DEN00GA050

The pilot's failure to roll throttle back on (return the power to the normal operating range) during an attempted power recovery from an autorotation, and his subsequent failure to maintain aircraft control.

The pilot of the helicopter was to perform an autorotation during a maintenance flight to perform a functional check of the free-wheeling unit. A witness observed the helicopter at 100 to 150 feet agl, and he said that the main rotor blades 'stopped' and the aircraft started a slow spiral to the left, nose down. He further said that the helicopter was shaking violently, and its skids were flexing in and out. Postcrash examination revealed that the fuel control pointer, on the fuel control, was slightly above flight idle. Both cockpit throttles were observed positioned in slightly above the flight idle position. The helicopter's power analyzer and recorder (PAR) documented that at the time of impact, the engine's torque (TRQ) was at 13.5% and the main rotor speed (NR) was at 65.8%. The procedure for a power recovery from an autorotation is to smoothly roll throttle back on, confirm rotor and N2 needles are joined and in normal operating range, and simultaneously pull up collective while applying left pedal.

HISTORY OF FLIGHT On February 11, 2000, at 1404 mountain standard time, a military surplus Bell OH-58A+ helicopter, N7UT, was destroyed when it impacted terrain while performing an autorotation during a maintenance flight at Skypark Airport, Woods Cross, Utah. The commercial pilot and his mechanic passenger were both fatally injured. The public use helicopter was being operated by the Utah Department of Public Safety under Title 14 CFR Part 91. Visual meteorological conditions prevailed for the maintenance test flight that originated 13 minutes before the accident. The pilot had not filed a flight plan. According to maintenance personnel, the helicopter was being test flown to evaluate the fuel control for engine RPM (revolutions per minute) droop and to conduct a functional check of the free-wheeling unit. The ground crew reported that the pilot started the engine at approximately 1320, and the helicopter became airborne at approximately 1350. Radar data indicates that the helicopter departed runway 16 and made a left turn to an approximate 360 degree ground track. The pilot reported to Salt Lake City approach control that he was "over Bountiful northbound to Lgoon and back." Lgoon is the name of a step-down fix on the Salt Lake City ILS approach to runway 16L (an estimated 6 nautical miles [nm] north of Skypark Airport). At 1357:27, radar data indicates that the helicopter reversed course southbound. At 1401, the helicopter turned westbound (at approximately 750 feet above ground level [agl]) on a 1 nm base-leg for runway 16. Radar contact with the helicopter was last recorded at 1403:18, when it was at approximately 700 to 800 feet agl. A witness sitting in his airplane at the approach end of runway 16 observed the helicopter on final approach. He heard the pilot transmit that he was going to practice an autorotation. He said that 2 to 5 seconds later, the helicopter was "100 to 150 feet agl, the main blades of the Jet Ranger [OH-58] stopped, and the craft started a slow spiral to the left, nose down." He said that the helicopter was "shaking violently, and the skids were flexing in and out." The main rotor was flexing up and down in an "extreme" manner; the tail rotor separated from the helicopter at approximately 50 to 60 feet agl. The witness said that the "Jet Ranger [OH-58] continued a slow left spiral until impacting on its left side." He said that he heard no transmissions from the pilot after "control was lost." Another witness said, "I heard a helicopter and so I looked up and then the blades curled up weird and then made a weird left turn and plunged to the ground." Another witness reported that during the helicopter's fall, the main "rotor almost stop[ped] turning." PERSONNEL INFORMATION The pilot began flying in 1971, and flew only fixed winged aircraft until October 1991 when he received his commercial pilot certificate for helicopters. He began flying for the state of Utah in May 1978, and over the next 22 years flew for Wildlife Resources, Department of Transportation, and Department of Public Safety (DPS). At the time of the accident, DPS records indicate that the pilot had a total of 9,655 hours of flight experience. Approximately 1,313 hours of this time was in helicopters, of which 937 hours was in turbine powered helicopters. The pilot's last flight prior to the accident flight was in the accident helicopter, 23 days before the accident. According to a DPS pilot, DPS helicopter pilots went to a flight training recurrency school once a year, and that was the only time that they practiced autorotations to the ground. With their own helicopters, they occasionally practiced autorotations with power recovery. He said that a consultant flight instructor came to Salt Lake City on November 2-5, 1999, and provided training to the pilot and himself in the use of night vision goggles. During this training, both DPS pilots flew three autorotations (during the day) to power recoveries. On one of these practice autorotations, the accident pilot over sped the main rotor (110% plus was observed by the flight instructor), and a maintenance inspection was performed. The consulting flight instructor said that the pilot had "good air sense." He further stated that the pilot "had a tendency to concentrate on one thing, and leave other items out of his scan." When he left Salt Lake City, he made the recommendation that the two DPS helicopter pilots practice autorotations together. On the morning of the accident, while the helicopter was being prepared to fly, the pilot said to one of the maintenance men that he was "not really very good at doing autorotations." He further said to the maintenance man that "I'll kind of do it; I'll let Steve do it later." AIRCRAFT INFORMATION The helicopter was a single engine, two-bladed main rotor, four seat aircraft, which was manufactured by Bell Helicopter in 1971. It was designed and manufactured for military use, and in May 1998 it was recertificated for government use (public use). The helicopter was powered by a T63-A720 (Allison 250-C20C) turboshaft, reverse flow engine that had a maximum rating of 420 horsepower, but was derated to 317 horsepower. The engine was last overhauled by the US Army on February 16, 1995, and had accumulated approximately 823 hours of operation by the time of the accident. The aircraft records indicate that the airframe (S/N 41703, Army No.71-20842) had accumulated approximately 5,015 hours, at the time of the accident. The model designation of the helicopter was OH-58A+, which is the OH-58A with a bigger engine. The OH-58A+ and the OH-58C helicopters have the same engine and maximum gross weight of 3,200 pounds; the differences are in the instrument panel and avionics. The accident helicopter had several modifications: long range extender fuel tank (71 to 89 gallons usable), Night Bright light, external hook with mirror, power analyzer and recorder (PAR), and Bear Paws on the landing skids for snow landings. The engine manufacturer's representative estimated that the engine's average fuel consumption was between 24 to 25 gallons per hour. The airframe manufacturer's representative said that the main rotor normal operating speed was from 93% to 110% RPM. The pilot flew the helicopter from Salt Lake City International Airport to Skypark Airport, on January 19, 2000, for maintenance. The normal 25 hour inspection was scheduled; additionally, the fuel control rigging was to be adjusted, and a leaking freewheeling unit was to be repaired. According to a Utah DPS pilot, the procedures for performing an autorotation are as follows: collective full down, smoothly roll throttle off [out of the fuel governor range], cyclic adjust for airspeed (too fast or too slow and the rate of decent can get excessive), confirm rotor in the green to ensure that the free wheeling unit disengaged, and confirm N1 stabilized showing that the engine was still making power. For the power recovery, smoothly roll throttle back on, confirm rotor and N2 (power turbine) needles are joined and in normal operating range, and simultaneously pull up collective while applying left pedal. Proceed with the climb out. He further stated that when they practiced autorotations, they entered them at approximately 1,200 feet agl. The DPS pilot said the helicopter's main rotor rotates counter-clockwise (from the perspective of the pilot's seat), and that left anti torque pedal was required whenever torque was being generated by use of the collective. The left anti torque pedal counteracts the fuselage right turning tendencies whenever torque is being generated. He said that if torque is not being generated, and left anti torque pedal is applied, the helicopter would rotate to the left. METEOROLOGICAL INFORMATION At 1356, the weather conditions at the Salt Lake City International Airport (elevation 4,227 feet),