HISTORY OF FLIGHT On May 22, 2009, about 1330 mountain standard time (MST), an experimental homebuilt helicopter, Gauchat Safari, N147MD, impacted terrain near Rock Springs, Arizona, following the separation of both of the main rotor blades. The builder/pilot was operating the helicopter under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The private pilot and one passenger were fatally injured; impact forces and the post crash fire substantially damaged the helicopter. The local personal flight departed Rock Springs about 1325, with a planned destination of Phoenix, Arizona. Visual meteorological conditions prevailed, and no flight plan had been filed. Witnesses reported that the helicopter had just departed from a parking lot .3 nautical miles north of the accident site. They observed the helicopter flying southbound parallel to highway 17, when one of the main rotor blades departed the helicopter. The helicopter then fell to the ground. PERSONNEL INFORMATION No personal flight records were located for the pilot. The National Transportation Safety Board investigator-in-charge (IIC) obtained the aeronautical experience listed in this report from a review of the Federal Aviation Administration (FAA) airmen medical records on file in the Airman and Medical Records Center located in Oklahoma City, Oklahoma. The pilot reported on his medical application dated May 5, 2008, that he had a total time of 270 hours, with 50 hours logged in the last 6 months. AIRCRAFT INFORMATION The experimental homebuilt helicopter, a Gauchat Safari, serial number 2129, was issued a special airworthiness certificate on May 30, 2006. A review of the helicopter’s logbooks revealed that the helicopter had a total airframe time of 237.3 hours at the last conditional inspection dated May 10, 2009. WRECKAGE AND IMPACT INFORMATION An inspector from the FAA responded to the scene. The accident site consisted of the helicopter's fuselage, tailboom, and tail rotor system. The debris field contained both main rotor blades; one blade was located 620 feet northwest of the main wreckage, and the second blade was located 300 feet east of the main wreckage. One of the push pull control tubes was found 170 feet northwest of the main wreckage, and an operating handheld Global Position Satellite unit was located 100 feet northwest on the main wreckage. MEDICAL AND PATHOLOGICAL INFORMATION The Maricopa County Coroner completed an autopsy on the pilot May 26, 2009. The cause of death was determined to be as a result of blunt force injuries. The FAA Civil Aerospace Medical Institute (CAMI), Oklahoma City, Oklahoma, performed toxicological testing of specimens of the pilot. Analysis of the specimens contained no findings for carbon monoxide, cyanide, and volatiles. The report contained the following findings for tested drugs: 0.101 (ug/ml, ug/g) Doxylamine detected in blood, Doxylamine detected in liver. TESTS AND RESEARCH Investigators examined the wreckage at Air Transport, Phoenix, on June 29, 2009, and on August 14, 2010. Portions of the main rotor head were shipped to the NTSB materials laboratory in Washington, D.C., for further examination. The materials specialist found that the main rotor head spindle had failed in fatigue that initiated in machining marks at a radius located at the intersection of the bearing diameter with the larger inboard diameter normally obscured by the grip nut. The full report is in the public docket. ADDITIONAL INFORMATION Because of this accident and the ensuing investigation, the manufacturer issued the mandatory inspection bulletin MI-002. The bulletin requires inspection of the Main Rotor Spindle for distinct machining marks of irregular depth. In addition, any spindle which has been subjected to shock loads resulting from any accident of sufficient force to cause damage to other areas of the helicopter, re-engagement of the clutch while the rotor blades are still in motion, hard starts of the engine, over-torque of the castle nut, or repeated over speed of the main rotor head should be inspected. A copy of the mandatory inspection bulletin is located in the public docket. According to FAA Advisory Circular AC 20-27F, Certification and Operation of Amateur-Built Aircraft, "Amateur builders are free to develop their own designs or build from existing designs. We do not approve these designs and it would be impractical to develop design standards for the wide variety of design configurations, created by designers, kit manufacturers, and amateur builders."