The answer is yes. Though a commercial airplane is capable of flying inverted, the flight mostly falls under theoretical paradigm. The reason I push the model towards a theoretical paradigm is because, such airplanes are not designed to fly inverted for a long time. If it was a fighter plane or an aerobatic plane, the answer would’ve been a lot simpler to explain.
If you are picturing the 2012 movie, FLIGHT, you may ask if that landing is possible too. The case in the movie is that the pilots lose their elevator control, as the jackscrew fails and the horizontal stabilizer jams in the nose-down position. The jet plunges towards the ground in an uncontrollable dive. So as any captain would do, Denzel Washington as Whip Whitaker, orders his co-pilot to throw out spoilers, flaps and landing gears to obtain some aerodynamic drag as he reduced the speed. Theoretically with that speed from the rapid descent, the structural stress on the surfaces would be undesirable and it would’ve ripped out those surfaces off the plane. But still somehow, they manage to fly without any disasters and finally to counter the drag, the pilot rolls the plane an entire 360 degree to level the plane. (Somehow the jammed stabilizer works when he rolls back after the engine flameout, and that’s purely a Hollywood thing or a miracle!)
The reason why the plane is rolled upside down here is that the jammed elevator, in an inverted nose-down position will tend to keep the plane from diving further. On the contrary, the airplane’s wings will not, unless adjusted to balance the forces. As they are cambered, the lift will be now a negative lift and the only possible way to maintain the flight is to adjust it with the speed so that it balances the forces. So with more thrust from the engines the flight was able to maintain the altitude until the engine flameout occurred.
As seen here, it is possible for an airplane to fly in an inverted condition. But that flight would end too soon, as the fuel will stop reaching the engine’s combustion chambers, due to the reason that the fuel is usually sucked from the bottom of the wings. This eventually leads to a condition called flameout, where the engine shuts down due to the insufficient fuel supply. The oil pressure in the engine also drops. These explain why a commercial airplane cannot fly longer in an inverted position.
In reality, a Boeing 707 prototype was subjected to two barrel rolls by the test pilot, Tex Johnston in 1955.
However, he did not fly in the inverted position for a long time. There are too many complications involved for a commercial airplane, like an engine flameout and it has never been tested before.
And again, the answer is yes you can fly a plane upside down – more in a theoretical system than in a practical world.
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