CEN18LA251

The flight instructor and commercial pilot were about to make the base leg turn for a local instructional flight when the low rotor rpm horn activated. The flight instructor got on the flight controls with the pilot, immediately reduced the collective, and applied throttle. The flight instructor heard the low rotor rpm horn stop and observed the low rotor rpm light extinguish; he visually confirmed the engine and rotor rpm were about 97%. The flight instructor began the base leg turn and heard the low rotor rpm horn again. After noticing that the engine and rotor rpm were decaying, the flight instructor felt that the engine was not capable of maintaining the rotor rpm within safe operating limits and entered an autorotation. The helicopter touched down with a small amount of forward airspeed in a yard at a private residence, which resulted in substantial damage to the tailboom and the vertical stabilizer. A postaccident examination of the engine found no preimpact mechanical malfunctions or failures that would have precluded normal operation. Although the weather conditions at the time of the accident were conducive for the formation of carburetor icing at glide and cruise power, the helicopter was equipped with a carburetor heat assist device. The helicopter had an adequate amount of fuel on board at the time of the accident. The reason for the loss of engine power could not be determined.

On July 2, 2018, about 1445 central daylight time, a Robinson Helicopter Company R-22 Beta II, N830J, sustained substantial damage when it was involved in an accident near Georgetown, Texas. The flight instructor and the commercial pilot sustained no injury. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The flight instructor reported that the purpose of the local area flight was to conduct flight instructor training with the commercial pilot. While on the last traffic pattern iteration, on the downwind leg about 500 ft above ground level (agl) and about 70 kts, the flight instructor reported he was visually outside of the helicopter, scanning for traffic, and clearing the helicopter for the base leg turn when he heard the low rotor revolutions per minute (rpm) horn activate. The flight instructor came on the flight controls with the pilot and he immediately reduced the collective and applied throttle. The flight instructor heard the low rotor rpm horn cease and observed the low rotor rpm light extinguish, while he visually confirmed the engine and rotor rpm was about 97%. The flight instructor began the base leg turn and heard the low rotor rpm horn again. The flight instructor observed the tachometer and noticed that the engine and rotor rpm were decaying. The flight instructor assessed the situation and felt that the engine was not capable of maintaining the rotor rpm within safe operating limits and he entered an autorotation. The flight instructor scanned the instruments and observed the airspeed was about 55 kts. He reported he could not hear noise emitting from the engine and surmised that the engine had ceased producing power. After the entry to the flare of the autorotation, the flight instructor reported that he was focused on maintaining the rotor rpm and maneuvering the helicopter to his selected landing area. About 35 ft agl, he began the flare to reduce the forward airspeed and the rate of descent. The helicopter touched down on a yard at a private residence, with a small amount of forward airspeed. The skids impacted a concrete driveway at the residence. The impact with the driveway resulted in the helicopter pitching nose low with the tail elevated, along with a right yaw. Both tail rotor blades impacted the ground, resulting in both blades becoming separated about mid-span. The tail boom and the vertical stabilizer sustained substantial damage from the ground impact, along with minor damage sustained to the tail rotor stinger and skids. Once the helicopter came to rest, the flight instructor observed that the engine was at idle and he performed an emergency shutdown. Both occupants egressed from the helicopter without further incident. The flight instructor reported that the helicopter had an adequate amount of fuel for the flight. A postaccident examination of the airframe and engine revealed no preimpact mechanical malfunctions or failures with the airframe and engine thatwould have precluded normal operation. An examination of the maintenance records provided by the operator revealed no evidence of any uncorrected mechanical discrepancies with the helicopter. The operator reported that the pilot receiving instruction may have inadvertently gripped and reduced the throttle while in flight. The pilot was historically known for being "heavy" or "rough" on the flight controls. A postaccident flight with the pilot by the operator showed the pilot being "heavy" or "rough" again on the flight controls. The helicopter was equipped with a carburetor heat assist device. The Robinson R-22 Pilot's Operating Handbook discusses the carburetor heat assist device and states, "the carb heat assist correlates application of carburetor heat with changes in collective setting to reduce pilot workload. Lowering collective mechanically adds heat and raising collective reduces heat." The temperature and dewpoint at the time of the accident were conducive to the formation of carburetor icing (for glide and cruise power) per the Federal Aviation Administration Special Airworthiness Information Bulletin CE-09-35 Carburetor Icing Prevention.