WPR13LA188

During most of the flight, the right-seat pilot was the flying-pilot. As the flight approached the destination airport, the left-seat pilot assumed authority of the helicopter's flight controls and noted that the wind was calm. The pilot then maneuvered the helicopter from about 20 ft above ground level toward the intended touchdown zone. The pilot subsequently lost control of the helicopter; he stated that the flight controls felt "mushy" and unresponsive. The other pilot unsuccessfully attempted to help him regain control, and the helicopter subsequently descended near-vertically and landed hard. An examination of the hydraulic servos, reservoir, and pump and the flight control system revealed no evidence of preimpact mechanical malfunctions or failures that would have precluded normal operation.

HISTORY OF FLIGHT On April 12, 2013, about 0800 Pacific daylight time, a Robinson R44 II, N442FG, was landing at Hogan's Corner Airport, Ocean Shores, Washington, when the pilot experienced a loss of control. Oregon Roses, Inc., owned and operated the helicopter under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The commercial pilot and pilot-rated passenger sustained minor injuries; the helicopter sustained substantial damage. The pilot departed a private helipad in Forest Grove, Oregon, about 0645, with a planned destination of Hogan's Corner Airport. Visual meteorological conditions prevailed, and no flight plan had been filed. The pilot stated that after departure, they flew north over the Oregon coastline. He planned to pick up his son at the Hogan's Corner Airport and continue the flight to Copalis State Airport, Copalis, Washington. His daughter (positioned in the right seat) was the flying-pilot for the main duration of the flight, although as they approached the airport, the pilot took over the flight controls. The pilot maneuvered over runway 24 about 20 feet above ground level (agl) toward the hangars positioned on the west end of the airport. The pilot further stated that he experienced a loss of control and his daughter attempted to help him regain control of the helicopter. He stated the flight controls felt "mushy" and unresponsive. The helicopter descended near-vertically and landed hard. He added that he had no yaw problems, nor was there a low rotor rpm indication. He remarked that the wind was calm. AIRCRAFT INFORMATION The maintenance records were obtained from the operator, which outsourced a majority of their maintenance to Leading Edge Aviation, Bend, Oregon. In addition, information was obtained from the Robinson manufacturing records and the official FAA Aircraft and Registry files. According to the records examined, the helicopter was a Robinson R44 Raven II, serial number 10444, manufactured in 2004. At the time of the accident, the airframe had accumulated a total time in service of 469.9 hours. The most recent annual inspection was completed on February 26, 2013, 2.9 hours prior to the accident. The records indicate that during that inspection, maintenance personnel removed the hydraulic pump output fitting and replaced the retainer and o-ring. Comparison of the Airworthiness Directive (AD) compliance listing in the log book against a list of AD's applicable to the aircraft's serial number revealed that all had been endorsed as complied with. From the purchase of the helicopter in 2004, the pilot made one modification of the installation of a cargo hook with an approval endorsed on FAA 337 form covering the work performed. On January 10, 2010, at an airframe time of 358.4 (about 110 hours before the accident) the records indicate that the hydraulic filter, a disposable cartridge rated at 10 microns (part number AN6235-1A), was replaced. According to the maintenance manual section 8.005 the filteris to be replaced during 100-hour inspections. In the maintenance manual "Table 1 Scheduled Maintenance and Inspections" Page 1.3C, the replacement of the filter was listed as to occur every 300 hours. Following the accident, this discrepancy was changed for both sections to reflect a 300 hour requirement. Flight Controls According to the helicopter's pilot operating handbook (POH), dual controls are standard equipment and all primary controls are actuated through push-pull tubes and bellcranks. The main rotor flight controls are hydraulically boosted to eliminate cyclic and collective feedback forces. The hydraulic system consists of a pump, three servos, a reservoir, and interconnecting lines. Normal operating pressure for the system is 450 to 500 pounds per square inch (psi). The pump is mounted on and driven by the main rotor gearbox to maintain hydraulic pressure in the event of an engine failure. A servo is connected to each of the three push-pull tubes that support the main rotor swashplate. The swashplate push-pull tubes are connected to the swashplate assembly and the upper linkage of the servos. The bottom linkage of each servo is connected to a bellcrank/fork assembly, which then connects to the cyclic and collective thru a series of push-pull tubes and bellcranks. Prior Problems The pilot stated that he bought the helicopter new from the factory in August 2004. He had a similar problem where the controls felt if they temporarily were unresponsive in September 2012. He did nothing at that time because it was due for an annual inspection in a few flight hours thereafter. Maintenance personnel were unaware that the pilot had this problem. TEST AND RESEARCH Airframe Investigators examined the flight control systems and located numerous discontinuities throughout the flight control assemblies. Examinations of the fracture surfaces associated with the flight control discontinuities were all observed to be consistent with overload. No evidence of pre impact failures of the flight control systems was found. A detailed examination of the hydraulic servos, reservoir, and pump revealed no evidence of mechanical malfunction. The complete examination report is appended to this accident in the public docket. The cabin area was relatively intact with upper aft ceiling and bulkhead crushed inward consistent with the main rotor gearbox making contact during impact. The alignment marks on the cooling fan were no longer aligned with the roll pin. According to a Robinson representative, the lower and upper sheaves appeared to have normal wear. Two V-belts were ripped between the v-grooves. Only one belt remained in the grooves of both sheaves. The V-belts were cut and removed for examination. No defects or abnormal wear was observed. V-Belt Examination The fractured v-belt was sent to the National Transportation Safety Board (NTSB) materials laboratory. The belt was of a banded design with a single reinforcing layer and raw edges. Evaluation of thefractures at the ends revealed that the fracture surfaces of the rubber bottom or cushion did not mate together, consistent with the loss or fragmentation of rubber material from the belt ends. The fractured ends of the v-belt piece were examined with a stereo-zoom microscope and a digital microscope. Examination of the fractured fiber ends revealed a predominately mushroom morphology which is consistent with rapid application of tensile stresses to the point of mechanical overload. Fracture of the rubber bottom or cushion at the ends exhibited rough features and lips consistent with tensile overload. Fracture features of the top fabric backing layer and the bottom fabric ply layers is consistent with tensile overload.