HISTORY OF FLIGHTOn August 27, 2012, at 0803 Pacific daylight time, an Arrow Falcon Exporters Inc OH-58C, N503DR, crashed in an almond orchard near Escalon, California. Del Rio Aviation, Inc., operated the helicopter under the provisions of Title 14 Code of Federal Regulations Part 137. The commercial pilot was seriously injured, and the helicopter was substantially damaged. Visual meteorological conditions prevailed, and a flight plan had not been filed. The pilot had flown a 30-minute flight from his base to the almond orchard, where the helicopter's hoppers were loaded with 80 gallons of application product from a mixing truck located near the orchard. The truck driver stated to the sheriff that it appeared that the pilot was just about done with the load of chemicals when he observed the helicopter about a mile away. The helicopter banked up to the right at an angle that appeared to be steeper than normal, then it disappeared and never reappeared. The driver went to the location where he last saw the helicopter and found it crashed in the almond orchard. There was no post accident fire. The pilot stated in the NTSB Form 6120 Pilot Aircraft Accident Report that he had no memory of the accident. PERSONNEL INFORMATIONThe pilot, age 71, held commercial pilot certificates for airplane single engine and multiengine land, airplane single engine sea, instrument airplane, and rotorcraft-helicopter issued January 15, 2007. He held a second-class medical certificate with the limitation that he must have available glasses for near vision, issued January 12, 2012. The pilot reported that he had 15,653 hours of total flight time, and 11,075 hours flying helicopters in agricultural application. AIRCRAFT INFORMATIONThe conventionally configured helicopter, serial number 71-20679, was manufactured in 1971. It was powered by a Rolls Royce T63-A-720 turboshaft engine rated at 420 horsepower. The operator reported that the most recent annual inspection was completed on July 18, 2012, at a total airframe time of 6,429.2 hours. Engine total time was 4,318.3 hours. The most recent 100-hour inspection was completed on August 26, 2012, at a total aircraft time of 7,019.3 hours. An Arrow Falcon Exporters Inc, Model 3900-OH58 Spray System was installed on the helicopter, Supplemental Type Certificate (STC) SR00268LA. The Model 3900-OH58 Spray System consists of two 70-gallon cylindrical chemical tanks attached by quick disconnect pins on the left- and right-hand side of an "H" frame support that is bolted to the hard points of the landing gear attach fittings. The tanks are connected together through a cross feed tube so that they can be filled from either side by pressure or gravity fill provisions. The chemical is routed through the cross feed tube to a center outlet on the tube to the chemical pump. The center spray boom is 70" long and is mounted at airframe station 22 on the "H" frame support. It has provisions for mounting 12 spray nozzles or down tubes. Each outboard spray boom is connected to the center boom through a connector and to the "H" frame by one each vertical and horizontal strut for support. WRECKAGE & IMPACT INFORMATION The main wreckage was located between rows of almond trees laying on its right side. Several almond trees were damaged in the area of the wreckage. The main rotor hub was attached to the mast, both rotor blades had sheared off about 3 feet from the center of the rotor hub. The tail boom was attached and the tail rotor was connected. The right side hopper tank was crushed and the right landing skid had separated from the cross tubes at the attachment points. The hopper cross feed tube was connected to both left and right hopper tanks. The right spray bar was bent and collapsed under the helicopter, the left spray bar remained in place. The sheriff reported that on-scene he could detect the odor of agricultural application chemical and jet fuel. A Federal Aviation Administration (FAA) inspector examined the helicopter on-scene. He reported that the tail rotor and engine to transmission drive shafts had separated in shear. The tail rotor gearbox rotated freely and no metal chips were identified on the gearbox chip detector. The engine oil level was full, and the lower chip detector was free of metal chips. He traced the control system and established control continuity. No mechanical malfunctions or failures were found that would have precluded the normal operation of the helicopter. AIRPORT INFORMATIONThe conventionally configured helicopter, serial number 71-20679, was manufactured in 1971. It was powered by a Rolls Royce T63-A-720 turboshaft engine rated at 420 horsepower. The operator reported that the most recent annual inspection was completed on July 18, 2012, at a total airframe time of 6,429.2 hours. Engine total time was 4,318.3 hours. The most recent 100-hour inspection was completed on August 26, 2012, at a total aircraft time of 7,019.3 hours. An Arrow Falcon Exporters Inc, Model 3900-OH58 Spray System was installed on the helicopter, Supplemental Type Certificate (STC) SR00268LA. The Model 3900-OH58 Spray System consists of two 70-gallon cylindrical chemical tanks attached by quick disconnect pins on the left- and right-hand side of an "H" frame support that is bolted to the hard points of the landing gear attach fittings. The tanks are connected together through a cross feed tube so that they can be filled from either side by pressure or gravity fill provisions. The chemical is routed through the cross feed tube to a center outlet on the tube to the chemical pump. The center spray boom is 70" long and is mounted at airframe station 22 on the "H" frame support. It has provisions for mounting 12 spray nozzles or down tubes. Each outboard spray boom is connected to the center boom through a connector and to the "H" frame by one each vertical and horizontal strut for support. WRECKAGE & IMPACT INFORMATION The main wreckage was located between rows of almond trees laying on its right side. Several almond trees were damaged in the area of the wreckage. The main rotor hub was attached to the mast, both rotor blades had sheared off about 3 feet from the center of the rotor hub. The tail boom was attached and the tail rotor was connected. The right side hopper tank was crushed and the right landing skid had separated from the cross tubes at the attachment points. The hopper cross feed tube was connected to both left and right hopper tanks. The right spray bar was bent and collapsed under the helicopter, the left spray bar remained in place. The sheriff reported that on-scene he could detect the odor of agricultural application chemical and jet fuel. A Federal Aviation Administration (FAA) inspector examined the helicopter on-scene. He reported that the tail rotor and engine to transmission drive shafts had separated in shear. The tail rotor gearbox rotated freely and no metal chips were identified on the gearbox chip detector. The engine oil level was full, and the lower chip detector was free of metal chips. He traced the control system and established control continuity. No mechanical malfunctions or failures were found that would have precluded the normal operation of the helicopter.