Mcdonnell Douglas Helicopter 369E N527BB accident near Acworth, Georgia

Probable cause

The loss of engine power due to the fatigue failure of the third-stage turbine wheel airfoil.

NTSB analysis

The pilot stated that he and an observer were conducting an aerial observation when during the descent he heard a loud noise. Subsequently, he received an "ENG OUT" audio and caution lights, and made an emergency autorotation into a field. An examination of the engine’s turbine section revealed rub marks throughout the turbine section consistent with an out-of-balance condition caused by a third-stage turbine airfoil release. The third-stage wheel airfoil fractured in fatigue near the root of the airfoil and no anomalies were found at the fatigue origin. The fracture surface of the failed third-stage blade revealed high-cycle fatigue failure over an extended period of time. The crack propagation is estimated to be greater than 2000 cycles. No additional cracks were found on the other third-stage wheel airfoils.

Review of the logbook revealed that the airframe engine total time was 3,820 hours and the engine had gone through a 100- and 300-hour inspection at 3,809.6 engine hours. All airworthiness directives and applicable service bulletins as well as all instructions for continued airworthiness were complied with. The hot section and turbine inspection was completed on February 21, 2008, at 2,958 hours. The third-stage turbine wheel was overhauled on February 3, 2004, at 1210.6 hours and 1633.0 cycles and was due to be replaced at 4,710.6 hours. At the time of the accident the wheel had 2609.7 hours and 2412.0 cycles.

Text from the NTSB. Open the NTSB docket for ERA09LA460 for the full record.