On September 16, 2004, approximately 1620 mountain daylight time, a Robinson R22, N7533E, piloted by a commercial pilot, sustained substantial damage when it made a hard landing during a simulated power loss and practice autorotation at the Spanish Fork-Springvale Municipal Airport (U77), Spanish Fork, Utah. Visual meteorological conditions prevailed at the time of the accident. The local instructional flight was being conducted under the provisions of Title 14 CFR Part 91 without a flight plan. The pilot received minor injuries and flight instructor was not injured. The flight originated at Provo (PVU), Utah, approximately 1600.

According to the flight instructor's written statement and telephone interview, he was preparing the commercial pilot for his upcoming flight instructor practical test. He asked the pilot to demonstrate a simulated engine failure with autorotation to landing. The pilot rolled off power and entered an autorotation. Airspeed was between 65 and 70 knots, and rpm was maintained between 98 and 100 percent. The rate of descent was 2,000 feet per minute (fpm) in the 180-degree turn, but decreased to 1,800 fpm when they lined up with the runway. Rpm was at 97 percent and started to drop. The warning horn and light activated at 100 feet agl. Rpm was at 94 percent. The instructor took control of the helicopter and applied full power and "a small cyclic flare, and lowered the collective slightly to recover rpm." The helicopter began to shake with a low frequency vibration. Rpm was between 92 and 94 percent. Approximately 50 feet agl, the instructor applied "a strong cyclic flare" to reduce the rate of descent. The vibrations continued and the helicopter continued to settle. Just before ground contact, the instructor noted the rpm needles were "married at 92 percent (sic)." The helicopter contacted the runway tail first, then the rear portion of the skids hit. The helicopter bounced and began to spin. The helicopter came to rest right side up and the engine continued to run.

The following is an excerpt from Section 4, "Normal Procedures," of the Robinson R22 PILOT'S OPERATING HANDBOOK, p. 4-10:

"CAUTION. The R22 has a light, low-inertia rotor system. Most of the energy required for an autorotation is stored in the forward momentum of the aircraft, not in the rotor. Therefore, a well timed cyclic flare is required and rotor RPM must be kept in the green until just before ground contact.

"CAUTION. During simulated engine failures, a rapid decrease in rotor RPM will occur, requiring immediate lowering of collective control to avoid dangerously low rotor RPM. Catastrophic rotor stall could occur if the RPM ever drops below 80 percent plus 1 percent per 1000 feet of altitude."

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