History of Flight
On December 29, 2016, at 1131 Pacific standard time, a Robinson Helicopter Company R44 II, registration N324RS, landed hard near the peak of Mount San Antonio (Mount Baldy), California. The flight instructor sustained serious injuries, and three passengers received minor injuries. The helicopter sustained substantial damage. The helicopter was registered to November Alpha LLC and operated under 14 CFR Part 91. Visual meteorological conditions prevailed, and no flight plan was filed. The personal flight departed Fullerton Municipal Airport at 1100 with a planned destination of Mount Baldy.
The pilot reported performing a weight and balance check before flight, filling the main fuel tank to half capacity and the auxiliary tank to one quarter. The departure and flight to Mount Baldy were uneventful. As the helicopter approached the summit from the south, the pilot noticed hikers on a ridgeline. While executing a right turn orbit around the summit, the low rotor RPM warning horn sounded. The pilot lowered the collective and increased engine power with the throttle, causing the horn to cease. He then checked the manifold pressure placard and determined he could pull 19.6 inches of power.
As the pilot started to descend from the south, he felt a tailwind and decided to change the approach to a low pass to circle back to the north and land with a headwind. He made the pass at 35 to 40 knots, but seconds later the low rotor RPM horn sounded again. He lowered the collective, but the helicopter rapidly descended toward the mountain face. He reported insufficient altitude to recover or an escape path. He warned everyone of an imminent crash and, just before impact, applied full left foot pedal, causing the helicopter to land sideways rather than nose-down. After impact, all occupants exited unimpeded; the pilot set the transponder to 7700 and turned the fuel valve off.
The helicopter came to rest below a ridge at elevation 9,860 ft, about 1,500 ft west of the summit. The aft fuselage was partially submerged in snow with buckling damage extending to the tailboom. The pilot reported no preimpact mechanical malfunctions or failures that would have precluded normal operation.
Aircraft Information
The helicopter, manufactured in 2003, was equipped with a Lycoming IO-540-AE1A5 engine. On July 6, 2015, both a helicopter overhaul and engine rebuild were completed. The most recent maintenance was a 50/100-hour inspection on December 10, 2016, 28 flight hours before the accident. At that time, the airframe and engine had 789.4 flight hours since overhaul/rebuild.
Meteorological Information
An upper air sounding created using the Weather Research and Forecasting model indicated that at 1100, at 9,920 ft mean sea level, the temperature would have been about 5.4 °C, dew point -13.9 °C, and wind from 147° at 12 knots. Using these values and the pressure reading (30.15 inHg) at Ontario International Airport, the density altitude at the accident site would have been about 10,900 ft. A Los Angeles County Sheriff's deputy who arrived at the site at 1330 reported temperature 10 °C and wind from the east at 10 to 15 knots.
Weight and Performance
The pilot and front passenger weighed 145 lb and 235 lb respectively; total rear seat occupants and baggage weighed 399 lb. Based on the pilot's fuel statement, the main tank held 15.25 gallons (91.5 lb) and auxiliary tank 4.25 gallons (25.5 lb) at takeoff. The helicopter's maximum gross weight was 2,500 lb, and basic empty weight was 1,565.2 lb. At takeoff, the helicopter was about 38.8 lb short of maximum gross weight.
The R44 II Pilot Operating Handbook indicated that the in-ground-effect hover ceiling at full throttle, zero wind, and 2,460 lb gross weight was about 8,800 ft at 5 °C and 9,400 ft at -5 °C. The out-of-ground-effect hover ceiling was about 5,400 ft and 6,600 ft respectively. The maximum operating density altitude was 14,000 ft. The helicopter was equipped with a manifold pressure chart, required to be in full view and readable by the pilot. The pilot's reference to 19.6 inches of power corresponded to a pressure altitude of 10,000 ft and outside temperature of -10 °C.