United, Alaska Find Loose Parts on Some Boeing 737 MAX 9 Jets

United Airlines and Alaska Airlines have discovered loose parts on Boeing 737 MAX 9 jets that they have inspected after a near-catastrophe on a flight Friday, signaling Boeing’s issues go beyond the aircraft that made an emergency landing.

U.S. air safety officials grounded the Boeing jets and are still investigating what caused an emergency-door plug to detach from an Alaska Airlines plane flying at 16,000 feet, leaving it with a gaping hole.