Glendora, CA, USA
N8045K
Robinson R22 Beta
The helicopter rolled over following an autorotative landing on a sloped mountain side. According to the pilot's statements, during the flight, the student had failed to maintain adequate main rotor rpm while orbiting a mountain peak, and the helicopter entered a descent. The student relinquished the controls to the certified flight instructor (CFI); however, he was unsuccessful at restoring the requisite rpm, so he autorotated to a landing downsloping mountainous terrain. Thereafter, the helicopter rolled over. Neither pilot reported having heard the low rotor rpm warning horn, observed illumination of any annunciator light, or felt any unusual vibration. During the subsequent wreckage examination, the low rotor rpm warning systems were found functional. No evidence of any preimpact mechanical malfunction was found with the airframe or drive system. The engine was run up to full power, and no malfunctions were noted. During the accident flight, the helicopter was operating near its maximum certificated gross weight and under a high density altitude (over 4,300 feet) condition.
HISTORY OF FLIGHT On February 21, 2002, about 1330 Pacific standard time, a Robinson R22 Beta, N8045K, experienced a loss of main rotor rpm while maneuvering around a mountain peak near Glendora, California. The commercial pilot, who held a certified flight instructor (CFI) certificate, entered an autorotative descent and made a forced landing on the mountainside's uneven terrain. After touching down, the helicopter rolled over. Neither the CFI nor the student, who held a pilot certificate, was injured. The helicopter was substantially damaged. The student had rented the helicopter from the Universal Air Academy, Inc., El Monte, California. Visual meteorological conditions prevailed during the instructional flight, and no flight plan had been filed. The flight was performed under the provisions of 14 CFR Part 91, and it originated from El Monte about 1300. According to the two pilots, they had performed a preflight inspection prior to taking off, and all systems were found functional. Initially, the CFI had not planned to provide the student with flight instruction. He planned to just accompany the student as a friend. However, as the flight progressed, the CFI's role changed and he provided specific instructional guidance to the student. The CFI reported that he was aware of the current conditions including the density altitude and the possible danger of downdrafts over the mountains. The CFI reported that he advised the student to be careful. Seconds prior to the accident, the student performed an orbit around a 2,900-foot mean sea level mountain peak, about 300 feet above ground level. Nearing the conclusion of a second orbit, the helicopter suddenly commenced descending as the main rotor rpm decreased. The student relinquished control of the helicopter to the CFI when the CFI said, "I have control." Neither pilot recalled having heard activation of the low rotor warning horn, observed illumination of any annunciator light, or felt any unusual vibration. The carburetor heat control was partially on. The CFI, unable to regain the rotor rpm, entered an autorotation. The helicopter touched down softly on the underlying sloping terrain. According to the CFI, because of the slope the helicopter rolled over and came to rest partially upside down. PERSONNEL INFORMATION Flight Instructor (Left Seat). Federal Aviation Administration's (FAA) records indicate that as of November 2001, the pilot's weight was 192 pounds. The pilot held a commercial pilot certificate with a rotorcraft-helicopter rating. Also, the pilot held a certified flight instructor certificate with a rotorcraft-helicopter rating that was issued on November 24, 2001. According to the FAA, the pilot's total flight time, and his total time flying Robinson R22s, was about 300 hours. Student Pilot (Right Seat). According to the FAA, the student held a private pilot certificate with a rotorcraft-helicopter rating. The pilot's weight was about 220 pounds. The pilot's total flight time was about 69 hours, all of which were in the Robinson R22. AIRCRAFT INFORMATION The helicopter's approximate basic empty weight was 871 pounds. The operator estimated that about the time of the accident, the helicopter's fuel tank should have contained at least 12 gallons of fuel, for a total of 72 pounds. The gross weight of the helicopter at the time of the accident was estimated to be 1,355 pounds. The maximum certificated gross weight for the helicopter is 1,370 pounds. According to the Robinson Helicopter Company, at its certificated maximum gross weight, the accident model of helicopter can hover out of ground effect up to an altitude of 