Finally, a manga that acknowledges the law of physics.
There is a certain height where you can jump into the water without hurting yourself. At some point, such as stated here more than 10 meters fall (not 10 meters deep, the translator probably misunderstood what was said), it's as if you're jumping on concrete.
It's the reason why Kyochu Rettou piss off so much from the very first chapter. At that height, everyone on the plane would've died or at least broke their bones, which in turn kills them eventually.