What happened
The aircraft experienced a loss of control while executing a left turn into a wind condition with a 20-knot tailwind component. The pilot indicated that the engine had failed during the maneuver. At the time of the incident, winds were reported from 080 degrees at 20 knots, gusting to 29 knots.
The investigation
Following the accident, the engine was removed and subjected to testing on an engine test stand. The mechanical inspection revealed no deficiencies or defects in the powerplant. Additionally, a fuel sample was analyzed and found to be within specified parameters, ruling out fuel contamination or exhaustion as immediate causes.
Findings
The investigation highlighted critical factors regarding helicopter controllability in high-wind environments. Advisory Circular 61-13B notes that hovering turns should be avoided in winds strong enough to prevent sufficient aft cyclic control to maintain the helicopter on a selected surface reference point when headed downwind. It further states that hovering power requires a large amount of left pedal to maintain heading, and sufficient left pedal must be available to prevent an uncontrolled turn to the right once the turn has begun.
While the operator's manual for the Hughes Model 269C stated that controllability had been shown to be adequate in 20 mph (17.4 knots) winds from any direction, the actual conditions exceeded this with gusts up to 29 knots. The combination of a left turn into a tailwind likely exceeded the available pedal authority, leading to the loss of control.