What do you absolutely need to land?
"A plane can land anywhere it can slide to dissipate its horizontal motion," Bibel said. If it can find a flat enough space where it can decelerate before hitting something that'll break it apart, it should be fine -- provided it lands at a slow enough sink rate.
Even when a plane finds a perfectly flat surface -- even a runway -- a fast fall will break the plane apart. A typical commercial jet descends at about 1ft per second, which is why you begin your initial descent about half an hour from your destination. It can drop faster at the beginning, obviously, but once it touches down its sink rate must be tiny. For example, those landings that feel rough or jolted hit at a mere 4ft per second. No one will survive a landing faster than 42ft per second, Bibel said.
"There was a flight in 1972 where an L-1011 fell in the Everglades at about 37ft per second," he said. "It was an absolute disaster."
A plane must also land at a minimal angle. Even if landing gear doesn't deploy, a plane landing more or less parallel to the ground will suffer limited damage, as when the jet skidded into the Amazon on its belly. But trying to descend against a rise of just 20 degrees would mean game over.