A LARGE piece of an Alaska Airlines plane that was torn off mid-flight has finally been found after a teacher discovered it in his yard.

Passengers were left terrified when the refrigerator-sized part came off the plane as it traveled from Portland, Oregon, to Ontario, California, on Friday.

The terrifying scene saw people’s phones ripped from their hands and sucked through the large hole in the aircraft.

Bob Sauer, a 64-year-old physics teacher in Portland, Oregon, found the door two days later in his backyard and was instantly astounded. 

Sauer said his neighbor had insisted that he check his backyard since a phone from the flight was found in their area.

He went searching for the plane’s missing piece with a flashlight and found it leaning on 50-foot cedar trees in his yard, The New York Times reported.

“My heart started beating a little faster,” Sauer told The New York Times. 

“And I thought, ‘There’s no way.’”

The physics teacher believes that the trees acted as airbags and protected the part as it barreled toward the ground. 

He added that the door was cushioned by the trees through the physics term called impulse.

“Impulse is what you do to change the momentum of something,” Sauer said.

“You can do it with a big force over a short time, or a smaller force over a longer time.”

Sauer called the National Transportation Safety Board on Sunday and they came to retrieve the door on Monday morning.

The board said investigators were “currently examining the door plug” and that it will go to a lab in Washington, D.C., for further examination.

WORRYING DISCOVERY 

While no one was seated next to the door when it flung off, Alaska Airlines announced it had grounded all of its Boeing 737 Max-9 flights on Saturday following the incident.

The company said it would focus on “safety” after shocking images showed a hole gaping on the side of the plane, with passengers clutching oxygen masks while waiting for assistance.

United Airlines has since added to concerns, becoming the second carrier to find faults with its Boeing 737 Max 9 fleet.

The company said on Monday that it found loose parts on multiple grounded MAX 9 aircraft.

“Since we began preliminary inspections on Saturday, we have found instances that appear to relate to installation issues in the door plug — for example, bolts that needed additional tightening,” United said in a statement.

“These findings will be remedied by our Tech Ops team to safely return the aircraft to service.”

A source familiar with the matter told Reuters that United found up to 10 planes with loose bolts during its preliminary checks.

This figure is up from an initial five first reported by industry publication The Air Current and it’s feared the number could rise.

Alaska Airlines said late on Monday that initial reports from its technicians indicated “loose hardware” was visible on some aircraft in the relevant area when it conducted checks of its fleet.

The Federal Aviation Administration grounded all Boeing 737 Max 9s with other airlines following the Alaska Airlines incident.

The FAA said that its priority is keeping the public safe at this time and that the planes would remain grounded “until operators complete enhanced inspections which include both left and right cabin door exit plugs, door components, and fasteners.”

“The FAA’s first priority is keeping the flying public safe,” the agency said in a statement.

“We have grounded the affected airplanes, and they will remain grounded until the FAA is satisfied that they are safe.”