History of Flight
On April 12, 2013, about 0800 Pacific daylight time, a Robinson R44 II (registration N442FG) was landing at Hogan's Corner Airport in Ocean Shores, Washington, when the pilot experienced a loss of control. Oregon Roses, Inc. owned and operated the helicopter under 14 Code of Federal Regulations Part 91. The commercial pilot and a pilot-rated passenger sustained minor injuries, and the helicopter sustained substantial damage. The pilot had 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 was filed.
The pilot stated that after departure, they flew north over the Oregon coastline. He planned to pick up his son at Hogan's Corner Airport and continue to Copalis State Airport in Copalis, Washington. His daughter, seated in the right seat, was the flying pilot for most of the flight, but as they approached the airport, the pilot took over the flight controls. He maneuvered over runway 24 about 20 feet above ground level toward hangars on the west end of the airport.
The pilot reported that he experienced a loss of control, and his daughter attempted to help him regain control. He described the flight controls as feeling "mushy" and unresponsive. The helicopter descended near-vertically and landed hard. He noted no yaw problems, no low rotor rpm indication, and calm wind conditions.
Aircraft Information
The Robinson R44 Raven II (serial number 10444) was manufactured in 2004. At the time of the accident, the airframe had accumulated 469.9 total hours. The most recent annual inspection was completed on February 26, 2013, 2.9 hours prior to the accident. During that inspection, maintenance personnel removed the hydraulic pump output fitting and replaced the retainer and o-ring. All applicable airworthiness directives had been complied with. The helicopter had one modification: installation of a cargo hook, documented on an FAA Form 337.
A discrepancy was noted in maintenance records regarding the hydraulic filter replacement interval. The filter, a disposable cartridge rated at 10 microns (part number AN6235-1A), was replaced on January 10, 2010, at an airframe time of 358.4 hours (about 110 hours before the accident). According to maintenance manual section 8.005, the filter was to be replaced during 100-hour inspections, while Table 1 on page 1.3C listed a 300-hour replacement interval. Following the accident, the manual was updated to reflect the 300-hour requirement.
Examination Findings
Investigators examined the flight control systems and found numerous discontinuities throughout the assemblies. Fracture surfaces were consistent with overload, and no evidence of pre-impact failures was found. Detailed examination of the hydraulic servos, reservoir, and pump revealed no mechanical malfunction.
The cabin area was relatively intact, with the upper aft ceiling and bulkhead crushed inward, consistent with the main rotor gearbox making contact during impact. Cooling fan alignment marks were no longer aligned with the roll pin. V-belts were ripped between v-grooves; only one belt remained in the grooves. The belts were examined and showed no defects or abnormal wear.
The fractured v-belt was sent to the NTSB materials laboratory. The belt had a banded design with a single reinforcing layer and raw edges. Fracture surfaces of the rubber bottom did not mate together, consistent with loss or fragmentation of rubber material. Fractured fiber ends showed a predominantly mushroom morphology, consistent with rapid tensile stress application. Fracture features of the rubber bottom and fabric layers were consistent with tensile overload.
The pilot reported a similar problem in September 2012, when controls felt temporarily unresponsive. He took no action at that time because the helicopter was due for an annual inspection soon afterward. Maintenance personnel were unaware of the issue.