NTSB Identification: FTW04FA029.
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Nonscheduled 14 CFR
Accident occurred Monday, December 01, 2003 in High Island 573, GM
Probable Cause Approval Date: 09/13/2005
Aircraft: Bell 407, registration: N457PH
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, which had a FADEC controlled turboshaft engine installed, was in cruise flight over open ocean water in the Gulf of Mexico when the 14,000-hour helicopter pilot radioed a brief MAYDAY distress call on an area operating frequency. Details of the in-flight emergency were not relayed by the pilot, and no further communications were heard. Three hours later, the pilot's body was found floating in the area the helicopter was operating. After 3 days of search, the submerged helicopter wreckage was recovered from approximately 240 feet of water. Deformations of the airframe, along with the lack of damage to the main rotor blades, showed evidence that the helicopter impacted the water at a high vertical rate with low rotor RPM. Teardown examination of the engine revealed a catastrophic failure of the power turbine assembly (N2). Metallurgical examinations by the NTSB and Rolls Royce revealed evidence that the 3rd stage turbine wheel airfoil(s) had failed. A root cause of the failure was not determined, and further testing was conducted at Rolls Royce. As a result of some of the dynamic test results, Rolls Royce issued several Commercial Engine Bulletins (CEBs) regarding inspection of in-service turbine assemblies. Additionally, Bell Helicopter issued an Alert Service Bulletin (ASB), which introduced flight manual revisions to avoid power turbine RPM (Np) steady state operation between 68% and 97%. After examinations of the airframe (fuel system, rotor systems, flight control systems, drive systems, electronic control systems), no anomalies were found other than within the power turbine assembly.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The loss of engine power due to the failure of the 3rd stage turbine wheel and subsequent catastrophic failure of the turbine assembly. Full narrative available
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