Robinson Helicopter R44 N379SH accident near Hochatown, Oklahoma

Probable cause

A total loss of engine power during a practice autorotation due to the improper engine idle setting and rigging of the carburetor heat control which resulted in a hard landing.

NTSB analysis

The pilot reported that he was conducting a practice autorotation during a proficiency flight about 400 ft above ground level (agl). As he reduced the engine speed to idle, the engine lost total power. The pilot entered an autorotation and completed a forced landing to a field. The helicopter landed hard and the tailboom was severed by the main rotor blades.

Examination of the engine revealed that the idle speed was set below 50 percent, which was below the manufacturer’s recommendation of 60 to 65 percent. Additionally, the carburetor heat control cable was rigged improperly, and therefore, was jammed in the full heat position. The combination of these factors would have likely made the engine more susceptible to losing power, especially with an abrupt power reduction initiated by the pilot during the simulated autorotation.

After reviewing the available maintenance records, it is possible the engine idle speed was improperly set, and the carburetor heat control was improperly rigged when the engine was overhauled and installed in the helicopter; however, investigators were unable to establish exactly when the misrigging took place or why it was not noticed during subsequent maintenance.

Text from the NTSB. Open the NTSB docket for CEN24LA004 for the full record.