History of Flight
On April 11, 2014, at 1007 Pacific daylight time, an experimental amateur-built Bowers (Williams Myron G) Fly Baby 1A, registration N6054Q, collided with wooded terrain near Mariposa, California. The airplane was operated by the pilot under 14 CFR Part 91 as a personal flight. The commercial pilot sustained fatal injuries; the airplane sustained substantial damage to the forward fuselage and both wings. The local flight departed Mariposa-Yosemite Airport about 0950. Visual meteorological conditions prevailed, and no flight plan was filed.
A witness located about 3 miles northwest of the airport observed the airplane approaching from the southeast at about 1,000 feet above ground level (agl). The airplane began a left turn, appeared to descend, and the engine made a "missing" sound, as if power was intermittently interrupted. It then turned right, arcing around the witness, descending to about 300 feet agl. It gradually rolled out, flew toward hills to the northeast, slowed considerably, and pitched up to about 30 degrees before disappearing behind trees. No other sounds were heard. A family member called 911 at 1008.
Personnel Information
The 80-year-old pilot held a commercial pilot certificate with ratings for airplane single-engine land and instrument airplane, issued in 1972. His most recent FAA third-class medical certificate was issued in October 2007, with limitations requiring glasses for near vision. At that application, he reported 1,800 total flight hours. A logbook entry from June 22, 2013, showed 0.6 hours of flight training in a Cessna 152 practicing maneuvers, stalls, and slow flight; the most recent flight review was November 2007. In the two years preceding the accident, he logged 15.1 hours. His total experience in the accident airplane was 3.1 hours, all during four flights in the month before the accident.
Aircraft Information
The plans-built, single-seat, low-wing airplane had a primary structure of wood covered in fabric, with wings and landing gear braced by steel wires. It was powered by a four-cylinder Continental A65-8 engine with a wooden two-blade propeller.
A special airworthiness certificate was issued on October 20, 2006, and that day the airplane experienced a loss of power on its maiden flight. The pilot/builder self-reported failure to use carburetor heat as likely cause, and the NTSB determined the probable cause as "a loss of engine power due to the pilot's failure to use carburetor heat during conditions conducive to carburetor icing."
The accident pilot purchased the airplane in December 2012. Maintenance logbooks showed 29 total flight hours. Over the next three months, the pilot performed repairs to brakes, control surfaces, and flying cables, and replaced the propeller and right magneto cap. He described the build quality as "crude" and planned progressive restoration.
Taxi tests occurred in March 2013, but the airplane was not flown for the rest of that year. On March 3, 2014, an annual inspection was completed by an FAA certified airframe and powerplant mechanic with inspection authorization. The mechanic reported the engine was backfiring before his examination; he found magneto leads to two cylinders had been transposed.
The first flight after inspection occurred shortly thereafter and, according to the pilot's friend, was accidental during a high-speed taxi test. About two weeks before the accident, the pilot performed an intentional flight test, experiencing roll control difficulties and noting inconsistent airspeed indication. He planned to move the Pitot tube further outboard.
Meteorological Information
The closest weather reporting station at similar elevation was Columbia Airport, about 36 miles north-northwest. The 1015 report indicated calm wind, clear sky, temperature 23°C, dew point -14°C (source had 06 degrees F, which is about -14°C), altimeter 29.93 inHg.
Wreckage and Impact Information
The airplane came to rest at the base of an oak tree in densely wooded terrain at 2,250 feet msl, about 3 miles northwest of the airport. Surroundings included grass, poison oak, rocky outcroppings, and oak trees up to 20 feet tall. The airplane rested on a magnetic heading of about 60°, facing uphill on a 20° slope. A nearly vertical swath through tree branches was directly above the airplane; no other limb damage was noted.
The wings were inverted, with forward fuselage and engine under the wing root. The tailcone and empennage separated aft of the seat and rested undamaged on its right side. Both wings had aft crush damage to leading edges. The cabin structure forward of the tailcone was fragmented; the firewall was compressed against the rear of the engine. Cockpit flight controls had bending damage but remained functional. The fuel tank had multiple breaches and was detached within the center section.
No indications of bird strike or fire were found.
The engine remained attached to its mount. Both magnetos were attached, but plug caps fragmented, exposing timing gears, points, and coils, and detaching ignition wires and P-leads. The carburetor broke away from the inlet manifold; the inlet air filter assembly had crush damage. The throttle cable was full-forward at the cockpit. The carburetor heat control was in the aft (on) position. The fuel primer was forward and locked.
Spark plugs were three-prong with grey deposits and minimal wear. Exhaust pipes had light grey deposits. The crankshaft turned smoothly, compression was noted on all cylinders, and mechanical continuity was established. No pre-impact anomalies were found; all components were accounted for.
A propeller hub remained attached to the crankshaft, embedded in soil. Blades were fragmented, with fragments up to 40 feet away.
Medical and Pathological Information
An autopsy attributed cause of death to blunt injuries. Toxicological tests detected Warfarin in urine and blood (cavity), an anticoagulant with no specific flight warnings.
Tests and Research
The Stromberg NA-S3B carburetor was examined. It was of the low-altitude fixed mixture type, not configured with a cockpit adjustable mixture control. Minimal damage was observed; the fuel inlet hose was automotive type. No safety wire on venturi retainer or throttle valve lock screws. The idle mixture screw was set at 3/4 turn back from closed, rather than typical 3 turns. The throttle valve in the closed position completely obscured the venturi, indicating an incorrectly adjusted stop screw, which would inhibit idle operation. In the full-open position, the valve opened beyond center by about 5 degrees.
The fuel bowl was separated; an undamaged Delrin float needle was installed without the required brass float balance weight per Bendix Service Bulletin 84. Maintenance logs showed an unattributed entry on March 10, 2006 (before the first accident) stating "Installed delron needle in carburetor" without noting the weight.
The main metering jet body touched the float base, limiting float travel. Float drop measurement was 0.019 inches, below the minimum 0.048 inches. On a flow gauge, fuel overflowed immediately, consistent with float binding. When re-tried, fuel stopped at 1/16 inch from the bowl seam, whereas specification is 13/32 inch.
The float had an indentation adjacent to the chafe strip, corresponding to the main metering jet. The needle valve would not seal under low air pressure. Two level-adjustment gaskets (0.03 and 0.062 inches) exceeded the maximum 0.05 inches. The fuel inlet screen plug was overtightened, and the screen was installed upside down, bypassing its debris-capturing function.