Theoretically, any modern commercial aircraft like the Boeing 737 can fly upside down for a brief period if handled by a skilled pilot, but it is not designed or certified to do so. Unlike aerobatic planes, a 737’s fuel, hydraulic, and oil systems rely on gravity; sustained inverted flight would cause these systems to fail, likely resulting in engine flameouts and a loss of control. Furthermore, the immense structural stress of a "barrel roll" or inverted maneuver could lead to catastrophic airframe failure. While there are famous historical anecdotes—such as Tex Johnston rolling a Boeing 707 prototype in 1955—modern flight control software and strict safety regulations in 2026 make such maneuvers impossible in passenger service. In short, while it can be done in a flight simulator or under extreme test conditions, it is dangerous and prohibited in reality.