Missing door plug that blew off Alaska Airlines flight found in Portland teacher's backyard

Investigators have located the door plug that was blown off an Alaska Airlines flight after it was discovered by a schoolteacher in Portland, authorities said late Sunday night. National Transportation Safety Board officials announced that the teacher, identified only as "Bob," found the missing fuselage piece in his backyard.

Investigators had previously said finding that part could help them unlock clues to the midair emergency that opened a hole in the middle of the flight from Oregon to Southern California on the new Boeing 737 9 MAX. The door plug fell out while the plane was at 18,000 feet and authorities said it was fortunate it happened while passengers were still required to be wearing seatbelts.

"We are really pleased that Bob found this," NTSB Chairwoman Jennifer Homendy said. "He took a picture I can just see the outside of the door plug from the pictures, the white portions, we can't see anything else but we're going to go pick that up and make sure that we begin analyzing it.

Homendy had just concluded briefing reporters on the latest details into the investigation when she called them back to the room to announce the breaking development. There are also at least two passenger cellphones that fell out of the plane and were recovered, apparently with some of their functions intact.

One image, verified by ABC News, shows a passenger's luggage receipt for the flight still on the screen. Here's why that Boeing flight had a door plug and how it is key to the investigation The video in the player above is from a previous report. The door plug is on Boeing 737s that are flown in the United States but do not need an extra emergency exit.

Some flights on foreign airlines are required to have the extra exit because they pack in more seats and passengers. Some carriers, including Indonesia's Lion Air and Corendon Dutch Airlines, cram more than 200 seats into their Max 9s, so they must have extra emergency exits. However, Alaska Airlines and United Airlines configure their 737 Max 9s to have fewer than 180 seats, so the planes don't need the two mid cabin exits to comply with U.S.

evacuation rules. On Alaska and United, the only two U.S. airlines using the Max 9, those side exits near the back of the plane are replaced with a permanent plug the size of an exit door. DEVELOPING: This is a breaking story and will be updated. The Associated Press and ABC News contributed to this report..