Fielding, UT, USA
N7187B
ROBINSON HELICOPTER R44
The student pilot reported that, upon entering the mouth of a canyon, he slowed the helicopter to between 70 and 75 knots because he had experienced turbulence going through the canyon with his instructor the day before the accident. About halfway through the canyon, the helicopter dropped about 100 feet, and the main rotor rpm was between 80 and 85 percent. He lowered the collective and rolled on the throttle to regain rotor rpm and then turned toward a field to set up for a precautionary landing. During the turn, the main rotor rpm rose to about 90 percent, but, after leveling out, the pilot observed the rpm decrease again to between 80 and 85 percent. The pilot stated that, after he cleared a set of wires and landed the helicopter in the field, the front skid caught on something, and the helicopter tipped over on its left side, which resulted in substantial damage. The calculated density altitude at the time of the accident was 8,830 feet, which could have reduced the available engine torque and, subsequently, the rotor rpm. A postaccident examination of the helicopter's engine and airframe revealed no anomalies that would have precluded normal operation.
On June 27, 2013, about 1930 mountain daylight time, a Robinson R44 helicopter, N7187B, was substantially damaged following impact with terrain while maneuvering near Fielding, Utah. The student pilot, the sole occupant of the helicopter, was not injured. The helicopter was registered to AMW Aerospace LLC, and operated by Whirlybird Helicopters, located in Ogden, Utah. The instructional flight was conducted in accordance with 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed for the flight, and a flight plan was not filed. The helicopter departed the Brigham City Airport (BMC), Brigham City, Utah, about 1830, with its destination being Ogden-Hinckley Airport (OGD), Ogden, Utah.In a statement submitted to the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), the 44-hour student pilot reported that as he entered a canyon, he climbed to about 5,600 feet mean sea level (msl), which was 100 feet above his profile altitude of 5,500 feet msl. Upon entering the mouth of the canyon he slowed to between 70 to 75 knots, as there had been turbulence going through the canyon the day before with his instructor. The pilot stated that about halfway through the canyon the helicopter dropped about 100 feet, at which time he observed the [main rotor] revolutions per minute (rpm) were between 80 to 85 percent. The pilot reported that he then lowered the collective and rolled on throttle, maintained 70 knots, and turned towards a field. During the turn the rpms came up to about 90 percent, and after leveling out the rpms dropped back to between 80 to 85 percent. The pilot said that after he cleared a set of wires, he set up to land in the field. The pilot added that he did a "baby flare" at the bottom, then a full flare before adding a little pitch and setting the helicopter down. The pilot stated that after setting down "…it felt like my front skid caught, which tipped me and the helicopter onto its [left] side." As a result of the rollover, the helicopter's structure sustained substantial damage. The pilot reported no preimpact mechanical malfunctions or failures with the helicopter that would have precluded normal operation. A postaccident inspection of the engine was performed by a Federal Aviation Administration airworthiness inspector. The inspector stated that prior to performing an engine run the sparkplugs for cylinders #1, #3, and #5 were removed and drained of oil; the inspector speculated that the oil contamination had occurred during the shipment of the helicopter to the examination/testing facility. The inspector reported that to accommodate the engine run, a cylinder head temperature probe was installed at the #2 cylinder position. The oil pressure fitting to the oil pressure gauge was also replaced, as the original fitting was damaged as a result of the accident. The engine was then installed on an engine test stand, with a test club propeller installed. The inspector reported that the engine started with "no hesitation or stumbling." The inspector further reported that during the magneto drop test at 1,800 rpm, the right magneto (serial number E06DA051) was observed to create stumbling symptoms produced by the engine, with a drop between 400 to 425 rpm. The left magneto (serial number E08GA072R) dropped about 90 rpm when the engine was run up at 1,800 rpm. There was no hesitation or stumbling observed from the engine. The engine was then shut down. No other anomalies with either the airframe or engine were reported by the inspector that would have precluded normal operation. Under the supervision of the NTSB IIC, a subsequent examination of the right magneto (serial number E06DA051) was performed at the facilities of Aircraft Magneto Service, Bainbridge Island, Washington, on August 15, 2013. The technician reported that although he observed minimal oil in the magneto housing, this would not have resulted in operational difficulties of the magneto. He then assembled the magneto from the parts provided, and noted that the breaker point opening and internal timing was untouched. The technician briefly test ran the magneto and found it to function normally. At 1956, the weather reporting facility at the Logan-Cache Airport (LGU), Logan, Utah, which is located about 11 nm east of the accident site, reported wind variable at 3 knots, visibility 10 miles, sky clear, temperature 36° Celsius (C), dew point 7° C, and an altimeter setting of 30.20 inches of mercury. The density altitude at the time of the accident was calculated to be 8,830 feet.
The pilot's failure to maintain rotor rpm while traversing a canyon in high-density altitude and gusting wind conditions.
Source: NTSB Aviation Accident Database
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