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On June 6, 2013, at 1417 Pacific daylight time, a Robinson R44 II, N915BW, rolled over following a precautionary landing in Griffith Park, Los Angeles, California. The helicopter was registered to Southern California Helicopters, and operated as a personal flight by the pilot under the provisions of 14 Code of Federal Regulations Part 91. The flight instructor and private pilot sustained minor injuries; the two passengers were not injured. The helicopter sustained substantial damage during the accident sequence. The local flight departed Brackett Field Airport, La Verne, California, about 1315. Visual meteorological conditions prevailed, and no flight plan had been filed.
According to the flight instructor, the primary purpose of the flight was to return the helicopter to Southern California Helicopters Flight School, at Long Beach Airport, following maintenance at a facility at Redlands Municipal Airport, Redlands, California. The private pilot rated passenger's experience was limited to the Robinson R22 helicopter, so the flight instructor invited him along to gain familiarity with the operation of the R44. From Redlands, they flew to Bracket Field to pick up the two passengers, one of whom was related to the flight instructor. His intension was to give the passengers a tour of the Los Angeles area before returning them to Bracket Field and the helicopter back to Long Beach.
The flight instructor serviced the helicopter with fuel, departed, and flew towards Hollywood. The flight then continued west to Santa Monica and back inland over the Universal Studios Theme Park, Forest Lawn Cemetery, and the "HOLLYWOOD" sign. From there they transitioned past the Griffith Observatory, flying east about 1,700 feet msl (mean sea level). The flight instructor stated that a few seconds later, the Main Rotor Gearbox Chip (MR Chip) warning light illuminated. The helicopter continued to operate normally without any unusual sounds, and he immediately began looking for an area to land.
The flight instructor observed a potential landing site to the left, adjacent to a trail on the southern slopes of Griffith Park. As he approached, the helicopter began making a "whining" sound that he had never heard before. He could see people on the intended landing spot, so he turned the helicopter left towards the north, following a ridgeline in an effort to find an alternate landing site. He followed the ridge back around to the southwest, and spotted a small clearing on a pinnacle at the end of a trail. He initiated a descent while maneuvering the helicopter onto a west heading. They landed on the clearing, and before he had a chance to fully lower the collective control, he felt the helicopter slip. He then raised the collective, and the helicopter immediately spun to the right and rolled over.
The helicopter was manufactured in September 2006, and was equipped with its original Lycoming fuel injected IO-540-AE1A5 engine. It was involved in a hard landing in Broomfield, Colorado, on July 23, 2011, where it sustained substantial damage to the firewall and tail rotor assembly (See NTSB accident report CEN11CA511). Following the accident, the helicopter was disassembled and transported to the repair facility in Redlands where it was repaired, fuel tank bladders were installed, and an annual inspection was performed. The original main rotor gearbox was utilized for the repair, and serviced with new gearbox oil after completion of a "500 hour flush and drain".
The maintenance logbooks revealed that the annual inspection was completed on April 15, 2013, at which time the helicopter had accrued a total flight time of 1,541.4 flight hours, and an hour meter time of 1,143.4 hours. The hour meter indicated 1,145.6 hours at the accident site.
WRECKAGE AND IMPACT INFORMATION
The helicopter came to rest at an elevation of 1,189 feet msl, on the west slope of the ridge, about 5 feet downhill from the landing site. The general area overlooked the Roosevelt Municipal Golf Course, and Vermont Canyon Tennis Courts, about 300 feet below. The main cabin remained largely intact, with the tailboom bent 45 degrees upwards at the bulkhead seam.
One of the main rotor blades remained attached to the teeter hinge, and sustained bending damage midspan. The second blade exhibited downward curling damage along its entire length, had separated about 2-feet from the teeter hinge, and came to rest against the tailboom. The outboard leading edge sustained chordwise abrasions, with the adjacent trailing edge skin and honeycomb core separating from the spar. The tip cap mounting bolt remained attached to the spar with remnants of the tip cap still attached, but the bulk of the cap was not present. The immediate area surrounding the wreckage was searched, but the tip cap was not located.
