Las Vegas, NV, USA
N7020U
ROBINSON HELICOPTER R22
The student pilot was conducting approach and departure practice in the single main rotor helicopter. The practice area was a flood control basin located in the desert about 3 miles east of mountainous terrain. The basin was bounded on its east side by a 1-mile-long concrete levee oriented approximately north-south, which rose about 50 ft above the basin floor. The west-facing wall of the levee was sloped about 25 degrees to the horizontal and was topped by a level road. After an uneventful approach to the road from the north, the pilot slowed to a hover-taxi, and then, without touching down, he added power and control inputs to begin his departure straight ahead. The helicopter began to yaw to the right, and the pilot was unable to correct the rotation. The helicopter drifted west over the sloped part of the levee, continued to rotate while descending, and the pilot then attempted to land. The tail rotor struck the levee, and the helicopter landed hard on the sloped wall, facing uphill. Postaccident examination of the helicopter and several components did not reveal any deficiencies or failures that would have precluded normal operation. The only definitive wind information was from the pilot's departure airport about 9 miles away from the basin, which reported that the wind was about 6 knots from the east-southeast, and the pilot reported that the wind at the basin was similar. The late-morning timeframe, combined with the local topography and desert environment, led to unpredictable wind and/or gusts at the accident site. The pilot's description of the accident circumstances and events were consistent with a loss of tail rotor effectiveness that occurred as the pilot was attempting the transition from the hover-taxi to the departure segment.
HISTORY OF FLIGHTOn January 22, 2016, about 1100 Pacific standard time, a Robinson R22 Beta, N7020U, sustained substantial damage following the student pilot's loss of control while attempting to transition from a hover taxi to a climbing departure near Las Vegas, Nevada. The pilot received minor injuries. The solo instructional flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no FAA flight plan was filed for the flight. According to the pilot, the helicopter was rented from a fixed base operator (FBO) and FAR Part 61 flight school based at North Las Vegas airport (VGT), Las Vegas. The purpose of the flight was to practice maneuvers at a water retention basin that was located about 10 miles to the northwest of VGT. The area was a normal practice area for the FBO, and was referred to as the "northwest" practice area. A concrete levee, about 50 feet high, bounded the east side of the basin. The levee was oriented north-south, was topped by a roadway, and its west wall sloped about 25 degrees from horizontal. In his written statement regarding the accident, the pilot reported that he met with his flight instructor, briefed the flight, and then both individuals preflighted the helicopter. The instructor then returned to his office facility, while the student continued with the flight preparations. Engine start and run up were normal, and the reported VGT winds were "variable" at 7 knots out of the south. The pilot was cleared for departure by the air traffic control tower about 1040, and proceeded to the practice area uneventfully. The pilot intended to practice normal approaches to a pinnacle landing. He flew a right traffic pattern over the levee to verify wind direction, and to choose a location on the levee to which he would conduct the approach. He confirmed that the wind was still out of the south, and flew a northbound right downwind leg at approximately 500 feet above ground level (agl), at a speed of about 65 knots. He began a descent while turning onto the base leg, and maintained a descent rate of about 300 feet per minute (fpm) on final, while also decelerating. He brought the helicopter into a hover taxi at about 10 feet agl above the levee. The pilot reported that he then "pushed forward" on the cyclic control to begin a climb out for another pattern. The helicopter began to yaw to the right, and despite application of full left pedal, continued its right yawing motion. The pilot "rolled off" the throttle in an attempt to decrease the yaw rate, and concurrently lowered the collective control. The helicopter continued its right spin, and began drifting to the west, over the concrete sloped portion of the levee. The pilot then decided to "gradually raise collective" in an attempt to reduce the descent rate before ground contact. The helicopter made a hard landing almost immediately after, but remained upright. The pilot then shut down the helicopter, and telephoned his flight instructor, who had remained back at VGT. In his statements regarding the accident the pilot reported that he did not observe any engine anomalies, or the illumination of the low rotor rpm light. Sketches provided by the pilot indicated that his arrival flight path was along the top of the levee, as was his intended departure path. Damage to the helicopter included fracture-separated tail rotor blades, a buckled tail boom, and deformation of the landing skids. The helicopter was recovered to a secure location for subsequent examination. PERSONNEL INFORMATIONThe pilot reported that he held a student pilot certificate, and had a total flight experience of approximately 50 hours, all of which was in Robinson helicopters, and which included about 7 hours solo in the R22. He received his R22 solo endorsement in December 2015. His most recent FAA first-class medical certificate was issued in June 2015. AIRCRAFT INFORMATIONFederal Aviation Administration (FAA) information indicated that the helicopter was manufactured in 1998, and was equipped with a Lycoming O-360 series engine. When viewed from above, the main rotor blades rotate in a counter-clockwise direction. The tail rotor assembly is used