Too many sentence fragments in your writing might: make your readers think that you can't write well
make readers wonder what's happening
confuse your reader with too many incomplete thoughts
any of the above
Its number 3

Yu would have to break it down so it not to descriptive. Or they will think it’s to boring.

As the boys sleep, military airplanes battle fiercely above the island. none of the boys sees the explosions and flashes in the clouds because the twins sam and eric, who were supposed to watch the signal fire, have fallen asleep. during the battle, a parachutist drifts down from the sky onto the island, dead.