History of Flight
On June 6, 2013, at 1417 Pacific daylight time, a Robinson R44 II, registration N915BW, rolled over after a precautionary landing in Griffith Park, Los Angeles, California. The helicopter was registered to Southern California Helicopters and operated as a personal flight under 14 CFR Part 91. The local flight departed Brackett Field Airport, La Verne, California, about 1315. Visual meteorological conditions prevailed; no flight plan was filed.
According to the flight instructor, the primary purpose was to return the helicopter to Southern California Helicopters Flight School at Long Beach Airport after maintenance at Redlands Municipal Airport. The private pilot passenger was familiar only with the R22, so the instructor invited him to gain R44 experience. From Redlands, they flew to Brackett Field to pick up two passengers, one related to the instructor. The intention was to give a tour of Los Angeles before returning passengers to Brackett Field and the helicopter to Long Beach.
The instructor fueled the helicopter, departed, flew toward Hollywood, then west to Santa Monica, back inland over Universal Studios, Forest Lawn Cemetery, and the Hollywood sign, then past Griffith Observatory at about 1,700 feet msl. A few seconds later, the Main Rotor Gearbox Chip (MR Chip) warning light illuminated. The helicopter continued operating normally without unusual sounds. The instructor immediately began looking for a landing area.
He observed a potential site to the left adjacent to a trail on the southern slopes of Griffith Park. As he approached, a whining sound was heard. Seeing people on the intended spot, he turned left toward the north, following a ridgeline to find an alternate site. He followed the ridge southwest and spotted a small clearing on a pinnacle at the end of a trail. He initiated a descent onto a west heading. After landing, before fully lowering the collective, he felt the helicopter slip. He raised the collective, and the helicopter immediately spun right and rolled over.
Aircraft Information
The helicopter was manufactured in September 2006, equipped with its original Lycoming IO-540-AE1A5 engine. It had been involved in a hard landing in Broomfield, Colorado, on July 23, 2011, sustaining substantial damage to the firewall and tail rotor assembly (see NTSB report CEN11CA511). After that accident, the helicopter was disassembled, transported to a repair facility in Redlands, repaired, fitted with fuel tank bladders, and given an annual inspection. The original main rotor gearbox was reused and serviced with new oil after a "500 hour flush and drain."
Maintenance logbooks showed the annual inspection was completed on April 15, 2013, at 1,541.4 total flight hours and hour meter time of 1,143.4 hours. The hour meter read 1,145.6 hours at the accident site.
Wreckage and Impact Information
The helicopter came to rest at 1,189 feet msl on the west slope of the ridge, about 5 feet downhill from the landing site. The area overlooked Roosevelt Municipal Golf Course and Vermont Canyon Tennis Courts about 300 feet below. The main cabin remained largely intact; the tailboom was bent 45 degrees upward at the bulkhead seam.
One main rotor blade remained attached to the teeter hinge with midspan bending damage. The second blade had downward curling damage along its entire length, separated about 2 feet from the teeter hinge, and came to rest against the tailboom. Its outboard leading edge sustained chordwise abrasions; adjacent trailing edge skin and honeycomb core separated from the spar. The tip cap mounting bolt remained attached to the spar with remnants of the tip cap, but the bulk of the cap was not found. The area was searched but the tip cap was not located.
The landing spot showed multiple ground disruptions consistent with main rotor blade contact, and a 4-foot-long ground disturbance just below the crown of the peak opposite the main wreckage. Dry grass and brush bordered the disturbance. The left landing skid's toe exhibited longitudinal abrasions to its forward and upper surfaces.
Tests and Research
The helicopter was removed and examined at a remote facility. The flight control system was intact through the horizontal firewall; remaining controls showed bending damage and separation consistent with ground impact.
The main rotor gearbox, instrument panel, drive sheave, and sprag clutch assembly were examined at Robinson Helicopter, Inc. (RHC) in the presence of the NTSB investigator. Both forward gearbox mounting lugs had separated from the casting during the accident sequence, remaining attached to the airframe. Their separation left two 4-inch-wide holes in the gearbox case, expelling most gearbox oil. The gearbox was disassembled; drive gears and bearings showed no defects. About 5 teaspoons of blue oil were recovered from the sump; no debris or fragments were observed. No anomalies were noted that would have precluded normal operation.
The main rotor gearbox chip detector appeared undamaged and free of debris. Fine "fuzz" particles were present adjacent to contact surfaces. Electrical resistance testing showed an open circuit. 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; all filaments were intact with no stretching.
Maintenance records indicated the helicopter was retrofitted in April 2013 with fuel tank bladders per RHC Service Bulletin SB-78B, and replacement of rigid fuel lines with flexible hardware per SB-67 and SB-68. Examination showed both fuel tanks' outer skins buckled and breached, but inner bladders remained intact. For the main tank, supply and aux-to-main line fittings remained attached to the bladder with flexible hose portions broken at the fitting; the vent interconnecting line was severed at the tank skin. For the auxiliary tank, the flexible vent line had pulled away from its fitting nipple.
Additional Information
The RHC Maintenance Manual for the R44 recommends draining and straining gearbox oil and inspecting the chip detector after a chip light indication. For fuzz particles, it recommends cleaning with compressed air or a toothbrush and reinstalling. The RHC Pilot's Operating Handbook emergency procedures state: "Indicates metallic particles in main rotor gearbox… 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 (June 1994) describes 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."