The wing spar. The spar is the main structure of the wing that supports the load of the entire airplane. All the loads go through the wing into the wing spar and down to the center of it, which is called the "wing box". (You could call this the most important part,)
An airplane may fly without its engines. It might be able to fly without its flight controls. But it can not fly if the wing spar breaks.
The Wright brothers' most important accomplishment was the airplane.
the chioken
The wing of an aircraft is the most important part of the aircraft as it lifts the whole weight of the aircraft. All the maneuvering of the aircraft is done by using the control surfaces(places to control the air flow and thereby producing the desired changes in the aircraft course) in the wings.
The Fuselage is the main part of an airplane
Almost every aspect of an airplane landing is managed by computer. The most important aspect is decelerating the airplane so the brakes and landing gear can stop the plane.
the keystone is the most important part of an arched bridge. :]
The most important part of the electron microscope is the eyepiece and the magnifier.
The most important part of an oscilloscope is the cathode ray tube.
The airplane was probably the most important weapon introduced to warfare.
The most important part of the heart is all of it. There all equally as important.
The most important part of a watch is battery. With out a battery a watch is dead.
It is somewhat subjective what the most important part of a graph is. It is very important that you label each axis.