to counteract the resulting helicopter nose-right torque. Review of the maintenance records indicate that the most recent inspection of the helicopter was completed on December 22, 2015, when the helicopter had a total time in service (TT) of about 8,240 hours, and the hour meter registered 1,613.6 hours. That inspection was annotated as being in accordance with the manufacturer's "100/300 hour inspection." The most recent annual inspection of the helicopter was completed on October 8, 2015, when the helicopter had a TT of about 8,045 hours, and the hour meter registered 1,419.2 hours. The maintenance records indicated that the right magneto that was installed on the helicopter at the time of the accident had been overhauled by Aircraft Electrical Components, Inc., and installed on the helicopter on July 17, 2015, when the helicopter had a TT of about 8,015 hours, and the hour meter registered 1,389.8 hours. At that time the engine had a TT of about 4,953 hours, and a time since major overhaul (TSMOH) of 1,389.8 hours. The maintenance records indicated that a "B245-1 Gov Reg Motor Assy" was removed and replaced on November 24, 2014, when the helicopter had a TT of about 7,754 hours, and the hour meter registered 1,133.1 hours. The "245-1" citation incorrectly referred to the governor motor gear housing part number instead of the correct overall assembly designator "B247-5." METEOROLOGICAL INFORMATIONThe 1053 VGT automated weather observation included winds from 140 degrees at 6 knots, visibility 10 miles, clear skies, temperature 13 degrees C, dew point minus 6 degrees C, and an altimeter setting of 30.21 inches of mercury. Both the pilot's flight instructor and the FAA inspector, who had significant experience flying helicopters in that region, reported that the flood basin area was subject to unpredictable winds due to topography and local heating as each day progressed. AIRPORT INFORMATIONFederal Aviation Administration (FAA) information indicated that the helicopter was manufactured in 1998, and was equipped with a Lycoming O-360 series engine. When viewed from above, the main rotor blades rotate in a counter-clockwise direction. The tail rotor assembly is used to counteract the resulting helicopter nose-right torque. Review of the maintenance records indicate that the most recent inspection of the helicopter was completed on December 22, 2015, when the helicopter had a total time in service (TT) of about 8,240 hours, and the hour meter registered 1,613.6 hours. That inspection was annotated as being in accordance with the manufacturer's "100/300 hour inspection." The most recent annual inspection of the helicopter was completed on October 8, 2015, when the helicopter had a TT of about 8,045 hours, and the hour meter registered 1,419.2 hours. The maintenance records indicated that the right magneto that was installed on the helicopter at the time of the accident had been overhauled by Aircraft Electrical Components, Inc., and installed on the helicopter on July 17, 2015, when the helicopter had a TT of about 8,015 hours, and the hour meter registered 1,389.8 hours. At that time the engine had a TT of about 4,953 hours, and a time since major overhaul (TSMOH) of 1,389.8 hours. The maintenance records indicated that a "B245-1 Gov Reg Motor Assy" was removed and replaced on November 24, 2014, when the helicopter had a TT of about 7,754 hours, and the hour meter registered 1,133.1 hours. The "245-1" citation incorrectly referred to the governor motor gear housing part number instead of the correct overall assembly designator "B247-5." WRECKAGE AND IMPACT INFORMATIONThe pilot was practicing along the roadway atop the levee, which extended for about 1.1 miles, and that is where the accident occurred. The site was located about 8.6 miles, on a true bearing of about 305 degrees, from VGT. A mountain range was situated about 3 miles to the west of the site. An FAA Inspector traveled to the accident location on the day of the accident, and conducted a follow-up examination 3 days later. The helicopter came to rest upright, facing uphill, approximately 2/3 of the way down the sloped levee wall. Scrape marks from ground contact were limited to the sloped portion of the levee. Both skids were deformed upwards to the point that the remaining ground clearance was about 25 per cent of original. The cabin volume was not compromised, and the main rotor system, including the blades, was undamaged. The juncture of the tail boom and fuselage was deformed and partially fractured. Both tail rotor blades were fracture-separated from the hub assembly at about their 1/4 span points. The blade fractures were consistent with loads in the plane of rotation, as opposed to loads perpendicular to the plane of rotation. The lower vertical stabilizer was scraped and bent towards the helicopter starboard (right), consistent with ground contact while the helicopter spinning nose right. There were no fuel leaks, and no fire. No evidence of any preimpact mechanical malfunction or failures was noted during the examination of the helicopter. Refer to the public docket for this accident for additional examination details. ADDITIONAL INFORMATIONFAA Post-Recovery Examination On January 25, 2016, subsequent to its recovery to Apex Aviation at VGT, the helicopter was examined further by the FAA inspector who initially examined it at the accident site. His findings included the following; Both tail rotor (TR) pedals were free to make full travel movements. All TR push rod attachments were secure, and the rods had full and free movement. There was a minor anomaly with the forward bell crank in the gear box compartment; it showed evidence of a one-time contact with the firewall. However, although the clearance was limited, the bellcrank did not contact the firewall throughout its travel range, and the push rod in the gear box compartment operated freely with full movement. The TR links and blades had