HURON, CA, USA
N176SJ
Bell OH-58A
During the initial climb, the pilot noted that the fuel boost pump warning light had flickered on and then off, with a corresponding surge in the engine. Approximately 20 feet agl, engine power was lost and the helicopter impacted the ground. A functional field check of the fuel system was conducted and it was noted that there was a leak in the breakaway valve, which would have allowed air to enter the system. Further examination of the fuel boost pump and breakaway valve revealed that the O-rings were deteriorated. The field inspection further revealed that the inlet shutoff valve arm on the fuel boost pump was bent. According to the manufacturer's overhaul manual, if the inlet shutoff valve arm is bent it may prevent the valve from opening and restrict the fuel flow. According to the component overhaul manuals, the O-ring seals in both the fuel boost pump and the fuel breakaway valve are not required to be inspected during routine inspections and are replaced as on-condition items. A hydro leakage test and performance flow test check was conducted on the fuel boost pump with the original O-rings. The fuel boost pump did not pass the manufacturer's tests. The O-ring seals were replaced with new ones, and the fuel boost pump functioned within manufacturer's limits. The fuel control unit and fuel pump were tested and no discrepancies were found. The fuel nozzle was also tested and flowed within manufacturer's limits. Maintenance records disclosed that the last time the fuel boost pump was worked on was 5 years prior to the accident.
On April 8, 1998, at 2300 hours Pacific daylight time, a Bell OH-58A, N176SJ, experienced a loss of power after takeoff while maneuvering to spray a field near Huron, California. The helicopter, operated by San Joaquin Helicopters under 14 CFR Part 137 for aerial application, sustained substantial damage. The commercial pilot received minor injuries. Visual meteorological conditions existed for the night flight which was originating at the time of the accident. No flight plan was filed. The pilot reported that he had just loaded 100 gallons of water onboard the helicopter to rinse a cabbage field. He had taken off and was making a left climbing turn to begin spraying the field when the fuel boost pump warning light flickered on and then off, with a corresponding surge in the engine. He stated that he continued the takeoff and was approximately 20 feet above ground level (agl) when he lost all engine power. At this point all the warning lights illuminated. The pilot stated that the helicopter struck the ground, 180 degrees from the direction of flight, and the main rotor sliced through the tail boom. AIRCRAFT INFORMATION The helicopter was a United States military surplus aircraft. The operator had purchased the helicopter from the Washington D.C. Police Department and modified it with a hydraulic-driven accessory drive for agricultural applications. The helicopter had been inspected by a Federal Aviation Administration (FAA) Aircraft Certification Office inspector and issued a new Type Certificate with the operator as the holder of the Type Certificate. An FAA airworthiness inspector reported that 20 gallons of fuel was drained from the aircraft. The logbooks were examined and it was noted that on November 24, 1993, the fuel boost pump had undergone a one-time inspection of the cartridge. TESTS AND RESEARCH Inspection of the fuel system revealed a bent arm on the fuel boost pump, a leaking breakaway fuel valve, and deteriorated O-ring seals in both components. According to Bell Helicopter's fuel boost pump overhaul manual, if the inlet shutoff valve arm is bent it may "prevent the shutoff valve from completely opening causing a restricted fuel flow." A field functional check of the breakaway valve was conducted on April 22, 1998. It was noted when water under 8 psi was introduced into the fuel system from the fuel boost pump fuel line that the breakaway valve showed evidence of a leak (see attached photo). The fuel boost pump was inspected and tested at the Bell Helicopter Laboratory under the supervision of the Safety Board, on June 11, 1998. Bell stated that the pump functioned properly. They did note that there was a damaged O-ring in the relief valve in the fuel boost pump body. Bell reported that this would have allowed a large volume of "aerated air to enter into the fuel line to the engine." The fuel boost pump and fuel boost pump cartridge were further inspected at the Parker Hannifin Corporation on September 10, 1998, under the supervision of the FAA. The first test was conducted with the original parts. In the as received condition, the fuel boost pump assembly did not pass either the hydro leakage test or the performance flow test. The O-rings in the boost pump cover (one under the inlet seal and one around the cover) were replaced, as well as three O-rings in the cartridge body. The hydro leakage test, as well as the performance flow test, was performed with no discrepancies noted. The breakaway valve unit was inspected by the Safety Board's Materials Laboratory on December 21, 1998. It was noted that the O-ring located between the pressure switch and the breakaway valve unit were degraded as a result of aging. The O-ring was not tested due to guidance from the manufacturer of the switch who stated that the switch and O-ring is replaced as an on-condition item. The metallurgists at the Safety Board reported that no corrosion or defects were noted on the O-ring or corresponding mating surfaces that would have permitted a fuel leak. Review of the fuel boost pump overhaul manual disclosed that the O-ring seals in both the fuel boost pump and the fuel breakaway valve are not required to be inspected during routine inspections. The O-ring seals are to be replaced "on condition." The fuel control unit and the Power Turbine Governor were functionally tested by Allied Signal on May 7, 1998, under the supervision of the Safety Board. No discrepancies were noted. The fuel pump and fuel nozzle were flow tested in accordance with the manufacturer's specifications at H.E.R.O.S., Inc., in Riverside, California, on June 10, 1998, by installation in a calibrated test bench. No discrepancies were noted with the fuel pump. The fuel nozzle flowed within manufacturer limits; however, it was noted that a streaking condition existed. The test technician reported that the streaking condition was not significant in terms of the operational capability of the nozzle.
A loss of engine power due to deteriorated O-ring seals in the fuel boost pump, which allowed air to enter the fuel lines. Factors in the accident were the inadequate manufacturer's inspection criteria for the fuel boost pump O-ring seals and the resulting failure of the operator's maintenance personnel failure to detect the condition.
Source: NTSB Aviation Accident Database
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