United Airlines says loose bolts, other 'installation issues' found in grounded Boeing 737-9 Max jets

United Airlines said Monday it found loose bolts and other "installation issues" on a part of some Boeing 737-9 Maxjets that were inspected after a mid-flight blowout on a similar Alaska Airlines jet on Friday.

The inspections are focused on plugs used to seal an area set aside for extra emergency doors that are not required on United and Alaska Max 9s.

"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," Chicago-based United said.

The U.S. Federal Aviation Administration (FAA) grounded all Max 9s operated by Alaska and United and some flown by foreign airlines after a door onAlaska Airlines Flight 1282 blew out at 16,000 feet Friday night, prompting an emergency landing in Oregon. None of the 171 passengers and six crew members was seriously injured.

The U.S. National Transportation Safety Board said the lost door plug was found Sunday near Portland, Ore., in a the backyard of a home. Investigators will examine the plug, which is 66 by 121 centimetresand weighs 28.5 kilograms, for signs of how it broke free.

On Monday, the FAA approved guidelines for inspecting the door plugs on other Max 9 jets and repairing them, if necessary. That move could speed the return to service of the 171 planes that the FAA grounded.

Alaska has 64 other Max 9s, and United Airlines owns 79 of them. No other U.S. airlines operate that model of the Boeing 737.

WATCH | Alaska Airlines plane had issues before mid-air blowout:

Loose bolts reported on some Boeing 737 Max 9 planes

9 months ago

Duration 2:59

United Airlines says it found loose bolts on some of its Boeing 737 Max 9 planes during inspections prompted by a panel that blew out during an Alaska Airlines flight last week. Investigators also say warning lights on the plane that suffered the blowout had gone off during previous flights.