United Airlines found loose hardware and bolts during inspections of Boeing 737 Max 9 aircraft that needed "additional tightening." The inspections were prompted by an incident on an Alaska Airlines 737 Max 9 where a section of the fuselage fell off mid-flight on January 5th, forcing an emergency landing. Alaska Airlines also found some loose hardware during preliminary inspections of its Max 9 fleet. A total of 171 Boeing 737 Max 9 aircraft operated by United, Alaska, and some other airlines have been grounded until inspection and any remedial work is completed.