NTSB Identification: LAX99TA066.
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Accident occurred Saturday, January 02, 1999 in VAN NUYS, CA
Probable Cause Approval Date: 11/30/2000
Aircraft: Bell 205A-1, registration: N58126
Injuries: 1 Serious,2 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this public aircraft accident report.
During a night training flight over mountainous terrain the pilot heard a loud 'clunking' sound, which was accompanied by vibrations. The engine then emitted a loud grinding, metallic grating sound. Simultaneously, warning lights, engine chip lights, and the rpm decay light became illuminated. The pilot lowered the collective and entered an autorotation but did not have sufficient airspeed and altitude to reach a dirt road, so he turned down a canyon and performed a hard flare and near-vertical descent with little forward speed. The helicopter landed hard and came to rest on rough uneven terrain surrounded by trees and high vegetation. Postaccident examination revealed that the engine power turbine as viewed from the exhaust exhibited damage. The number 4 turbine wheel was missing all of its blades and the blades on the number 3 turbine wheel were damaged. Scoring was evidenced on the inside diameter of the turbine case in the area of the Nos. 3 and 4 turbine wheels. All the vanes and inner and outer supports of the second stage power turbine nozzle were displaced and/or missing, and fragments of the outer vane support were torn and distorted. The third stage turbine nozzle exhibited extensive damage on the trailing edges of the vanes and on the shroud/outer housing. Metallurgical examination of the turbine components disclosed features indicative of overload fractures without evidence of material defects or fatigue. The metallurgist concluded that the overall type and degree of engine damage was indicative of a component failure in the second stage power turbine nozzle area; however, the cause of the component failure was not determined.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: A loss of engine power due to an undetermined component failure in the second stage power turbine nozzle area. Factors in the accident were the mountainous/hilly nature of the terrain and the dark night lighting conditions which precluded the pilot from selecting a suitable forced landing area. Full narrative available
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