NTSB Identification: LAX01TA119.
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Accident occurred Saturday, March 17, 2001 in Hayward, CA
Probable Cause Approval Date: 11/29/2006
Aircraft: Eurocopter France AS350-B2, registration: N996PD
Injuries: 3 Uninjured.
NTSB investigators may have traveled in support of this investigation and used data provided by various sources to prepare this public aircraft accident report.
The airline transport certificated helicopter pilot was conducting nighttime aerial surveillance in support of law enforcement activities over a densely populated residential area. As he orbited the helicopter about 600 feet above a residential area, all engine power was lost. The pilot entered an autorotation, and attempted to make an emergency landing on a residential lawn, located within the dimly lit residential area. The helicopter struck a small gauge residential power supply line that was stretched across the emergency glide path. After striking the power line, the helicopter landed hard and nosed down, coming to rest in the front lawn of a residence. The helicopter sustained substantial damage to the main rotor hub assembly (starflex), tail boom, and fuselage. Postaccident examination of the Turbomeca Arriel 1D1 turbo shaft engine revealed a fractured bevel gear, part number 0292107960, located in the engine accessory gearbox. A metallurgical examination of the fractured bevel gear disclosed evidence of radial cracks between the teeth of the gear, consistent with high cycle fatigue (HCF) phenomenon. As a result, Turbomeca issued a service letter to all operators of Arriel engines outlining an inspection method for engines currently in service, suggesting that the bevel gear will be checked systematically. The service letter reported, in part: "The fracture was the result of a fatigue propagation. Metallurgical and dimensional analyses have not revealed any defect." The failure of the accessory bevel gear will result in the failure of the fuel pump and fuel control unit, and a loss of engine power.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The fatigue fracture of the engine accessory drive gear while maneuvering, which resulted in a loss of engine power and collision with a residential transmission line during the ensuing forced landing. A factor associated with the accident was the residential transmission line.
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