On July 24, 2017, about 1930 mountain daylight time, a Robinson Helicopter Company R44 II, N233JD, sustained substantial damage during a forced landing following a loss of engine power near Lake Sutherlin, Montana. The airline transport pilot and his passenger were not injured. The helicopter was registered to a private individual and operated by the pilot as a Title 14 Code of Federal Regulations Part 91 personal flight. Visual meteorological conditions prevailed about the time of the accident and no flight plan was filed for the cross-country flight. The flight originated from White Sulphur Springs Airport (7S6), White Sulphur Springs, Montana, about 1915, with a destination of Sutherlin Lake.The pilot reported that prior to departing 7S6, they refueled the helicopter to a level about one gallon under full. Following an uneventful takeoff and flight to Lake Sutherlin, located about 10 miles northeast of 7S6, they descended to about 25 to 50 ft above ground level (agl), and began a slow recon around the lake for a place to land and camp for the night. The pilot stated he touched down in one spot, however, decided it was unsuitable and lifted off, at which time he noticed the rotor rpm was low, and twisted the throttle to full, noting the rotor rpm increased immediately.

The pilot stated he 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, when the low rotor warning horn sounded, and the engine began to lose power. The pilot further stated that since he already had set the throttle at full power, he decided his only option was to lower the collective and drive down the hill to gain [air]speed and regain rotor rpm. The pilot added that at this point, he thought the engine had failed, and initiated a right turn into the wind, and did not notice the engine manifold pressure or airspeed at this time. The pilot leveled the helicopter just above the lake surface, and recalled the rotor rpm was near 80%, and increased the collective to cushion the landing, at an airspeed of about 5 knots. As the helicopter settled into the water, it rolled over onto its left side and became partially submerged.

The pilot reported that the helicopter weighed 2,400 lbs and the outside air temperature was 80° at the time of the accident.

Examination of the helicopter by a Federal Aviation Administration (FAA) inspector revealed that the tailboom and vertical stabilizer were structurally damaged.

Wreckage Examination

Examination of the recovered helicopter by representatives from Robinson Helicopter, FAA, and the National Transportation Safety Board (NTSB), revealed that control continuity was obtained from the cockpit throughout 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 remained secured to the engine and had no abnormal wear or defects. The engine oil sump contained about 3.5 gallons of water and water was evident throughout the remainder of the engine. The spark plugs were removed and contained debris and moisture from the engine. Once the spark plugs were dried and cleaned, the spark plugs were tested and functioned normally.

Thumb compression was obtained on all cylinders. Initially, cylinder no. 6 had minimal compression, however, once the engine was rotated through several times, compression was obtained. The magnetos were removed from the engine and contained significant water. The magnetos were dried and then rotated using a drill. Spark was obtained at all posts. Control continuity from the cockpit mixture and throttle controls to the engine were obtained.

The intake and exhaust systems were unobstructed, and all connections remained 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.

For further information, see the wreckage examination notes within the public docket for this accident.

The fuel servo was removed and shipped to the manufacturer for further examination. The fuel servo was placed on the test bench as received with a flexible fuel hose with attached fuel flow meter attached to the outlet fitting. The fuel servo functioned within specifications on all tests except for test point 1 which measures the fuel flow available for engine start. During this test, the fuel servo unit flowed 45 pounds per hour (pph), or 3.0 pph over the maximum calibration limit of 42 pph, and 1.95 pph high when compared with allowed service limits. For further information see the Fuel Servo Examination report within the public docket for this accident.

Performance

The performance section of the R44 II Pilot Operating Handbook (POH), stated that the in ground effect (IGE) hover ceiling, based on full throttle, zero wind, and a gross weight of 2,400 pounds was about 8,100 ft. The out of ground effect (OGE) hover ceiling for the same parameters was about 4,800 ft. Using the accident site elevation of 5,500 ft, reported temperature of 80° F, and an altimeter setting of 29.88 inches of mercury, the calculated density altitude was about 7,900 ft, with a pressure altitude of about 5,538 ft.

The ravine that the flight flew over varied in depth, from 15 to 25 ft from the tops of either side to the floor of the ravine.