full and complete pitch travel in both directions. The pitch change bearing operated normally, through its full travel range. All controls were free and easily movable. All the rod ends were intact and did not appear to be worn or eroded. Throughout the system, no foreign objects were found that would impede movement. The TR drive system was intact, without damage. The main rotor appeared to be undamaged. When the tail rotor was manually rotated in one direction, the main rotor also turned freely, per design. However, as expected and normal, rotation in the opposite direction was more difficult, due the clutch being engaged with tensioned drive belts. All TR drive shaft flex couplings were intact and undamaged. All "Telatemp" decals appeared normal, with no indications of abnormal operating temperatures on any components. The tail rotor gear box had sufficient oil. The only observed damage to the TR drive and control systems was to the TR blades, due to impact with the concrete levee. The inspector removed and examined the light bulb for the low rotor rpm warning light, and observed the filament to be intact. Component Removals On February 2, 2016, a technician from Apex Aviation and the FAA inspector removed three components (Governor Controller Box, Magneto, and Governor Motor) from the subject helicopter for subsequent examination. Component Examinations and Tests On February 9, 2016, at Robinson Helicopter Company (RHC), Torrance, California, examinations and some tests were performed on the three removed components, with oversight by investigators from Robinson and the NTSB. With one minor exception involving the magneto, all three components satisfactorily met all applicable condition and functionality criteria. A visual inspection of the Governor Controller Box revealed that the box had not been opened or overhauled since its production. No external damage, with the exception of a small area of bubbled paint, was present. The electrical connector was clean and undamaged. A functional test was performed using the production acceptance criteria. The controller satisfactorily met (passed) all of the test criteria. A visual examination of the interior found no indication of heat coming from the internal circuitry that would account for the bubbled paint, and no abnormalities were observed with the internal components. The bubbled paint was presumed to be the result of an unknown event during manufacture. The engine right (helicopter left) magneto was examined. A visual inspection of the magneto revealed that the data plate was yellow in color, indicating that it had been overhauled in the field (not by the manufacturer). No external damage was noted. The point cover was removed, and no oil or grease contamination was evident on or near the points. Although one holddown screw appeared to be slightly undertorqued, the tachometer point base was secure, and all the proper hardware was intact and in place. The points opened and closed on manual magneto rotation. The tachometer points, which provide a signal to the tachometer and the governor, had a gap between the contact points of less than .012 inches; (manufacturer's specification is .019 + .003 inches). The tachometer points were undamaged, and the contact pads were clean and smooth. A visual inspection of the governor motor revealed no external damage. A functional test was performed, with satisfactory results, and the motor was determined to be in compliance with production specifications. The functional test included directionality, and appropriate "friction disc slippage" checks, as indicated by motor current draw with a jammed actuator link. Loss of Tail Rotor Effectiveness (LTE) According to the Helicopter Flying Handbook (HFH, FAA-8083-H-21A), loss of tail rotor effectiveness (LTE) is an aerodynamic result of a control margin deficiency in the tail rotor that affects all single-rotor helicopters that utilize a tail rotor. The design of main and tail rotor blades and the tail boom assembly can affect the characteristics and susceptibility of LTE but will not nullify the phenomenon entirely. Rotor system efficiency is a direct function of the stability (absence of turbulence) of the air entering the rotor system. The less disturbed the air, the more efficient and effective the rotor system, and conversely, the more disturbed the air, the less efficient and effective the rotor system is. Highly disturbed air can result in a loss of tail rotor thrust and yaw control. The HFH stated that loss of tail rotor thrust can be affected by numerous external factors, and that the main factors contributing to LTE are: 1. Airflow and downdraft generated by the main rotor blades interfering with the airflow entering the tail rotor assembly. 2. Main blade vortices developed at the main blade tips entering the tail rotor. 3. Turbulence and other natural phenomena affecting the airflow surrounding the tail rotor. 4. A high power setting, hence large main rotor pitch angle, induces considerable main rotor blade downwash and hence more turbulence than when the helicopter is in a low power condition. 5. A slow forward airspeed, typically at speeds where translational lift and translational thrust are in the process of change and airflow around the tail rotor will vary in direction and speed. 6. The local ambient airflow relative to the helicopter. The worst case is a relative wind from about 285 to 315 degrees ( ±15 degrees from the 10 o'clock position) from the nose of the helicopter; this can generate vortices that can blow directly into the tail rotor. The conditions at the time of the pilot's loss of control were consistent with those cited in items 3 through 5, and the reported winds were in approximate agreement with the sector specified in item 6.
The loss of helicopter control as a result of the loss of tail rotor effectiveness.
Source: NTSB Aviation Accident Database
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