How realistic is the plane scene in Captain America: The First Avenger? In Captain America: The First Avenger, there's a scene in which Captain America gets into the villain's plane by holding onto the landing gear as it's taking off and waiting for it to be retracted. How realistic is this scene, when applied to modern airplanes? 

Could you theoretically gain access to a large, modern airplane by just holding onto the landing gear - assuming, of course, you managed to hold on? Do the landing gears of large modern planes retract into interiors that have access to the rest of the plane, or do those interiors tend to be sealed off? And for that matter, how hard would it be to hold on to a plane's landing gear as it's taking off?
Though 'getting on/off aircraft through landing gear' is a favorite trope in movies, it is practically impossible in most of the modern airliners. Airliners are pressurized, and as a result, the cabin (and cockpit) area is in reality one big cylinder, cut off from everything else. So, no accessibility from the landing gear area.

For example, the following image shows the landing gear bay (the area into which the landing gear retracts into) of a Boeing 787. 



Image from dailymail.co.uk

As a result, though the list of stowaways in landing gear area is long, to the best of my knowledge, no one has entered the aircraft through it.