Complex sentence: He attempts to climb into the helicopter, but falls to his death into the explosion when Casey shuts the helicopter door on his hands, severing his fingers and the explosion cause the helicopter to spin out of control but the pilot is able to control the helicopter.
Split into simpler sentences: He attempts to climb into the helicopter, but falls to his death into the explosion when Casey shuts the helicopter door on his hands, severing his fingers. The explosion causes the helicopter to spin out of control, but the pilot is able to regain control of the helicopter.