Accident Summary
On October 25, 2016, about 1220 Pacific daylight time, a Textron Aviation (formerly Beechcraft) A36 Bonanza, registration N364RM, was destroyed when it impacted powerlines and terrain during a steep descent near Pittsburg, California. The private pilot and a pilot-rated passenger received fatal injuries. The airplane was registered to Accretion LLC and operated by the pilot under Part 91. Visual meteorological conditions prevailed, and no flight plan was filed for the local personal flight that departed from Buchanan Field Airport (CCR), Concord, California, about 1215.
Flight History
According to individuals familiar with the occupants, the airplane had recently undergone installation of a new avionics suite. The accident flight was the second flight since the upgrade, intended for the passenger to assist the pilot in becoming familiar with the new equipment. They planned to fly to a known practice area east of CCR. Coroner's forensic evidence indicated the pilot was in the left seat and the passenger in the right seat.
Fuel records showed the airplane was fueled with 37.0 gallons of 100LL aviation gasoline on the day of the accident. FAA air traffic control audio and radar data indicated the airplane departed from CCR runway 19R, made a left turnout, and had no further communications. It climbed east to about 3,600 ft, then began a left turn and steep descent, striking high-tension powerlines and the sloped face of a ravine.
Aircraft Information
The airplane, manufactured in 1995 (serial number E-2957), was owned by the pilot's company for about 10 years. It was equipped with a Continental Motors IO-520 series engine converted to a TIO-550 via Supplemental Type Certificate (STC) SE02881AT, and modified with a Tornado Alley turbonormalizer system (STC SA5223NM) and Osborne wingtip fuel tanks in September 2007. The most recent annual inspection was completed in May 2016, with about 2,626 total hours and 681 hours since engine major overhaul.
The new avionics suite included Garmin GTN 650, GTN 750, GTX 345R, and two GA35 WAAS antennae. The installation was completed on October 19, 2016, at Westover Field/Amador County Airport (JAQ), Jackson, California. Ground tests were satisfactory. The first post-installation flight occurred on October 20, 2016, when the accident passenger flew the airplane solo from JAQ to CCR. He reported an unspecified anomaly during preflight but still flew the airplane. He later advised the installer that the new avionics operated satisfactorily except for a sidetone volume issue.
Wreckage and Impact
The accident site was in rolling open hills about 8 miles east of CCR. The wreckage was highly fragmented, and a post-impact fire consumed much of the airplane. Two of six powerlines (170 ft towers, highest lines at 165 ft) were damaged but not severed. Debris field fragments were primarily from the empennage or right wing, with no smoke or thermal distress. The main wreckage was tightly contained, consistent with a steep, approximately upright impact followed by nose-over to inverted.
The left aileron remained attached; the right aileron was separated. Aileron trim was set to about 4° left trailing edge down. Flaps were retracted. Landing gear was retracted. The engine separated and was found about 15 ft downslope, with significant impact and thermal damage. Three propeller blades were found with minor tip damage. No pre-impact anomalies were observed in flight controls, engine, or propeller.
Medical and Pathological Information
An autopsy of the 67-year-old pilot cited cause of death as multiple blunt force injuries, with inconclusive findings for natural disease due to trauma. Toxicology detected pseudoephedrine (57 ng/g in liver), atorvastatin, valsartan, and bupropion in liver and muscle tissue. Bupropion carries a boxed warning about neurocognitive effects and seizure risk.
The 58-year-old passenger's autopsy also cited multiple blunt force injuries as cause of death. Toxicology identified ethanol in liver (0.074 gm%) and muscle (0.010 gm%), but postmortem production could not be ruled out.
Additional Data
Radar tracking showed the airplane reached a maximum altitude of about 3,600 ft about 4.5 minutes after takeoff. It then entered a 30-second descent with increasing rate, averaging 5,000 fpm and peaking at 10,000 fpm. The last ADS-B return indicated 1,175 ft. Airspeed increased from about 120 to nearly 250 kts, with pitch attitude decreasing to nearly 30° nose down and load factor dropping to 0.4g. The airplane exceeded maneuvering speed (Va, 139 kts), maximum structural cruising speed (Vno, 165 kts), and never-exceed speed (Vne, 203 kts) during the descent.
The A36 is a low-drag design; with gear and flaps retracted, acceleration in a dive was high. Elevator trim settings could significantly affect recovery forces. No cockpit-controlled rudder trim was installed.