The Federal Aviation Administration (FAA) ordered a temporary grounding of about 171 Boeing Max 9 airplanes after an incident on an Alaska Airlines airplane.

“The FAA will order the temporary grounding of certain Boeing 737 MAX 9 aircraft operated by U.S. airlines or in U.S. territory,” the federal agency said on Saturday in a statement. “The Emergency Airworthiness Directive (EAD) that will be issued shortly will require operators to inspect aircraft before further flight that do not meet the inspection cycles specified in the EAD. The required inspections will take around four to eight hours per aircraft.”

The FAA estimated that around 171 airplanes will be affected worldwide by this order.

The civil aviation authority issued the order after an incident happened on an Alaska Airlines flight.

An Alaska Airlines flight en route from Portland, Oregon, to Ontario, California, made an emergency landing on Friday night following a mid-air incident where a portion of the aircraft blew out.

Social media footage shows a window and a portion of a side wall panel missing on the airplane and oxygen masks deployed.

Images of the aircraft shared by passengers onboard seem to indicate that, during the flight, the rear mid-cabin exit door became detached from the aircraft, reported Flightradar24 on its website.

Alaska Airlines Flight 1282, a Boeing 737 MAX 9, departed from Portland International Airport at 4:52 p.m. PST, according to FlightAware.

The incident occurred approximately six minutes into the flight when the aircraft reached an altitude of around 16,000 feet.

The jet, carrying 171 passengers and six crew members, safely returned to Portland International Airport and landed at approximately 5:30 p.m, the airline confirmed.

The pilot declared an emergency, notifying air traffic control of a depressurization issue, stating, “We’re declaring an emergency. We do need to come down to 10,000.”

The Federal Aviation Administration (FAA) confirmed that a “pressurization issue” occurred.

Both the FAA and the National Transportation Safety Board are investigating.

Alaska Airlines released a statement, saying, “The safety of our guests and employees is always our primary priority, so while this type of occurrence is rare, our flight crew was trained and prepared to safely manage the situation.”

The airline is actively investigating the incident and has pledged to share more information as it becomes available.

The new Boeing 737 MAX 9 was delivered in late October to Alaska Airlines and certified in early November, according to FAA data.

Boeing said in a statement that it was looking into the emergency landing.

“We are aware of the incident involving Alaska Airlines Flight 1282,“ the company said in a statement. ”We are working to gather more information and are in contact with our airline customer. A Boeing technical team stands ready to support the investigation.”

Boeing has faced previous issues with its 737 MAX 8 model, leading to its grounding worldwide between March 2019 and December 2020. The groundings followed two fatal crashes involving the model: Lion Air Flight 610 on Oct. 29, 2018, and Ethiopian Airlines Flight 302 on March 10, 2019, resulting in a combined total of 346 fatalities.

In April, a manufacturing issue was discovered in the 737 MAX 8 model related to the installation of fittings in the rear fuselage. Boeing insisted it was not an immediate safety concern, and the FAA validated that conclusion, allowing affected planes to continue flying while inspections were conducted.

This article has been updated to reflect an update from the FAA.