THE VEHICLE IS EQUIPPED WITH A GEAR DRIVEN POWER LIFTGATE THAT OPENS AND CLOSES THE REAR HATCH AT THE TOUCH OF A BUTTON. I APPROACHED THE REAR HATCH OF THE ACADIA TO LOAD GROCERIES, AND SIGNALED IT TO OPEN. THE HATCH POWERED OPEN NORMALLY TO ITS FULL HEIGHT. I WALKED UNDERNEATH IT. WITH NO WARNING, THE HATCH SUDDENLY FELL AND STRUCK ME IN THE HEAD / BACK OF NECK / SHOULDER AREA. IT HIT HARD ENOUGH TO CAUSE SERIOUS INJURY. *TR