United Airlines and Alaska Airlines have grounded their Boeing 737 Max 9 jets after loose bolts and other "installation issues" were found on a part of the aircraft. The inspections were prompted by a mid-flight blowout on an Alaska Airlines jet on Friday. The focus of the inspections is on the plugs used to seal an area reserved for extra emergency doors that are not required on United and Alaska Max 9s. United Airlines stated that during preliminary inspections, they found instances of installation issues in the door plug, such as bolts that needed additional tightening.

The Federal Aviation Administration (FAA) has grounded all Max 9s operated by Alaska and United, as well as some flown by foreign airlines, following the terrifying flight on Friday night. The Boeing jetliner experienced an inflight blowout over Oregon, but it was not being used for flights to Hawaii due to a warning light indicating a potential pressurization problem. Alaska Airlines made the decision to restrict the aircraft from long flights over water to ensure it could quickly return to an airport if the warning light reappeared.

Jennifer Homendy, chair of the National Transportation Safety Board, cautioned that the pressurization light may be unrelated to Friday's incident where a plug covering an unused exit door blew off the Boeing 737 Max 9. However, on Monday, the FAA approved guidelines for inspecting the door plugs on other Max 9 jets and repairing them if necessary. This move could expedite the return to service of the 171 planes that were grounded by the FAA. Alaska Airlines owns 64 other Max 9s, while United Airlines owns 79. No other U.S. airlines operate this model of the Boeing 737.

The incident has had a significant impact on the stock market, with shares of The Boeing Co. falling 8% and Spirit AeroSystems, which builds the fuselage for Boeing's 737 Max, tumbling 11% on the first day of trading since the incident occurred. However, shares of Alaska Airlines remained relatively unchanged after initially slumping.

Further details about a previous warning light incident in December were not provided by Homendy.