flight cancellations after major US airlines grounded dozens of Boeing jets after a mid-flight blowout over Oregon.
The US aviation regulator said 171 Boeing 737 Max 9s must be grounded for checks after part of an Alaska Airlines plane’s fuselage fell off on Friday.
Alaska said flight disruptions are expected to last into next week. United Airlines has grounded 79 planes.
Disruptions are likely to primarily affect flights in the US.
It follows regulator the Federal Aviation Administration (FAA) ordering “immediate inspections” of 737 Max 9s worldwide.
Required inspections would take around four to eight hours per aircraft, it said.
The European Union Aviation Safety Agency (EASA) is following the FAA approach, but flight disruptions on the continent are expected to be minimal.
EASA said it believes no European airlines operate Max 9s with the configuration covered by the FAA order.
One of the world’s largest intercontinental airports, London Heathrow, said there was no impact on flights.
The bulk of the affected planes are owned by US airlines. United Airlines has grounded all 79 of its Max 9 planes.
Alaska said it cancelled 160 flights on Saturday, affecting about 23,000 passengers.
Other airlines which also fly the planes have temporarily taken them out of service.
Boeing said it welcomed the FAA’s decision, adding its teams were in close contact with the regulator.
During Friday’s incident, Alaska Airlines flight 1282 from Portland, Oregon, to Ontario, California, reached 16,000ft (4,876m) when it began an emergency descent, according to flight tracking data.
Passengers on board said a large section of the plane’s outer shell fell to the ground shortly after take-off.
Images sent to news outlets show the night sky and lights of Portland visible through the gap in the fuselage, with insulation material and other debris also seen.
One passenger said the gap was “as wide as a refrigerator” while another said a child’s shirt was ripped off in the wind as the plane made its emergency landing.
The plane, carrying 177 passengers and crew, landed safely back in Portland. Alaska said several passengers were injured, but not seriously.
“My heart goes out to those who were on this flight – I am so sorry for what you experienced,” Alaska’s CEO Ben Minicucci said after the firm volunteered to ground 65 of its 737 Max 9 planes.
“I am so grateful for the response of our pilots and flight attendants,” he added.
Alaska later said that, as of Saturday afternoon, it had cancelled 160 flights.
The airline said on Saturday that 18 of its Max 9 planes – about a quarter – had received “in-depth inspections as part of heavy maintenance checks” and were returned to service, but following the FAA’s orders these have since been “pulled from service”.
“We are in touch with the FAA to determine what, if any, further work is required before these aircraft are returned to service,” Alaska said in a statement.
It added: “The aircraft involved in flight 1282 was delivered to us on 31 October. The part of the aircraft involved in this event is called a plug door – a specific panel of the fuselage near the rear of the aircraft.”
The rear mid-cabin exit door is used in dense seating configurations on some Max 9 planes to meet evacuation requirements, but is “plugged” on other planes, including the Alaska flight.
United Airlines says it has carried out the inspections required by the FAA on some of its 737 Max 9 planes.
Removing some of its aircraft from service was expected to cause about 60 cancellations on Saturday, the airline said in a statement.
Turkish Airlines has grounded five of its 737 Max 9s.
Flydubai said its three 737 Max 9s were not affected as they had a “different configuration” compared to the Alaska Airline planes and have completed recent safety checks.
British regulator the Civil Aviation Authority (CAA) said there are no registered Boeing 737 Max 9 planes in the UK and therefore the impact would be “minimal”.
“We have written to all non-UK and foreign permit carriers to ask for confirmation that inspections have been undertaken prior to any operation into UK airspace,” a CAA spokesman said.
In the US, the National Transportation Safety Board (NTSB) has taken charge of the Alaska investigation and its chair confirmed no passenger had been sat next to the affected section.
“We are very, very fortunate here that this didn’t end up in something more tragic,” Jennifer Homendy said.
Meanwhile, authorities are still searching for the plug door, which they believe fell to the ground in the community of Cedar Hills, about 11 km (seven miles) west of central Portland.
Boeing’s 737 Max has been described as “the most scrutinised transport aircraft in history” after a series of safety issues.
The Max was grounded in March 2019 for a year-and-a-half after two of the type crashed in similar circumstances to each other killing those on board.
Aviation expert John Strickland said the Alaska Airlines incident was very different to those crashes, adding that since the 737 Max came back into service it had “an enormous safety record”.
“While we know little evidence of why this section of the fuselage has come out – this has nothing to do with the aircraft being grounded for 18 months,” he told BBC News.
“But, it is natural Alaska Airlines is taking a cautious approach grounding its fleet”
More recently, Boeing said it would increase the pace of 737 Max deliveries after resolving a supply error that required it to conduct lengthy inspections of new planes and its inventory.
About 1,300 737 Max aircraft have been delivered to customers, Boeing data shows.
Last month, the FAA urged airlines to inspect Max models for a possible loose bolt in rudder control systems.