Symbolism, Imagery, Allegory
Injustice League
The two planes Louie flies on are both named after famous comic book characters. Like Superman, the Super Man is kinda awesome, and like the Green Hornet, the Green Hornet kinda isn't awesome.
The Super Man becomes a "dear friend" (2.10.25) to the men, especially after it gets riddled with 594 bullet holes and somehow manages to hold together. Of course, Phil deserves a lot of credit for landing the machine, but the plane seems to take on a personality of its own.
The Green Hornet has a personality too, but not a good one. It's known as "the craziest plane" (2.10.31) and all the men are scared of it. Can't say we blame them.
The real injustice here isn't the fact that one plane is of shoddier construction than the other, it's that the U.S. military put these men in the Green Hornet even though it was a "faltering plane" (2.10.31) that wasn't nearly well equipped enough to survive a crash landing. Louie, Phil, and Mac might survive partly because of the Super Man's construction, but when it comes to the Green Hornet, they survive in spite of what a winged disaster it is.
The planes are reminders of how unpredictable war is, and how many variables are at play at any given moment. They also make it explicitly clear that the men fighting are forced to make do with whatever equipment they're given—for better and for worse.