There is an example of a flight attendant, Vensa Vulovic, who survived a Serbian plane crash in 1972 after falling 33,000 feet. How she survived is not fully clear. Some scientists think one raises their chances of survival by becoming "wreckage riders," holding on to parts of the plane debris like a glider to lessen the impact forces. But it highly unrealistic to have so many panicked passengers thinking about improvising paragliders while the plane falls a part around them.  Besides, we know that the passengers "landed" on the ground (or ocean) such as Jack in the bamboo field.

In another example, a World War II pilot survived a bail out of his plane at 20,000 feet when he crashed through a glass roof which science believes "spread out the impact" of the crash force to survivable levels. (Mythbusters tried to re-create a similar story where an airman fell toward a building that blew up below him, creating an "air cushion" to lessen his impact. It was not confirmed.)

The facts seem straight forward. 

Terminal velocity is 120 miles per hour. That is the maximum speed an object, like a human body, reaches when in free fall. 

It is not the height that causes fatal injuries, it is the impact.

First, physics  how and where you land is one of the major factors in whether you get up from the ground or go 6 feet further into it. If you can make the time [landing] longer, the force needed to stop you is smaller. Think of punching a wall or a mattress. The wall is rigid and the time of interaction is short so the force is large. People who have survived falls, they’ve managed to increase that time, even if it’s in milliseconds. From one millisecond to three, that’s three times longer, three times less force needed for the same change in momentum. 

Second, survivors who have plummeted into snow, trees, or something that can better absorb your landing than, say, concrete or water, have a better chance of survival. Spreading out the force of impact away from one's body is a key factor in survival.

Third, another factor is slowing the descent. Increasing surface area means more energy is required to push air out of your way, slowing you down. The “flying squirrel” position, body splayed out, is preferred over falling feet or head first. By increasing that drag is the biggest factor in keeping you alive.  This is why a parachute’s large surface area is best to slow descent speed.  

But some scientists state that there are issues even before one hits the ground. If you start your fall from high altitude, the air is thin. You may not have enough oxygen to survive. Further, if one body spins in the fall turbulence, the blood can rush to one's head and will kill you. Also, the friction of the fall could burn skin or beat up internal organs causing hemorrhages.

So it is probable that falling passengers could die during the fall (especially if they had pre-existing health conditions) or upon impact with the ground.

Now, many will remember the scene from the barracks that showed Flight 815 breaking up over the island at an apparent "low" altitude. This is debatable continuity error, because the prior "on board" sequence of events clearly showed no elevation change of the plane from its cruising 30-35,000 feet level when in seconds, the plane broke a part. Perhaps the second scene was used in order to "white wash" or change the perception of the story from the cries that fans who theorized that everyone died in the plane crash and the show was about purgatory.

But from the physical, objective evidence seen in the show's first season, one has to assume in the normal course of events, there would have been no survivors of the plane crash. But LOST is a fictional show, so it is possible to stretch the truth to create a plausible reality. But the writers did not fully explain how so many passengers could have survived a high altitude plane crash. If the writers said that the plane got caught in the island's sci-fi "unique" electromagnetic field that lessened the impact of the free fall, then why did most of the passengers die anyway? And when the writers added the fact that only Jacob could "bring" people to the island, this shows that the island was not a "real" island but some supernatural place in another dimension of time or space (such as purgatory).

It would have been much easier to start the series premises with a cruise ship disaster and the survivors floating ashore (such as was the case with Rousseau's ship). But having a questionable survival situation from a plane crash, coupled with an immortal being collecting "candidates" to play a game with a smoke monster tends to put the evidence clearly in the camp that the characters never survived the plane crash. Likewise, such sci-fi elements call into question whether the characters were ever even on a plane to begin with . . .  an open ended premise that we can continue to debate ad nauseaum.