HISTORY OF FLIGHT On June 18, 2006, about 0615 mountain standard time, a Cessna 180, N1535C, collided with terrain near Payson, Arizona. The pilot/owner was operating the airplane under the provisions of 14 Code of Federal Regulations Part 91. The commercial pilot and three passengers were killed; the airplane sustained substantial damage. The cross-country personal flight departed Pegasus Airpark, Queen Creek, Arizona, about 0555 en route to Payson. Visual meteorological conditions prevailed, and no flight plan had been filed. The National Transportation Safety Board investigator-in-charge (IIC) interviewed a friend of the accident pilot. The friend, who owned an airplane based at Pegasus, said that he talked to the accident pilot earlier in the week. The accident pilot indicated that he was planning to fly to Payson for breakfast on the day of the accident. The friend departed Pegasus about 0540 en route to a backcountry dirt airstrip called Red Creek that was west of Payson. He said that the accident pilot was very familiar with Red Creek. After departing Pegasus, the friend switched to a frequency that backcountry pilots frequently use. As he neared Red Creek, he established radio contact with the accident pilot. The friend landed at Red Creek, shut down, and let his passenger go to a sign-in log on the airstrip. He observed the accident airplane south of the airstrip. It flew over the airstrip about 150 feet above ground level (agl), but he did not continue to look at it, and focused his attention on inspecting his airplane. He was aware of the engine sounds, but they were not unusual and did not draw his attention. He heard a "thud," and the engine sounds stopped. He looked up and saw either the wing or tail of the airplane as it cartwheeled near the pinnacle of a hillside located north of the airstrip. The friend immediately took off in his airplane, and tried to contact Payson UNICOM. When no one responded, he broadcast on 121.5. He received a response, and reported the crash. He landed back at the airstrip, and walked to the accident site. He waited at the accident site about 45 minutes, and noticed his passenger starting toward the site. He decided to return to the airstrip. As he started back, emergency personnel landed at the airstrip. PERSONNEL INFORMATION A review of Federal Aviation Administration (FAA) airman records revealed that the 51 year old pilot held a commercial pilot certificate with ratings for airplane single-engine land, multiengine land, and instrument airplane. The pilot held a second-class medical certificate issued on October 25, 2005. It had no limitations or waivers. No personal flight records were located for the pilot. The flight time indicated on the pilot's application for the medical certificate indicated a total flight time of 2,690 hours with 65 hours in the previous 6 months time. AIRCRAFT INFORMATION The airplane was a Cessna 180, serial number 30235. A review of logbook excerpts provided to the IIC revealed an entry dated July 1, 2005, of an annual inspection at a total airframe time of 4,310.3 hours with a corresponding tachometer reading of 892.4 hours. Investigators found a flight log that the accident pilot kept in the airplane. It had an entry dated June 16, 2006, that noted a tachometer time of 1,133.6 hours. The engine was a Teledyne Continental Motors IO-520-D, serial number 158337-6-D, modified to a P. Ponk Aviation O-470-50, serial number 2274. An engine logbook entry dated July 1, 2005, noted an annual inspection at an engine time of 892.4 hours since major overhaul. The last entry was an oil change on August 25, 2005, at a tachometer time of 944.6 hours. WRECKAGE AND IMPACT INFORMATION The wreckage was examined on site by investigators on June 19 and June 21, 2006. The wreckage was on the west side of a small pinnacle, and about 50 feet below its crest. The first identified point of contact (FIPC) consisted of broken tree limbs. The debris field began on a bearing of 045 degrees and curved to the right as it went uphill. All distances noted of the wreckage distribution are from the FIPC toward the main wreckage and left or right of the debris path centerline. About 10 feet from the FIPC was the initial ground scar, which contained green lens fragments and the right wing tip fairing. About 30 feet from the FIPC was the principle impact crater (PIC), which contained one propeller blade. Thirty feet further into the debris field on the debris path centerline was part of the propeller hub and another propeller blade. Ten feet past the hub was a section of the outboard right wing and pieces of the left wing tip fairing. Twenty feet right of these pieces was the third propeller blade. The main wreckage came to rest on a magnetic heading of 351 degrees about 150 feet from the FIPC. The outboard sections of both wings separated. The aileron control cables separated in a broom straw pattern. Control continuity was established for the rudder and elevators. The left wings fuel tank contained a blue fluid that smelled similar to aviation fuel. Water detecting paste did not indicate the presence of water in this fluid. The manually operated flap handle, which is between the seats in the cockpit, was in the retracted position. The engine separated and came to rest downhill about 50 feet past the main wreckage and 50 feet left of the debris path centerline. Investigators removed the spark plugs. The top spark plugs were clean with no mechanical deformation. The spark plug electrodes were gray, which corresponded to normal operation according to the Champion Aviation Check-A-Plug AV-27 Chart. All of the bottom plugs were oily. Investigators manually rotated the crankshaft with a tool in an accessory drive gear. The crankshaft rotated freely, and the valves moved approximately the same amount of lift in the proper firing order. The gears in the accessory case turned freely. Investigators obtained thumb compression in all cylinders in the proper firing order. Investigators manually rotated the magnetos, and both magnetos produced spark at all posts. All three propeller blade tips separated in a jagged pattern. The blade at the PIC bent aft, had leading edge gouges, and S-bending on the trailing edge. The blade in the hub had leading and trailing edge gouges, curled toward the low pitch position, and had chordwise striations. The third blade bent aft, twisted toward the low pitch position, and had trailing edge S-bending. MEDICAL AND PATHOLOGICAL INFORMATION The Yavapai County Coroner completed an autopsy. The FAA Bioaeronautical Sciences Research Laboratory, 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: ibuprofen detected in blood and urine. ADDITIONAL INFORMATION Sun and moon calculations indicated that the sun was 11.4 degrees above the horizon, and the magnetic bearing to the sun was 56 degrees.