By Paradise Afshar and Elizabeth Wolfe, CNN

(CNN) — Federal officials examining the horrifying midflight blowout of part of an Alaska Airlines aircraft’s fuselage said the lost piece has been found – a key detail in the investigation of what happened during the plane’s “explosive decompression,” as certain Boeing 737 MAX 9 aircraft are now grounded nationwide.

A Portland schoolteacher named Bob found the refrigerator-sized Boeing 737 MAX 9 fuselage door plug in his yard and reached out to the National Transportation Safety Board, NTSB Chair Jennifer Homendy said at a news conference.

A manufacturer will sometimes put a door plug in place of an emergency exit door, depending on the configuration requested by an airline.

The component had been missing since it blew off the aircraft Friday, leaving a gaping hole in the side of the plane as it flew at 16,000 feet shortly after taking off from Portland, Oregon, carrying 177 people. The harrowing ordeal – which included headrests ripped off seats and items sucked from the cabin – has led to the nationwide grounding and a slew of flight cancellations.

Complicating the investigation is the loss of critical cockpit audio recordings because of a device setting, said Homendy.

“(The blowout) was a described to us by the flight crew that it was a very violent, explosive event when it occurred, and you can see that from inside the aircraft,” Homendy said Monday, a day after she toured the aircraft.

“We were able to inspect to the airframe itself from the exterior and found absolutely no structural damage to the airplane,” she told “CNN This Morning.” “Inside, there was a lot of damage to non-critical components.”

There was damage to trim, insulation, windows and seats, Homendy said.

“It must have been truly terrifying.”

Unanswered questions remain over previous warnings about the plane’s pressurization and whether other Boeing aircraft are safe to fly.

“Our focus right now is on this aircraft to determine what happened, how it happened and to prevent it from happening again,” Homendy said. “Once we determine that we can see if there’s a greater concern that we want to issue an urgent safety recommendation for.”

NTSB officials will continue the painstaking examination of the interior of the plane and will recover and examine the detached door plug, Homendy said.

The supplier that makes the fuselage of Boeing’s 737 MAX jets, Spirit AeroSystems, said it is working with Boeing on the issue.

“We are grateful the Alaska Airlines crew performed the appropriate procedures to land the airplane with all passengers and crew safe,” the company said in a statement Monday. “At Spirit AeroSystems, our primary focus is the quality and product integrity of the aircraft structures we deliver.”

Alaska Airlines has also said it is working with Boeing to understand what happened on Flight 1282.

Plane was restricted from flying over water amid auto pressurization fail lights

The airline had restricted the aircraft in Friday’s incident from flying from over the ocean to Hawaii to ensure the plane could “return very quickly to an airport” in case any warning lights in the aircraft went off, according to Homendy.

That decision came after the plane’s auto pressurization fail light came on three times in the past month, Homendy said. It’s not clear whether there is a connection between the warning lights and Friday’s incident, she noted.

While the repeated pressurization alert is “very disconcerting to investigators,” who are looking into the issue with Boeing and Alaska Airlines, Homendy said, “it may have absolutely nothing to do with what occurred in the cabin of the aircraft during that event.”

The fail light came on December 7 and on January 3 and 4 –- the days leading up to the blowout, she said. Each time, the flight crew flipped a switch to the system’s backup, Homendy said, describing the move as “very normal.”

“They flipped it, they reported it, it was tested by maintenance and then reset.”

“They did order additional maintenance to look at the light that was not complete before (the fuselage blowout). We plan to look at that more and we’ve requested documentation on all defects since delivery of the aircraft on October 31,” she said.

CNN has sought comment from Alaska Airlines on the plane’s flight restriction and warning lights.

The plane involved in Friday’s incident had been in service for about three months and flown about 150 times since October 2023, according to FlightAware and FAA records.

Crew interviews, interior damage illustrate terrifying scene

Interviews with flight crew and the examinations of the damage left behind inside the cabin shed light on the loud, “violent” and chaotic scene inside the aircraft when the door plug tore off, causing an incredibly forceful depressurization and sending flight attendants rushing to the side of children on the flight, the NTSB chief said.

After the “explosive event,” flight attendants scrambled to ensure four unaccompanied minors onboard were wearing oxygen masks and lap belts, Homendy said, praising the attendants as “heroic.”

Several guests on the flight were injured and required medical attention but had all since been medically cleared, the airline said in a Saturday statement.

But “communication was a serious issue” between the pilots and flight attendants, who said they were having difficulty quickly sharing information, she added.

“I do want to emphasize that the actions of the flight crew were really incredible,” she said.

The impact of the event caused damage to the interior paneling, trim and plastic around the windows inside the plane, all of which are “not critical” to the aircraft’s structure, Homendy said.

The damage extended to several rows on the plane – not just the row next to the hole, according to Homendy. The two seats next to the door plug – 26A and 26B – were empty when the blowout happened, but had their headrests torn off, she said previously. The back of 26A is completely gone.

There was no structural damage to the aircraft and airframe, she noted.

Cockpit recorder setting wipes crucial evidence

The cockpit voice recorder, which captures sounds such as engine noises and pilots’ voices, was “completely overwritten,” since devices are currently only required to retain two hours of audio at a time, Homendy said.

“There is nothing on the cockpit voice recorder,” she said, noting the maintenance team went out to get the recorder around the two-hour mark when the devices begin a new recording cycle.

“We’re disappointed that the cockpit voice recorder was overwritten,” Homendy said Monday.

The audio captured by the recorders is “critical” to helping investigators understand what occurred during the incident, Homendy said. Without it, there is no record of communications between pilots and flight attendants as the crisis was unfolding.

“If that communication is not recorded, that is, unfortunately, a loss for (the NTSB), and a loss for the FAA and a loss for safety because that information is key not just for our investigation, but for improving aviation safety,” Homendy said.

Though the Federal Aviation Administration has proposed a new rule that would require new aircraft to extend their cockpit voice recordings to 25 hours, the rule would not require older aircraft to be retrofitted, Homendy noted. The NTSB chief called on the FAA and Congress to require 25-hour recordings in all aircraft.

“I cannot emphasize enough how important that is for safety,” she said.

CNN asked Alaska Airlines about about the wiped cockpit audio and the airline’s previous decision to restrict the plane from flying from over the ocean. The company replied in a statement Monday:

“Because this is an active investigation, we must receive permission from the NTSB to provide information about the aircraft and its prior maintenance,” Alaska Airlines said. “We have asked for permission from the NTSB to address these questions – they will not permit us to comment at this time. We will provide information as soon as the NTSB gives us permission to do so.”

Fallen cell phones may provide insight

Two cell phones that were likely flung from the plane were found in a yard and on the side of a road and turned in to investigators, who may be able to use them as evidence, Homendy said.

“Cell phones have actually helped us determine some things that occurred after tragedies … But it also helps in telling us, ‘Are we looking in the right area?,” the agency chief said just minutes before finding out the door plug had been discovered.

Sean Bates told CNN he spotted a phone on an Oregon roadside and turned it over to the NTSB, who were already in the area investigating the accident.

The phone didn’t have a security lock, and a photo of the phone shows an emailed Alaska Airlines baggage receipt for two bags, Bates said.

NTSB spokesman Jennifer Gabris told CNN that the agency took custody of the phone Sunday and has since turned the phone over to Alaska Airlines.

CNN’s Lauren Mascarenhas, Gregory Wallace, Joe Sutton, Pete Muntean, Mike Valerio, Anna-Maja Rappard and Chris Boyette contributed to this report.