Introduction
On November 1, 2012, at 1546 central daylight time, a Robinson R22 helicopter, registration N231TM, was substantially damaged during a precautionary landing at Thomas C. Russell Field Airport (ALX) in Alexander City, Alabama. The commercial pilot was seriously injured, and the commercial pilot-rated passenger sustained minor injuries. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight conducted under 14 CFR Part 91. The flight was originating at the time of the accident.
Accident Sequence
According to the pilot, she and her co-worker were en route to Sarasota, Florida after stopping for lunch. The pilot-rated passenger was conducting the takeoff when, shortly after departure while turning crosswind, the helicopter began to shake. The pilot assumed control and decided to return to the airport for a precautionary landing in the grass. She did not observe any abnormal flight instrument indications but stated that she did not look at the manifold pressure gauge.
Approximately 100 feet above ground level and at an airspeed of 45 to 50 knots, the pilot initiated an autorotation but reported that she could not control the helicopter. She then reduced collective pitch and applied forward cyclic to gain airspeed for landing. As the helicopter neared the landing site, she applied aft cyclic to flare. The low rotor rpm horn activated, and the helicopter impacted the ground, coming to rest on its right side. The main rotor blades and fuselage sustained substantial damage.
The pilot-rated passenger stated that about one minute after takeoff at an altitude of 300 feet, the flight controls began to vibrate. The pilot assumed control, and the passenger declared an emergency over the radio. The passenger reported that the pilot appeared to have difficulty controlling the helicopter during the return and may have entered an autorotation. He stated that the helicopter did not lose airspeed and did not appear to flare before impact, contacting the ground at 40 to 50 knots with the low rotor rpm horn activated. After impact, the helicopter rolled onto its right side, and both pilots egressed.
Pilot Information
The pilot held a commercial pilot certificate and a flight instructor certificate with a rating for rotorcraft-helicopter. Her most recent FAA second-class medical certificate was issued on May 21, 2012. At the time of the accident, she reported 1,165 total hours of flight experience, all in the accident helicopter make and model.
Aircraft Information
The helicopter was manufactured in 1993 and equipped with a Lycoming O-320-B2C, 160-horsepower reciprocating engine and float-type landing gear. The most recent annual inspection was completed on September 14, 2012, at a total airframe time of 1684.2 hours and time since engine overhaul of 531.6 hours. Maintenance records indicated that the governor had been replaced on October 31, 2012.
Weather Conditions
The 1555 automated weather observation at ALX reported winds from 300 degrees at 7 knots with gusts to 14 knots, visibility 10 statute miles, clear sky, temperature 21°C, dew point -4°C, and altimeter setting 29.97 inches of mercury.
Wreckage and Postaccident Examination
The main wreckage came to rest east of the runway prior to the threshold of runway 18, oriented on a heading of about 180 degrees magnetic. Examination by an FAA inspector revealed impact damage to flight control tubes and rods, but flight control continuity was established from the cockpit to the main rotor and tail rotor gearbox. The main rotor driveshaft and mast had separated from the gearbox and were found near the main wreckage. The swashplate system displayed minor impact damage. One main rotor blade had separated at the hub and was located approximately 500 feet away; the other blade remained attached but showed impact damage. No foreign objects or debris were found near the engine cooling fan, which remained on its shaft. The V-belts, alternator belt, and float strap were intact.
A postaccident engine examination by an overhaul facility revealed normal wear of components, including crankshaft, camshaft, lifters, rods, gears, cylinders, and crankcase. Bench testing of the magnetos showed no anomalies, and the carburetor showed no evidence of fuel contamination. The NTSB materials laboratory examined the main rotor blades and found no corrosion, leading edge paint erosion, or debonding between blade spar and skin. Fracture surfaces exhibited signatures consistent with overstress separation.
Relevant Manufacturer Guidance
The manufacturer's pilots operating handbook (POH) stated that autorotations should be conducted at an airspeed between 60-70 knots while maintaining rotor rpm within the green arc. The POH cautioned that the R22 has a light, low-inertia rotor system, and most autorotation energy is stored in forward momentum, not in the rotor. It emphasized the need for a well-timed cyclic flare and maintaining rotor rpm in the green until just before ground contact.