Aviation expert says missing piece of Alaska Airlines plane holds a lot of clues

Federal investigators are trying to figure out what caused a window panel to blow off an Alaska Airlines plane mid-air on Friday night.

In the meantime, they've grounded all Boeing 737-9 Max jetliners. North Texas-based American and Southwest Airlines told NBC 5 they do not have that model plane in their fleet.

"We just heard like a loud bang or like a boom," said passenger Elizabeth Le, who saw masks drop from the ceiling and then looked to her left.

"There's just this huge, like, gaping hole," she said.

The plane was flying from Oregon to Southern California when it made an emergency landing shortly after takeoff.

No one was seriously hurt.

"There was a mom and a son sitting in that aisle. And the son's shirt was completely blown off and his body was extremely red, I'm assuming from irritation from the wind," Le said.

A refrigerator-sized hole in the plane was a "plugged door," which looks like a regular window seat to passengers.

Aviation expert Armen Kurdian said he immediately thought of two incidents that happened about 30 years ago: Aloha Flight 243 and United Flight 811.

"I remember the Aloha. It was like a big chunk of the top of the fuselage just sort of blew off. And on the United flight, several people were actually killed," said Kurdian, who is a retired U.S. Navy Captain / Naval flight officer and aerospace engineer.

He was also grateful that the plane wasn't at a higher altitude when the blowout happened.

"At 16,000 feet, explosive decompression is a lot less severe than it would be, say, at 32, 33,000 feet, because the pressure up there is much slower, it's much colder, and the impact to the human body is exceptionally severe at that altitude," Kurdian explained.

He said he hopes investigators can recover the plugged door, the key to discovering what happened.

"By having that and matching it up with the aircraft and basically reassembling, they'll be able to determine the cause of the failure, perhaps the exact point of the failure, based on the stress," Kurdian said.

He said it would likely come down to two things: "Either there was a maintenance practice that... was not properly executed, or there was quite simply a material failure of, say, fasteners or a bulkhead or a joint," Kurdian said.

He said investigators will also likely talk to the flight crew.

"I think you will see perhaps a lot of debriefing of the flight crew as to perhaps any issues they had during the emergency, some best practices, what they did," he said.

Kurdian credits the Alaska Air flight crew for staying calm and keeping passengers calm.

"I will say that I feel that a lot of people around me were a lot calmer than I would have thought for a situation like this," said passenger Emma Vu.

A calm crew that passengers appreciated, too.

"They got us down safe," said Evan Smith. "Everything went well. Like I said, the cabin crew did an excellent job. The pilot did a great job. Can't say anything bad about them at all."