NTSB Identification: FTW01FA017.
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Accident occurred Saturday, October 28, 2000 in E. Cameron 200, GM
Probable Cause Approval Date: 07/15/2002
Aircraft: Aerospatiale AS-350BA, registration: N26WW
Injuries: 1 Fatal.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
The helicopter departed from a helipad located on an offshore oil platform, and was 3 minutes from landing at a refueling helipad on another platform, when the pilot transmitted two distress calls indicating the helicopter was "going down." There were no witnesses to the accident; however, 9 minutes after the distress calls were heard, the helicopter was found floating inverted in 3-4 foot seas. Subsequently, the helicopter sank and was later recovered and examined. Examination of the helicopter revealed no anomalies with the airframe or flight control systems. Examination of the engine revealed that the first and second stage turbine blades were fractured due to extreme heating. One blade of the second stage tubine disk had liberated from its retention slot, and all the blade roots and retention slots of this disk exhibited permanent outboard deformation, due to a combination of centripetal forces from engine operation and excessive heat. In contrast, the blade roots and retention slots of the first stage turbine disk did not exhibit evidence of outboard deformation, most likely since they were located further away from the heat source. The rear bearing assembly (located aft of the second stage disk) was contaminated with coke. The coking suggests that oil was leaking from the engine and migrating from the rear bearing assembly. The aft side of the second stage turbine disk displayed dark stain marks in the form of streaks. A passage exists that would allow oil to flow from the rear bearing to the aft face of the second stage turbine disk. Oil that strikes the disk would flow into the hot stream of gases and auto-ignite, starting a fire. Oil migration can occur if the rear bearing scavenge and vent tubes become blocked; however, the scavenge and vent tubes were checked during the engine examination and were not found blocked.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: the loss of engine power due to an internal engine oil leak that started an internal engine fire and the pilot's inadequate autorotation which resulted in a hard landing. A contributing factor to the accident was the rough water condition. Full narrative available
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