Accident Description
On July 24, 2017, about 1930 mountain daylight time, a Robinson Helicopter Company R44 II, registration N233JD, sustained substantial damage during a forced landing following a loss of engine power near Lake Sutherlin, Montana. The helicopter was operated by the airline transport pilot as a personal flight under Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed for the cross-country flight. The flight originated from White Sulphur Springs Airport (7S6) about 1915, with a destination of Sutherlin Lake.
The pilot reported that prior to departure, the helicopter was refueled to about one gallon below full. After an uneventful takeoff and flight to Lake Sutherlin, located about 10 miles northeast of 7S6, the pilot descended to about 25 to 50 ft above ground level (agl) and began a slow reconnaissance of the lake for a suitable landing and camping spot. The pilot touched down in one spot but deemed it unsuitable and lifted off, noticing low rotor rpm. He twisted the throttle to full, and rotor rpm increased immediately.
The pilot then proceeded across a small ravine toward another hill at an airspeed of about 10 to 20 knots and an altitude of 25 ft agl. The low rotor warning horn sounded, and the engine began to lose power. With the throttle already at full, the pilot lowered the collective to drive down the hill and regain rotor rpm. He thought the engine had failed, initiated a right turn into the wind, and leveled the helicopter just above the lake surface. Rotor rpm was near 80%, and he increased the collective to cushion the landing at about 5 knots. The helicopter settled into the water, rolled onto its left side, and became partially submerged.
The pilot reported the helicopter weighed 2,400 lbs and the outside air temperature was 80°F at the time of the accident.
Wreckage Examination
Examination of the helicopter by an FAA inspector revealed structural damage to the tailboom and vertical stabilizer. Subsequently, representatives from Robinson Helicopter, FAA, and the NTSB examined the recovered helicopter. Control continuity was confirmed from the cockpit through the control systems to the main rotor and tail rotor. The main rotor remained attached; the tail rotor remained attached, but the outer portions of both blades had separated.
The V-belts were secured to the engine with no abnormal wear or defects. The engine oil sump contained about 3.5 gallons of water, and water was present throughout the engine. Spark plugs were removed and found with debris and moisture; after drying and cleaning, they functioned normally. Thumb compression was obtained on all cylinders; cylinder no. 6 initially had minimal compression but improved after rotating the engine several times. Magnetos contained significant water; after drying and rotating with a drill, spark was obtained at all posts. Control continuity from cockpit mixture and throttle controls to the engine was established.
The intake and exhaust systems were unobstructed with all connections secure. The heater shroud was partially separated from the exhaust, consistent with impact damage. The gascolator screen was clear, and fuel was identified in the gascolator.
The fuel servo was removed and shipped to the manufacturer for examination. On the test bench, the fuel servo functioned within specifications on all tests except test point 1 (fuel flow for engine start), where it flowed 45 pounds per hour (pph), which is 3.0 pph over the maximum calibration limit of 42 pph and 1.95 pph high compared to allowed service limits.
Performance
According to the R44 II Pilot Operating Handbook (POH), the in-ground-effect (IGE) hover ceiling at full throttle, zero wind, and a gross weight of 2,400 lbs was about 8,100 ft. The out-of-ground-effect (OGE) hover ceiling for the same parameters was about 4,800 ft. The accident site elevation was 5,500 ft, and with a reported temperature of 80°F and altimeter setting of 29.88 inches of mercury, the calculated density altitude was about 7,900 ft (pressure altitude about 5,538 ft). The ravine traversed by the flight varied in depth from 15 to 25 ft from the tops of either side to the floor.