Alta, UT, USA
N712U
ROBINSON HELICOPTER COMPANY R22
The flight instructor reported that the outbound training flight on the morning of the accident followed roads through mountain passes. For the return flight, the flight instructor decided to take a more direct route and fly over 11,000-foot-high mountainous peaks. The pilot undergoing instruction was controlling the helicopter during the climb, which was uneventful. As the helicopter crested the peak, the pilot initiated a descent and then began to raise the collective to reduce the descent rate; however, as he did so, the rotor speed began to decay, and the low rotor rpm warning sounded. The flight instructor took over the flight controls but was unable to arrest the descent, and he subsequently chose to perform a forced landing to rocky terrain. The helicopter struck the ground, tumbled, and was destroyed; both occupants sustained serious injuries. The helicopter was operating at a density altitude equal to or just above the helicopter's maximum operating density altitude of 14,000 feet. At the altitude of the accident site, the helicopter was not capable of hovering in-ground-effect; therefore, it was unlikely that a landing could have been successfully accomplished in the rocky terrain. Further, after cresting the peak, the helicopter likely encountered downdrafts due to the mountainous terrain surrounding the accident site, which further degraded the helicopter's performance. A postaccident examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation.
HISTORY OF FLIGHTOn July 8, 2013, about 0820 mountain daylight time, a Robinson R22 Beta II, N712U, collided with mountainous terrain in a wilderness area near Alta, Utah. The helicopter was registered to Tumbleweed Leasing Co, Inc., and operated by Upper Limit Aviation, Inc., under the provisions of 14 Code of Federal Regulations Part 91. The flight instructor (CFI) and private pilot undergoing instruction sustained minor injuries. The helicopter was destroyed during the accident sequence. The local instructional flight departed Heber City Municipal Airport - Russ McDonald Field, Heber, Utah, about 0800, with a planned destination of Salt Lake City International Airport, Salt Lake City, Utah. Visual meteorological conditions prevailed, and a company flight plan had been filed. The CFI stated that on the outbound journey that morning, they departed from Salt Lake City about 0630, taking a route of flight that followed roads through mountain passes to the north of the accident site. The passes were lower than the accident elevation. The pilot undergoing instruction reported that for the return flight, the CFI decided to take a more direct route, overflying the mountain peaks east of Salt Lake City. The pilot undergoing instruction was controlling the helicopter for both the departure from Heber City, and the climb to the west towards the Lone Peak Wilderness area. The CFI reported that throughout the ascent, the helicopter was able to maintain a climb rate of about 500 feet per minute. The outside air temperature gauge indicated 12 degrees C, the manifold pressure indicated 20 inches of mercury, and carburetor heat was on in order to keep the carburetor temperature gauge within the yellow band. He stated that the helicopter was maintaining an airspeed of 65 knots as they passed along a ridge at an elevation of about 10,000 feet msl, and by that time the manifold pressure had reduced to 18 inches. They began the descent down the back side of the ridge, during which time the pilot began to raise the collective in order to lower the descent rate. As soon as he did, the rotor speed began to decay, and the low rotor rpm warning sounded. The CFI took control of the helicopter, and lowered the collective, while simultaneously increasing engine power with the throttle control. Rotor speed increased, and a short time later the CFI raised the collective in order to arrest the descent; however, the low rotor rpm warning sounded again. The CFI again lowered the collective and applied power, and the rotor speed again began to decay. This cycle continued two more times, and as the helicopter approached the ground, the CFI applied aft cyclic control in an effort to reduce forward speed. A few seconds later, the main skids struck rocks, and the helicopter tumbled. The helicopter came to rest at an elevation of about 9,700 feet, 1.3 miles west of the 11,321-foot-tall summit of Mount Baldy. The ridge line adjacent to the accident site traversed from north to south, and was at an elevation of about 11,000 feet along the presumed flight path. The terrain at the accident site fell away over the next 5 miles to the southwest, towards the city of Alpine, 5,000 feet below. The CFI stated that they maintained a ground clearance of between 300 and 400 feet both during the climb, and ridge traversal. METEOROLOGICAL INFORMATIONAn automated surface weather observation at Salt Lake City International Airport (KSLC) (elevation 4,227 feet msl, 22 miles northwest of the accident site) was issued at 0753. It indicated wind from 160 degrees at 10 knots, 10 miles visibility, few clouds at 11,000 feet, scattered clouds 14,000 feet, temperature at 24 degrees C, dew point 12 degrees C, and an altimeter setting of 30.06 inches of mercury. The weather reporting station at Heber City Airport reported calm winds at 0815, with clear skies, a temperature of 16 degrees C, dew point 12 degrees C, and an altimeter setting of 30.21 inches of mercury. Utilizing the Heber City and Salt Lake City weather information, the calculated density altitude at 11,000 feet was about 14,000 feet. Wind information was retrieved from a rawinsonde launched at 0500 from Salt Lake City. This data indicated that at 8,000 feet msl the wind was from 200 degrees true at 15 knots. At 9,000 feet the wind was from 230 degrees at 7 knots, and at 10,400 feet the wind was from 250 degrees at 12 knots. Calculations made by the Rawinsonde Observation Program did not identify anything greater than moderate turbulence below 18,000 feet in the region. ADDITIONAL INFORMATIONThe helicopter was equipped with a Lycoming O-360-J2A, 145 BHP engine. Its maximum gross weight was 1,370 pounds, and the operator reported a weight of 1,313 pounds at the time of the accident. The helicopter was examined by a Federal Aviation Administration inspector following recovery. No anomalies were noted that would have precluded normal operation. The limitations section of the R22 Pilot Operating Handbook stated a maximum operating density altitude of 14,000 feet. The in ground effect hover (HIGE) ceiling versus gross weight chart in the handbook's performance section stated that at a weight of 1,313 pounds, with zero wind, and a temperature of 12 degrees C, the maximum altitude for a hover in ground effect (2-foot skid clearance) would have been about 9,600 feet.
The flight instructor's decision to follow a route over mountainous terrain in conditions that exceeded the helicopter’s ability to maintain terrain clearance.
Source: NTSB Aviation Accident Database
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