History of Flight
On September 25, 2015, about 1126 mountain daylight time, a Beech S35 single-engine airplane, N193Q, impacted terrain following a loss of engine power while maneuvering near Pagosa Springs, Colorado. The private pilot and passenger sustained fatal injuries. The airplane was destroyed by impact and postaccident fire. The flight was operated under 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed, and no flight plan was filed. The airplane departed Durango-La Plata County Airport (DRO), Durango, Colorado, at an unknown time, en route to Stevens Field Airport (PSO), Pagosa Springs.
The accident airplane departed DRO with another airplane; both pilots planned to participate in an air race competition in the Pagosa Springs area on September 26. Before landing at PSO, the pilots decided to execute a circuit in the race course. The accident airplane followed the other. After the first waypoint, the accident pilot radioed that the engine had lost power and the airplane was going down. No further communications were heard.
Witnesses in the Pagosa Springs area observed white smoke coming from the underside of the accident airplane. The airplane turned left, descended below rising terrain, and a smoke plume was seen shortly after. Witnesses reported clear skies and calm winds.
Personnel Information
The pilot, age 70, held a private pilot certificate with ratings for airplane single-engine land, airplane multi-engine land, and rotorcraft-helicopter. He also held an airframe and powerplant mechanic certificate. His most recent FAA third-class medical certificate was issued August 19, 2014, with a limitation requiring glasses for near vision. On his medical application, he reported 5,640 total flight hours and 20 hours in the preceding six months. The pilot's logbook was not located.
Aircraft Information
The airplane was a 1964 Beech S35, serial number D-7708, powered by a Continental Motors IO-520-B reciprocating engine and a Hartzell controllable pitch propeller. It was issued a standard airworthiness certificate on December 7, 1964. Maintenance logbooks were not located, so total airframe and engine time could not be determined. According to a family member, the airplane had its most recent annual inspection in November 2014, and the engine cylinders had been chromed approximately 2 to 3 years earlier. The family member was unaware of any additional maintenance. The engine oil filter had a date of June 9, 2015, and a tach time of 2037.3 hours.
Meteorological Information
At 1153, the DRO automated surface observing system, about 45 miles west of the accident site, reported calm wind, 10 miles visibility, clear sky, temperature 21°C, dew point 4°C, and altimeter setting 30.44 inches of mercury.
Wreckage and Impact Information
The airplane struck a 4-inch steel pole adjacent to a gravel road, leaving white paint transfer and paint chips. It then traveled about 200 yards before coming to rest inverted in a field. The main wreckage comprised the fuselage, both wings, and empennage. The engine separated from the airframe and came to rest within the debris field. The three-blade propeller assembly separated and was found about 75 feet from the main wreckage. The fuselage and cockpit were consumed by postaccident fire.
The left wing was inverted and partially attached, with the flap extended and aileron attached. The left main landing gear was retracted. Approximately 25 to 30 gallons of fuel was drained from the left wing tank during recovery. The right wing was also inverted and partially attached, with the flap extended; the outboard aileron section showed thermal damage. The right main landing gear was retracted and thermally damaged. The right wing fuel tank was consumed by fire.
The fuselage, cockpit, instrument panel, and controls were fire-damaged. Three seat frames were found; one seat belt buckle and tag were clasped, but the shoulder harness bayonet fitting was not engaged in the buckle. The main cabin door latch bolt was retracted and the upper latch bolt hook not extended, consistent with an unlocked door.
The empennage was partially consumed by fire. The right stabilizer was bent upward; the elevator remained partially attached and was fractured mid-span. The left stabilizer had thermal damage, and the elevator remained attached. Flight control continuity was established from the cockpit to the control surfaces. The down elevator cable arm was separated from the pitch idler bellcrank. The pitch trim actuator was extended 15/16 inch, corresponding to 0 to 5 degrees trailing edge up. The left flap actuator was extended 6 1/4 inches, consistent with flaps down (30 degrees).
The engine separated from the mount. The upper cowling separated and came to rest near the engine. The left interior and exterior cowling doors were coated with oil, with streaking in a forward-to-aft direction. The propeller assembly separated near the crankshaft flange; one blade was bent aft mid-span, and two were curled aft. Scratches were along the blade lengths, but no leading edge damage.
Medical and Pathological Information
Autopsies performed by Rocky Mountain Forensic Services listed the immediate causes of death as smoke and soot inhalation as a result of the accident. FAA toxicology on the pilot detected 25% carbon monoxide in blood (heart), 0.7 ug/ml cyanide in blood (heart), azacyclonol in urine, fexofenadine in urine, and ibuprofen in urine. Cyanide and carbon monoxide can be produced by burning materials. Fexofenadine (Allegra) is a non-sedating antihistamine; azacyclonol is its metabolite. Ibuprofen is a common over-the-counter pain reliever.
Tests and Research
On January 20, 2016, the engine was examined at Continental Motors under NTSB supervision. A hole was found in the crankcase above the No. 6 cylinder. Disassembly revealed the Nos. 5 and 6 connecting rods were fractured and separated from the crankshaft. Debris consistent with connecting rod and bearing material was in the oil sump. The No. 5 crankshaft journal appeared undamaged; the No. 6 journal showed thermal damage and rolled metal covering the oil transfer passage. Crankcase thru-bolt torque was below Continental Motors specifications. The No. 4 main bearing supports showed fretting, and the No. 4 main bearing journal exhibited bearing shift and movement consistent with partial or complete blocking of the oil transfer passage to the No. 6 connecting rod. The No. 4 main bearing displayed deterioration and delamination.
The pistons were removed; castings showed "NFS-C 550" on the inside and "C-510" near the piston pin. An internet search identified the manufacturer as Need For Speed (NFS) Pistons. According to the manufacturer's website, these pistons are not approved for certified aircraft use and are for experimental aircraft and airboat use only. NFS company records indicated the pistons were shipped to the pilot on February 2, 2011.