All of the explanations in this thread have made excellent reading. A hearty Bravo Nolan to you all. Allow me to submit an alternative hypothesis:
The main character of the Plane Scene is the Plane itself.
Consider: the plane is the entity which is on the screen the most throughout the scene. Its character evolves along with the others. It undergoes a dramatic arc, full of meaning and symbolism. And all of the other characters are contained within it.
I think I will lose many people as I continue my train of thought here, however. So please feel free to disregard anything you feel is an abomination unto Nolan.
I suggest that the Plane is, in fact, not only a character, but the only female character present in the Plane Scene.
The Plane stands behind CIA in the opening, behind, yes, but equally present. It is a big piece of the classic "CIA-powerstance" shot, looming behind him, equally proud and in charge. It is a vital part of the flight plan, for without a plane, there can be no flight plan. It watches on as the negotiations takes place, expectant and ready to be boarded.
Once in the air, its role becomes even more crucial, playing the role of the assistant executioner to CIA in his little sleight of hand. The plane feels exultant, full of potential. One imagines it expects a feather in its cap as much as CIA does. But this changes with the arrival of Bane's Big Craft. It is the first character (other than Bane, who knows it is coming) to react, trying to warn its passengers about the threat, to no avail.
The way the plane is taken apart is a truly horrifying way to go for a plane. First its windows are shot open, exposing its delicate passengers to the outside world. Then it is physically grabbed and rendered helpless, its wings forced off by the force of Bigness that has grappled it. Finally, to add insult to injury, its tail is ripped off to allow the Ropetta Men access. All of this occurs as CIA, once the Plane's equal, is similarly defeated cruelly by Bane.
Finally, we see what I believe identifies the Plane as a woman. The relationship between CIA and the Plane now changes from that of equals, to that of a mother and child. CIA falls to the bottom of the plane, in the foetal position, where the Plane can best protect him in its vulnerable state. Bane, meanwhile, is busy continuing what can easily be viewed as a rape. He forcibly impregnates the Plane with a false passenger, and, in a twisted parody of birth, yanks Pavel out into the cold air, as the helpless mother Plane and her child are discarded, falling to the ground together as they rose only a few minutes before.