HISTORY OF FLIGHT On June 21, 2010, about 0910 Pacific daylight time, a Cessna 172N, N733AS, impacted hilly terrain near Angels Camp, California. The pilot operated the borrowed airplane under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. The pilot, the sole occupant was fatally injured; the airplane sustained substantial damage. Visual meteorological conditions prevailed for the flight that departed Modesto City-County Airport-Harry Sham Field (MOD), Modesto, California, about 0845. According to witnesses in the surrounding area, they were drawn to the accident airplane because it was circling the area, flying low, and performing aerobatics (loops and wide turns) for about 20 minutes before the witnesses lost sight of the airplane behind a mountain and heard a loud bang, metal crumpling, and the engine sound stopped. One of the witnesses stated that the airplane was doing sharp turns and nosedives. An airborne witness, a certified flight instructor (CFI), who was with a student at the time, observed the accident airplane. The CFI reported that the accident airplane was at 6,000 feet mean sea level (msl), and they were at 4,500 feet msl. They were traveling eastbound toward their destination airport. He contacted NorCal TRACON, and reported that they had the airplane in sight and would maintain visual separation. NorCal reported that they were not in contact with the pilot of the accident airplane. The CFI observed the accident airplane circling, and he thought the pilot was performing a simulated engine out approach/steep spiral to Calaveras County-Maury Rasmussen Field Airport (CPU), San Andreas, California. Once the CFI realized that the pilot was not landing at CPU, he watched him more closely, and observed the airplane doing steep spiraling maneuvers that he estimated to be close to a 70- to 90-degree bank. On two occasions he did see a reduction of the angle of bank toward wings level, but the airplane never attained a wings level attitude before it rolled back to a steep spiral maneuver. The owner of the airplane reported to the Calaveras County Sheriff’s Department that the pilot often borrowed the airplane, and did not always tell him that he (the pilot) was taking it. The detective inquired as to whether the pilot would have been using the oxygen system as the oxygen mask was found partially on the pilot at the accident site. The owner indicated that as far as he knew, the pilot did not use the oxygen system. PERSONNEL INFORMATION According to the Federal Aviation Administration (FAA) airman and medical records, the 59-year-old pilot held a private pilot certificate with ratings for airplane single-engine land and instrument airplane. He held a third-class medical issued in March 2009, and it had no restrictions. A review of the pilot's logbook revealed that the pilot had an estimated 1,436.3 hours of flight time. In the past 90 days the pilot had accrued a total of 15.9 flight hours, and 6.7 flight hours in the last 30 days. The pilot's last flight review was September 22, 2009. According to the pilot’s wife, the pilot was taking a blood pressure medication, and that he had been practicing with the airplane’s oxygen system. She also reported that the pilot seemed to be in good spirits. AIRCRAFT INFORMATION The airplane was a Cessna 172N, serial number 17268149. The airplane was returned to service following the completion of an annual inspection on April 16, 2010. The aircraft logbook entry indicated that the total time on the airframe was 5,451.1 hours. A Textron Lycoming engine, O-320-H2AD, serial number L-752-76, was installed on the airplane. WRECKAGE AND IMPACT INFORMATION The airplane came to rest on a hillside on a 30-degree slope in thick vegetation and manzanita trees. The debris field was 150 feet. The first identified point of contact (FIPC) was the nose, with the cowling remaining at the FIPC, and debris located in the trees. The engine came to rest just forward of the main wreckage. The FAA inspector that responded to the accident site reported that there was no fuel or smell of fuel at the accident site. MEDICAL AND PATHOLOGICAL INFORMATION The Calaveras County Coroner completed an autopsy on the pilot on June 22, 2010. The cause of death was listed as multiple traumatic injuries due to an aircraft accident. The FAA Forensic Toxicology Research Team 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: Atenolol in urine and blood (cavity), and quinine was detected in urine. TEST AND RESEARCH According to the radar data, the airplane tracked to the northeast for about 25 nautical miles (nm), with a gradual climb to 11,800 feet msl before initiating a left 180-degree turn toward the southwest. The radar track showed the airplane continuing to climb to an altitude of 12,500 feet msl, where it made a right 360-degree turn. The radar track reached an altitude of 12,800 feet msl. Between the times of 0900:47 and 0910:50, the radar data depicted approximately 20 descending left 360-degree turns, ending at 2,400 msl (450 feet above ground level). The average rate of descent was 1,376 feet per minute. The National Transportation Safety Board (NTSB), along with a representative from Cessna Aircraft Company, inspected the airframe and engine. Investigators were able to establish flight control continuity via the flight control cables and associated hardware to all of the flight surfaces. Both wings were separated about midspan with leading to trailing edge damage. The trim was set to a neutral position and the flaps were retracted. Investigators noted that the fuel filter was free of debris. The oxygen bottle had been compromised and could not be tested. A visual inspection of the engine revealed that the engine was intact with no obvious mechanical anomalies. The propeller hub assembly separated from the crankshaft; the crankshaft flange was deformed with 45-degree sheer lip fracture surfaces. The starter drive had horizontal striations on it. The propeller blades showed S-bending. One blade had chordwise scratching the length of the blade, the other propeller blade had chordwise scratching near the outboard section of the blade. Both propeller blades showed leading and trailing edge gouging. The top spark plugs were removed and found to exhibit normal operating signatures. The dual-drive magneto remained attached at its mounting pad, but had sustained impact damage. The carburetor had separated from its mounting pad. Mechanical and drive train continuity was achieved through manual rotation of the crankshaft via the accessory drive.