WPR09LA039 · Brantly B-2B

The owner/student and certified flight instructor (CFI) reported that they made one successful trip around the landing pattern, and landed. The second takeoff was progressing with the engine revolutions per minute (rpm) and manifold pressure in the high normal range. The CFI stated that about 30 to 50 feet above ground level (agl) at 45 to 50 miles per hour (mph), the engine just stopped. It did not sputter, skip, or give any indications that there was a problem. The CFI took the controls, and steered the helicopter to a grassy area on the left side of the runway. He kept it upright, and touched down hard on the skids first. Examination of the helicopter by a Federal Aviation Administration inspector revealed no evidence of catastrophic engine failure, or any other reason for the loss of power. Review of a video of the accident indicated that the helicopter maintained an almost level attitude throughout the descent. It descended at a constant attitude with no apparent flare/deceleration. A factory pilot for the manufacturer reported that in order to make a safe autorotation, the air speed must be above 40 miles per hour, the rotor rpm must be in the green, and a deceleration must occur in the last 25 to 35 feet that will allow using airspeed to slow the rate of descent. The factory pilot stated that the helicopter was probably outside of the parameters for a successful autorotation and he did not think that the instructor had enough time and altitude to make a safe autorotation.

Verbatim NTSB analysis and probable cause from the NTSB dataset