Robinson Helicopter Company R44 II N808WH accident near Scottsdale, Arizona

Probable cause

The flight instructor’s failure to maintain adequate rotor rpm during a practice autorotation, which resulted in a loss of helicopter control and subsequent hard landing.

NTSB analysis

The flight instructor reported that, during the power recovery portion of a practice autorotation, he rolled on the throttle to increase the engine rpm. However, the engine rpm did not increase, and the main rotor rpm started to decay. The flight instructor's attempts to regain the main rotor rpm were unsuccessful, and he performed an emergency autorotation to the ground. The helicopter impacted a soft landing surface and came to rest on its left side. The fuselage and the tailboom sustained substantial damage. A postaccident examination of the helicopter revealed no evidence of preimpact mechanical malfunctions or failures that would have precluded normal operation. During an engine test run, the engine ran smoothly at idle and 100 percent rpm.

According to Federal Aviation Administration guidance, the power recovery portion of a practice autorotation should be achieved by properly coordinating the upward collective pitch control with an increase in the throttle. It is likely that the pilot did not increase the throttle in proportion to the increase in collective pitch, which resulted in the loss of rotor rpm.

Text from the NTSB. Open the NTSB docket for WPR12LA267 for the full record.