Accident Overview
A helicopter equipped with a FADEC-controlled turboshaft engine was in cruise flight over open ocean waters in the Gulf of Mexico. The pilot, who had accumulated 14,000 flight hours, radioed a brief MAYDAY distress call on an area operating frequency. No details of the in-flight emergency were provided, and no further communications were received. Approximately three hours later, the pilot's body was discovered floating in the area where the helicopter had been operating. Following a three-day search, the submerged wreckage was recovered from a depth of about 240 feet.
Investigation Findings
Examination of the recovered airframe revealed deformations consistent with a high vertical rate of descent upon water impact. The main rotor blades exhibited a lack of damage, indicating that the helicopter impacted the water with low rotor RPM. Detailed inspections of the airframe, including the fuel system, rotor systems, flight control systems, drive systems, and electronic control systems, found no anomalies.
Engine Examination
The engine underwent a teardown examination, which disclosed a catastrophic failure of the power turbine assembly (N2). Metallurgical analyses conducted by the National Transportation Safety Board (NTSB) and Rolls-Royce identified evidence that the third-stage turbine wheel airfoil(s) had failed. The root cause of this failure was not determined, and further testing was performed at Rolls-Royce.
Post-Accident Actions
Based on dynamic test results, Rolls-Royce issued several Commercial Engine Bulletins (CEBs) addressing the inspection of in-service turbine assemblies. Additionally, Bell Helicopter released an Alert Service Bulletin (ASB) that introduced revisions to the flight manual to avoid steady-state operation of the power turbine RPM (Np) between 68% and 97%.