What we know so far about the mid-air blowout aboard Alaska Airlines flight

Investigators are trying to determine what led to the terrifying incident aboard a Boeing 737 Max 9 jet Friday, when a piece of the aircraft blew out mid-flight forcing pilots to make an emergency landing with a hole in the fuselage. 

Alaska Airlines Flight 1282 had 171 passengers and six crew on board and was flying at an altitude of more than 4,800 metres when a door plug — a panel in place of an optional exit door located near the rear of the aircraft — ripped off about 20 minutes into the Jan. 5 evening flight from Portland, Ore., to Ontario, Calif.

Fortunately, the two seats next to the panel were vacant and there were no serious injuries, though several passengers did require medical attention after the pilots made an emergency landing at Portland International Airport.

By the next day, U.S. aviation authorities had grounded certain Max 9 planes in order for emergency safety inspections to be carried out. 

It’s still unclear what caused the door plug on the Alaska Airlines flight to blow out. But this is just the latest safety concern for Boeing’s 737 Max series, following two deadly crashes involving Max 8 planes five years ago in Indonesia and Ethiopia, resulting in a worldwide grounding that lasted nearly two years.

Here’s what you need to know about what’s happening with the Boeing 737 Max 9 and the investigation into the frightening flight. 

WATCH | Emergency landing after blowout: 

FAA investigates after Boeing 737 cabin panel blows out at 16,000 feet

U.S. airline regulators have temporarily grounded 171 Boeing 737 Max 9 planes after a terrifying non-fatal incident aboard an Alaska Airlines flight. A cabin window blew out and depressurized the passenger cabin in mid-air, forcing an emergency landing.

Which planes were grounded? 

Saturday, the U.S. Federal Aviation Authority (FAA) issued an Emergency Airworthiness Directive to the owners and operators of Boeing 737 Max 9 planes with similar mid-cabin door plugs. 

The FAA said the directive affected 171 planes out of 218 Max 9s in operation worldwide. 

In the U.S., only two airlines fly the 737 Max 9: Alaska Airlines, which operates 64 of the aircraft, and United Airlines with 79 Max 9s in its fleet.

Both airlines have been…