On November 6, 1999, about 0950 hours Pacific standard time, a Bell OH-58A, N911RN, was destroyed when it made a forced landing on a city street in La Puente, California, following a loss of engine power. The commercial pilot, the sole occupant, received minor injuries. The public-use helicopter was being operated by the Huntington Park, California, Police Department at the time of the accident. The flight originated from El Monte, California, about 0945, and was en route to the City of Industry, California, to take on additional fuel. Visual meteorological conditions prevailed and no flight plan had been filed. Use your browsers 'back' function to return to synopsisReturn to Query Page
A review of maintenance records revealed that the Huntington Beach Police Department (HPPD) took possession of the helicopter from the Army in December 1996. Maintenance technicians completed phase checks prior to entering the helicopter into service in September 1998. Total time on the airframe was 3,550 hours, and the engine total time was 249 hours.
The pilot stated that he had experienced a slight fluctuation in fuel pressure on approach to landing on August 30, 1999, which resulted in a momentary loss of power. His observer from that flight reported that he saw a master caution light illuminate following the loss of power. The observer said that the engine regained power and the pilot continued the approach and entered a normal hover. The pilot monitored the engine's performance and then hover-taxied to the landing pad with no other problems.
Following this incident, the maintenance records show that technicians removed and replaced the fuel pump and fuel control units on September 7, 1999. They checked the fuel control rigging and performed ground run and hover checks. The engine satisfactorily completed all of the operational checks. Total time on the engine was 449 hours.
A maintenance entry dated September 24, 1999, noted completion of a compressor wash and dry.
The next logbook entry recorded a 50-hour inspection on November 3, 1999. The pilot stated the accident flight was the first flight since the inspection. He performed a 100 percent power check on the ground followed by a hover check and noted no discrepancies.
While in cruise flight at 100 knots and 600 feet above ground level, the N1 engine speed began to bleed off. The pilot stated that he modulated the throttle and heard a "pop." He lowered the collective and engaged the starter. The N1 speed continued to bleed off and the pilot began a right turn for a 180-degree autorotation. He planned to land on a city street where traffic had stopped for a light. As he slowed from 80 knots to 50 knots and prepared to flare, a vehicle moved onto the road. He entered a cyclic flare and turned to land on a raised road divider island. He stated that the rotor rpm was in the green arc at the initiation of the flare. The helicopter slid forward on the ground and the main rotor blades severed a power pole. The cabin buckled on the right side and the right windshield cracked. The pilot stated that he did not recall observing the engine-out light, but did recall seeing the master caution light illuminate.
Investigators from the Safety Board and Rolls-Royce Allison examined the wreckage on November 10, 1999. All connections for the oil supply and scavenge lines were secure and there was evidence of oil in the lines at the connections. All pneumatic lines were intact and secure. The maintenance records contained results of oil analysis completed periodically throughout the previous year. All values appeared in the normal range.
Fuel was present in all the fuel lines and investigators performed a vacuum check on the fuel system. The system maintained vacuum for the duration of a 2-minute test. The fuel spray nozzle was sooty but clear. Investigators disconnected the fuel line between the fuel filter and engine. They operated the electric fuel pump and discharged over 1 gallon of fuel in 1 minute. They pumped out a total of 30 gallons of fuel from the helicopter's fuel tank. The engine driven fuel pump filter was absent of contaminants. The airframe external fuel filter contained visible contaminants; some particles were brown and irregular in shape, while others were flat and blue.
The oil screen was clean. The engine and transmission chip detectors were clean. The compressor, N1 turbine, and N2 turbine turned freely when manually rotated. Investigators removed the PG governor pressure line and applied 50 psi (pounds per square inch) of air pressure, with no leaks detected.
The Safety Board sent the engine to Air Services International, LLC, an Allison authorized maintenance center. Technicians placed the engine in a test cell. The technicians, under the supervision of the Safety Board investigator, tested the engine in accordance with the Allison overhaul manual. The technicians performed accelerations, decelerations, and horsepower checks. The engine tested satisfactorily in all parameters.