Scottsdale, AZ, USA
N808WH
ROBINSON HELICOPTER COMPANY R44 II
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.
On June 17, 2012, about 1045 mountain standard time, a Robinson Helicopter Company (RHC) R44 II, N808WH, was substantially damaged following a demonstration of an autorotation near Scottsdale, Arizona. The certified flight instructor was not injured; one passenger received minor injuries, and the other passenger was not injured. The helicopter was registered to Aquilla Aviation LLC, and operated by Sky Blue Helicopters LLC, under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The local flight originated from Scottsdale Municipal Airport, Scottsdale, at 1040. Visual meteorological conditions prevailed, and no flight plan was filed. The pilot reported that he was conducting an introductory flight. He entered a practice autorotation at 800 feet above ground level (agl). About 100 feet agl, the pilot flared and rolled on the throttle to initiate a power recovery. The engine rpm did not increase, and the main rotor rpm started to decay. The pilot'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 tail boom sustained substantial damage. Postaccident examination by a Federal Aviation Administration (FAA) inspector and representatives from RHC and Lycoming Engines did not reveal any mechanical malfunctions or failures with the helicopter or engine that would have precluded normal operations. The engine was prepared for an engine run. The engine started and was run up to 100 percent for approximately 10 minutes. The engine was found to run smoothly at idle and 100 percent rpm. The throttle operated smoothly throughout its range. The FAA Rotorcraft Flying Handbook (FAA-H-8083-21A) describes a technique for a practice autorotation with a power recovery. It states that "Just prior to achieving level attitude, with the nose slightly up, coordinate upward collective pitch control with an increase in the throttle to join the needles at operating rpm. The throttle and collective pitch must be coordinated properly. If the throttle is increased too fast or too much, an engine overspeed can occur; if throttle is increased too slowly or too little in proportion to the increase in collective pitch, a loss of rotor rpm results."
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.
Source: NTSB Aviation Accident Database
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