FLORISTON, CA, USA
N47NH
ROBINSON R22B
The CFI was instructing his student in performing pinnacle approaches and landings to high density altitude mountainous locations. The student was initially flying. When the R22 had descended to 50 feet above the 6,100 ft MSL pinnacle, the CFI elected to made a go-around after observing that the terrain was not appropriate for the landing. The CFI took control of the helicopter, began turning right, and observed that the main rotor RPM decreased. The CFI attempted to recover RPM by reducing collective and rolling on full throttle. The R22 continued descending until colliding with a tree and terrain.
On September 10, 1993, at 1240 Pacific daylight time, a Robinson R22 Beta, N47NH, operated by Helicopter Adventures, Inc., Concord, California, descended into mountainous terrain during an instructional flight about 14 miles north of Floriston, California. Visual meteorological conditions prevailed at the time and the helicopter was substantially damaged. The flight instructor (CFI) and the student pilot received minor injuries. The flight originated from Reno, Nevada, on September 10, 1993, at 1145 PDT. On September 13, 1993, the CFI was interviewed via telephone. The CFI reported that during the flight lesson he planned to teach his student mountain flying techniques including how to perform "pinnacle landings." The CFI stated the student was initially flying the helicopter. However, during the pinnacle approach he took the controls to make a go-around because the landing site appeared to be unsatisfactory. The CFI further reported that at about 50 feet above ground level he turned the helicopter to the right toward lower elevation terrain. In the course of the turn, the main rotor RPM decayed and he lowered the collective. Rotor RPM was not restored and the helicopter descended into the mountainside. The CFI also stated that no mechanical problems were experienced during the flight. At the time of the accident, the helicopter's gross weight was about 1,290 pounds, the air temperature was 82 degrees Fahrenheit, and the pinnacle's elevation was about 6,100 feet mean sea level. In the CFI's completed "Aircraft Accident Report," NTSB Form 6120.1, he reported that during the attempted go-around "...the aircraft seemed to lose lift." According to the CFI, he rolled on full throttle; however, the helicopter continued descending until initially striking a tree about 50 feet above the ground at an airspeed of 40 knots. The CFI further indicated that, according to Robinson performance data, under certain conditions a R22 helicopter would have OUT and IN Ground Effect Hover Ceilings of 5,500 feet and 7,200 feet, respectively.
the flight instructor's failure to maintain main rotor RPM after initiating a go-around from a pinnacle approach. A factor in the accident was the high density altitude condition.
Source: NTSB Aviation Accident Database
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