Examination of the landing spot revealed multiple ground disruptions consistent with main rotor blade contact, as well as a 4-foot-long ground disturbance just below the crown of the peak on the opposite side of the main wreckage. A growth of dry grass and brush bordered the disturbance; additionally, the left landing skid's toe exhibited longitudinal abrasions to its forward and upper surfaces.
TESTS AND RESEARCH
The helicopter was removed from the accident site, and examined at a remote storage facility. The flight control system was examined, and was intact through to the horizontal firewall. All remaining flight controls exhibited varying degrees of bending damage and separation, consistent with ground impact.
Main Rotor Gearbox
The main rotor gearbox, instrument panel, along with the drive sheave and sprag clutch assembly were removed and examined at the facilities of Robinson Helicopter, Inc. (RHC) in the presence of the NTSB investigator-in-charge.
Both forward gearbox mounting lugs had separated from the casting during the accident sequence, and remained attached to the airframe. Their separation resulted in two 4-inch-wide holes in the gearbox case, and the expulsion of most of the gearbox oil onto the airframe. The gearbox case was disassembled, and the drive gears along with all bearings were examined, with no defects noted. About 5 teaspoons of blue-colored oil was recovered from the sump, and no debris or fragments were observed within the sump area or gear surfaces. No anomalies were noted with the gearbox that would have precluded normal operation; a full examination report is included within the public docket.
The main rotor gearbox chip detector appeared undamaged and free of debris. Closer examination revealed the presence of fine "fuzz" particles in the area adjacent to the contact surfaces. The electrical resistance of the chip detector was tested, with an open circuit detected.
The Clutch, MR Temp, MR Chip, Carbon Dioxide, Starter On, TR Chip, Low Fuel, Low rpm, Fuel Filter, Aux Fuel Pump, and ALT lamps were removed, and their filaments were examined. All filaments were intact, with no stretching observed.
Maintenance records indicated that in April 2013 the helicopter had been retrofitted in accordance with RHC R44 Service Bulletin SB-78B (inclusion of fuel tank bladders), and both SB-67 and SB-68 (replacement of rigid fuel lines and clamps with flexible hardware).
Examination of both fuel tanks revealed that their outer skin surfaces had buckled and been breached during the accident sequence, however, the inner bladders remained intact. For the main fuel tank, the fuel tank supply line and aux-to-main line fittings remained attached to the bladder, with their flexible hose portions broken away at the fitting. Additionally, the flexible portion of the vent interconnecting line was severed at its junction with the tank skin. For the auxiliary fuel tank, the flexible portion of the vent interconnecting line had pulled away from its fitting nipple.
Main Rotor Gearbox Chip Light Indicator
The RHC Maintenance Manual for the R44 series recommends draining and straining the gearbox oil and inspecting the chip detector following a chip light indication. In particular, it recommends the following corrective action if no significant debris is found on the chip detector,
"For fuzz particles: Clean chip detector with compressed air or toothbrush (do not use magnet) and reinstall. Normal wear, especially new gearboxes, will produce fine fuzz."
The emergency procedures section of the RHC Pilot's Operating Handbook (POH) for the R44 series recommends the following action in the event of a main rotor gearbox chip light indication,
"Indicates metallic particles in main rotor gearbox.... NOTE: If light is accompanied by any indication of a problem such as noise, vibration, or temperature rise, land immediately. If there is no other indication of a problem, land as soon as practical."
RHC Safety Notice SN-9 issued in June 1994 was included in the POH and stated the following regarding dynamic rollover,
"A dynamic rollover can occur whenever the landing gear contacts a fixed object, forcing the aircraft to pivot about the object instead of about its own center of gravity. The fixed object can be any obstacle or surface which prevents the skid from moving sideways."