Which component is essential to keep an airplane aloft?

The component that is essential to keep an airplane aloft is the aerodynamic forces on its wings. When an airplane flies, its wings generate lift, which is the force that counters the weight of the aircraft and allows it to rise and remain in the air. This lift is produced due to the shape of the wings and the airflow over them, adhering to Bernoulli's principle and Newton's third law of motion.

The wings are designed in such a way (with a specific airfoil shape) that as air flows over and under them, a pressure difference is created, resulting in lift. Without sufficient lift, the airplane cannot overcome its weight, and it would not be able to stay aloft, regardless of any other systems that the airplane may have.

While the propulsion system plays a crucial role in providing the forward thrust necessary to maintain airflow over the wings for lift to be generated, it is the lift from the wing's aerodynamic forces that fundamentally keeps an airplane airborne. Other components like landing gear and navigation systems are important for operations on the ground and in flight, but they do not contribute directly to maintaining flight.