A loud boom, a blast of icy wind and sheer terror on Alaska Airlines Flight 1282

The airplane was three miles into the sky and still climbing when passengers heard the boom and felt the blast of icy wind. A chunk of the metal membrane separating the 171 passengers and six crew members from the freezing mid-troposphere had unexpectedly “departed the airplane,” as transportation officials clinically put it.

No serious injuries were reported aboard Alaska Airlines Flight 1282, which made an emergency landing at Portland International Airport in Oregon on Friday night with a door-shaped gap in its side and a cabin full of frightened people.

But transportation officials say the midair blowout could have been calamitous if it had happened a little later in the flight, when the plane was at cruising altitude with passengers unbuckled and walking around.

This photo provided by an unnamed source shows the damaged part of Alaska Airlines Flight 1282, a Boeing 737 Max 9, which was forced to return to Portland International Airport.

(Associated Press)

“We are very, very fortunate here that this didn’t end up in something more tragic,” said Jennifer Homendy, chair of the National Transportation Safety Board, the federal agency responsible for investigating transportation accidents.

“I imagine this was a pretty terrifying event,” Homendy said. “We don’t often talk about psychological injury, but I’m sure that occurred here.”

The airliner was a new one, a Boeing 737 Max 9 that went into service late last year. Investigators will try to figure out what caused one of its so-called plug doors — described by some experts as “fake doors” — to be ripped loose in the air above Oregon.

With 178 seats, the plane is not required to have emergency exit doors at the spot, so builders installed sealed panels where the doors otherwise would have stood on each side.

Investigators are searching for the missing plug door, which is believed to have landed near the Cedar Hills neighborhood of Greater Portland. The NTSB is asking anyone who finds it to contact police.

Alaska Airlines said Sunday that all 65 of its Max 9s were grounded, and that it had canceled 170 flights Sunday affecting 25,000 passengers. On Saturday, United Airlines said it had grounded all 79 of its Boeing 737 Max 9 aircraft for inspection, and that 270 flights were canceled over the weekend as a result of Friday night’s incident.

Flight 1282 left Portland International Airport just after 5 p.m. Friday, headed to Ontario International in Southern California on an expected two-hour flight. It was traveling about 440 mph , at an altitude of about 16,000 feet, and had been airborne about 10 minutes.

Then passengers heard what some called a boom and some called a pop, as the faux door flew off and exposed bare insulation around it. Some passengers screamed and hurried to put on oxygen masks that had dropped. One passenger told KTLA-Channel 5 that the blowout ripped the shirt completely off a teenage boy.

The blowout ripped the headrests off some seats. There were seven empty seats in the plane, authorities said, and by a stroke of luck the two closest to the hole — 26A and 26B — happened to be empty.

An audio recording between the pilot and an air traffic controller describes what happened next. The pilot calmly explained that the plane had depressurized and needed to return to Portland International.

“We’re now leveling 12,000 and left turn heading 340,” the pilot said. “We do have information zero. We’d like to get lower, if possible ...”

“Did you declare an emergency?” asked the air traffic controller. “Or did you just need to return to ...”

“Yes, we are emergency. We are depressurized. We do need to return back to ... Our fuel is 18,900 pounds and we have 177 passengers on board.”

“Do you need time to burn off some fuel before you land?”

“Negative.”

“Are you ready to approach now?”

The pilot said the plane was about 10 minutes away.

“Roger. Just let me know when you’re ready,” the air traffic controller said.

“We’ll let you know. Alaska 1282.”

“The only information we have is a depressurization issue. ... The emergency aircraft will be the next arrival,” the air traffic controller said. “They are on a two-mile final. And you can expect access to the runway.”

Passengers applauded as the plane landed safely, about 13 minutes after the blowout.

The Associated Press contributed to this story.