The Transportation Safety Board of Canada recently released the report of a fatal AS350 accident.
Report:
From the report:...
3.1 Findings as to Causes and Contributing Factors
After experiencing a hydraulic system failure, the helicopter departed controlled flight and crashed while manoeuvring for landing. The reason for the departure from controlled flight could not be determined.
It is likely that the hydraulic pump drive belt failed in flight, precipitating the hydraulic failure.
It is likely that the hydraulic circuit breaker was in the tripped position in flight, rendering the hydraulic CUTOFF and HYD TEST switches inoperative. This would result in hydraulic pressure from the main-rotor servos being depleted asymmetrically
Report http://www.tsb.gc.ca/en/reports/air/...2/A03O0012.asp