Md Helicopter 369 N551CP accident near Columbus, Ohio

Probable cause

The failure of a 4th-stage turbine blade due to high-cycle fatigue, which resulted in the loss of engine power.

NTSB analysis

The pilot reported that, shortly after leveling off the helicopter at 1,500 ft mean sea level, he heard a "loud exploding noise" coming from the rear of the helicopter followed by a "long sustained whining noise" coming from the engine and a constant warning tone in the background. The pilot then saw the gas producer (N1) and power turbine (N2) gauge needles falling rapidly. He identified the situation as an engine failure, so he performed an autorotation. The helicopter subsequently touched down on a street, slid, rotated counterclockwise about 1 1/2 turns, then came to a stop. The main rotor blades contacted a utility pole adjacent to the street, and the tail fin, stabilizer, and tail rotor broke off.

A postaccident examination of the engine revealed that a 4-inch segment of the 4th-stage turbine shroud was fractured in the plane of the 4th-stage turbine wheel. The 4th-stage turbine was missing one blade, and the blade had fractured off near the inner platform. A three-blade span of the related segment of the rim was also missing. An examination of the missing blades' fracture surfaces showed evidence consistent with high-cycle fatigue likely caused by an engine speed/airframe interaction of unknown origin, which resulted in the blade failure and subsequent loss of engine power.

Text from the NTSB. Open the NTSB docket for CEN12TA550 for the full record.