Reprinted from: Rotor Journal –No.44 May/June 2002 (published by Eurocopter)
In fact, twin and single-engine helicopters offer practically the same degree of safety. Evidence shows that 95% of the causes of helicopter accidents (ground impacts, power line collisions, etc) have nothing to do with whether the aircraft was a twin or single-engine model. It is only amongst the remaining 5%, which includes accidents caused by equipment failure not due to maintenance faults that the single-engine helicopter proves to be more accident-prone.
Statistics show that overall, a difference of only 2% exists between single and twin-engine flight safety. A striking contrast to this figure is the 30 to 50% increase in the acquisition and operating costs of a twin-engine helicopter.
Having said that; operating in hostile environments such as rough ocean or mountainous terrain may push the decision towards a Twin Engine Helicopter. A Twin Engine Helicopter generally has more sophisticated avionics such as an auto-pilot, terrain awareness, and weather radar, which can add significantly to safety.