The missing portion of an Alaska Airlines plane has been located in Portland, Oregon, according to the NTSB

Federal officials investigating 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 plane's "explosive decompression," as United Airlines found loose door plug bolts on several Boeing 737 Max 9s.

Some Boeing 737 Max 9s are grounded countrywide. United said on Monday that it found loose fasteners on an undetermined number of 737 Max 9s during FAA-mandated inspections after the Friday incident.

“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 officials said in a statement. The United news was first reported by The Air Current, an aviation industry publication.

Depending on airline configuration, a manufacturer may install a door plug instead of an emergency exit door.

The component broke off Friday, leaving a huge hole in the plane's side as it traveled at 16,000 feet after taking off from Portland, Oregon, with 177 people. The terrifying incident, which featured headrests pulled off seats and things vacuumed from the cabin, led to a nationwide grounding and flight cancellations.