Complex sentence: They were waked by the shaking of the stalling plane, and mistaking the shakes for engine surges, they reduced the engine power, sending the plane further into a deep stall and unrecoverable flat spin.
Split into simpler sentences: They were waked by the shaking of the stalling plane, which surprised crew mistook for engine surges. They then reduced the engine power, sending the plane further into a deep stall and unrecoverable flat spin.