San Clemente, CA, USA
N608BP
MCDONNELL DOUGLAS HELICOPTER 600
During cruise flight the helicopter experienced a loss of engine power. The pilot performed an autorotation, maneuvering the helicopter to avoid obstacles. The helicopter sustained substantial damage after landing hard, semi-submerged in the surf zone of a beach. During the landing sequence, a main rotor blade made contact with the tail boom and the helicopter sustained crush damage to the lower fuselage. Post accident examination of the airframe did not reveal evidence of any failure or malfunction. Examination of the engine revealed a failure of the number two bearing, resulting in a subsequent failure of the engine’s gas generator and power turbine sections. Examination of the bearing revealed signatures consistent with the inner and outer bearing races experiencing misalignment. The misalignment resulted in the associated balls becoming mechanically locked against the ball cage, leading to raceway compromise, heat damage, and bearing failure. As a result of this accident, and other in-service wear issues related to the number two bearing, the engine manufacturer has embarked on a bearing redesign process for this engine series.
HISTORY OF FLIGHT On February 19, 2009, about 1930 Pacific standard time, a McDonnell Douglas Helicopter 600N, N608BP, force landed hard on a beach in San Clemente, California, as the result of an engine failure encountered during cruise flight. The airline transport pilot and commercial copilot received serious injuries. The passenger received minor injuries. The helicopter, which was operated by United States Customs and Border Protection (USCBP), sustained substantial damage. Night visual meteorological conditions prevailed for the public-use flight, and a company visual flight rules (VFR) flight plan was filed. The helicopter departed from Long Beach Airport (Daugherty Field), Long Beach, California, about 1900, with an intended destination of Brown Field Municipal Airport, San Diego, California. The helicopter departed Long Beach with the commercially rated pilot at the controls, and seated in the left seat. Approximately 30 minutes into the flight, at an altitude of about 1,500 feet mean sea level (msl), the 'ECU Degrade' light illuminated on the helicopter caution panel. The airline transport pilot, who was positioned in the right seat, then took over control of the helicopter. A few seconds later the occupants heard an "explosion" coming from the rear of the helicopter, followed by multiple illuminations of lights on the instrument, warning, and caution panels. The passenger, located in the rear seat, then heard a sound similar to the engine increasing in speed and observed flames emitting from the rear of the helicopter. The pilot performed an autorotation with the intention of landing on a parking lot. As the helicopter approached the lot, he observed power lines and the domes of the San Onofre Nuclear Generating Station; he then elected to turn the helicopter 180 degrees, and land on an adjacent beach. The helicopter landed hard semi-submerged in the surf zone of the beach. During the landing sequence a main rotor blade made contact with, and severed, the tail boom. Additionally, the lower fuselage and skids sustained crush damage. PERSONNEL INFORMATION Pilot A review of the Federal Aviatin Administration (FAA) airman records revealed that the 47-year-old pilot held an airline transport pilot certificate with ratings for airplane multiengine land, and a commercial pilot certificate with ratings for airplane single-engine land, helicopter, and instrument helicopter. The pilot held a flight instructor certificate with ratings for helicopter, airplane single-engine land, airplane multiengine land, instrument airplane, and instrument helicopter. According to the USCBP his total time in all aircraft was 6,000 hours, with 1,370 hours in the accident helicopter make and model. Copilot A review of the FAA airman records revealed that the copilot held a commercial pilot certificate with ratings for airplane single-engine land, helicopter, instrument airplane, and instrument helicopter. According to the USCBP his total time in all aircraft was 1,200 hours, with 18 hours in the accident helicopter make and model. AIRCRAFT INFORMATION Airframe The no tail rotor (NOTAR) helicopter, serial number RN037, was manufactured in 1998. A review of the helicopter's maintenance logbooks revealed that it had accumulated a total airframe time of 3,571 hours at the time of the accident, which occurred 74 flight hours after its last 100-hour inspection in October 2008. The maintenance logbooks indicated that the helicopter was in compliance with all applicable service bulletins and airworthiness directives. Engine The engine is located in the aft section of the fuselage behind the main cabin. The design of the helicopter is such that the engine is mounted forward facing, at an angle of about 45 degrees relative to the longitudinal plane of the helicopter. The helicopter was equipped with a Rolls-Royce 250-C47M gas turbine engine. The engine and its associated gearbox were overhauled in December 2005, and installed on the accident helicopter in May 2006. At the time of the overhaul, the engine and gearbox had accrued a total time in service of 2,278.9 