What happened
While operating in cruise flight at an altitude of 1,200 feet MSL, approximately 22 miles south of its destination, a helicopter experienced a loss of engine power. After verifying the engine failure, the pilot issued a "May Day" call and initiated an autorotation toward the water while inflating the emergency floats.
Prior to contacting the water, the pilot pulled all available collective pitch. The aircraft impacted the water in a slight nose-low, right-banking attitude. During the impact, the right front float bag ruptured. The helicopter rolled to the right and remained floating inverted as the pilot egressed the aircraft. At the time of the accident, weather conditions were VMC with winds from the southwest at approximately 10 knots and sea states featuring wave heights of two to three feet. The pilot reported difficulty determining the aircraft's height above the water surface.
The investigation
An examination of the helicopter identified a fracture in the PC air line located between the tee for the power turbine governor and the fuel control, specifically under the "B" nut at the fuel control.
Further analysis of the tube assembly at the NTSB Materials Laboratory revealed fatigue cracking within the flared portion of the tube end. The origin areas of these cracks were found on the inside surface of the tube at circumferential scoring marks. These origin areas corresponded approximately to the inside diameter of the fitting ("B" nut) that mates with the flared end. According to the engine maintenance manual, applying excessive torque to pneumatic sensing system connections can result in cracking of the flare or the adjacent tube area in contact with the ferrule.