Helicopters can auto-rotate, "gliding" on the momentum of the main rotor. This allows for a controllable landing under loss of power. There have been rare cas

Helicopters can auto-rotate, "gliding" on the momentum of the main rotor. This allows for a controllable landing under loss of power. There have been rare cases where a mechanical failure seizes the main rotor, such as the crash of the WNBC news chopper (N8617B) in 1986. This particular incident was caused by poor maintenance, however. https://en.wikipedia.org/wiki/Autorotation https://en.wikipedia.org/wiki/Autorotation http://www.check-six.com/Crash_Sites/Dornacker-N8617B.htm http://www.check-six.com/Crash_Sites/Dornacker-N8617B.htm