NTSB Factual Report

On September 3, 2018, about 1537 Pacific daylight time, a Guimbal Cabri G2 helicopter, N401SH, was substantially damaged during an autorotative landing near Santa Ana, California. The flight instructor and student pilot were not injured. The airplane was owned and operated by Spitzer Helicopters and operated by One Above Aviation under the provisions of Title 14 Code of Federal Regulations Part 91 as an instructional flight. Visual meteorological conditions (VMC) prevailed, and a flight plan was not filed for the cross-country flight, that departed John Wayne-Orange County Airport (SNA), Santa Ana California about 1400 and had flown to El Monte, California through an intermediate airport before returning to SNA.

According to the flight instructor and student pilot, they returned to SNA after conducting some cross-country flight training. They initiated an autorotation to simulate an inflight loss of engine power from about 700 ft mean sea level (msl) and 60 kts and maintained 50 kts during the subsequent glide, which was uneventful. As they reached 150 ft msl the flight instructor prepared for a power recovery by opening the throttle slightly, with the intention of preventing the rotor RPM from entering the normal range before they flared the helicopter. Two seconds later, the flight instructor realized that she did not have enough power and advanced the throttle further. The flight instructor added that as the helicopter reached 40 ft msl the student pilot raised the collective pitch control to stop the descent, but did not complete the flare. While descending in a near flat attitude, the flight instructor rolled the throttle to its full power position to complete the power recovery, but the engine power did not rise as the instructor and student pilot had anticipated. The low rotor rpm horn engaged and the nose yawed to the left. The helicopter rolled to the left from an altitude of about 4 ft before coming to rest on its left side.

Postaccident photos furnished by the helicopter operator showed substantial damage to the main rotor blades. Additionally, the helicopter fuselage had separated from the skid attachment points.

In subsequent interviews with the flight instructor and student pilot, the instructor noted that the throttle seemed stiffer than normal. The student pilot remarked that during the accident flight the engine power responded about 2 seconds after it was advanced to full power. In his experience during previous flights, the engine normally takes about one half second to advance to full power.

According to the "Aborting autorotation practice" section of the Rotorcraft Flight Manual,

If power recovery is decided during autorotation:

1. Roll-in throttle until governor engages,

2. Gradually raise collective pitch to stop autorotation and descent,

3. Control yaw during power recovery with pedals

Additionally, the excerpt advises that the helicopter will yaw to the left when the power recovers.