History of Flight
On July 8, 2013, at approximately 0820 mountain daylight time, a Robinson R22 Beta II (registration 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 Part 91 of the Federal Aviation Regulations. The flight instructor (CFI) and a private pilot undergoing instruction were on board; both sustained minor injuries. The helicopter was destroyed in the accident sequence.
The local instructional flight departed Heber City Municipal Airport - Russ McDonald Field, Heber, Utah, at 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.
According to the CFI, earlier that morning they departed Salt Lake City at about 0630, following a route that used roads through mountain passes north of the accident site. The passes were at lower elevations than the accident location. The pilot undergoing instruction reported that for the return flight, the CFI chose a more direct route over the mountain peaks east of Salt Lake City.
The pilot undergoing instruction was controlling the helicopter for the departure from Heber City and the climb westward toward the Lone Peak Wilderness area. The CFI stated that during the ascent, the helicopter maintained a climb rate of about 500 feet per minute. The outside air temperature gauge showed 12 degrees Celsius, manifold pressure indicated 20 inches of mercury, and carburetor heat was on to keep the carburetor temperature gauge in the yellow band. The helicopter maintained an airspeed of 65 knots as they passed a ridge at an elevation of about 10,000 feet mean sea level (msl); by then, manifold pressure had dropped to 18 inches.
As they began descending the back side of the ridge, the pilot under instruction raised the collective to reduce the descent rate. Immediately, rotor speed began to decay and the low rotor rpm warning sounded. The CFI took control, lowered the collective, and increased engine power with the throttle. Rotor speed recovered briefly, but when the CFI raised the collective again to arrest the descent, the low rotor rpm warning sounded again. This cycle repeated two more times. As the helicopter neared the ground, the CFI applied aft cyclic to reduce forward speed. Moments 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 summit of Mount Baldy. The ridge line adjacent to the site ran north-south at about 11,000 feet along the presumed flight path. The terrain fell away over the next 5 miles to the southwest toward Alpine, 5,000 feet below. The CFI stated they maintained a ground clearance of 300 to 400 feet during the climb and ridge traversal.
Meteorological Information
An automated surface weather observation at Salt Lake City International Airport (KSLC), elevation 4,227 feet and 22 miles northwest of the accident site, issued at 0753, reported wind from 160 degrees at 10 knots, visibility 10 miles, few clouds at 11,000 feet, scattered clouds at 14,000 feet, temperature 24 degrees Celsius, dew point 12 degrees Celsius, and an altimeter setting of 30.06 inches of mercury.
At Heber City Airport, at 0815, winds were calm with clear skies, temperature 16 degrees Celsius, dew point 12 degrees Celsius, and an altimeter setting of 30.21 inches of mercury.
Using the Heber City and Salt Lake City data, the calculated density altitude at 11,000 feet was about 14,000 feet.
Wind information from a rawinsonde launched at 0500 from Salt Lake City indicated at 8,000 feet msl wind from 200 degrees true at 15 knots; at 9,000 feet wind from 230 degrees at 7 knots; at 10,400 feet wind from 250 degrees at 12 knots. Calculations did not identify more than moderate turbulence below 18,000 feet in the region.
Additional Information
The helicopter was equipped with a Lycoming O-360-J2A engine producing 145 BHP. Its maximum gross weight was 1,370 pounds; the operator reported a weight of 1,313 pounds at the time of the accident. A Federal Aviation Administration inspector examined the helicopter after recovery and found no anomalies that would have precluded normal operation.
The R22 Pilot Operating Handbook listed a maximum operating density altitude of 14,000 feet. The hover in ground effect (HIGE) ceiling chart at 1,313 pounds, zero wind, and 12 degrees Celsius indicated a maximum altitude for a hover in ground effect (2-foot skid clearance) of about 9,600 feet.