ABSOLUTELY NOT! A helicopter can "glide" with power off using a technique called an "autorotation".  As the helicopter descends, the air moving up through the rotor blades causes them to turn, providing lift, which allows the helicopter to come down at a constant rate, almost like a parachute.  Part of your helicopter training will involve learning to perform autorotations.  However, real engine failures in properly-maintained, FAA-certified helicopters, like the ones operated at Heli-Ops, are extremely rare.