Abstract: In this paper, the main phenomena and features of in-flight oscillation failure on helicopters are summarized. Then, the experimental investigation of the failure is deescribed. The investigaiton consists of the research approaches, the flight dynamic model of the helicopter. The experimental investigation on the control system -autopilot loop oscillation and pilot-induced helicopter oscillation, and the research results are also presented. Accordingly, some failure prevention principles and measures for design and operation are proposed.

Key words: Helicopter, failure, experimental investigation