A helicopter with an engine failure in flight does not always crash. A phase may occur called autorotation. In fact, during the fall air turns the blades, which gives sufficient lift the device to land quickly. This technique is taught to helicopter pilots to deal with emergencies.
The pilot first performs a dive, so blades pick up speed and then pitches the aircraft attitude during landing so as to slow the rotor and allow a hard landing. However, it needs to be at a minimum altitude of 100 m to make the maneuver.
- More Info: Autorotation seems a bit scary at first but once you realize how precise an autorotation can be, flying helicopters seems much safer. Helicopter pilots have to demonstrate an autorotation to an examiner as part of earning a license and practice the technique frequently.