ERA13LA045

After departure, the helicopter began to vibrate at an altitude of about 300 feet above ground level (agl). The pilot chose to return to the airport to perform a precautionary landing. The pilot initiated an autorotation about 100 feet agl at an airspeed of between 45 to 50 knots but could not control the helicopter. The pilot applied aft cyclic to flare the helicopter; however, it did not lose airspeed. The low rotor rpm aural warning activated during the maneuver, and the helicopter subsequently landed hard and rolled over on its right side. Postaccident examinations of the engine and airframe did not reveal any anomalies that would have caused the vibration the helicopter experienced after takeoff. If the pilot had initiated the autorotation sooner, she may have had adequate airspeed to establish the glide and a sufficient amount of rotor rpm to cushion the landing and retain positive control of the helicopter.

On November 1, 2012, at 1546 central daylight time, a Robinson R22, N231TM, sustained substantial damage during a precautionary landing at Thomas C. Russell Field Airport (ALX), Alexander City, Alabama. The commercial pilot was seriously injured, and the commercial pilot-rated passenger received minor injuries. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight, which was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. The flight was originating at the time of the accident. According to the pilot, she and her co-worker were en route to Sarasota, Florida and were departing ALX after stopping for lunch. The pilot rated passenger was conducting the takeoff when, shortly after departure while turning crosswind, the helicopter started to shake. The pilot assumed control of the helicopter and elected to return to the airport to perform a precautionary landing in the grass. The pilot did not observe any abnormal indications on the flight instruments, but stated that she did not look at the manifold pressure gauge. About 100 feet above ground level and approximately 45 to 50 knots, the pilot initiated an autorotation, but "could not control" the helicopter. She then reduced the collective pitch and applied forward pressure on the cyclic control to gain airspeed for landing. As the helicopter approached the landing site, the pilot applied aft cyclic to flare the helicopter. The low rotor rpm horn activated, and the helicopter impacted the ground and came to rest on its right side, resulting in substantial damage to the main rotor blades and fuselage. 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 of the helicopter, 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 to the airport, and "may have" entered an autorotation. He stated that the helicopter did not lose airspeed and did not appear to flare prior to impact, contacting the ground at an airspeed of 40 to 50 knots with the low rotor rpm horn activated. The helicopter rolled to its right side after impact, and the pilots egressed. The pilot held a commercial pilot certificate and flight instructor certificate with a rating for rotorcraft-helicopter. Her most recent Federal Aviation Administration (FAA) second-class medical certificate was issued on May 21, 2012. At the time of the accident, the pilot reported 1,165 total hours of flight experience, all of which were in the accident helicopter make and model. The 1555 automated weather observation at ALX included winds from 300 degrees at 7 knots with gusts to 14 knots; 10 statute miles visibility; sky clear; temperature 21 degrees Celsius (C); dew point -4 degrees C, and an altimeter setting of 29.97 inches of mercury. According to FAAairworthiness records, the helicopter was manufactured in 1993 and was equipped with a Lycoming O-320-B2C, 160-hp, reciprocating engine and float-type landing gear. Review of the helicopter's maintenance records revealed that its most recent annual inspection was completed on September 14, 2012, at a total airframe time of 1684.2 hours, and a time since engine overhaul of 531.6 hours. Records also indicated that the governor had been replaced on October 31, 2012. 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. A postaccident examination conducted by an FAA inspector revealed impact damage to the flight control tubes and rods. Flight control continuity was established from the cockpit area to the main rotor and to the tail rotor gearbox. The main rotor driveshaft and mast were separated from the gearbox and located near the main wreckage. The swashplate system displayed minor impact damage.. One main rotor blade was separated at the hub, exhibited significant impact damage and was located approximately 500 feet away from the main wreckage. The other blade remained attached to the hub and also exhibited impact damage. No foreign objects or debris were observed in the vicinity of the engine cooling fan, and the fan remained on its shaft. The V-belts and alternator belt were examined and found to be intact. The strap connecting the floats to the skids remained attached. A postaccident examination of the engine by an overhaul facility revealed normal wear of the engine components, including the crankshaft, camshaft, lifters, rods, gears, cylinders and crankcase. Bench testing of the magnetos revealed no anomalies, and examination of the carburetor revealed no evidence of fuel contamination. Examination of the main rotor blades was conducted by the NTSB materials laboratory and revealed no evidence of corrosion, leading edge paint erosion, or debonding between the blade spar and skin. Examination of the fracture surfaces revealed signatures consistent with separation due to overstress. 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 further cautioned, "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."