Accident Overview
On May 15, 2008, at 1640 eastern daylight time, a Robinson R44 II, registration 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 had departed Bartow Municipal Airport (BOW), Bartow, Florida, approximately 1 hour earlier.
Pilot Statements
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 ground level (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.
Weather and Inspection
The reported weather at Bartow Municipal Airport, 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, dew point 12 degrees Celsius, 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.
Procedural References
According to the Robinson R44 II Pilot's Operating Handbook, Chapter 4, Normal Procedures, Practice Autorotation Power Recovery outlines steps including lowering collective to down stop and adjusting throttle, raising collective to keep rotor RPM in the green arc, maintaining airspeed between 60 and 70 knots indicated airspeed (KIAS), beginning a cyclic flare at about 40 feet agl, and at about 8 feet agl, applying forward cyclic to level the aircraft and raising collective to control descent, adding throttle if required.
The FAA Airplane Rotorcraft Flying Handbook FAA-H-8083-21, Chapter 11, Helicopter Emergencies, lists common errors associated with power recovery from practice autorotation, such as initiating recovery too late, failing to obtain a level attitude near the surface, failing to coordinate throttle and collective pitch properly, and failing to coordinate antitorque pedal with the increase in power.