5,200 feet. METEOROLOGICAL INFORMATION The Brackett Field, elevation 1,011 feet mean sea level, is located about 6 miles southeast of the accident site. At 1347, the Brackett Field reported that its temperature and dew point were 29 and 2 degrees, Celsius, respectively. The altimeter was 30.25 inches of mercury. The estimated density altitude at the accident site was over 4,300 feet. WRECKAGE AND IMPACT INFORMATION The accident site is located in the San Gabriel Mountains, near Glendora. The approximate global positioning satellite coordinates of the accident site are 34 degrees 10.4 minutes north latitude by 117 degrees 51.1 minutes west longitude. The estimated accident site elevation is 2,600 feet mean sea level. Terrain beneath the helicopter wreckage was uneven, and the helicopter was found partially upside down. An examination of the helicopter structure revealed that its cabin sustained impact damage to its right side. The right side window and the windshield were broken out. The doorpost and roof were collapsed. The vertical firewall was buckled on the right side along with the lower cabin skins. The tail cone was bent at the forward end of the first bay. The horizontal and lower vertical stabilizers were bent. There was no evidence of fire. TESTS AND RESEARCH The helicopter was recovered from the accident site and examined at the direction of the National Transportation Safety Board investigator while under FAA supervision at the Robinson Helicopter Company. Results of the examination are summarized as follows: Airframe and Driveline Examination. Both main rotor blades were bent, with the trailing edge wrinkled. Both elastomeric teeter stops were split horizontally, and the supporting brackets were bent. Both main rotor pitch horns were bent. The main rotor drive shaft rotated freely. The mast tube was broken at its base. The forward flex coupling was undamaged. The V-belts were out of position on the upper sheave (one groove forward) with one V-belt over the forward edge of the sheave. This belt was partially split in the web between the V-belts. Both belts were in position on the lower sheave. The clutch shaft rotated freely when turned counterclockwise (looking forward) and locked up when reversed, which corresponds to proper operation according to Robinson Helicopter Company personnel. The tail rotor drive shaft damper bearing was undamaged along with the aft flex coupling. The tail rotor gearbox rotated smoothly. The tail rotor pitch change slider was free to slide along the tail rotor gearbox output shaft. The helicopter's low rotor warning horn circuitry and the associated annunciator light were examined. The warning horn system was found functional, and the light illuminated. The gascolator was found devoid of contaminates. The carburetor's fuel screen was clear. Both fuel caps were secure. No evidence of preimpact failures of the flight control system was found, according to the FAA. Engine Controls, Engine and Accessory Examination. The fuel mixture control knob was found in the full rich position, as was the mixture arm on the carburetor. The return spring was in place. The mixture cable housing was secure and the cable operated upon application of push-pull force. The rpm governor controller and wiring were tested using a test box provided by the Robinson Helicopter Company. When the test box simulated an engine rpm of 84 percent (its present test point), the governor rolled on throttle properly, according to Robinson personnel. The upper drive belt sheave exhibited circumferential scoring on the rear surface. The steel tube frame exhibited scoring in a direction parallel to sheave rotation direction. The FAA opined that this signature was indicative of the engine rotating at the time of impact. The lower spark plugs were removed to allow any accumulated oil to drain, and then they were replaced. The rotor brake switch was taped into the open position. The drive belts were cut and removed. A battery was attached and the engine was started and run up to 104 percent. The FAA reported that no malfunctions were noted. ADDITIONAL INFORMATION AND WRECKAGE RELEASE The Safety Board investigator requested that the operator complete the Safety Board's "Aircraft Accident Report," form 6120.1/2. No completed form was received from the operator. The wreckage was verbally released to the operator following completion of its examination at the Robinson Helicopter Company.
The student's failure to maintain adequate main rotor rpm, and the flight instructor's inadequate supervision. Contributing factors were the high helicopter gross weight and density altitude, and the descending mountainous terrain.
Source: NTSB Aviation Accident Database
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