An order by US officials to ground 737 Max 9s for inspection will affect 171 aircraft worldwide.

The incident took place on Saturday. Social media images showed emergency oxygen masks hanging from the ceiling as passengers huddled in their seats in trepidation.

Here’s what you need to know about the incident, and the Boeing 737 Max 9 jetliner:

What happened to the flight?

• Alaska Air Flight 1282 suffered a blowout that left a gaping hole in the side of the fuselage.
• En route to Ontario, California, the plane made an emergency landing in Portland, in the US state of Oregon.
• Flight data showed the plane climbed to 16,000 feet (4,876 metres) before the incident took place, with the hole causing the cabin to depressurise.

What happened to the blown-off piece?

• The door fell off over the Portland suburb of Cedar Hills, according to the chair of the National Transportation Safety Board (NTSB), Jennifer Homendy.
• Homendy called on residents to come forward if they found it.

Were any passengers affected?

• The plane landed safely with all 174 passengers and six crew members.
• No passengers were seated next to the cabin panel, said Homendy. However, The Oregonian newspaper quoted passengers as saying a young boy seated in the row had his shirt ripped off by the sudden decompression, injuring him slightly.
• Several other passengers also suffered injuries.

What was the cause of the incident?

• Alaska Airlines has not provided information about the possible cause, but the NTSB and the US Federal Aviation Administration (FAA) have said they will investigate the incident.

How old was the plane?

• The new Boeing 737 Max 9 involved in the incident was delivered to Alaska Airlines in late October and certified in early November, according to FAA data. It had been in service for just eight weeks.
• The Max is Boeing’s newest version of the 737 and went into service in May 2017.

How many planes have been grounded as a result and what is the impact?

• Federal officials in the United States have ordered the temporary grounding of all Boeing 737 Max 9 jetliners operated by US airlines or flown in the US by foreign carriers until they are fully inspected.
• The order affects 171 planes worldwide, with inspections expected to take about four to eight hours per aircraft.
• In the US, Alaska Airlines and United Airlines are the only carriers using the MAX 9.
• Alaska Airlines cancelled 160 flights on Saturday, 20 percent of scheduled trips, while United cancelled 104 flights, 4 percent of departures.
• Alaska Airlines said disruptions were likely to last through at least midweek.

What have been past safety concerns about Boeing 737 Max jets?

• Boeing 737 Max jets were grounded worldwide for almost two years after a crash in Indonesia in October 2018 which killed 189 people, and another in Ethiopia five months later, which killed 157 people.
• The aircraft was cleared to fly again after Boeing revamped its automated flight-control system that had activated erroneously in both crashes.

What have been the reactions of international airlines to the incident?

• The European Union Aviation Safety Agency adopted the FAA’s grounding directive, but said no EU member state airlines “currently operate an aircraft in the affected configuration”.
• Turkish Airlines said it had withdrawn its five Boeing 737 Max 9 aircraft from service for inspection.
• Panamanian carrier Copa Airlines has temporarily grounded 21 737 Max 9 aircraft.
• A British air safety regulator said it would require any 737 Max 9 operator to comply with the FAA directive to enter its airspace.
• Aeromexico said it was grounding all of its 737 Max 9 planes while inspections are carried out.
• Icelandair said none of its 737 Max 9s featured the plane configuration specified in the FAA grounding order.
• Airline flydubai said on Sunday that the three Boeing 737 Max 9 planes in its fleet were not affected, according to Dubai-based Khaleej Times newspaper.