On May 15, 2008, at 1640 eastern daylight time, a Robinson R44 II, N911GJ, operated by the Polk County, Florida, Sheriffs Office, was substantially damaged during a practice autorotation at Lake Wales Municipal Airport (X07), Lake Wales, Florida. The certificated flight instructor (CFI) and the certificated commercial pilot sustained minor injuries. Visual meteorological conditions prevailed, and no flight plan was filed for the public use training flight which departed Bartow Municipal Airport (BOW), Bartow, Florida, approximately 1 hour earlier.
According to the CFI, he was demonstrating an autorotation to runway 6, which he entered at "800 feet indicated and at zero airspeed." He lowered the nose of the helicopter and attained a 60-knot descent with a rotor rpm of 95 percent. At 40 feet above the ground (agl), he began a flare and began "rolling throttle on." At 8 feet agl, he raised the collective; however, the helicopter impacted the runway in a level attitude, bounced, landed again, and rolled onto its left side.
According to the commercial pilot, the rotor and engine rpm remained at the "low end" of the green (normal) range during the autorotation. Approximately 500 feet agl, the CFI started to decelerate the helicopter, and approximately 40 feet agl, he began to add power as the rotor rpm began decreasing. The helicopter continued its descent, and impacted the runway in a level attitude. It then bounced, veered to the right, and rolled over on its left side.
The CFI reported 6,766 hours of flight experience as pilot in command in rotorcraft, 300 hours in make and model, 60 hours of flight experience within the 90 days preceding the accident flight, and 1,500 hours of flight time as a CFI.
The reported weather at BOW, located approximately 8 miles from the accident site, at 1650, included variable winds at 5 knots, visibility 8 miles, lowest cloud layer at 25,000 feet, temperature 31 degrees Celsius (C), dew point 12 degrees C, and an altimeter setting of 30.02 inches of mercury.
According to a Federal Aviation Administration (FAA) inspector, the helicopter came to rest, on its left side at the approach end of runway 6. All major components were accounted for at the scene, and flight control continuity was confirmed from the cockpit to all flight control surfaces. No preimpact mechanical anomalies were noted by either the pilots or the FAA inspector.
According to the Robinson R44 II Pilot's Operating Handbook, Chapter 4, Normal Procedures, Practice Autorotation Power Recovery:
1. Lower collective to down stop and adjust throttle as required for small tachometer needle separation. CAUTION To avoid inadvertent engine stoppage, do not roll throttle to full idle. Roll throttle off smoothly only enough for a small visible needle split. 2. Raise collective as required to keep rotor RPM from going above green arc and adjust throttle for small needle separation. 3. Keep RPM in green arc and airspeed 60 to 70 KIAS [knots indicated airspeed] 4. At about 40 feet AGL, begin cyclic flare to reduce rate of descent and forward speed. 5. At about 8 feet AGL, apply forward cyclic to level aircraft and raise collective to control descent. ADD throttle if required to keep RPM in green arc.
According to the FAA Airplane Rotorcraft Flying Handbook FAA-H-8083-21, Chapter 11, Helicopter Emergencies, Power Recovery from Practice Autorotation some of the common errors associated with this maneuver are:
1. Initiating recovery too late, requiring a rapid application of controls, resulting in overcontrolling. 2. Failing to obtain and maintain a level attitude near the surface. 3. Failing to coordinate throttle and collective pitch properly, resulting in either an engine overspeed or a loss of r.p.m. 4. Failing to coordinate proper antitorque pedal with the increase in power.