History of Flight
On June 21, 2010, at approximately 0910 Pacific daylight time, a Cessna 172N, registration N733AS, impacted hilly terrain near Angels Camp, California. The pilot, who was the sole occupant, was operating the borrowed airplane under 14 Code of Federal Regulations Part 91 as a personal flight. The flight departed Modesto City-County Airport-Harry Sham Field (MOD) at about 0845. Visual meteorological conditions prevailed.
Witnesses in the surrounding area reported being drawn to the accident airplane because it was circling, flying low, and performing aerobatics—including loops and wide turns—for about 20 minutes before they lost sight of it behind a mountain. They subsequently heard a loud bang, the sound of metal crumpling, and the engine stop. One witness stated the airplane was making sharp turns and nosedives.
An airborne witness, a certified flight instructor (CFI) with a student, observed the accident airplane at 6,000 feet mean sea level (msl) while they were at 4,500 feet msl, traveling eastbound. The CFI contacted NorCal TRACON and reported that they had the airplane in sight and would maintain visual separation. NorCal stated they were not in contact with the accident pilot. The CFI observed the airplane circling and initially thought the pilot was performing a simulated engine-out approach or steep spiral to Calaveras County-Maury Rasmussen Field Airport (CPU). When the pilot did not land, the CFI watched more closely and observed steep spiraling maneuvers estimated at a 70- to 90-degree bank. On two occasions, he saw a reduction in bank angle toward wings level, but the airplane never achieved wings-level before rolling back to a steep spiral.
The airplane's owner reported to the Calaveras County Sheriff’s Department that the pilot often borrowed the airplane and did not always inform him of doing so. The detective inquired about oxygen system use because an oxygen mask was found partially on the pilot at the accident site; the owner stated that as far as he knew, the pilot did not use the oxygen system.
Personnel Information
The pilot, aged 59, held a private pilot certificate with ratings for airplane single-engine land and instrument airplane. He held a third-class medical certificate issued in March 2009 with no restrictions. According to his logbook, he had an estimated 1,436.3 total flight hours, with 15.9 hours in the previous 90 days and 6.7 hours in the last 30 days. His last flight review occurred on September 22, 2009. The pilot's wife reported that he was taking blood pressure medication, had been practicing with the airplane's oxygen system, and seemed in good spirits.
Aircraft Information
The airplane was a Cessna 172N, serial number 17268149, returned to service after an annual inspection on April 16, 2010. The airframe had a total time of 5,451.1 hours. The engine was a Textron Lycoming O-320-H2AD, serial number L-752-76.
Wreckage and Impact Information
The airplane came to rest on a hillside with a 30-degree slope, in thick vegetation and manzanita trees. The debris field spanned 150 feet. The first identified point of contact (FIPC) was the nose, with the cowling remaining at the FIPC and debris in the trees. The engine came to rest just forward of the main wreckage. The FAA inspector reported no fuel or smell of fuel at the site.
Medical and Pathological Information
An autopsy conducted by the Calaveras County Coroner on June 22, 2010, listed the cause of death as multiple traumatic injuries due to an aircraft accident. Toxicological testing by the FAA Forensic Toxicology Research Team found no carbon monoxide, cyanide, or volatiles. Atenolol was detected in urine and blood (cavity), and quinine was detected in urine.
Test and Research
Radar data showed the airplane tracking northeast for about 25 nautical miles, climbing gradually to 11,800 feet msl, then making a left 180-degree turn toward the southwest. It continued climbing to 12,500 feet msl, where it performed a right 360-degree turn, and reached 12,800 feet msl. Between 0900:47 and 0910:50, radar depicted approximately 20 descending left 360-degree turns, ending at 2,400 feet msl (450 feet above ground level) with an average descent rate of 1,376 feet per minute.
NTSB and Cessna Aircraft Company representatives inspected the airframe and engine. Flight control continuity was established via cables and hardware to all flight surfaces. Both wings were separated about midspan with leading-to-trailing-edge damage. The trim was neutral, flaps retracted, and the fuel filter was free of debris. The oxygen bottle was compromised and could not be tested.
Visual inspection of the engine revealed no obvious mechanical anomalies. The propeller hub assembly had separated from the crankshaft; the crankshaft flange was deformed with 45-degree shear lip fracture surfaces. The starter drive had horizontal striations. Propeller blades showed S-bending, chordwise scratching, and leading/trailing-edge gouging. Top spark plugs exhibited normal operating signatures. The dual-drive magneto remained attached but had 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.