hours. At the time of the accident, the engine and gearbox had accumulated 778.4 hours of total flight time since the overhaul. The last 150-hour inspection occurred in October 2008, 98.4 flight hours prior to the accident. The engine logbooks did not reflect any maintenance involving the separation of the engine and gearbox since its overhaul. TESTS AND RESEARCH Airframe Examination of the airframe did not reveal any evidence of failure or malfunction. Engine Control Unit The Engine Control Unit (ECU) remained attached to the airframe and did not sustain obvious signs of damage. The unit was sent to the facilities of Goodrich Pump and Engine Control Systems (GPECS), Hartford, Connecticut. Data from the ECU was extracted under the supervision of the National Transportation Safety Board investigator-in-charge (IIC), and representatives from Rolls-Royce, USCBP, and MD Helicopters. Data extraction, in part, revealed the following log: Fault View: Last Engine Run Faults Fault Name Description ---------- ----------- OSFlt - Overspeed Fault NpOSFlt - Np Overspeed Fault Np1Flt - Np1 Fault Np1RtFlt - Np1 Rate Fault Np2Flt - Np2 Fault Np2RtFlt - Np2 Rate Fault Np12Flt - Np Hard Fault MGTLmTOut - MGT Limit Exceedance MGTRLmTOut - MGT Run Limit Exceedance for 12 seconds SgFlag - Surge Event Indicator MGTFlt - MGT Fault MGTRgFlt - MGT Range Fault TempFlt - MGT Temperature Fault Al28Flt - 28 Volt Alternator Fault CPUHardFlt - FADEC System Hard Fault WDTHardFlt - FADEC System Hard Fault Engine The engine was removed from the airframe, and examined at the Rolls-Royce facility in Indianapolis, Indiana. The examination was conducted under the supervision of the IIC, and representatives from Rolls-Royce, the FAA, USCBP, and MD Helicopters. Inspection of the upper and lower engine chip detectors revealed the presence of metallic chips and flakes. The gas generator and power turbine drive trains could not be rotated manually. During the examination, the accessory gearbox was separated from the engine. Further inspection revealed that the number two bearing retainer ring had become dislodged from its seat, and had come to rest against the oil delivery tube. The number two bearing was in place within the housing; however, the majority of its separator cage was missing. The remaining sections of the cage were located within the bearing, which still retained its compliment of balls. The bearing, its oil delivery tube, and the surrounding areas appeared oil wetted. Disassembly of the compressor section revealed rubbing in the area of the 'knee' around its full circumference. The associated number 1 bearing was in place and oil wetted. Thermal damage was observed throughout the entire gas path. The damage began aft of the number 1 nozzle, compromising all of the turbine blades, turbine wheels, nozzles, and vanes. Examination of the gas generator and power turbine shafting revealed them to be in the correct location and oil wetted. Disassembly of the accessory gearbox revealed no significant damage to the gas generator or power turbine drive trains, both of which could be rotated by hand. Small metallic chips were observed throughout the gearbox casing, and all gears and internal surfaces were oil wetted. The remaining sections of the number two bearing cage were located within the gearbox housing. Residual oil was noted throughout the lubrication system, and the external sump contained oil. The number two bearing was further examined by the Rolls-Royce metallurgical department. The examination revealed that the bearing surfaces were dark in color and oil wetted. Extrusion deformation was noted on the shoulder of the aft inner ring shoulder and the forward outer ring shoulder; Rolls-Royce stated that this damage could indicate ball excursion. The remaining fragments of the ball separator exhibited fracture features along some of their surfaces, which the report stated were consistent with fatigue. All sections of the bearing exhibited signs of heat distress. According to Rolls-Royce, semi-quantitative x-ray energy dispersive analysis determined that the material for the bearing’s outer ring, inner ring, separator, and balls met design specifications. The report was reviewed by the NTSB Office of Research and Engineering, Materials Laboratory Division. The engine logbooks revealed that the number two bearing was replaced in January 2002, 1,756 hours prior to the accident. According to the logbooks, the bearing was replaced as part of a disassembly following the engine experiencing a 'compressor stall/erosion.' The number two bearing was not replaced during the engine’s overhaul in December 2005. The Rolls-Royce overhaul manual applicable to the engine series defines specific criteria for bearing inspection during overhaul. It additionally states, "Used bearings, if properly processed, will have a reliability equal to that of a new bearing in most applications." ADDITIONAL INFORMATION As a result of this accident, and other in-service wear issues related to the number two bearing, Rolls-Royce has embarked on a bearing redesign process for this engine series.
Failure of the engine’s number two bearing during cruise flight, which resulted in a loss of engine power.
Source: NTSB Aviation Accident Database
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